source: mainline/uspace/lib/c/generic/async.c@ 649f087

/*
 * Copyright (c) 2006 Ondrej Palkovsky
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * - Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 * - Redistributions in binary form must reproduce the above copyright
 *   notice, this list of conditions and the following disclaimer in the
 *   documentation and/or other materials provided with the distribution.
 * - The name of the author may not be used to endorse or promote products
 *   derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

/** @addtogroup libc
 * @{
 */
/** @file
 */

/**
 * Asynchronous library
 *
 * The aim of this library is to provide a facility for writing programs which
 * utilize the asynchronous nature of HelenOS IPC, yet using a normal way of
 * programming.
 *
 * You should be able to write very simple multithreaded programs. The async
 * framework will automatically take care of most of the synchronization
 * problems.
 *
 * Example of use (pseudo C):
 *
 * 1) Multithreaded client application
 *
 *   fibril_create(fibril1, ...);
 *   fibril_create(fibril2, ...);
 *   ...
 *
 *   int fibril1(void *arg)
 *   {
 *     conn = async_connect_me_to(...);
 *
 *     exch = async_exchange_begin(conn);
 *     c1 = async_send(exch);
 *     async_exchange_end(exch);
 *
 *     exch = async_exchange_begin(conn);
 *     c2 = async_send(exch);
 *     async_exchange_end(exch);
 *
 *     async_wait_for(c1);
 *     async_wait_for(c2);
 *     ...
 *   }
 *
 *
 * 2) Multithreaded server application
 *
 *   main()
 *   {
 *     async_manager();
 *   }
 *
 *   my_client_connection(icallid, *icall)
 *   {
 *     if (want_refuse) {
 *       async_answer_0(icallid, ELIMIT);
 *       return;
 *     }
 *     async_answer_0(icallid, EOK);
 *
 *     callid = async_get_call(&call);
 *     somehow_handle_the_call(callid, call);
 *     async_answer_2(callid, 1, 2, 3);
 *
 *     callid = async_get_call(&call);
 *     ...
 *   }
 *
 */

#define LIBC_ASYNC_C_
#include <ipc/ipc.h>
#include <async.h>
#undef LIBC_ASYNC_C_

#include <futex.h>
#include <fibril.h>
#include <adt/hash_table.h>
#include <adt/list.h>
#include <assert.h>
#include <errno.h>
#include <sys/time.h>
#include <libarch/barrier.h>
#include <bool.h>
#include <malloc.h>
#include <mem.h>
#include <stdlib.h>
#include <macros.h>
#include "private/async.h"

#define CLIENT_HASH_TABLE_BUCKETS  32
#define CONN_HASH_TABLE_BUCKETS    32

/** Async framework global futex */
atomic_t async_futex = FUTEX_INITIALIZER;

/** Number of threads waiting for IPC in the kernel. */
atomic_t threads_in_ipc_wait = { 0 };

/** Naming service session */
async_sess_t *session_ns;

/** Call data */
typedef struct {
        link_t link;
        
        ipc_callid_t callid;
        ipc_call_t call;
} msg_t;

/* Client connection data */
typedef struct {
        link_t link;
        
        task_id_t in_task_id;
        atomic_t refcnt;
        void *data;
} client_t;

/* Server connection data */
typedef struct {
        awaiter_t wdata;
        
        /** Hash table link. */
        link_t link;
        
        /** Incoming client task ID. */
        task_id_t in_task_id;
        
        /** Incoming phone hash. */
        sysarg_t in_phone_hash;
        
        /** Link to the client tracking structure. */
        client_t *client;
        
        /** Messages that should be delivered to this fibril. */
        list_t msg_queue;
        
        /** Identification of the opening call. */
        ipc_callid_t callid;
        /** Call data of the opening call. */
        ipc_call_t call;
        /** Local argument or NULL if none. */
        void *carg;
        
        /** Identification of the closing call. */
        ipc_callid_t close_callid;
        
        /** Fibril function that will be used to handle the connection. */
        async_client_conn_t cfibril;
} connection_t;

/** Identifier of the incoming connection handled by the current fibril. */
static fibril_local connection_t *fibril_connection;

static void *default_client_data_constructor(void)
{
        return NULL;
}

static void default_client_data_destructor(void *data)
{
}

static async_client_data_ctor_t async_client_data_create =
    default_client_data_constructor;
static async_client_data_dtor_t async_client_data_destroy =
    default_client_data_destructor;

void async_set_client_data_constructor(async_client_data_ctor_t ctor)
{
        async_client_data_create = ctor;
}

void async_set_client_data_destructor(async_client_data_dtor_t dtor)
{
        async_client_data_destroy = dtor;
}

/** Default fibril function that gets called to handle new connection.
 *
 * This function is defined as a weak symbol - to be redefined in user code.
 *
 * @param callid Hash of the incoming call.
 * @param call   Data of the incoming call.
 * @param arg    Local argument
 *
 */
static void default_client_connection(ipc_callid_t callid, ipc_call_t *call,
    void *arg)
{
        ipc_answer_0(callid, ENOENT);
}

/** Default fibril function that gets called to handle interrupt notifications.
 *
 * This function is defined as a weak symbol - to be redefined in user code.
 *
 * @param callid Hash of the incoming call.
 * @param call   Data of the incoming call.
 * @param arg    Local argument.
 *
 */
static void default_interrupt_received(ipc_callid_t callid, ipc_call_t *call)
{
}

static async_client_conn_t client_connection = default_client_connection;
static async_interrupt_handler_t interrupt_received = default_interrupt_received;

/** Setter for client_connection function pointer.
 *
 * @param conn Function that will implement a new connection fibril.
 *
 */
void async_set_client_connection(async_client_conn_t conn)
{
        client_connection = conn;
}

/** Setter for interrupt_received function pointer.
 *
 * @param intr Function that will implement a new interrupt
 *             notification fibril.
 */
void async_set_interrupt_received(async_interrupt_handler_t intr)
{
        interrupt_received = intr;
}

/** Mutex protecting inactive_exch_list and avail_phone_cv.
 *
 */
static FIBRIL_MUTEX_INITIALIZE(async_sess_mutex);

/** List of all currently inactive exchanges.
 *
 */
static LIST_INITIALIZE(inactive_exch_list);

/** Condition variable to wait for a phone to become available.
 *
 */
static FIBRIL_CONDVAR_INITIALIZE(avail_phone_cv);

static hash_table_t client_hash_table;
static hash_table_t conn_hash_table;
static LIST_INITIALIZE(timeout_list);

static hash_index_t client_hash(unsigned long key[])
{
        assert(key);
        
        return (((key[0]) >> 4) % CLIENT_HASH_TABLE_BUCKETS);
}

static int client_compare(unsigned long key[], hash_count_t keys, link_t *item)
{
        assert(key);
        assert(keys == 2);
        assert(item);
        
        client_t *client = hash_table_get_instance(item, client_t, link);
        return (key[0] == LOWER32(client->in_task_id) &&
            (key[1] == UPPER32(client->in_task_id)));
}

static void client_remove(link_t *item)
{
}

/** Operations for the client hash table. */
static hash_table_operations_t client_hash_table_ops = {
        .hash = client_hash,
        .compare = client_compare,
        .remove_callback = client_remove
};

/** Compute hash into the connection hash table based on the source phone hash.
 *
 * @param key Pointer to source phone hash.
 *
 * @return Index into the connection hash table.
 *
 */
static hash_index_t conn_hash(unsigned long key[])
{
        assert(key);
        
        return (((key[0]) >> 4) % CONN_HASH_TABLE_BUCKETS);
}

/** Compare hash table item with a key.
 *
 * @param key  Array containing the source phone hash as the only item.
 * @param keys Expected 1 but ignored.
 * @param item Connection hash table item.
 *
 * @return True on match, false otherwise.
 *
 */
static int conn_compare(unsigned long key[], hash_count_t keys, link_t *item)
{
        assert(key);
        assert(item);
        
        connection_t *conn = hash_table_get_instance(item, connection_t, link);
        return (key[0] == conn->in_phone_hash);
}

static void conn_remove(link_t *item)
{
}

/** Operations for the connection hash table. */
static hash_table_operations_t conn_hash_table_ops = {
        .hash = conn_hash,
        .compare = conn_compare,
        .remove_callback = conn_remove
};

/** Sort in current fibril's timeout request.
 *
 * @param wd Wait data of the current fibril.
 *
 */
void async_insert_timeout(awaiter_t *wd)
{
        assert(wd);
        
        wd->to_event.occurred = false;
        wd->to_event.inlist = true;
        
        link_t *tmp = timeout_list.head.next;
        while (tmp != &timeout_list.head) {
                awaiter_t *cur
                    = list_get_instance(tmp, awaiter_t, to_event.link);
                
                if (tv_gteq(&cur->to_event.expires, &wd->to_event.expires))
                        break;
                
                tmp = tmp->next;
        }
        
        list_insert_before(&wd->to_event.link, tmp);
}

/** Try to route a call to an appropriate connection fibril.
 *
 * If the proper connection fibril is found, a message with the call is added to
 * its message queue. If the fibril was not active, it is activated and all
 * timeouts are unregistered.
 *
 * @param callid Hash of the incoming call.
 * @param call   Data of the incoming call.
 *
 * @return False if the call doesn't match any connection.
 * @return True if the call was passed to the respective connection fibril.
 *
 */
static bool route_call(ipc_callid_t callid, ipc_call_t *call)
{
        assert(call);
        
        futex_down(&async_futex);
        
        unsigned long key = call->in_phone_hash;
        link_t *hlp = hash_table_find(&conn_hash_table, &key);
        
        if (!hlp) {
                futex_up(&async_futex);
                return false;
        }
        
        connection_t *conn = hash_table_get_instance(hlp, connection_t, link);
        
        msg_t *msg = malloc(sizeof(*msg));
        if (!msg) {
                futex_up(&async_futex);
                return false;
        }
        
        msg->callid = callid;
        msg->call = *call;
        list_append(&msg->link, &conn->msg_queue);
        
        if (IPC_GET_IMETHOD(*call) == IPC_M_PHONE_HUNGUP)
                conn->close_callid = callid;
        
        /* If the connection fibril is waiting for an event, activate it */
        if (!conn->wdata.active) {
                
                /* If in timeout list, remove it */
                if (conn->wdata.to_event.inlist) {
                        conn->wdata.to_event.inlist = false;
                        list_remove(&conn->wdata.to_event.link);
                }
                
                conn->wdata.active = true;
                fibril_add_ready(conn->wdata.fid);
        }
        
        futex_up(&async_futex);
        return true;
}

/** Notification fibril.
 *
 * When a notification arrives, a fibril with this implementing function is
 * created. It calls interrupt_received() and does the final cleanup.
 *
 * @param arg Message structure pointer.
 *
 * @return Always zero.
 *
 */
static int notification_fibril(void *arg)
{
        assert(arg);
        
        msg_t *msg = (msg_t *) arg;
        interrupt_received(msg->callid, &msg->call);
        
        free(msg);
        return 0;
}

/** Process interrupt notification.
 *
 * A new fibril is created which would process the notification.
 *
 * @param callid Hash of the incoming call.
 * @param call   Data of the incoming call.
 *
 * @return False if an error occured.
 *         True if the call was passed to the notification fibril.
 *
 */
static bool process_notification(ipc_callid_t callid, ipc_call_t *call)
{
        assert(call);
        
        futex_down(&async_futex);
        
        msg_t *msg = malloc(sizeof(*msg));
        if (!msg) {
                futex_up(&async_futex);
                return false;
        }
        
        msg->callid = callid;
        msg->call = *call;
        
        fid_t fid = fibril_create(notification_fibril, msg);
        if (fid == 0) {
                free(msg);
                futex_up(&async_futex);
                return false;
        }
        
        fibril_add_ready(fid);
        
        futex_up(&async_futex);
        return true;
}

/** Return new incoming message for the current (fibril-local) connection.
 *
 * @param call  Storage where the incoming call data will be stored.
 * @param usecs Timeout in microseconds. Zero denotes no timeout.
 *
 * @return If no timeout was specified, then a hash of the
 *         incoming call is returned. If a timeout is specified,
 *         then a hash of the incoming call is returned unless
 *         the timeout expires prior to receiving a message. In
 *         that case zero is returned.
 *
 */
ipc_callid_t async_get_call_timeout(ipc_call_t *call, suseconds_t usecs)
{
        assert(call);
        assert(fibril_connection);
        
        /* Why doing this?
         * GCC 4.1.0 coughs on fibril_connection-> dereference.
         * GCC 4.1.1 happilly puts the rdhwr instruction in delay slot.
         *           I would never expect to find so many errors in
         *           a compiler.
         */
        connection_t *conn = fibril_connection;
        
        futex_down(&async_futex);
        
        if (usecs) {
                gettimeofday(&conn->wdata.to_event.expires, NULL);
                tv_add(&conn->wdata.to_event.expires, usecs);
        } else
                conn->wdata.to_event.inlist = false;
        
        /* If nothing in queue, wait until something arrives */
        while (list_empty(&conn->msg_queue)) {
                if (conn->close_callid) {
                        /*
                         * Handle the case when the connection was already
                         * closed by the client but the server did not notice
                         * the first IPC_M_PHONE_HUNGUP call and continues to
                         * call async_get_call_timeout(). Repeat
                         * IPC_M_PHONE_HUNGUP until the caller notices.
                         */
                        memset(call, 0, sizeof(ipc_call_t));
                        IPC_SET_IMETHOD(*call, IPC_M_PHONE_HUNGUP);
                        futex_up(&async_futex);
                        return conn->close_callid;
                }
                
                if (usecs)
                        async_insert_timeout(&conn->wdata);
                
                conn->wdata.active = false;
                
                /*
                 * Note: the current fibril will be rescheduled either due to a
                 * timeout or due to an arriving message destined to it. In the
                 * former case, handle_expired_timeouts() and, in the latter
                 * case, route_call() will perform the wakeup.
                 */
                fibril_switch(FIBRIL_TO_MANAGER);
                
                /*
                 * Futex is up after getting back from async_manager.
                 * Get it again.
                 */
                futex_down(&async_futex);
                if ((usecs) && (conn->wdata.to_event.occurred)
                    && (list_empty(&conn->msg_queue))) {
                        /* If we timed out -> exit */
                        futex_up(&async_futex);
                        return 0;
                }
        }
        
        msg_t *msg = list_get_instance(list_first(&conn->msg_queue), msg_t, link);
        list_remove(&msg->link);
        
        ipc_callid_t callid = msg->callid;
        *call = msg->call;
        free(msg);
        
        futex_up(&async_futex);
        return callid;
}

static client_t *async_client_get(task_id_t client_id, bool create)
{
        unsigned long key[2] = {
                LOWER32(client_id),
                UPPER32(client_id),
        };
        client_t *client = NULL;

        futex_down(&async_futex);
        link_t *lnk = hash_table_find(&client_hash_table, key);
        if (lnk) {
                client = hash_table_get_instance(lnk, client_t, link);
                atomic_inc(&client->refcnt);
        } else if (create) {
                client = malloc(sizeof(client_t));
                if (client) {
                        client->in_task_id = client_id;
                        client->data = async_client_data_create();
                
                        atomic_set(&client->refcnt, 1);
                        hash_table_insert(&client_hash_table, key, &client->link);
                }
        }

        futex_up(&async_futex);
        return client;
}

static void async_client_put(client_t *client)
{
        bool destroy;
        unsigned long key[2] = {
                LOWER32(client->in_task_id),
                UPPER32(client->in_task_id)
        };
        
        futex_down(&async_futex);
        
        if (atomic_predec(&client->refcnt) == 0) {
                hash_table_remove(&client_hash_table, key, 2);
                destroy = true;
        } else
                destroy = false;
        
        futex_up(&async_futex);
        
        if (destroy) {
                if (client->data)
                        async_client_data_destroy(client->data);
                
                free(client);
        }
}

void *async_get_client_data(void)
{
        assert(fibril_connection);
        return fibril_connection->client->data;
}

void *async_get_client_data_by_id(task_id_t client_id)
{
        client_t *client = async_client_get(client_id, false);
        if (!client)
                return NULL;
        if (!client->data) {
                async_client_put(client);
                return NULL;
        }

        return client->data;
}

void async_put_client_data_by_id(task_id_t client_id)
{
        client_t *client = async_client_get(client_id, false);

        assert(client);
        assert(client->data);

        /* Drop the reference we got in async_get_client_data_by_hash(). */
        async_client_put(client);

        /* Drop our own reference we got at the beginning of this function. */
        async_client_put(client);
}

/** Wrapper for client connection fibril.
 *
 * When a new connection arrives, a fibril with this implementing function is
 * created. It calls client_connection() and does the final cleanup.
 *
 * @param arg Connection structure pointer.
 *
 * @return Always zero.
 *
 */
static int connection_fibril(void *arg)
{
        assert(arg);
        
        /*
         * Setup fibril-local connection pointer.
         */
        fibril_connection = (connection_t *) arg;
        
        /*
         * Add our reference for the current connection in the client task
         * tracking structure. If this is the first reference, create and
         * hash in a new tracking structure.
         */

        client_t *client = async_client_get(fibril_connection->in_task_id, true);
        if (!client) {
                ipc_answer_0(fibril_connection->callid, ENOMEM);
                return 0;
        }

        fibril_connection->client = client;
        
        /*
         * Call the connection handler function.
         */
        fibril_connection->cfibril(fibril_connection->callid,
            &fibril_connection->call, fibril_connection->carg);
        
        /*
         * Remove the reference for this client task connection.
         */
        async_client_put(client);
        
        /*
         * Remove myself from the connection hash table.
         */
        futex_down(&async_futex);
        unsigned long key = fibril_connection->in_phone_hash;
        hash_table_remove(&conn_hash_table, &key, 1);
        futex_up(&async_futex);
        
        /*
         * Answer all remaining messages with EHANGUP.
         */
        while (!list_empty(&fibril_connection->msg_queue)) {
                msg_t *msg =
                    list_get_instance(list_first(&fibril_connection->msg_queue),
                    msg_t, link);
                
                list_remove(&msg->link);
                ipc_answer_0(msg->callid, EHANGUP);
                free(msg);
        }
        
        /*
         * If the connection was hung-up, answer the last call,
         * i.e. IPC_M_PHONE_HUNGUP.
         */
        if (fibril_connection->close_callid)
                ipc_answer_0(fibril_connection->close_callid, EOK);
        
        free(fibril_connection);
        return 0;
}

/** Create a new fibril for a new connection.
 *
 * Create new fibril for connection, fill in connection structures and insert
 * it into the hash table, so that later we can easily do routing of messages to
 * particular fibrils.
 *
 * @param in_task_id    Identification of the incoming connection.
 * @param in_phone_hash Identification of the incoming connection.
 * @param callid        Hash of the opening IPC_M_CONNECT_ME_TO call.
 *                      If callid is zero, the connection was opened by
 *                      accepting the IPC_M_CONNECT_TO_ME call and this function
 *                      is called directly by the server.
 * @param call          Call data of the opening call.
 * @param cfibril       Fibril function that should be called upon opening the
 *                      connection.
 * @param carg          Extra argument to pass to the connection fibril
 *
 * @return New fibril id or NULL on failure.
 *
 */
fid_t async_new_connection(task_id_t in_task_id, sysarg_t in_phone_hash,
    ipc_callid_t callid, ipc_call_t *call,
    async_client_conn_t cfibril, void *carg)
{
        connection_t *conn = malloc(sizeof(*conn));
        if (!conn) {
                if (callid)
                        ipc_answer_0(callid, ENOMEM);
                
                return (uintptr_t) NULL;
        }
        
        conn->in_task_id = in_task_id;
        conn->in_phone_hash = in_phone_hash;
        list_initialize(&conn->msg_queue);
        conn->callid = callid;
        conn->close_callid = 0;
        conn->carg = carg;
        
        if (call)
                conn->call = *call;
        
        /* We will activate the fibril ASAP */
        conn->wdata.active = true;
        conn->cfibril = cfibril;
        conn->wdata.fid = fibril_create(connection_fibril, conn);
        
        if (conn->wdata.fid == 0) {
                free(conn);
                
                if (callid)
                        ipc_answer_0(callid, ENOMEM);
                
                return (uintptr_t) NULL;
        }
        
        /* Add connection to the connection hash table */
        unsigned long key = conn->in_phone_hash;
        
        futex_down(&async_futex);
        hash_table_insert(&conn_hash_table, &key, &conn->link);
        futex_up(&async_futex);
        
        fibril_add_ready(conn->wdata.fid);
        
        return conn->wdata.fid;
}

/** Handle a call that was received.
 *
 * If the call has the IPC_M_CONNECT_ME_TO method, a new connection is created.
 * Otherwise the call is routed to its connection fibril.
 *
 * @param callid Hash of the incoming call.
 * @param call   Data of the incoming call.
 *
 */
static void handle_call(ipc_callid_t callid, ipc_call_t *call)
{
        assert(call);
        
        /* Unrouted call - take some default action */
        if ((callid & IPC_CALLID_NOTIFICATION)) {
                process_notification(callid, call);
                return;
        }
        
        switch (IPC_GET_IMETHOD(*call)) {
        case IPC_M_CONNECT_ME:
        case IPC_M_CONNECT_ME_TO:
                /* Open new connection with fibril, etc. */
                async_new_connection(call->in_task_id, IPC_GET_ARG5(*call),
                    callid, call, client_connection, NULL);
                return;
        }
        
        /* Try to route the call through the connection hash table */
        if (route_call(callid, call))
                return;
        
        /* Unknown call from unknown phone - hang it up */
        ipc_answer_0(callid, EHANGUP);
}

/** Fire all timeouts that expired. */
static void handle_expired_timeouts(void)
{
        struct timeval tv;
        gettimeofday(&tv, NULL);
        
        futex_down(&async_futex);
        
        link_t *cur = list_first(&timeout_list);
        while (cur != NULL) {
                awaiter_t *waiter =
                    list_get_instance(cur, awaiter_t, to_event.link);
                
                if (tv_gt(&waiter->to_event.expires, &tv))
                        break;
                
                list_remove(&waiter->to_event.link);
                waiter->to_event.inlist = false;
                waiter->to_event.occurred = true;
                
                /*
                 * Redundant condition?
                 * The fibril should not be active when it gets here.
                 */
                if (!waiter->active) {
                        waiter->active = true;
                        fibril_add_ready(waiter->fid);
                }
                
                cur = list_first(&timeout_list);
        }
        
        futex_up(&async_futex);
}

/** Endless loop dispatching incoming calls and answers.
 *
 * @return Never returns.
 *
 */
static int async_manager_worker(void)
{
        while (true) {
                if (fibril_switch(FIBRIL_FROM_MANAGER)) {
                        futex_up(&async_futex);
                        /*
                         * async_futex is always held when entering a manager
                         * fibril.
                         */
                        continue;
                }
                
                futex_down(&async_futex);
                
                suseconds_t timeout;
                if (!list_empty(&timeout_list)) {
                        awaiter_t *waiter = list_get_instance(
                            list_first(&timeout_list), awaiter_t, to_event.link);
                        
                        struct timeval tv;
                        gettimeofday(&tv, NULL);
                        
                        if (tv_gteq(&tv, &waiter->to_event.expires)) {
                                futex_up(&async_futex);
                                handle_expired_timeouts();
                                continue;
                        } else
                                timeout = tv_sub(&waiter->to_event.expires, &tv);
                } else
                        timeout = SYNCH_NO_TIMEOUT;
                
                futex_up(&async_futex);
                
                atomic_inc(&threads_in_ipc_wait);
                
                ipc_call_t call;
                ipc_callid_t callid = ipc_wait_cycle(&call, timeout,
                    SYNCH_FLAGS_NONE);
                
                atomic_dec(&threads_in_ipc_wait);
                
                if (!callid) {
                        handle_expired_timeouts();
                        continue;
                }
                
                if (callid & IPC_CALLID_ANSWERED)
                        continue;
                
                handle_call(callid, &call);
        }
        
        return 0;
}

/** Function to start async_manager as a standalone fibril.
 *
 * When more kernel threads are used, one async manager should exist per thread.
 *
 * @param arg Unused.
 * @return Never returns.
 *
 */
static int async_manager_fibril(void *arg)
{
        futex_up(&async_futex);
        
        /*
         * async_futex is always locked when entering manager
         */
        async_manager_worker();
        
        return 0;
}

/** Add one manager to manager list. */
void async_create_manager(void)
{
        fid_t fid = fibril_create(async_manager_fibril, NULL);
        if (fid != 0)
                fibril_add_manager(fid);
}

/** Remove one manager from manager list */
void async_destroy_manager(void)
{
        fibril_remove_manager();
}

/** Initialize the async framework.
 *
 */
void __async_init(void)
{
        if (!hash_table_create(&client_hash_table, CLIENT_HASH_TABLE_BUCKETS,
            2, &client_hash_table_ops))
                abort();
        
        if (!hash_table_create(&conn_hash_table, CONN_HASH_TABLE_BUCKETS,
            1, &conn_hash_table_ops))
                abort();
        
        session_ns = (async_sess_t *) malloc(sizeof(async_sess_t));
        if (session_ns == NULL)
                abort();
        
        session_ns->mgmt = EXCHANGE_ATOMIC;
        session_ns->phone = PHONE_NS;
        session_ns->arg1 = 0;
        session_ns->arg2 = 0;
        session_ns->arg3 = 0;
        
        list_initialize(&session_ns->exch_list);
        fibril_mutex_initialize(&session_ns->mutex);
        atomic_set(&session_ns->refcnt, 0);
}

/** Reply received callback.
 *
 * This function is called whenever a reply for an asynchronous message sent out
 * by the asynchronous framework is received.
 *
 * Notify the fibril which is waiting for this message that it has arrived.
 *
 * @param arg    Pointer to the asynchronous message record.
 * @param retval Value returned in the answer.
 * @param data   Call data of the answer.
 *
 */
void reply_received(void *arg, int retval, ipc_call_t *data)
{
        assert(arg);
        
        futex_down(&async_futex);
        
        amsg_t *msg = (amsg_t *) arg;
        msg->retval = retval;
        
        /* Copy data after futex_down, just in case the call was detached */
        if ((msg->dataptr) && (data))
                *msg->dataptr = *data;
        
        write_barrier();
        
        /* Remove message from timeout list */
        if (msg->wdata.to_event.inlist)
                list_remove(&msg->wdata.to_event.link);
        
        msg->done = true;
        if (!msg->wdata.active) {
                msg->wdata.active = true;
                fibril_add_ready(msg->wdata.fid);
        }
        
        futex_up(&async_futex);
}

/** Send message and return id of the sent message.
 *
 * The return value can be used as input for async_wait() to wait for
 * completion.
 *
 * @param exch    Exchange for sending the message.
 * @param imethod Service-defined interface and method.
 * @param arg1    Service-defined payload argument.
 * @param arg2    Service-defined payload argument.
 * @param arg3    Service-defined payload argument.
 * @param arg4    Service-defined payload argument.
 * @param dataptr If non-NULL, storage where the reply data will be
 *                stored.
 *
 * @return Hash of the sent message or 0 on error.
 *
 */
aid_t async_send_fast(async_exch_t *exch, sysarg_t imethod, sysarg_t arg1,
    sysarg_t arg2, sysarg_t arg3, sysarg_t arg4, ipc_call_t *dataptr)
{
        if (exch == NULL)
                return 0;
        
        amsg_t *msg = malloc(sizeof(amsg_t));
        if (msg == NULL)
                return 0;
        
        msg->done = false;
        msg->dataptr = dataptr;
        
        msg->wdata.to_event.inlist = false;
        
        /*
         * We may sleep in the next method,
         * but it will use its own means
         */
        msg->wdata.active = true;
        
        ipc_call_async_4(exch->phone, imethod, arg1, arg2, arg3, arg4, msg,
            reply_received, true);
        
        return (aid_t) msg;
}

/** Send message and return id of the sent message
 *
 * The return value can be used as input for async_wait() to wait for
 * completion.
 *
 * @param exch    Exchange for sending the message.
 * @param imethod Service-defined interface and method.
 * @param arg1    Service-defined payload argument.
 * @param arg2    Service-defined payload argument.
 * @param arg3    Service-defined payload argument.
 * @param arg4    Service-defined payload argument.
 * @param arg5    Service-defined payload argument.
 * @param dataptr If non-NULL, storage where the reply data will be
 *                stored.
 *
 * @return Hash of the sent message or 0 on error.
 *
 */
aid_t async_send_slow(async_exch_t *exch, sysarg_t imethod, sysarg_t arg1,
    sysarg_t arg2, sysarg_t arg3, sysarg_t arg4, sysarg_t arg5,
    ipc_call_t *dataptr)
{
        if (exch == NULL)
                return 0;
        
        amsg_t *msg = malloc(sizeof(amsg_t));
        
        if (msg == NULL)
                return 0;
        
        msg->done = false;
        msg->dataptr = dataptr;
        
        msg->wdata.to_event.inlist = false;
        
        /*
         * We may sleep in the next method,
         * but it will use its own means
         */
        msg->wdata.active = true;
        
        ipc_call_async_5(exch->phone, imethod, arg1, arg2, arg3, arg4, arg5,
            msg, reply_received, true);
        
        return (aid_t) msg;
}

/** Wait for a message sent by the async framework.
 *
 * @param amsgid Hash of the message to wait for.
 * @param retval Pointer to storage where the retval of the answer will
 *               be stored.
 *
 */
void async_wait_for(aid_t amsgid, sysarg_t *retval)
{
        assert(amsgid);
        
        amsg_t *msg = (amsg_t *) amsgid;
        
        futex_down(&async_futex);
        if (msg->done) {
                futex_up(&async_futex);
                goto done;
        }
        
        msg->wdata.fid = fibril_get_id();
        msg->wdata.active = false;
        msg->wdata.to_event.inlist = false;
        
        /* Leave the async_futex locked when entering this function */
        fibril_switch(FIBRIL_TO_MANAGER);
        
        /* Futex is up automatically after fibril_switch */
        
done:
        if (retval)
                *retval = msg->retval;
        
        free(msg);
}

/** Wait for a message sent by the async framework, timeout variant.
 *
 * @param amsgid  Hash of the message to wait for.
 * @param retval  Pointer to storage where the retval of the answer will
 *                be stored.
 * @param timeout Timeout in microseconds.
 *
 * @return Zero on success, ETIMEOUT if the timeout has expired.
 *
 */
int async_wait_timeout(aid_t amsgid, sysarg_t *retval, suseconds_t timeout)
{
        assert(amsgid);
        
        amsg_t *msg = (amsg_t *) amsgid;
        
        /* TODO: Let it go through the event read at least once */
        if (timeout < 0)
                return ETIMEOUT;
        
        futex_down(&async_futex);
        if (msg->done) {
                futex_up(&async_futex);
                goto done;
        }
        
        gettimeofday(&msg->wdata.to_event.expires, NULL);
        tv_add(&msg->wdata.to_event.expires, timeout);
        
        msg->wdata.fid = fibril_get_id();
        msg->wdata.active = false;
        async_insert_timeout(&msg->wdata);
        
        /* Leave the async_futex locked when entering this function */
        fibril_switch(FIBRIL_TO_MANAGER);
        
        /* Futex is up automatically after fibril_switch */
        
        if (!msg->done)
                return ETIMEOUT;
        
done:
        if (retval)
                *retval = msg->retval;
        
        free(msg);
        
        return 0;
}

/** Wait for specified time.
 *
 * The current fibril is suspended but the thread continues to execute.
 *
 * @param timeout Duration of the wait in microseconds.
 *
 */
void async_usleep(suseconds_t timeout)
{
        amsg_t *msg = malloc(sizeof(amsg_t));
        
        if (!msg)
                return;
        
        msg->wdata.fid = fibril_get_id();
        msg->wdata.active = false;
        
        gettimeofday(&msg->wdata.to_event.expires, NULL);
        tv_add(&msg->wdata.to_event.expires, timeout);
        
        futex_down(&async_futex);
        
        async_insert_timeout(&msg->wdata);
        
        /* Leave the async_futex locked when entering this function */
        fibril_switch(FIBRIL_TO_MANAGER);
        
        /* Futex is up automatically after fibril_switch() */
        
        free(msg);
}

/** Pseudo-synchronous message sending - fast version.
 *
 * Send message asynchronously and return only after the reply arrives.
 *
 * This function can only transfer 4 register payload arguments. For
 * transferring more arguments, see the slower async_req_slow().
 *
 * @param exch    Exchange for sending the message.
 * @param imethod Interface and method of the call.
 * @param arg1    Service-defined payload argument.
 * @param arg2    Service-defined payload argument.
 * @param arg3    Service-defined payload argument.
 * @param arg4    Service-defined payload argument.
 * @param r1      If non-NULL, storage for the 1st reply argument.
 * @param r2      If non-NULL, storage for the 2nd reply argument.
 * @param r3      If non-NULL, storage for the 3rd reply argument.
 * @param r4      If non-NULL, storage for the 4th reply argument.
 * @param r5      If non-NULL, storage for the 5th reply argument.
 *
 * @return Return code of the reply or a negative error code.
 *
 */
sysarg_t async_req_fast(async_exch_t *exch, sysarg_t imethod, sysarg_t arg1,
    sysarg_t arg2, sysarg_t arg3, sysarg_t arg4, sysarg_t *r1, sysarg_t *r2,
    sysarg_t *r3, sysarg_t *r4, sysarg_t *r5)
{
        if (exch == NULL)
                return ENOENT;
        
        ipc_call_t result;
        aid_t aid = async_send_4(exch, imethod, arg1, arg2, arg3, arg4,
            &result);
        
        sysarg_t rc;
        async_wait_for(aid, &rc);
        
        if (r1)
                *r1 = IPC_GET_ARG1(result);
        
        if (r2)
                *r2 = IPC_GET_ARG2(result);
        
        if (r3)
                *r3 = IPC_GET_ARG3(result);
        
        if (r4)
                *r4 = IPC_GET_ARG4(result);
        
        if (r5)
                *r5 = IPC_GET_ARG5(result);
        
        return rc;
}

/** Pseudo-synchronous message sending - slow version.
 *
 * Send message asynchronously and return only after the reply arrives.
 *
 * @param exch    Exchange for sending the message.
 * @param imethod Interface and method of the call.
 * @param arg1    Service-defined payload argument.
 * @param arg2    Service-defined payload argument.
 * @param arg3    Service-defined payload argument.
 * @param arg4    Service-defined payload argument.
 * @param arg5    Service-defined payload argument.
 * @param r1      If non-NULL, storage for the 1st reply argument.
 * @param r2      If non-NULL, storage for the 2nd reply argument.
 * @param r3      If non-NULL, storage for the 3rd reply argument.
 * @param r4      If non-NULL, storage for the 4th reply argument.
 * @param r5      If non-NULL, storage for the 5th reply argument.
 *
 * @return Return code of the reply or a negative error code.
 *
 */
sysarg_t async_req_slow(async_exch_t *exch, sysarg_t imethod, sysarg_t arg1,
    sysarg_t arg2, sysarg_t arg3, sysarg_t arg4, sysarg_t arg5, sysarg_t *r1,
    sysarg_t *r2, sysarg_t *r3, sysarg_t *r4, sysarg_t *r5)
{
        if (exch == NULL)
                return ENOENT;
        
        ipc_call_t result;
        aid_t aid = async_send_5(exch, imethod, arg1, arg2, arg3, arg4, arg5,
            &result);
        
        sysarg_t rc;
        async_wait_for(aid, &rc);
        
        if (r1)
                *r1 = IPC_GET_ARG1(result);
        
        if (r2)
                *r2 = IPC_GET_ARG2(result);
        
        if (r3)
                *r3 = IPC_GET_ARG3(result);
        
        if (r4)
                *r4 = IPC_GET_ARG4(result);
        
        if (r5)
                *r5 = IPC_GET_ARG5(result);
        
        return rc;
}

void async_msg_0(async_exch_t *exch, sysarg_t imethod)
{
        if (exch != NULL)
                ipc_call_async_0(exch->phone, imethod, NULL, NULL, true);
}

void async_msg_1(async_exch_t *exch, sysarg_t imethod, sysarg_t arg1)
{
        if (exch != NULL)
                ipc_call_async_1(exch->phone, imethod, arg1, NULL, NULL, true);
}

void async_msg_2(async_exch_t *exch, sysarg_t imethod, sysarg_t arg1,
    sysarg_t arg2)
{
        if (exch != NULL)
                ipc_call_async_2(exch->phone, imethod, arg1, arg2, NULL, NULL,
                    true);
}

void async_msg_3(async_exch_t *exch, sysarg_t imethod, sysarg_t arg1,
    sysarg_t arg2, sysarg_t arg3)
{
        if (exch != NULL)
                ipc_call_async_3(exch->phone, imethod, arg1, arg2, arg3, NULL,
                    NULL, true);
}

void async_msg_4(async_exch_t *exch, sysarg_t imethod, sysarg_t arg1,
    sysarg_t arg2, sysarg_t arg3, sysarg_t arg4)
{
        if (exch != NULL)
                ipc_call_async_4(exch->phone, imethod, arg1, arg2, arg3, arg4,
                    NULL, NULL, true);
}

void async_msg_5(async_exch_t *exch, sysarg_t imethod, sysarg_t arg1,
    sysarg_t arg2, sysarg_t arg3, sysarg_t arg4, sysarg_t arg5)
{
        if (exch != NULL)
                ipc_call_async_5(exch->phone, imethod, arg1, arg2, arg3, arg4,
                    arg5, NULL, NULL, true);
}

sysarg_t async_answer_0(ipc_callid_t callid, sysarg_t retval)
{
        return ipc_answer_0(callid, retval);
}

sysarg_t async_answer_1(ipc_callid_t callid, sysarg_t retval, sysarg_t arg1)
{
        return ipc_answer_1(callid, retval, arg1);
}

sysarg_t async_answer_2(ipc_callid_t callid, sysarg_t retval, sysarg_t arg1,
    sysarg_t arg2)
{
        return ipc_answer_2(callid, retval, arg1, arg2);
}

sysarg_t async_answer_3(ipc_callid_t callid, sysarg_t retval, sysarg_t arg1,
    sysarg_t arg2, sysarg_t arg3)
{
        return ipc_answer_3(callid, retval, arg1, arg2, arg3);
}

sysarg_t async_answer_4(ipc_callid_t callid, sysarg_t retval, sysarg_t arg1,
    sysarg_t arg2, sysarg_t arg3, sysarg_t arg4)
{
        return ipc_answer_4(callid, retval, arg1, arg2, arg3, arg4);
}

sysarg_t async_answer_5(ipc_callid_t callid, sysarg_t retval, sysarg_t arg1,
    sysarg_t arg2, sysarg_t arg3, sysarg_t arg4, sysarg_t arg5)
{
        return ipc_answer_5(callid, retval, arg1, arg2, arg3, arg4, arg5);
}

int async_forward_fast(ipc_callid_t callid, async_exch_t *exch,
    sysarg_t imethod, sysarg_t arg1, sysarg_t arg2, unsigned int mode)
{
        if (exch == NULL)
                return ENOENT;
        
        return ipc_forward_fast(callid, exch->phone, imethod, arg1, arg2, mode);
}

int async_forward_slow(ipc_callid_t callid, async_exch_t *exch,
    sysarg_t imethod, sysarg_t arg1, sysarg_t arg2, sysarg_t arg3,
    sysarg_t arg4, sysarg_t arg5, unsigned int mode)
{
        if (exch == NULL)
                return ENOENT;
        
        return ipc_forward_slow(callid, exch->phone, imethod, arg1, arg2, arg3,
            arg4, arg5, mode);
}

/** Wrapper for making IPC_M_CONNECT_TO_ME calls using the async framework.
 *
 * Ask through phone for a new connection to some service.
 *
 * @param exch            Exchange for sending the message.
 * @param arg1            User defined argument.
 * @param arg2            User defined argument.
 * @param arg3            User defined argument.
 * @param client_receiver Connection handing routine.
 *
 * @return Zero on success or a negative error code.
 *
 */
int async_connect_to_me(async_exch_t *exch, sysarg_t arg1, sysarg_t arg2,
    sysarg_t arg3, async_client_conn_t client_receiver, void *carg)
{
        if (exch == NULL)
                return ENOENT;
        
        task_id_t task_id;
        sysarg_t task_id_lo;
        sysarg_t task_id_hi;
        sysarg_t phone_hash;
        int rc = async_req_3_5(exch, IPC_M_CONNECT_TO_ME, arg1, arg2, arg3,
            NULL, NULL, &task_id_lo, &task_id_hi, &phone_hash);
        if (rc != EOK)
                return rc;

        task_id = (task_id_t) MERGE_LOUP32(task_id_lo, task_id_hi);
        
        if (client_receiver != NULL)
                async_new_connection(task_id, phone_hash, 0, NULL,
                    client_receiver, carg);
        
        return EOK;
}

/** Wrapper for making IPC_M_CONNECT_ME calls using the async framework.
 *
 * Ask through for a cloned connection to some service.
 *
 * @param mgmt Exchange management style.
 * @param exch Exchange for sending the message.
 *
 * @return New session on success or NULL on error.
 *
 */
async_sess_t *async_connect_me(exch_mgmt_t mgmt, async_exch_t *exch)
{
        if (exch == NULL) {
                errno = ENOENT;
                return NULL;
        }
        
        async_sess_t *sess = (async_sess_t *) malloc(sizeof(async_sess_t));
        if (sess == NULL) {
                errno = ENOMEM;
                return NULL;
        }
        
        ipc_call_t result;
        
        amsg_t *msg = malloc(sizeof(amsg_t));
        if (msg == NULL) {
                free(sess);
                errno = ENOMEM;
                return NULL;
        }
        
        msg->done = false;
        msg->dataptr = &result;
        
        msg->wdata.to_event.inlist = false;
        
        /*
         * We may sleep in the next method,
         * but it will use its own means
         */
        msg->wdata.active = true;
        
        ipc_call_async_0(exch->phone, IPC_M_CONNECT_ME, msg,
            reply_received, true);
        
        sysarg_t rc;
        async_wait_for((aid_t) msg, &rc);
        
        if (rc != EOK) {
                errno = rc;
                free(sess);
                return NULL;
        }
        
        int phone = (int) IPC_GET_ARG5(result);
        
        if (phone < 0) {
                errno = phone;
                free(sess);
                return NULL;
        }
        
        sess->mgmt = mgmt;
        sess->phone = phone;
        sess->arg1 = 0;
        sess->arg2 = 0;
        sess->arg3 = 0;
        
        list_initialize(&sess->exch_list);
        fibril_mutex_initialize(&sess->mutex);
        atomic_set(&sess->refcnt, 0);
        
        return sess;
}

static int async_connect_me_to_internal(int phone, sysarg_t arg1, sysarg_t arg2,
    sysarg_t arg3, sysarg_t arg4)
{
        ipc_call_t result;
        
        amsg_t *msg = malloc(sizeof(amsg_t));
        if (msg == NULL)
                return ENOENT;
        
        msg->done = false;
        msg->dataptr = &result;
        
        msg->wdata.to_event.inlist = false;
        
        /*
         * We may sleep in the next method,
         * but it will use its own means
         */
        msg->wdata.active = true;
        
        ipc_call_async_4(phone, IPC_M_CONNECT_ME_TO, arg1, arg2, arg3, arg4,
            msg, reply_received, true);
        
        sysarg_t rc;
        async_wait_for((aid_t) msg, &rc);
        
        if (rc != EOK)
                return rc;
        
        return (int) IPC_GET_ARG5(result);
}

/** Wrapper for making IPC_M_CONNECT_ME_TO calls using the async framework.
 *
 * Ask through for a new connection to some service.
 *
 * @param mgmt Exchange management style.
 * @param exch Exchange for sending the message.
 * @param arg1 User defined argument.
 * @param arg2 User defined argument.
 * @param arg3 User defined argument.
 *
 * @return New session on success or NULL on error.
 *
 */
async_sess_t *async_connect_me_to(exch_mgmt_t mgmt, async_exch_t *exch,
    sysarg_t arg1, sysarg_t arg2, sysarg_t arg3)
{
        if (exch == NULL) {
                errno = ENOENT;
                return NULL;
        }
        
        async_sess_t *sess = (async_sess_t *) malloc(sizeof(async_sess_t));
        if (sess == NULL) {
                errno = ENOMEM;
                return NULL;
        }
        
        int phone = async_connect_me_to_internal(exch->phone, arg1, arg2, arg3,
            0);
        
        if (phone < 0) {
                errno = phone;
                free(sess);
                return NULL;
        }
        
        sess->mgmt = mgmt;
        sess->phone = phone;
        sess->arg1 = arg1;
        sess->arg2 = arg2;
        sess->arg3 = arg3;
        
        list_initialize(&sess->exch_list);
        fibril_mutex_initialize(&sess->mutex);
        atomic_set(&sess->refcnt, 0);
        
        return sess;
}

/** Wrapper for making IPC_M_CONNECT_ME_TO calls using the async framework.
 *
 * Ask through phone for a new connection to some service and block until
 * success.
 *
 * @param mgmt Exchange management style.
 * @param exch Exchange for sending the message.
 * @param arg1 User defined argument.
 * @param arg2 User defined argument.
 * @param arg3 User defined argument.
 *
 * @return New session on success or NULL on error.
 *
 */
async_sess_t *async_connect_me_to_blocking(exch_mgmt_t mgmt, async_exch_t *exch,
    sysarg_t arg1, sysarg_t arg2, sysarg_t arg3)
{
        if (exch == NULL) {
                errno = ENOENT;
                return NULL;
        }
        
        async_sess_t *sess = (async_sess_t *) malloc(sizeof(async_sess_t));
        if (sess == NULL) {
                errno = ENOMEM;
                return NULL;
        }
        
        int phone = async_connect_me_to_internal(exch->phone, arg1, arg2, arg3,
            IPC_FLAG_BLOCKING);
        
        if (phone < 0) {
                errno = phone;
                free(sess);
                return NULL;
        }
        
        sess->mgmt = mgmt;
        sess->phone = phone;
        sess->arg1 = arg1;
        sess->arg2 = arg2;
        sess->arg3 = arg3;
        
        list_initialize(&sess->exch_list);
        fibril_mutex_initialize(&sess->mutex);
        atomic_set(&sess->refcnt, 0);
        
        return sess;
}

/** Connect to a task specified by id.
 *
 */
async_sess_t *async_connect_kbox(task_id_t id)
{
        async_sess_t *sess = (async_sess_t *) malloc(sizeof(async_sess_t));
        if (sess == NULL) {
                errno = ENOMEM;
                return NULL;
        }
        
        int phone = ipc_connect_kbox(id);
        if (phone < 0) {
                errno = phone;
                free(sess);
                return NULL;
        }
        
        sess->mgmt = EXCHANGE_ATOMIC;
        sess->phone = phone;
        sess->arg1 = 0;
        sess->arg2 = 0;
        sess->arg3 = 0;
        
        list_initialize(&sess->exch_list);
        fibril_mutex_initialize(&sess->mutex);
        atomic_set(&sess->refcnt, 0);
        
        return sess;
}

static int async_hangup_internal(int phone)
{
        return ipc_hangup(phone);
}

/** Wrapper for ipc_hangup.
 *
 * @param sess Session to hung up.
 *
 * @return Zero on success or a negative error code.
 *
 */
int async_hangup(async_sess_t *sess)
{
        assert(sess);
        
        if (atomic_get(&sess->refcnt) > 0)
                return EBUSY;
        
        int rc = async_hangup_internal(sess->phone);
        if (rc == EOK)
                free(sess);
        
        return rc;
}

/** Interrupt one thread of this task from waiting for IPC. */
void async_poke(void)
{
        ipc_poke();
}

/** Start new exchange in a session.
 *
 * @param session Session.
 *
 * @return New exchange or NULL on error.
 *
 */
async_exch_t *async_exchange_begin(async_sess_t *sess)
{
        if (sess == NULL)
                return NULL;
        
        async_exch_t *exch;
        
        fibril_mutex_lock(&async_sess_mutex);
        
        if (!list_empty(&sess->exch_list)) {
                /*
                 * There are inactive exchanges in the session.
                 */
                exch = (async_exch_t *)
                    list_get_instance(list_first(&sess->exch_list),
                    async_exch_t, sess_link);
                
                list_remove(&exch->sess_link);
                list_remove(&exch->global_link);
        } else {
                /*
                 * There are no available exchanges in the session.
                 */
                
                if ((sess->mgmt == EXCHANGE_ATOMIC) ||
                    (sess->mgmt == EXCHANGE_SERIALIZE)) {
                        exch = (async_exch_t *) malloc(sizeof(async_exch_t));
                        if (exch != NULL) {
                                link_initialize(&exch->sess_link);
                                link_initialize(&exch->global_link);
                                exch->sess = sess;
                                exch->phone = sess->phone;
                        }
                } else {  /* EXCHANGE_PARALLEL */
                        /*
                         * Make a one-time attempt to connect a new data phone.
                         */
                        
                        int phone;
                        
retry:
                        phone = async_connect_me_to_internal(sess->phone, sess->arg1,
                            sess->arg2, sess->arg3, 0);
                        if (phone >= 0) {
                                exch = (async_exch_t *) malloc(sizeof(async_exch_t));
                                if (exch != NULL) {
                                        link_initialize(&exch->sess_link);
                                        link_initialize(&exch->global_link);
                                        exch->sess = sess;
                                        exch->phone = phone;
                                } else
                                        async_hangup_internal(phone);
                        } else if (!list_empty(&inactive_exch_list)) {
                                /*
                                 * We did not manage to connect a new phone. But we
                                 * can try to close some of the currently inactive
                                 * connections in other sessions and try again.
                                 */
                                exch = (async_exch_t *)
                                    list_get_instance(list_first(&inactive_exch_list),
                                    async_exch_t, global_link);
                                
                                list_remove(&exch->sess_link);
                                list_remove(&exch->global_link);
                                async_hangup_internal(exch->phone);
                                free(exch);
                                goto retry;
                        } else {
                                /*
                                 * Wait for a phone to become available.
                                 */
                                fibril_condvar_wait(&avail_phone_cv, &async_sess_mutex);
                                goto retry;
                        }
                }
        }
        
        fibril_mutex_unlock(&async_sess_mutex);
        
        if (exch != NULL) {
                atomic_inc(&sess->refcnt);
                
                if (sess->mgmt == EXCHANGE_SERIALIZE)
                        fibril_mutex_lock(&sess->mutex);
        }
        
        return exch;
}

/** Finish an exchange.
 *
 * @param exch Exchange to finish.
 *
 */
void async_exchange_end(async_exch_t *exch)
{
        if (exch == NULL)
                return;
        
        async_sess_t *sess = exch->sess;
        
        atomic_dec(&sess->refcnt);
        
        if (sess->mgmt == EXCHANGE_SERIALIZE)
                fibril_mutex_unlock(&sess->mutex);
        
        fibril_mutex_lock(&async_sess_mutex);
        
        list_append(&exch->sess_link, &sess->exch_list);
        list_append(&exch->global_link, &inactive_exch_list);
        fibril_condvar_signal(&avail_phone_cv);
        
        fibril_mutex_unlock(&async_sess_mutex);
}

/** Wrapper for IPC_M_SHARE_IN calls using the async framework.
 *
 * @param exch  Exchange for sending the message.
 * @param dst   Destination address space area base.
 * @param size  Size of the destination address space area.
 * @param arg   User defined argument.
 * @param flags Storage for the received flags. Can be NULL.
 *
 * @return Zero on success or a negative error code from errno.h.
 *
 */
int async_share_in_start(async_exch_t *exch, void *dst, size_t size,
    sysarg_t arg, unsigned int *flags)
{
        if (exch == NULL)
                return ENOENT;
        
        sysarg_t tmp_flags;
        int res = async_req_3_2(exch, IPC_M_SHARE_IN, (sysarg_t) dst,
            (sysarg_t) size, arg, NULL, &tmp_flags);
        
        if (flags)
                *flags = (unsigned int) tmp_flags;
        
        return res;
}

/** Wrapper for receiving the IPC_M_SHARE_IN calls using the async framework.
 *
 * This wrapper only makes it more comfortable to receive IPC_M_SHARE_IN
 * calls so that the user doesn't have to remember the meaning of each IPC
 * argument.
 *
 * So far, this wrapper is to be used from within a connection fibril.
 *
 * @param callid Storage for the hash of the IPC_M_SHARE_IN call.
 * @param size   Destination address space area size.
 *
 * @return True on success, false on failure.
 *
 */
bool async_share_in_receive(ipc_callid_t *callid, size_t *size)
{
        assert(callid);
        assert(size);
        
        ipc_call_t data;
        *callid = async_get_call(&data);
        
        if (IPC_GET_IMETHOD(data) != IPC_M_SHARE_IN)
                return false;
        
        *size = (size_t) IPC_GET_ARG2(data);
        return true;
}

/** Wrapper for answering the IPC_M_SHARE_IN calls using the async framework.
 *
 * This wrapper only makes it more comfortable to answer IPC_M_DATA_READ
 * calls so that the user doesn't have to remember the meaning of each IPC
 * argument.
 *
 * @param callid Hash of the IPC_M_DATA_READ call to answer.
 * @param src    Source address space base.
 * @param flags  Flags to be used for sharing. Bits can be only cleared.
 *
 * @return Zero on success or a value from @ref errno.h on failure.
 *
 */
int async_share_in_finalize(ipc_callid_t callid, void *src, unsigned int flags)
{
        return ipc_share_in_finalize(callid, src, flags);
}

/** Wrapper for IPC_M_SHARE_OUT calls using the async framework.
 *
 * @param exch  Exchange for sending the message.
 * @param src   Source address space area base address.
 * @param flags Flags to be used for sharing. Bits can be only cleared.
 *
 * @return Zero on success or a negative error code from errno.h.
 *
 */
int async_share_out_start(async_exch_t *exch, void *src, unsigned int flags)
{
        if (exch == NULL)
                return ENOENT;
        
        return async_req_3_0(exch, IPC_M_SHARE_OUT, (sysarg_t) src, 0,
            (sysarg_t) flags);
}

/** Wrapper for receiving the IPC_M_SHARE_OUT calls using the async framework.
 *
 * This wrapper only makes it more comfortable to receive IPC_M_SHARE_OUT
 * calls so that the user doesn't have to remember the meaning of each IPC
 * argument.
 *
 * So far, this wrapper is to be used from within a connection fibril.
 *
 * @param callid Storage for the hash of the IPC_M_SHARE_OUT call.
 * @param size   Storage for the source address space area size.
 * @param flags  Storage for the sharing flags.
 *
 * @return True on success, false on failure.
 *
 */
bool async_share_out_receive(ipc_callid_t *callid, size_t *size, unsigned int *flags)
{
        assert(callid);
        assert(size);
        assert(flags);
        
        ipc_call_t data;
        *callid = async_get_call(&data);
        
        if (IPC_GET_IMETHOD(data) != IPC_M_SHARE_OUT)
                return false;
        
        *size = (size_t) IPC_GET_ARG2(data);
        *flags = (unsigned int) IPC_GET_ARG3(data);
        return true;
}

/** Wrapper for answering the IPC_M_SHARE_OUT calls using the async framework.
 *
 * This wrapper only makes it more comfortable to answer IPC_M_SHARE_OUT
 * calls so that the user doesn't have to remember the meaning of each IPC
 * argument.
 *
 * @param callid Hash of the IPC_M_DATA_WRITE call to answer.
 * @param dst    Destination address space area base address.
 *
 * @return Zero on success or a value from @ref errno.h on failure.
 *
 */
int async_share_out_finalize(ipc_callid_t callid, void *dst)
{
        return ipc_share_out_finalize(callid, dst);
}

/** Start IPC_M_DATA_READ using the async framework.
 *
 * @param exch    Exchange for sending the message.
 * @param dst     Address of the beginning of the destination buffer.
 * @param size    Size of the destination buffer (in bytes).
 * @param dataptr Storage of call data (arg 2 holds actual data size).
 *
 * @return Hash of the sent message or 0 on error.
 *
 */
aid_t async_data_read(async_exch_t *exch, void *dst, size_t size,
    ipc_call_t *dataptr)
{
        return async_send_2(exch, IPC_M_DATA_READ, (sysarg_t) dst,
            (sysarg_t) size, dataptr);
}

/** Wrapper for IPC_M_DATA_READ calls using the async framework.
 *
 * @param exch Exchange for sending the message.
 * @param dst  Address of the beginning of the destination buffer.
 * @param size Size of the destination buffer.
 *
 * @return Zero on success or a negative error code from errno.h.
 *
 */
int async_data_read_start(async_exch_t *exch, void *dst, size_t size)
{
        if (exch == NULL)
                return ENOENT;
        
        return async_req_2_0(exch, IPC_M_DATA_READ, (sysarg_t) dst,
            (sysarg_t) size);
}

/** Wrapper for receiving the IPC_M_DATA_READ calls using the async framework.
 *
 * This wrapper only makes it more comfortable to receive IPC_M_DATA_READ
 * calls so that the user doesn't have to remember the meaning of each IPC
 * argument.
 *
 * So far, this wrapper is to be used from within a connection fibril.
 *
 * @param callid Storage for the hash of the IPC_M_DATA_READ.
 * @param size   Storage for the maximum size. Can be NULL.
 *
 * @return True on success, false on failure.
 *
 */
bool async_data_read_receive(ipc_callid_t *callid, size_t *size)
{
        assert(callid);
        
        ipc_call_t data;
        *callid = async_get_call(&data);
        
        if (IPC_GET_IMETHOD(data) != IPC_M_DATA_READ)
                return false;
        
        if (size)
                *size = (size_t) IPC_GET_ARG2(data);
        
        return true;
}

/** Wrapper for answering the IPC_M_DATA_READ calls using the async framework.
 *
 * This wrapper only makes it more comfortable to answer IPC_M_DATA_READ
 * calls so that the user doesn't have to remember the meaning of each IPC
 * argument.
 *
 * @param callid Hash of the IPC_M_DATA_READ call to answer.
 * @param src    Source address for the IPC_M_DATA_READ call.
 * @param size   Size for the IPC_M_DATA_READ call. Can be smaller than
 *               the maximum size announced by the sender.
 *
 * @return Zero on success or a value from @ref errno.h on failure.
 *
 */
int async_data_read_finalize(ipc_callid_t callid, const void *src, size_t size)
{
        return ipc_data_read_finalize(callid, src, size);
}

/** Wrapper for forwarding any read request
 *
 */
int async_data_read_forward_fast(async_exch_t *exch, sysarg_t imethod,
    sysarg_t arg1, sysarg_t arg2, sysarg_t arg3, sysarg_t arg4,
    ipc_call_t *dataptr)
{
        if (exch == NULL)
                return ENOENT;
        
        ipc_callid_t callid;
        if (!async_data_read_receive(&callid, NULL)) {
                ipc_answer_0(callid, EINVAL);
                return EINVAL;
        }
        
        aid_t msg = async_send_fast(exch, imethod, arg1, arg2, arg3, arg4,
            dataptr);
        if (msg == 0) {
                ipc_answer_0(callid, EINVAL);
                return EINVAL;
        }
        
        int retval = ipc_forward_fast(callid, exch->phone, 0, 0, 0,
            IPC_FF_ROUTE_FROM_ME);
        if (retval != EOK) {
                async_wait_for(msg, NULL);
                ipc_answer_0(callid, retval);
                return retval;
        }
        
        sysarg_t rc;
        async_wait_for(msg, &rc);
        
        return (int) rc;
}

/** Wrapper for IPC_M_DATA_WRITE calls using the async framework.
 *
 * @param exch Exchange for sending the message.
 * @param src  Address of the beginning of the source buffer.
 * @param size Size of the source buffer.
 *
 * @return Zero on success or a negative error code from errno.h.
 *
 */
int async_data_write_start(async_exch_t *exch, const void *src, size_t size)
{
        if (exch == NULL)
                return ENOENT;
        
        return async_req_2_0(exch, IPC_M_DATA_WRITE, (sysarg_t) src,
            (sysarg_t) size);
}

/** Wrapper for receiving the IPC_M_DATA_WRITE calls using the async framework.
 *
 * This wrapper only makes it more comfortable to receive IPC_M_DATA_WRITE
 * calls so that the user doesn't have to remember the meaning of each IPC
 * argument.
 *
 * So far, this wrapper is to be used from within a connection fibril.
 *
 * @param callid Storage for the hash of the IPC_M_DATA_WRITE.
 * @param size   Storage for the suggested size. May be NULL.
 *
 * @return True on success, false on failure.
 *
 */
bool async_data_write_receive(ipc_callid_t *callid, size_t *size)
{
        assert(callid);
        
        ipc_call_t data;
        *callid = async_get_call(&data);
        
        if (IPC_GET_IMETHOD(data) != IPC_M_DATA_WRITE)
                return false;
        
        if (size)
                *size = (size_t) IPC_GET_ARG2(data);
        
        return true;
}

/** Wrapper for answering the IPC_M_DATA_WRITE calls using the async framework.
 *
 * This wrapper only makes it more comfortable to answer IPC_M_DATA_WRITE
 * calls so that the user doesn't have to remember the meaning of each IPC
 * argument.
 *
 * @param callid Hash of the IPC_M_DATA_WRITE call to answer.
 * @param dst    Final destination address for the IPC_M_DATA_WRITE call.
 * @param size   Final size for the IPC_M_DATA_WRITE call.
 *
 * @return Zero on success or a value from @ref errno.h on failure.
 *
 */
int async_data_write_finalize(ipc_callid_t callid, void *dst, size_t size)
{
        return ipc_data_write_finalize(callid, dst, size);
}

/** Wrapper for receiving binary data or strings
 *
 * This wrapper only makes it more comfortable to use async_data_write_*
 * functions to receive binary data or strings.
 *
 * @param data       Pointer to data pointer (which should be later disposed
 *                   by free()). If the operation fails, the pointer is not
 *                   touched.
 * @param nullterm   If true then the received data is always zero terminated.
 *                   This also causes to allocate one extra byte beyond the
 *                   raw transmitted data.
 * @param min_size   Minimum size (in bytes) of the data to receive.
 * @param max_size   Maximum size (in bytes) of the data to receive. 0 means
 *                   no limit.
 * @param granulariy If non-zero then the size of the received data has to
 *                   be divisible by this value.
 * @param received   If not NULL, the size of the received data is stored here.
 *
 * @return Zero on success or a value from @ref errno.h on failure.
 *
 */
int async_data_write_accept(void **data, const bool nullterm,
    const size_t min_size, const size_t max_size, const size_t granularity,
    size_t *received)
{
        assert(data);
        
        ipc_callid_t callid;
        size_t size;
        if (!async_data_write_receive(&callid, &size)) {
                ipc_answer_0(callid, EINVAL);
                return EINVAL;
        }
        
        if (size < min_size) {
                ipc_answer_0(callid, EINVAL);
                return EINVAL;
        }
        
        if ((max_size > 0) && (size > max_size)) {
                ipc_answer_0(callid, EINVAL);
                return EINVAL;
        }
        
        if ((granularity > 0) && ((size % granularity) != 0)) {
                ipc_answer_0(callid, EINVAL);
                return EINVAL;
        }
        
        void *_data;
        
        if (nullterm)
                _data = malloc(size + 1);
        else
                _data = malloc(size);
        
        if (_data == NULL) {
                ipc_answer_0(callid, ENOMEM);
                return ENOMEM;
        }
        
        int rc = async_data_write_finalize(callid, _data, size);
        if (rc != EOK) {
                free(_data);
                return rc;
        }
        
        if (nullterm)
                ((char *) _data)[size] = 0;
        
        *data = _data;
        if (received != NULL)
                *received = size;
        
        return EOK;
}

/** Wrapper for voiding any data that is about to be received
 *
 * This wrapper can be used to void any pending data
 *
 * @param retval Error value from @ref errno.h to be returned to the caller.
 *
 */
void async_data_write_void(sysarg_t retval)
{
        ipc_callid_t callid;
        async_data_write_receive(&callid, NULL);
        ipc_answer_0(callid, retval);
}

/** Wrapper for forwarding any data that is about to be received
 *
 */
int async_data_write_forward_fast(async_exch_t *exch, sysarg_t imethod,
    sysarg_t arg1, sysarg_t arg2, sysarg_t arg3, sysarg_t arg4,
    ipc_call_t *dataptr)
{
        if (exch == NULL)
                return ENOENT;
        
        ipc_callid_t callid;
        if (!async_data_write_receive(&callid, NULL)) {
                ipc_answer_0(callid, EINVAL);
                return EINVAL;
        }
        
        aid_t msg = async_send_fast(exch, imethod, arg1, arg2, arg3, arg4,
            dataptr);
        if (msg == 0) {
                ipc_answer_0(callid, EINVAL);
                return EINVAL;
        }
        
        int retval = ipc_forward_fast(callid, exch->phone, 0, 0, 0,
            IPC_FF_ROUTE_FROM_ME);
        if (retval != EOK) {
                async_wait_for(msg, NULL);
                ipc_answer_0(callid, retval);
                return retval;
        }
        
        sysarg_t rc;
        async_wait_for(msg, &rc);
        
        return (int) rc;
}

/** Wrapper for sending an exchange over different exchange for cloning
 *
 * @param exch       Exchange to be used for sending.
 * @param clone_exch Exchange to be cloned.
 *
 */
int async_exchange_clone(async_exch_t *exch, async_exch_t *clone_exch)
{
        return async_req_1_0(exch, IPC_M_CONNECTION_CLONE, clone_exch->phone);
}

/** Wrapper for receiving the IPC_M_CONNECTION_CLONE calls.
 *
 * If the current call is IPC_M_CONNECTION_CLONE then a new
 * async session is created for the accepted phone.
 *
 * @param mgmt Exchange management style.
 *
 * @return New async session or NULL on failure.
 *
 */
async_sess_t *async_clone_receive(exch_mgmt_t mgmt)
{
        /* Accept the phone */
        ipc_call_t call;
        ipc_callid_t callid = async_get_call(&call);
        int phone = (int) IPC_GET_ARG1(call);
        
        if ((IPC_GET_IMETHOD(call) != IPC_M_CONNECTION_CLONE) ||
            (phone < 0)) {
                async_answer_0(callid, EINVAL);
                return NULL;
        }
        
        async_sess_t *sess = (async_sess_t *) malloc(sizeof(async_sess_t));
        if (sess == NULL) {
                async_answer_0(callid, ENOMEM);
                return NULL;
        }
        
        sess->mgmt = mgmt;
        sess->phone = phone;
        sess->arg1 = 0;
        sess->arg2 = 0;
        sess->arg3 = 0;
        
        list_initialize(&sess->exch_list);
        fibril_mutex_initialize(&sess->mutex);
        atomic_set(&sess->refcnt, 0);
        
        /* Acknowledge the cloned phone */
        async_answer_0(callid, EOK);
        
        return sess;
}

/** Wrapper for receiving the IPC_M_CONNECT_TO_ME calls.
 *
 * If the current call is IPC_M_CONNECT_TO_ME then a new
 * async session is created for the accepted phone.
 *
 * @param mgmt Exchange management style.
 *
 * @return New async session.
 * @return NULL on failure.
 *
 */
async_sess_t *async_callback_receive(exch_mgmt_t mgmt)
{
        /* Accept the phone */
        ipc_call_t call;
        ipc_callid_t callid = async_get_call(&call);
        int phone = (int) IPC_GET_ARG5(call);
        
        if ((IPC_GET_IMETHOD(call) != IPC_M_CONNECT_TO_ME) ||
            (phone < 0)) {
                async_answer_0(callid, EINVAL);
                return NULL;
        }
        
        async_sess_t *sess = (async_sess_t *) malloc(sizeof(async_sess_t));
        if (sess == NULL) {
                async_answer_0(callid, ENOMEM);
                return NULL;
        }
        
        sess->mgmt = mgmt;
        sess->phone = phone;
        sess->arg1 = 0;
        sess->arg2 = 0;
        sess->arg3 = 0;
        
        list_initialize(&sess->exch_list);
        fibril_mutex_initialize(&sess->mutex);
        atomic_set(&sess->refcnt, 0);
        
        /* Acknowledge the connected phone */
        async_answer_0(callid, EOK);
        
        return sess;
}

/** Wrapper for receiving the IPC_M_CONNECT_TO_ME calls.
 *
 * If the call is IPC_M_CONNECT_TO_ME then a new
 * async session is created. However, the phone is
 * not accepted automatically.
 *
 * @param mgmt   Exchange management style.
 * @param call   Call data.
 *
 * @return New async session.
 * @return NULL on failure.
 * @return NULL if the call is not IPC_M_CONNECT_TO_ME.
 *
 */
async_sess_t *async_callback_receive_start(exch_mgmt_t mgmt, ipc_call_t *call)
{
        int phone = (int) IPC_GET_ARG5(*call);
        
        if ((IPC_GET_IMETHOD(*call) != IPC_M_CONNECT_TO_ME) ||
            (phone < 0))
                return NULL;
        
        async_sess_t *sess = (async_sess_t *) malloc(sizeof(async_sess_t));
        if (sess == NULL)
                return NULL;
        
        sess->mgmt = mgmt;
        sess->phone = phone;
        sess->arg1 = 0;
        sess->arg2 = 0;
        sess->arg3 = 0;
        
        list_initialize(&sess->exch_list);
        fibril_mutex_initialize(&sess->mutex);
        atomic_set(&sess->refcnt, 0);
        
        return sess;
}

int async_state_change_start(async_exch_t *exch, sysarg_t arg1, sysarg_t arg2,
    sysarg_t arg3, async_exch_t *other_exch)
{
        return async_req_5_0(exch, IPC_M_STATE_CHANGE_AUTHORIZE,
            arg1, arg2, arg3, 0, other_exch->phone);
}

bool async_state_change_receive(ipc_callid_t *callid, sysarg_t *arg1,
    sysarg_t *arg2, sysarg_t *arg3)
{
        assert(callid);

        ipc_call_t call;
        *callid = async_get_call(&call);

        if (IPC_GET_IMETHOD(call) != IPC_M_STATE_CHANGE_AUTHORIZE)
                return false;
        
        if (arg1)
                *arg1 = IPC_GET_ARG1(call);
        if (arg2)
                *arg2 = IPC_GET_ARG2(call);
        if (arg3)
                *arg3 = IPC_GET_ARG3(call);

        return true;
}

int async_state_change_finalize(ipc_callid_t callid, async_exch_t *other_exch)
{
        return ipc_answer_1(callid, EOK, other_exch->phone);
}

/** @}
 */