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- /* -*- mode:c; c-file-style:"k&r"; c-basic-offset: 4; tab-width:4; indent-tabs-mode:nil; mode:auto-fill; fill-column:78; -*- */
- /* vim: set ts=4 sw=4 et tw=78 fo=cqt wm=0: */
- /* Copyright (C) 2014 OSCAR lab, 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 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 General Public License for more details.
- You should have received a copy of the GNU General Public License
- along with this program. If not, see <http://www.gnu.org/licenses/>. */
- /*
- * db_mutex.c
- *
- * This file contains APIs that provide operations of (futex based) mutexes.
- * Based on "Mutexes and Condition Variables using Futexes"
- * (http://locklessinc.com/articles/mutex_cv_futex)
- */
- #include "pal_defs.h"
- #include "pal_linux_defs.h"
- #include "pal.h"
- #include "pal_internal.h"
- #include "pal_linux.h"
- #include "pal_linux_error.h"
- #include "pal_error.h"
- #include "pal_debug.h"
- #include "api.h"
- #include <linux/futex.h>
- #include <limits.h>
- #include <atomic.h>
- #include <linux/time.h>
- #include <errno.h>
- #include <asm/errno.h>
- #define MUTEX_SPINLOCK_TIMES 100
- #define MUTEX_UNLOCKED 0
- #define MUTEX_LOCKED 1
- int
- _DkMutexCreate (PAL_HANDLE handle, int initialCount)
- {
- /*
- * Allocation and free of the handle are done outside of host-specific code.
- * This code initializes the mutex state that is host-specific,
- * including how initialCount is encoded.
- */
- SET_HANDLE_TYPE(handle, mutex);
- atomic_set(&handle->mutex.mut.nwaiters, 0);
- handle->mutex.mut.locked = initialCount;
- return 0;
- }
- void _DkMutexDestroy (PAL_HANDLE handle)
- {
- free(handle);
- }
- int _DkMutexLockTimeout (struct mutex_handle * m, uint64_t timeout)
- {
- int ret = 0;
- if (MUTEX_UNLOCKED == cmpxchg(&m->locked, MUTEX_UNLOCKED, MUTEX_LOCKED))
- goto success;
- if (timeout == 0) {
- ret = -PAL_ERROR_TRYAGAIN;
- goto out;
- }
- // Bump up the waiters count; we are probably going to block
- atomic_inc(&m->nwaiters);
- while (MUTEX_LOCKED == cmpxchg(&m->locked, MUTEX_UNLOCKED, MUTEX_LOCKED)) {
- // This is broken. The mutex is in enclave memory, the URTS can't
- // do FUTEX_WAIT on it. This call will always fail and the next level
- // up needs to retry.
- ret = ocall_futex((int *) m, FUTEX_WAIT, MUTEX_LOCKED, timeout == -1 ? NULL : &timeout);
- if (ret < 0) {
- if (-ret == EWOULDBLOCK) {
- ret = -PAL_ERROR_TRYAGAIN;
- atomic_dec(&m->nwaiters);
- goto out;
- }
- ret = unix_to_pal_error(ERRNO(ret));
- atomic_dec(&m->nwaiters);
- goto out;
- }
- }
- atomic_dec(&m->nwaiters);
- success:
- ret = 0;
- out:
- return ret;
- }
- int _DkMutexLock (struct mutex_handle * m)
- {
- int ret = 0, i;
- return _DkMutexLockTimeout(m, -1);
- }
- int _DkMutexAcquireTimeout (PAL_HANDLE handle, int _timeout)
- {
- struct mutex_handle * mut = &handle->mutex.mut;
- return _DkMutexLockTimeout(mut, _timeout);
- }
- int _DkMutexUnlock (struct mutex_handle * m)
- {
- int ret = 0;
- int need_wake;
- /* Unlock */
- m->locked = 0;
- /* We need to make sure the write to locked is visible to lock-ers
- * before we read the waiter count. */
- mb();
- need_wake= atomic_read(&m->nwaiters);
- /* If we need to wake someone up... */
- if (need_wake)
- ocall_futex((int *) m, FUTEX_WAKE, 1, NULL);
- return ret;
- }
- void _DkMutexRelease (PAL_HANDLE handle)
- {
- struct mutex_handle * mut = &handle->mutex.mut;
- int ret = _DkMutexUnlock(mut);
- if (ret < 0)
- _DkRaiseFailure(ret);
- return;
- }
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