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// Copyright (c) 2013-2014 Sandstorm Development Group, Inc. and contributors
// Licensed under the MIT License:
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.
#if _WIN32
#define WIN32_LEAN_AND_MEAN 1 // lolz
#define WINVER 0x0600
#define _WIN32_WINNT 0x0600
#endif
#include "mutex.h"
#include "debug.h"
#if KJ_USE_FUTEX
#include <unistd.h>
#include <sys/syscall.h>
#include <linux/futex.h>
#include <limits.h>
#ifndef SYS_futex
// Missing on Android/Bionic.
#define SYS_futex __NR_futex
#endif
#ifndef FUTEX_WAIT_PRIVATE
// Missing on Android/Bionic.
#define FUTEX_WAIT_PRIVATE FUTEX_WAIT
#define FUTEX_WAKE_PRIVATE FUTEX_WAKE
#endif
#elif _WIN32
#include <windows.h>
#endif
namespace kj {
namespace _ { // private
#if KJ_USE_FUTEX
// =======================================================================================
// Futex-based implementation (Linux-only)
Mutex::Mutex(): futex(0) {}
Mutex::~Mutex() {
// This will crash anyway, might as well crash with a nice error message.
KJ_ASSERT(futex == 0, "Mutex destroyed while locked.") { break; }
}
void Mutex::lock(Exclusivity exclusivity) {
switch (exclusivity) {
case EXCLUSIVE:
for (;;) {
uint state = 0;
if (KJ_LIKELY(__atomic_compare_exchange_n(&futex, &state, EXCLUSIVE_HELD, false,
__ATOMIC_ACQUIRE, __ATOMIC_RELAXED))) {
// Acquired.
break;
}
// The mutex is contended. Set the exclusive-requested bit and wait.
if ((state & EXCLUSIVE_REQUESTED) == 0) {
if (!__atomic_compare_exchange_n(&futex, &state, state | EXCLUSIVE_REQUESTED, false,
__ATOMIC_RELAXED, __ATOMIC_RELAXED)) {
// Oops, the state changed before we could set the request bit. Start over.
continue;
}
state |= EXCLUSIVE_REQUESTED;
}
syscall(SYS_futex, &futex, FUTEX_WAIT_PRIVATE, state, NULL, NULL, 0);
}
break;
case SHARED: {
uint state = __atomic_add_fetch(&futex, 1, __ATOMIC_ACQUIRE);
for (;;) {
if (KJ_LIKELY((state & EXCLUSIVE_HELD) == 0)) {
// Acquired.
break;
}
// The mutex is exclusively locked by another thread. Since we incremented the counter
// already, we just have to wait for it to be unlocked.
syscall(SYS_futex, &futex, FUTEX_WAIT_PRIVATE, state, NULL, NULL, 0);
state = __atomic_load_n(&futex, __ATOMIC_ACQUIRE);
}
break;
}
}
}
void Mutex::unlock(Exclusivity exclusivity) {
switch (exclusivity) {
case EXCLUSIVE: {
KJ_DASSERT(futex & EXCLUSIVE_HELD, "Unlocked a mutex that wasn't locked.");
uint oldState = __atomic_fetch_and(
&futex, ~(EXCLUSIVE_HELD | EXCLUSIVE_REQUESTED), __ATOMIC_RELEASE);
if (KJ_UNLIKELY(oldState & ~EXCLUSIVE_HELD)) {
// Other threads are waiting. If there are any shared waiters, they now collectively hold
// the lock, and we must wake them up. If there are any exclusive waiters, we must wake
// them up even if readers are waiting so that at the very least they may re-establish the
// EXCLUSIVE_REQUESTED bit that we just removed.
syscall(SYS_futex, &futex, FUTEX_WAKE_PRIVATE, INT_MAX, NULL, NULL, 0);
}
break;
}
case SHARED: {
KJ_DASSERT(futex & SHARED_COUNT_MASK, "Unshared a mutex that wasn't shared.");
uint state = __atomic_sub_fetch(&futex, 1, __ATOMIC_RELEASE);
// The only case where anyone is waiting is if EXCLUSIVE_REQUESTED is set, and the only time
// it makes sense to wake up that waiter is if the shared count has reached zero.
if (KJ_UNLIKELY(state == EXCLUSIVE_REQUESTED)) {
if (__atomic_compare_exchange_n(
&futex, &state, 0, false, __ATOMIC_RELAXED, __ATOMIC_RELAXED)) {
// Wake all exclusive waiters. We have to wake all of them because one of them will
// grab the lock while the others will re-establish the exclusive-requested bit.
syscall(SYS_futex, &futex, FUTEX_WAKE_PRIVATE, INT_MAX, NULL, NULL, 0);
}
}
break;
}
}
}
void Mutex::assertLockedByCaller(Exclusivity exclusivity) {
switch (exclusivity) {
case EXCLUSIVE:
KJ_ASSERT(futex & EXCLUSIVE_HELD,
"Tried to call getAlreadyLocked*() but lock is not held.");
break;
case SHARED:
KJ_ASSERT(futex & SHARED_COUNT_MASK,
"Tried to call getAlreadyLocked*() but lock is not held.");
break;
}
}
void Once::runOnce(Initializer& init) {
startOver:
uint state = UNINITIALIZED;
if (__atomic_compare_exchange_n(&futex, &state, INITIALIZING, false,
__ATOMIC_RELAXED, __ATOMIC_RELAXED)) {
// It's our job to initialize!
{
KJ_ON_SCOPE_FAILURE({
// An exception was thrown by the initializer. We have to revert.
if (__atomic_exchange_n(&futex, UNINITIALIZED, __ATOMIC_RELEASE) ==
INITIALIZING_WITH_WAITERS) {
// Someone was waiting for us to finish.
syscall(SYS_futex, &futex, FUTEX_WAKE_PRIVATE, INT_MAX, NULL, NULL, 0);
}
});
init.run();
}
if (__atomic_exchange_n(&futex, INITIALIZED, __ATOMIC_RELEASE) ==
INITIALIZING_WITH_WAITERS) {
// Someone was waiting for us to finish.
syscall(SYS_futex, &futex, FUTEX_WAKE_PRIVATE, INT_MAX, NULL, NULL, 0);
}
} else {
for (;;) {
if (state == INITIALIZED) {
break;
} else if (state == INITIALIZING) {
// Initialization is taking place in another thread. Indicate that we're waiting.
if (!__atomic_compare_exchange_n(&futex, &state, INITIALIZING_WITH_WAITERS, true,
__ATOMIC_ACQUIRE, __ATOMIC_ACQUIRE)) {
// State changed, retry.
continue;
}
} else {
KJ_DASSERT(state == INITIALIZING_WITH_WAITERS);
}
// Wait for initialization.
syscall(SYS_futex, &futex, FUTEX_WAIT_PRIVATE, INITIALIZING_WITH_WAITERS, NULL, NULL, 0);
state = __atomic_load_n(&futex, __ATOMIC_ACQUIRE);
if (state == UNINITIALIZED) {
// Oh hey, apparently whoever was trying to initialize gave up. Let's take it from the
// top.
goto startOver;
}
}
}
}
void Once::reset() {
uint state = INITIALIZED;
if (!__atomic_compare_exchange_n(&futex, &state, UNINITIALIZED,
false, __ATOMIC_RELEASE, __ATOMIC_RELAXED)) {
KJ_FAIL_REQUIRE("reset() called while not initialized.");
}
}
#elif _WIN32
// =======================================================================================
// Win32 implementation
#define coercedSrwLock (*reinterpret_cast<SRWLOCK*>(&srwLock))
#define coercedInitOnce (*reinterpret_cast<INIT_ONCE*>(&initOnce))
Mutex::Mutex() {
static_assert(sizeof(SRWLOCK) == sizeof(srwLock), "SRWLOCK is not a pointer?");
InitializeSRWLock(&coercedSrwLock);
}
Mutex::~Mutex() {}
void Mutex::lock(Exclusivity exclusivity) {
switch (exclusivity) {
case EXCLUSIVE:
AcquireSRWLockExclusive(&coercedSrwLock);
break;
case SHARED:
AcquireSRWLockShared(&coercedSrwLock);
break;
}
}
void Mutex::unlock(Exclusivity exclusivity) {
switch (exclusivity) {
case EXCLUSIVE:
ReleaseSRWLockExclusive(&coercedSrwLock);
break;
case SHARED:
ReleaseSRWLockShared(&coercedSrwLock);
break;
}
}
void Mutex::assertLockedByCaller(Exclusivity exclusivity) {
// We could use TryAcquireSRWLock*() here like we do with the pthread version. However, as of
// this writing, my version of Wine (1.6.2) doesn't implement these functions and will abort if
// they are called. Since we were only going to use them as a hacky way to check if the lock is
// held for debug purposes anyway, we just don't bother.
}
static BOOL WINAPI nullInitializer(PINIT_ONCE initOnce, PVOID parameter, PVOID* context) {
return true;
}
Once::Once(bool startInitialized) {
static_assert(sizeof(INIT_ONCE) == sizeof(initOnce), "INIT_ONCE is not a pointer?");
InitOnceInitialize(&coercedInitOnce);
if (startInitialized) {
InitOnceExecuteOnce(&coercedInitOnce, &nullInitializer, nullptr, nullptr);
}
}
Once::~Once() {}
void Once::runOnce(Initializer& init) {
BOOL needInit;
while (!InitOnceBeginInitialize(&coercedInitOnce, 0, &needInit, nullptr)) {
// Init was occurring in another thread, but then failed with an exception. Retry.
}
if (needInit) {
{
KJ_ON_SCOPE_FAILURE(InitOnceComplete(&coercedInitOnce, INIT_ONCE_INIT_FAILED, nullptr));
init.run();
}
KJ_ASSERT(InitOnceComplete(&coercedInitOnce, 0, nullptr));
}
}
bool Once::isInitialized() noexcept {
BOOL junk;
return InitOnceBeginInitialize(&coercedInitOnce, INIT_ONCE_CHECK_ONLY, &junk, nullptr);
}
void Once::reset() {
InitOnceInitialize(&coercedInitOnce);
}
#else
// =======================================================================================
// Generic pthreads-based implementation
#define KJ_PTHREAD_CALL(code) \
{ \
int pthreadError = code; \
if (pthreadError != 0) { \
KJ_FAIL_SYSCALL(#code, pthreadError); \
} \
}
#define KJ_PTHREAD_CLEANUP(code) \
{ \
int pthreadError = code; \
if (pthreadError != 0) { \
KJ_LOG(ERROR, #code, strerror(pthreadError)); \
} \
}
Mutex::Mutex() {
KJ_PTHREAD_CALL(pthread_rwlock_init(&mutex, nullptr));
}
Mutex::~Mutex() {
KJ_PTHREAD_CLEANUP(pthread_rwlock_destroy(&mutex));
}
void Mutex::lock(Exclusivity exclusivity) {
switch (exclusivity) {
case EXCLUSIVE:
KJ_PTHREAD_CALL(pthread_rwlock_wrlock(&mutex));
break;
case SHARED:
KJ_PTHREAD_CALL(pthread_rwlock_rdlock(&mutex));
break;
}
}
void Mutex::unlock(Exclusivity exclusivity) {
KJ_PTHREAD_CALL(pthread_rwlock_unlock(&mutex));
}
void Mutex::assertLockedByCaller(Exclusivity exclusivity) {
switch (exclusivity) {
case EXCLUSIVE:
// A read lock should fail if the mutex is already held for writing.
if (pthread_rwlock_tryrdlock(&mutex) == 0) {
pthread_rwlock_unlock(&mutex);
KJ_FAIL_ASSERT("Tried to call getAlreadyLocked*() but lock is not held.");
}
break;
case SHARED:
// A write lock should fail if the mutex is already held for reading or writing. We don't
// have any way to prove that the lock is held only for reading.
if (pthread_rwlock_trywrlock(&mutex) == 0) {
pthread_rwlock_unlock(&mutex);
KJ_FAIL_ASSERT("Tried to call getAlreadyLocked*() but lock is not held.");
}
break;
}
}
Once::Once(bool startInitialized): state(startInitialized ? INITIALIZED : UNINITIALIZED) {
KJ_PTHREAD_CALL(pthread_mutex_init(&mutex, nullptr));
}
Once::~Once() {
KJ_PTHREAD_CLEANUP(pthread_mutex_destroy(&mutex));
}
void Once::runOnce(Initializer& init) {
KJ_PTHREAD_CALL(pthread_mutex_lock(&mutex));
KJ_DEFER(KJ_PTHREAD_CALL(pthread_mutex_unlock(&mutex)));
if (state != UNINITIALIZED) {
return;
}
init.run();
__atomic_store_n(&state, INITIALIZED, __ATOMIC_RELEASE);
}
void Once::reset() {
State oldState = INITIALIZED;
if (!__atomic_compare_exchange_n(&state, &oldState, UNINITIALIZED,
false, __ATOMIC_RELEASE, __ATOMIC_RELAXED)) {
KJ_FAIL_REQUIRE("reset() called while not initialized.");
}
}
#endif
} // namespace _ (private)
} // namespace kj