/* -*- 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 . */
/*
* 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
#include
#include
#include
#include
#include
#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;
}