graphene/Pal/src/host/Linux/db_events.c

/* Copyright (C) 2014 Stony Brook University
   This file is part of Graphene Library OS.

   Graphene Library OS is free software: you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public License
   as published by the Free Software Foundation, either version 3 of the
   License, or (at your option) any later version.

   Graphene Library OS is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public License
   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */

/*
 * db_event.c
 *
 * This file contains implementation of Drawbridge event synchronization APIs.
 */

#include "pal_defs.h"
#include "pal_linux_defs.h"
#include "pal.h"
#include "pal_internal.h"
#include "pal_linux.h"
#include "pal_error.h"
#include "pal_debug.h"
#include "api.h"

#include <atomic.h>
#include <linux/futex.h>
#include <asm/errno.h>
#include <linux/time.h>

int _DkEventCreate (PAL_HANDLE * event, bool initialState, bool isnotification)
{
    PAL_HANDLE ev = malloc(HANDLE_SIZE(event));
    SET_HANDLE_TYPE(ev, event);
    ev->event.isnotification = isnotification;
    atomic_set(&ev->event.signaled, initialState ? 1 : 0);
    atomic_set(&ev->event.nwaiters, 0);
    *event = ev;
    return 0;
}

int _DkEventSet (PAL_HANDLE event, int wakeup)
{
    int ret = 0;

    if (event->event.isnotification) {
        // Leave it signaled, wake all
        if (atomic_cmpxchg(&event->event.signaled, 0, 1) == 0) {
            int nwaiters = atomic_read(&event->event.nwaiters);
            if (nwaiters) {
                if (wakeup != -1 && nwaiters > wakeup)
                    nwaiters = wakeup;

                ret = INLINE_SYSCALL(futex, 6, &event->event.signaled,
                                     FUTEX_WAKE, nwaiters, NULL, NULL, 0);
                if (IS_ERR(ret))
                    atomic_set(&event->event.signaled, 0);
            }
        }
    } else {
        // Only one thread wakes up, leave unsignaled
        ret = INLINE_SYSCALL(futex, 6, &event->event.signaled, FUTEX_WAKE, 1,
                             NULL, NULL, 0);
    }

    return IS_ERR(ret) ? -PAL_ERROR_TRYAGAIN : ret;
}

int _DkEventWaitTimeout(PAL_HANDLE event, int64_t timeout_us)
{
    int ret = 0;

    if (timeout_us < 0)
        return _DkEventWait(event);

    if (!event->event.isnotification || !atomic_read(&event->event.signaled)) {
        struct timespec waittime;
        int64_t sec = timeout_us / 1000000UL;
        int64_t microsec = timeout_us - (sec * 1000000UL);
        waittime.tv_sec = sec;
        waittime.tv_nsec = microsec * 1000;

        atomic_inc(&event->event.nwaiters);

        do {
            ret = INLINE_SYSCALL(futex, 6, &event->event.signaled, FUTEX_WAIT,
                                 0, &waittime, NULL, 0);

            if (IS_ERR(ret)) {
                if (ERRNO(ret) == EWOULDBLOCK) {
                    ret = 0;
                } else {
                    ret = unix_to_pal_error(ERRNO(ret));
                    break;
                }
            }
        } while (event->event.isnotification &&
                 !atomic_read(&event->event.signaled));

        atomic_dec(&event->event.nwaiters);
    }

    return ret;
}

int _DkEventWait(PAL_HANDLE event) {
    int ret = 0;

    if (!event->event.isnotification || !atomic_read(&event->event.signaled)) {
        atomic_inc(&event->event.nwaiters);

        do {
            ret = INLINE_SYSCALL(futex, 6, &event->event.signaled, FUTEX_WAIT,
                                  0, NULL, NULL, 0);

            if (IS_ERR(ret)) {
                if (ERRNO(ret) == EWOULDBLOCK) {
                    ret = 0;
                } else {
                    ret = unix_to_pal_error(ERRNO(ret));
                    break;
                }
            }
        } while (event->event.isnotification &&
                 !atomic_read(&event->event.signaled));

        atomic_dec(&event->event.nwaiters);
    }

    return ret;
}

int _DkEventClear (PAL_HANDLE event)
{
    atomic_set(&event->event.signaled, 0);
    return 0;
}

static int event_close (PAL_HANDLE handle)
{
    _DkEventSet(handle, -1);
    return 0;
}

static int event_wait(PAL_HANDLE handle, int64_t timeout_us) {
    return _DkEventWaitTimeout(handle, timeout_us);
}

struct handle_ops event_ops = {
        .close              = &event_close,
        .wait               = &event_wait,
    };