source: mainline/uspace/lib/c/generic/fibril.c@ 95838f1

/*
 * 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 <stack.h>
#include <tls.h>
#include <stdlib.h>
#include <abi/mm/as.h>
#include <as.h>
#include <stdio.h>
#include <libarch/barrier.h>
#include <context.h>
#include <futex.h>
#include <assert.h>
#include <async.h>

#include "private/fibril.h"


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

static LIST_INITIALIZE(ready_list);
static LIST_INITIALIZE(manager_list);
static LIST_INITIALIZE(fibril_list);

/** 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.
 *
 */
static void fibril_main(void)
{
        /* fibril_futex is locked when a fibril is first started. */
        futex_unlock(&fibril_futex);

        fibril_t *fibril = fibril_self();

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

        futex_lock(&async_futex);
        fibril_switch(FIBRIL_FROM_DEAD);
        /* Not reached */
}

/** Setup fibril information into TCB structure
 *
 */
fibril_t *fibril_setup(void)
{
        tcb_t *tcb = tls_make();
        if (!tcb)
                return NULL;

        fibril_t *fibril = calloc(1, sizeof(fibril_t));
        if (!fibril) {
                tls_free(tcb);
                return NULL;
        }

        tcb->fibril_data = fibril;
        fibril->tcb = tcb;

        /*
         * We are called before __tcb_set(), so we need to use
         * futex_down/up() instead of futex_lock/unlock() that
         * may attempt to access TLS.
         */
        futex_down(&fibril_futex);
        list_append(&fibril->all_link, &fibril_list);
        futex_up(&fibril_futex);

        return fibril;
}

void fibril_teardown(fibril_t *fibril, bool locked)
{
        if (!locked)
                futex_lock(&fibril_futex);
        list_remove(&fibril->all_link);
        if (!locked)
                futex_unlock(&fibril_futex);
        tls_free(fibril->tcb);
        free(fibril);
}

/** Switch from the current fibril.
 *
 * If stype is FIBRIL_TO_MANAGER or FIBRIL_FROM_DEAD, the async_futex must
 * 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 0 if there is no ready fibril,
 * @return 1 otherwise.
 *
 */
int fibril_switch(fibril_switch_type_t stype)
{
        futex_lock(&fibril_futex);

        fibril_t *srcf = fibril_self();
        fibril_t *dstf = NULL;

        /* Choose a new fibril to run */
        switch (stype) {
        case FIBRIL_TO_MANAGER:
        case FIBRIL_FROM_DEAD:
                /* Make sure the async_futex is held. */
                assert((atomic_signed_t) async_futex.val.count <= 0);

                /* If we are going to manager and none exists, create it */
                while (list_empty(&manager_list)) {
                        futex_unlock(&fibril_futex);
                        async_create_manager();
                        futex_lock(&fibril_futex);
                }

                dstf = list_get_instance(list_first(&manager_list),
                    fibril_t, link);

                if (stype == FIBRIL_FROM_DEAD)
                        dstf->clean_after_me = srcf;
                break;
        case FIBRIL_PREEMPT:
        case FIBRIL_FROM_MANAGER:
                if (list_empty(&ready_list)) {
                        futex_unlock(&fibril_futex);
                        return 0;
                }

                dstf = list_get_instance(list_first(&ready_list), fibril_t,
                    link);
                break;
        }
        list_remove(&dstf->link);

        /* Put the current fibril into the correct run list */
        switch (stype) {
        case FIBRIL_PREEMPT:
                list_append(&srcf->link, &ready_list);
                break;
        case FIBRIL_FROM_MANAGER:
                list_append(&srcf->link, &manager_list);
                break;
        case FIBRIL_FROM_DEAD:
                // Nothing.
                break;
        case FIBRIL_TO_MANAGER:
                /*
                 * Don't put the current fibril into any list, it should
                 * already be somewhere, or it will be lost.
                 */
                break;
        }

        /* Swap to the next fibril. */
        context_swap(&srcf->ctx, &dstf->ctx);

        /* Restored by another fibril! */

        /* Must be after context_swap()! */
        futex_unlock(&fibril_futex);

        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.
                         */
                        as_area_destroy(stack);
                }
                fibril_teardown(srcf->clean_after_me, true);
                srcf->clean_after_me = NULL;
        }

        return 1;
}

/** Create a new fibril.
 *
 * @param func Implementing function of the new fibril.
 * @param arg Argument to pass to func.
 * @param stksz Stack size in bytes.
 *
 * @return 0 on failure or TLS of the new fibril.
 *
 */
fid_t fibril_create_generic(errno_t (*func)(void *), void *arg, size_t stksz)
{
        fibril_t *fibril;

        fibril = fibril_setup();
        if (fibril == NULL)
                return 0;

        size_t stack_size = (stksz == FIBRIL_DFLT_STK_SIZE) ?
            stack_size_get() : stksz;
        fibril->stack = as_area_create(AS_AREA_ANY, stack_size,
            AS_AREA_READ | AS_AREA_WRITE | AS_AREA_CACHEABLE | AS_AREA_GUARD |
            AS_AREA_LATE_RESERVE, AS_AREA_UNPAGED);
        if (fibril->stack == (void *) -1) {
                fibril_teardown(fibril, false);
                return 0;
        }

        fibril->func = func;
        fibril->arg = arg;

        context_create_t sctx = {
                .fn = fibril_main,
                .stack_base = fibril->stack,
                .stack_size = stack_size,
                .tls = fibril->tcb,
        };

        context_create(&fibril->ctx, &sctx);
        return (fid_t) fibril;
}

/** Delete a fibril that has never run.
 *
 * Free resources of a fibril that has been created with fibril_create()
 * but never readied using fibril_add_ready().
 *
 * @param fid Pointer to the fibril structure of the fibril to be
 *            added.
 */
void fibril_destroy(fid_t fid)
{
        fibril_t *fibril = (fibril_t *) fid;

        as_area_destroy(fibril->stack);
        fibril_teardown(fibril, false);
}

/** 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 *fibril = (fibril_t *) fid;

        futex_lock(&fibril_futex);
        list_append(&fibril->link, &ready_list);
        futex_unlock(&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 *fibril = (fibril_t *) fid;

        futex_lock(&fibril_futex);
        list_append(&fibril->link, &manager_list);
        futex_unlock(&fibril_futex);
}

/** Remove one manager from the manager list. */
void fibril_remove_manager(void)
{
        futex_lock(&fibril_futex);
        if (!list_empty(&manager_list))
                list_remove(list_first(&manager_list));
        futex_unlock(&fibril_futex);
}

fibril_t *fibril_self(void)
{
        return __tcb_get()->fibril_data;
}

/** 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) fibril_self();
}

void fibril_yield(void)
{
        fibril_switch(FIBRIL_PREEMPT);
}

/** @}
 */