source: mainline/uspace/lib/c/generic/fibril.c@ 1ef0fc3

/*
 * Copyright (c) 2006 Ondrej Palkovsky
 * Copyright (c) 2007 Jakub Jermar
 * 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
 */

#include <adt/list.h>
#include <fibril.h>
#include <thread.h>
#include <tls.h>
#include <malloc.h>
#include <unistd.h>
#include <stdio.h>
#include <arch/barrier.h>
#include <libarch/faddr.h>
#include <futex.h>
#include <assert.h>
#include <async.h>

#ifndef FIBRIL_INITIAL_STACK_PAGES_NO
#define FIBRIL_INITIAL_STACK_PAGES_NO   1
#endif

/**
 * This futex serializes access to ready_list, serialized_list and manager_list.
 */ 
static atomic_t fibril_futex = FUTEX_INITIALIZER;

static LIST_INITIALIZE(ready_list);
static LIST_INITIALIZE(serialized_list);
static LIST_INITIALIZE(manager_list);

static void fibril_main(void);

/** Number of threads that are executing a manager fibril. */
static int threads_in_manager;
/** Number of threads that are executing a manager fibril and are serialized. */
static int serialized_threads;  /* Protected by async_futex */
/** Fibril-local count of serialization. If > 0, we must not preempt */
static fibril_local int serialization_count;

/** Setup fibril information into TCB structure */
fibril_t *fibril_setup(void)
{
        fibril_t *f;
        tcb_t *tcb;

        tcb = __make_tls();
        if (!tcb)
                return NULL;

        f = malloc(sizeof(fibril_t));
        if (!f) {
                __free_tls(tcb);
                return NULL;
        }

        tcb->fibril_data = f;
        f->tcb = tcb;

        f->func = NULL;
        f->arg = NULL;
        f->stack = NULL;
        f->clean_after_me = NULL;
        f->retval = 0;
        f->flags = 0;

        return f;
}

void fibril_teardown(fibril_t *f)
{
        __free_tls(f->tcb);
        free(f);
}

/** Function that spans the whole life-cycle of a fibril.
 *
 * Each fibril begins execution in this function. Then the function implementing
 * the fibril logic is called.  After its return, the return value is saved.
 * The fibril then switches to another fibril, which cleans up after it.
 */
void fibril_main(void)
{
        fibril_t *f = __tcb_get()->fibril_data;

        /* Call the implementing function. */
        f->retval = f->func(f->arg);

        fibril_switch(FIBRIL_FROM_DEAD);
        /* not reached */
}

/** Switch from the current fibril.
 *
 * If calling with FIBRIL_TO_MANAGER parameter, the async_futex should be
 * held.
 *
 * @param stype         Switch type. One of FIBRIL_PREEMPT, FIBRIL_TO_MANAGER,
 *                      FIBRIL_FROM_MANAGER, FIBRIL_FROM_DEAD. The parameter
 *                      describes the circumstances of the switch.
 * @return              Return 0 if there is no ready fibril,
 *                      return 1 otherwise.
 */
int fibril_switch(fibril_switch_type_t stype)
{
        int retval = 0;
        
        futex_down(&fibril_futex);
        
        if (stype == FIBRIL_PREEMPT && list_empty(&ready_list))
                goto ret_0;
        
        if (stype == FIBRIL_FROM_MANAGER) {
                if ((list_empty(&ready_list)) && (list_empty(&serialized_list)))
                        goto ret_0;
                
                /*
                 * Do not preempt if there is not enough threads to run the
                 * ready fibrils which are not serialized.
                 */
                if ((list_empty(&serialized_list)) &&
                    (threads_in_manager <= serialized_threads)) {
                        goto ret_0;
                }
        }
        
        /* If we are going to manager and none exists, create it */
        if ((stype == FIBRIL_TO_MANAGER) || (stype == FIBRIL_FROM_DEAD)) {
                while (list_empty(&manager_list)) {
                        futex_up(&fibril_futex);
                        async_create_manager();
                        futex_down(&fibril_futex);
                }
        }
        
        fibril_t *srcf = __tcb_get()->fibril_data;
        if (stype != FIBRIL_FROM_DEAD) {
                
                /* Save current state */
                if (!context_save(&srcf->ctx)) {
                        if (serialization_count)
                                srcf->flags &= ~FIBRIL_SERIALIZED;
                        
                        if (srcf->clean_after_me) {
                                /*
                                 * Cleanup after the dead fibril from which we
                                 * restored context here.
                                 */
                                void *stack = srcf->clean_after_me->stack;
                                if (stack) {
                                        /*
                                         * This check is necessary because a
                                         * thread could have exited like a
                                         * normal fibril using the
                                         * FIBRIL_FROM_DEAD switch type. In that
                                         * case, its fibril will not have the
                                         * stack member filled.
                                         */
                                        free(stack);
                                }
                                fibril_teardown(srcf->clean_after_me);
                                srcf->clean_after_me = NULL;
                        }
                        
                        return 1;       /* futex_up already done here */
                }
                
                /* Save myself to the correct run list */
                if (stype == FIBRIL_PREEMPT)
                        list_append(&srcf->link, &ready_list);
                else if (stype == FIBRIL_FROM_MANAGER) {
                        list_append(&srcf->link, &manager_list);
                        threads_in_manager--;
                } else {
                        /*
                         * If stype == FIBRIL_TO_MANAGER, don't put ourselves to
                         * any list, we should already be somewhere, or we will
                         * be lost.
                         */
                }
        }
        
        /* Choose a new fibril to run */
        fibril_t *dstf;
        if ((stype == FIBRIL_TO_MANAGER) || (stype == FIBRIL_FROM_DEAD)) {
                dstf = list_get_instance(manager_list.next, fibril_t, link);
                if (serialization_count && stype == FIBRIL_TO_MANAGER) {
                        serialized_threads++;
                        srcf->flags |= FIBRIL_SERIALIZED;
                }
                threads_in_manager++;
                
                if (stype == FIBRIL_FROM_DEAD) 
                        dstf->clean_after_me = srcf;
        } else {
                if (!list_empty(&serialized_list)) {
                        dstf = list_get_instance(serialized_list.next, fibril_t,
                            link);
                        serialized_threads--;
                } else {
                        dstf = list_get_instance(ready_list.next, fibril_t,
                            link);
                }
        }
        list_remove(&dstf->link);
        
        futex_up(&fibril_futex);
        context_restore(&dstf->ctx);
        /* not reached */
        
ret_0:
        futex_up(&fibril_futex);
        return retval;
}

/** Create a new fibril.
 *
 * @param func          Implementing function of the new fibril.
 * @param arg           Argument to pass to func.
 *
 * @return              Return 0 on failure or TLS of the new fibril.
 */
fid_t fibril_create(int (*func)(void *), void *arg)
{
        fibril_t *f;

        f = fibril_setup();
        if (!f) 
                return 0;
        f->stack = (char *) malloc(FIBRIL_INITIAL_STACK_PAGES_NO *
            getpagesize());
        if (!f->stack) {
                fibril_teardown(f);
                return 0;
        }
        
        f->func = func;
        f->arg = arg;

        context_save(&f->ctx);
        context_set(&f->ctx, FADDR(fibril_main), f->stack,
            FIBRIL_INITIAL_STACK_PAGES_NO * getpagesize(), f->tcb);

        return (fid_t) f;
}

/** Add a fibril to the ready list.
 *
 * @param fid           Pointer to the fibril structure of the fibril to be
 *                      added.
 */
void fibril_add_ready(fid_t fid)
{
        fibril_t *f;

        f = (fibril_t *) fid;
        futex_down(&fibril_futex);
        if ((f->flags & FIBRIL_SERIALIZED))
                list_append(&f->link, &serialized_list);
        else
                list_append(&f->link, &ready_list);
        futex_up(&fibril_futex);
}

/** Add a fibril to the manager list.
 *
 * @param fid           Pointer to the fibril structure of the fibril to be
 *                      added.
 */
void fibril_add_manager(fid_t fid)
{
        fibril_t *f;

        f = (fibril_t *) fid;

        futex_down(&fibril_futex);
        list_append(&f->link, &manager_list);
        futex_up(&fibril_futex);
}

/** Remove one manager from the manager list. */
void fibril_remove_manager(void)
{
        futex_down(&fibril_futex);
        if (list_empty(&manager_list)) {
                futex_up(&fibril_futex);
                return;
        }
        list_remove(manager_list.next);
        futex_up(&fibril_futex);
}

/** Return fibril id of the currently running fibril.
 *
 * @return fibril ID of the currently running fibril.
 *
 */
fid_t fibril_get_id(void)
{
        return (fid_t) __tcb_get()->fibril_data;
}

/** Disable preemption
 *
 * If the fibril wants to send several message in a row and does not want to be
 * preempted, it should start async_serialize_start() in the beginning of
 * communication and async_serialize_end() in the end. If it is a true
 * multithreaded application, it should protect the communication channel by a
 * futex as well.
 *
 */
void fibril_inc_sercount(void)
{
        serialization_count++;
}

/** Restore the preemption counter to the previous state. */
void fibril_dec_sercount(void)
{
        serialization_count--;
}

/** @}
 */