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// Copyright (c) 2010 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef MUTEX_H__
#define MUTEX_H__
#include "sandbox_impl.h"
namespace playground {
class Mutex {
public:
typedef int mutex_t;
enum { kInitValue = 0 };
static void initMutex(mutex_t* mutex) {
// Mutex is unlocked, and nobody is waiting for it
*mutex = kInitValue;
}
static void unlockMutex(mutex_t* mutex) {
char status;
#if defined(__x86_64__) || defined(__i386__)
asm volatile(
"lock; addl %2, %0\n"
"setz %1"
: "=m"(*mutex), "=qm"(status)
: "ir"(0x80000000), "m"(*mutex));
#else
#error Unsupported target platform
#endif
if (status) {
// Mutex is zero now. No other waiters. So, we can return.
return;
}
// We unlocked the mutex, but still need to wake up other waiters.
Sandbox::SysCalls sys;
sys.futex(mutex, FUTEX_WAKE, 1, NULL);
}
static bool lockMutex(mutex_t* mutex, int timeout = 0) {
bool rc = true;
// Increment mutex to add ourselves to the list of waiters
#if defined(__x86_64__) || defined(__i386__)
asm volatile(
"lock; incl %0\n"
: "=m"(*mutex)
: "m"(*mutex));
#else
#error Unsupported target platform
#endif
for (;;) {
// Atomically check whether the mutex is available and if so, acquire it
char status;
#if defined(__x86_64__) || defined(__i386__)
asm volatile(
"lock; btsl %3, %1\n"
"setc %0"
: "=q"(status), "=m"(*mutex)
: "m"(*mutex), "ir"(31));
#else
#error Unsupported target platform
#endif
if (!status) {
done:
// If the mutex was available, remove ourselves from list of waiters
#if defined(__x86_64__) || defined(__i386__)
asm volatile(
"lock; decl %0\n"
: "=m"(*mutex)
: "m"(*mutex));
#else
#error Unsupported target platform
#endif
return rc;
}
int value = *mutex;
if (value >= 0) {
// Mutex has just become available, no need to call kernel
continue;
}
Sandbox::SysCalls sys;
Sandbox::SysCalls::kernel_timespec tm;
if (timeout) {
tm.tv_sec = timeout / 1000;
tm.tv_nsec = (timeout % 1000) * 1000 * 1000;
} else {
tm.tv_sec = 0;
tm.tv_nsec = 0;
}
if (NOINTR_SYS(sys.futex(mutex, FUTEX_WAIT, value, &tm)) &&
sys.my_errno == ETIMEDOUT) {
rc = false;
goto done;
}
}
}
static bool waitForUnlock(mutex_t* mutex, int timeout = 0) {
bool rc = true;
// Increment mutex to add ourselves to the list of waiters
#if defined(__x86_64__) || defined(__i386__)
asm volatile(
"lock; incl %0\n"
: "=m"(*mutex)
: "m"(*mutex));
#else
#error Unsupported target platform
#endif
Sandbox::SysCalls sys;
for (;;) {
mutex_t value = *mutex;
if (value >= 0) {
done:
// Mutex was not locked. Remove ourselves from list of waiters, notify
// any other waiters (if any), and return.
#if defined(__x86_64__) || defined(__i386__)
asm volatile(
"lock; decl %0\n"
: "=m"(*mutex)
: "m"(*mutex));
#else
#error Unsupported target platform
#endif
NOINTR_SYS(sys.futex(mutex, FUTEX_WAKE, 1, 0));
return rc;
}
// Wait for mutex to become unlocked
Sandbox::SysCalls::kernel_timespec tm;
if (timeout) {
tm.tv_sec = timeout / 1000;
tm.tv_nsec = (timeout % 1000) * 1000 * 1000;
} else {
tm.tv_sec = 0;
tm.tv_nsec = 0;
}
if (NOINTR_SYS(sys.futex(mutex, FUTEX_WAIT, value, &tm)) &&
sys.my_errno == ETIMEDOUT) {
rc = false;
goto done;
}
}
}
};
} // namespace
#endif // MUTEX_H__
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