source: mainline/uspace/lib/libc/generic/psthread.c@ b9641ee

/*
 * 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 <libadt/list.h>
#include <psthread.h>
#include <malloc.h>
#include <unistd.h>
#include <thread.h>
#include <stdio.h>
#include <libarch/faddr.h>
#include <futex.h>
#include <assert.h>
#include <async.h>

#ifndef PSTHREAD_INITIAL_STACK_PAGES_NO
#define PSTHREAD_INITIAL_STACK_PAGES_NO 1
#endif

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

static void psthread_main(void);

static atomic_t psthread_futex = FUTEX_INITIALIZER;
/** Count of real threads that are in async_serialized mode */
static int serialized_threads;  /* Protected by async_futex */
/** Thread-local count of serialization. If >0, we must not preempt */
static __thread int serialization_count;
/** Counter of threads residing in async_manager */
static int threads_in_manager;

/** Setup psthread information into TCB structure */
psthread_data_t *psthread_setup(void)
{
        psthread_data_t *pt;
        tcb_t *tcb;

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

        pt = malloc(sizeof(*pt));
        if (!pt) {
                __free_tls(tcb);
                return NULL;
        }

        tcb->pst_data = pt;
        pt->tcb = tcb;

        return pt;
}

void psthread_teardown(psthread_data_t *pt)
{
        __free_tls(pt->tcb);
        free(pt);
}

/** Function that spans the whole life-cycle of a pseudo thread.
 *
 * Each pseudo thread begins execution in this function.
 * Then the function implementing the pseudo thread logic is called.
 * After its return, the return value is saved for a potentional
 * joiner. If the joiner exists, it is woken up. The pseudo thread
 * then switches to another pseudo thread, which cleans up after it.
 */
void psthread_main(void)
{
        psthread_data_t *pt = __tcb_get()->pst_data;

        pt->retval = pt->func(pt->arg);

        /*
         * If there is a joiner, wake it up and save our return value.
         */
        if (pt->joiner) {
                list_append(&pt->joiner->link, &ready_list);
                pt->joiner->joinee_retval = pt->retval;
        }

        psthread_schedule_next_adv(PS_FROM_DEAD);
        /* not reached */
}

/** Schedule next userspace pseudo thread.
 *
 * If calling with PS_TO_MANAGER parameter, the async_futex should be
 * held.
 *
 * @param ctype         One of PS_SLEEP, PS_PREEMPT, PS_TO_MANAGER,
 *                      PS_FROM_MANAGER, PS_FROM_DEAD. The parameter describes
 *                      the circumstances of the switch.
 * @return              Return 0 if there is no ready pseudo thread,
 *                      return 1 otherwise.
 */
int psthread_schedule_next_adv(pschange_type ctype)
{
        psthread_data_t *srcpt, *dstpt;
        int retval = 0;
        
        futex_down(&psthread_futex);

        if (ctype == PS_PREEMPT && list_empty(&ready_list))
                goto ret_0;
        if (ctype == PS_SLEEP) {
                if (list_empty(&ready_list) && list_empty(&serialized_list))
                        goto ret_0;
        }

        if (ctype == PS_FROM_MANAGER) {
                if (list_empty(&ready_list) && list_empty(&serialized_list))
                        goto ret_0;
                /*
                 * Do not preempt if there is not sufficient count of thread
                 * managers.
                 */
                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 (ctype == PS_TO_MANAGER || ctype == PS_FROM_DEAD) {
                while (list_empty(&manager_list)) {
                        futex_up(&psthread_futex);
                        async_create_manager();
                        futex_down(&psthread_futex);
                }
        }
        
        srcpt = __tcb_get()->pst_data;
        if (ctype != PS_FROM_DEAD) {
                /* Save current state */
                if (!context_save(&srcpt->ctx)) {
                        if (serialization_count)
                                srcpt->flags &= ~PSTHREAD_SERIALIZED;
                        if (srcpt->clean_after_me) {
                                /*
                                 * Cleanup after the dead pseudo thread from
                                 * which we restored context here.
                                 */
                                free(srcpt->clean_after_me->stack);
                                psthread_teardown(srcpt->clean_after_me);
                                srcpt->clean_after_me = NULL;
                        }
                        return 1;       /* futex_up already done here */
                }

                /* Save myself to the correct run list */
                if (ctype == PS_PREEMPT)
                        list_append(&srcpt->link, &ready_list);
                else if (ctype == PS_FROM_MANAGER) {
                        list_append(&srcpt->link, &manager_list);
                        threads_in_manager--;
                } else {        
                        /*
                         * If ctype == PS_TO_MANAGER, don't save ourselves to
                         * any list, we should already be somewhere, or we will
                         * be lost.
                         *
                         * The ctype == PS_SLEEP case is similar. The pseudo
                         * thread has an external refernce which can be used to
                         * wake it up once that time has come.
                         */
                }
        }

        /* Choose new thread to run */
        if (ctype == PS_TO_MANAGER || ctype == PS_FROM_DEAD) {
                dstpt = list_get_instance(manager_list.next, psthread_data_t,
                    link);
                if (serialization_count && ctype == PS_TO_MANAGER) {
                        serialized_threads++;
                        srcpt->flags |= PSTHREAD_SERIALIZED;
                }
                threads_in_manager++;

                if (ctype == PS_FROM_DEAD)
                        dstpt->clean_after_me = srcpt;
        } else {
                if (!list_empty(&serialized_list)) {
                        dstpt = list_get_instance(serialized_list.next,
                            psthread_data_t, link);
                        serialized_threads--;
                } else {
                        dstpt = list_get_instance(ready_list.next,
                            psthread_data_t, link);
                }
        }
        list_remove(&dstpt->link);

        futex_up(&psthread_futex);
        context_restore(&dstpt->ctx);
        /* not reached */

ret_0:
        futex_up(&psthread_futex);
        return retval;
}

/** Wait for uspace pseudo thread to finish.
 *
 * Each pseudo thread can be only joined by one other pseudo thread. Moreover,
 * the joiner must be from the same thread as the joinee.
 *
 * @param psthrid       Pseudo thread to join.
 *
 * @return              Value returned by the finished thread.
 */
int psthread_join(pstid_t psthrid)
{
        psthread_data_t *pt;
        psthread_data_t *cur;

        /* Handle psthrid = Kernel address -> it is wait for call */
        pt = (psthread_data_t *) psthrid;

        /*
         * The joiner is running so the joinee isn't.
         */
        cur = __tcb_get()->pst_data;
        pt->joiner = cur;
        psthread_schedule_next_adv(PS_SLEEP);

        /*
         * The joinee fills in the return value.
         */
        return cur->joinee_retval;
}

/** Create a userspace pseudo thread.
 *
 * @param func          Pseudo thread function.
 * @param arg           Argument to pass to func.
 *
 * @return              Return 0 on failure or TLS of the new pseudo thread.
 */
pstid_t psthread_create(int (*func)(void *), void *arg)
{
        psthread_data_t *pt;

        pt = psthread_setup();
        if (!pt) 
                return 0;
        pt->stack = (char *) malloc(PSTHREAD_INITIAL_STACK_PAGES_NO *
            getpagesize());

        if (!pt->stack) {
                psthread_teardown(pt);
                return 0;
        }

        pt->arg= arg;
        pt->func = func;
        pt->clean_after_me = NULL;
        pt->joiner = NULL;
        pt->joinee_retval = 0;
        pt->retval = 0;
        pt->flags = 0;

        context_save(&pt->ctx);
        context_set(&pt->ctx, FADDR(psthread_main), pt->stack,
            PSTHREAD_INITIAL_STACK_PAGES_NO * getpagesize(), pt->tcb);

        return (pstid_t) pt;
}

/** Add a thread to the ready list.
 *
 * @param psthrid               Pinter to the pseudo thread structure of the
 *                              pseudo thread to be added.
 */
void psthread_add_ready(pstid_t psthrid)
{
        psthread_data_t *pt;

        pt = (psthread_data_t *) psthrid;
        futex_down(&psthread_futex);
        if ((pt->flags & PSTHREAD_SERIALIZED))
                list_append(&pt->link, &serialized_list);
        else
                list_append(&pt->link, &ready_list);
        futex_up(&psthread_futex);
}

/** Add a pseudo thread to the manager list.
 *
 * @param psthrid               Pinter to the pseudo thread structure of the
 *                              pseudo thread to be added.
 */
void psthread_add_manager(pstid_t psthrid)
{
        psthread_data_t *pt;

        pt = (psthread_data_t *) psthrid;

        futex_down(&psthread_futex);
        list_append(&pt->link, &manager_list);
        futex_up(&psthread_futex);
}

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

/** Return thread id of the currently running thread.
 *
 * @return              Pseudo thread ID of the currently running pseudo thread.
 */
pstid_t psthread_get_id(void)
{
        return (pstid_t) __tcb_get()->pst_data;
}

/** Disable preemption 
 *
 * If the thread 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. Interrupt messages can still be preempted.
 */
void psthread_inc_sercount(void)
{
        serialization_count++;
}

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

/** @}
 */