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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_error.h"
- #include "pal_debug.h"
- #include "api.h"
- #include <linux/futex.h>
- #include <limits.h>
- #include <atomic.h>
- #include <linux/time.h>
- #define MUTEX_SPINLOCK_TIMES 20
- int _DkMutexLockTimeout (struct mutex_handle * mut, int timeout)
- {
- int i, c = 0;
- if (timeout == -1)
- return -_DkMutexLock(mut);
- struct atomic_int * m = &mut->value;
- /* Spin and try to take lock */
- for (i = 0 ; i < MUTEX_SPINLOCK_TIMES ; i++)
- {
- c = atomic_dec_and_test(m);
- if (c)
- goto success;
- cpu_relax();
- }
- /* The lock is now contended */
- int ret;
- if (timeout == 0) {
- ret = c ? 0 : -PAL_ERROR_TRYAGAIN;
- goto out;
- }
- unsigned long waittime = timeout;
- while (!c) {
- int val = atomic_read(m);
- if (val == 1)
- goto again;
- ret = ocall_futex((int *) &m->counter, FUTEX_WAIT, 2, timeout ? &waittime : NULL);
- if (ret < 0)
- goto out;
- again:
- /* Upon wakeup, we still need to check whether mutex is unlocked or
- * someone else took it.
- * If c==0 upon return from xchg (i.e., the older value of m==0), we
- * will exit the loop. Else, we sleep again (through a futex call).
- */
- c = atomic_dec_and_test(m);
- }
- success:
- ret = 0;
- out:
- return ret;
- }
- int _DkMutexLock (struct mutex_handle * mut)
- {
- int i, c = 0;
- int ret;
- struct atomic_int * m = &mut->value;
- /* Spin and try to take lock */
- for (i = 0; i < MUTEX_SPINLOCK_TIMES; i++) {
- c = atomic_dec_and_test(m);
- if (c)
- goto success;
- cpu_relax();
- }
- /* The lock is now contended */
- while (!c) {
- int val = atomic_read(m);
- if (val == 1)
- goto again;
- ret = ocall_futex((int *) &m->counter, FUTEX_WAIT, 2, NULL);
- if (ret < 0)
- goto out;
- again:
- /* Upon wakeup, we still need to check whether mutex is unlocked or
- * someone else took it.
- * If c==0 upon return from xchg (i.e., the older value of m==0), we
- * will exit the loop. Else, we sleep again (through a futex call).
- */
- c = atomic_dec_and_test(m);
- }
- success:
- ret = 0;
- out:
- return ret;
- }
- int _DkMutexUnlock (struct mutex_handle * mut)
- {
- int ret = 0;
- int must_wake = 0;
- struct atomic_int * m = &mut->value;
- /* Unlock, and if not contended then exit. */
- if (atomic_read(m) < 0)
- must_wake = 1;
- atomic_set(m, 1);
- if (must_wake) {
- /* We need to wake someone up */
- ret = ocall_futex((int *) &m->counter, FUTEX_WAKE, 1, NULL);
- if (ret < 0)
- goto out;
- }
- if (ret < 0) {
- ret = -PAL_ERROR_TRYAGAIN;
- goto out;
- }
- ret = 0;
- out:
- return ret;
- }
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