/* -*- 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 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 . */
/*
* 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 "api.h"
#include
#include
#include
#include
#include
#include
#ifdef __x86_64__
# include
#endif
#define MUTEX_SPINLOCK_TIMES 100
#define MUTEX_UNLOCKED 0
#define MUTEX_LOCKED 1
/* Interplay between locked and nwaiters:
*
* If lock is unlocked and uncontended, just set the locked state.
*
* Important possible interleavings of lock and unlock:
*
* Case 1:
*
* Owner: Locker:
* Try lock and fail; increment nwaiters; sleep
* Set state to unlocked
* Read nwaiters; wake
* Try again and succeed.
*
* ***************************************************
*
* Case 2:
*
* Owner: Locker:
* Try lock and fail
* Set state to unlocked
* Read nwaiters (=0)
* Increment nwaiters.
* Can't go to sleep here; will cmpxchg locked and succeed
* Don't wake anyone
*/
int
_DkMutexCreate (PAL_HANDLE * handle, int initialCount)
{
PAL_HANDLE mut = malloc(HANDLE_SIZE(mutex));
SET_HANDLE_TYPE(mut, mutex);
atomic_set(&mut->mutex.mut.nwaiters, 0);
mut->mutex.mut.locked = initialCount;
*handle = mut;
return 0;
}
int _DkMutexLockTimeout (struct mutex_handle * m, uint64_t timeout)
{
int i, ret = 0;
#ifdef DEBUG_MUTEX
int tid = INLINE_SYSCALL(gettid, 0);
#endif
/* If this is a trylock-style call, break more quickly. */
int iterations = (timeout == 0) ? 1 : MUTEX_SPINLOCK_TIMES;
/* Spin and try to take lock. Ignore any contribution this makes toward
* the timeout.*/
for (i = 0; i < iterations; i++) {
if (MUTEX_UNLOCKED == cmpxchg(&m->locked, MUTEX_UNLOCKED, MUTEX_LOCKED))
goto success;
CPU_RELAX();
}
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)) {
struct timespec waittime, *waittimep = NULL;
if (timeout != NO_TIMEOUT) {
long sec = timeout / 1000000;
long microsec = timeout - (sec * 1000000);
waittime.tv_sec = sec;
waittime.tv_nsec = microsec * 1000;
waittimep = &waittime;
}
ret = INLINE_SYSCALL(futex, 6, m, FUTEX_WAIT, MUTEX_LOCKED, waittimep, NULL, 0);
if (IS_ERR(ret)) {
if (ERRNO(ret) == EWOULDBLOCK) {
if (timeout != NO_TIMEOUT) {
ret = -PAL_ERROR_TRYAGAIN;
atomic_dec(&m->nwaiters);
goto out;
}
} else {
#ifdef DEBUG_MUTEX
printf("futex failed (err = %d)\n", ERRNO(ret));
#endif
ret = unix_to_pal_error(ERRNO(ret));
atomic_dec(&m->nwaiters);
goto out;
}
}
}
atomic_dec(&m->nwaiters);
success:
#ifdef DEBUG_MUTEX
m->owner = tid;
#endif
ret = 0;
out:
#ifdef DEBUG_MUTEX
if (ret < 0)
printf("mutex failed (%s, tid = %d)\n", PAL_STRERROR(ret), tid);
#endif
return ret;
}
int _DkMutexLock (struct mutex_handle * m)
{
return _DkMutexLockTimeout(m, -1);
}
int _DkMutexAcquireTimeout (PAL_HANDLE handle, int timeout)
{
return _DkMutexLockTimeout(&handle->mutex.mut, timeout);
}
int _DkMutexUnlock (struct mutex_handle * m)
{
int ret = 0;
int need_wake;
#ifdef DEBUG_MUTEX
m->owner = 0;
#endif
/* 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)
INLINE_SYSCALL(futex, 6, m, FUTEX_WAKE, 1, NULL, NULL, 0);
return ret;
}
void _DkMutexRelease (PAL_HANDLE handle)
{
_DkMutexUnlock(&handle->mutex.mut);
return;
}
int _DkInternalLock (PAL_LOCK* lock) {
while (_DkMutexLock(lock) < 0); // Retry the lock if being interrupted by signals
return 0;
}
int _DkInternalUnlock (PAL_LOCK* lock) {
_DkMutexUnlock(lock);
return 0;
}
static int mutex_wait (PAL_HANDLE handle, uint64_t timeout)
{
return _DkMutexAcquireTimeout(handle, timeout);
}
struct handle_ops mutex_ops = {
.wait = &mutex_wait,
};