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android13/art/runtime/base/mutex.cc

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/*
* Copyright (C) 2011 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#include "mutex.h"
#include <errno.h>
#include <sys/time.h>
#include <sstream>
#include "android-base/stringprintf.h"
#include "base/atomic.h"
#include "base/logging.h"
#include "base/systrace.h"
#include "base/time_utils.h"
#include "base/value_object.h"
#include "mutex-inl.h"
#include "scoped_thread_state_change-inl.h"
#include "thread-inl.h"
#include "thread.h"
#include "thread_list.h"
namespace art {
using android::base::StringPrintf;
static constexpr uint64_t kIntervalMillis = 50;
static constexpr int kMonitorTimeoutTryMax = 5;
static const char* kLastDumpStackTime = "LastDumpStackTime";
struct AllMutexData {
// A guard for all_mutexes_ that's not a mutex (Mutexes must CAS to acquire and busy wait).
Atomic<const BaseMutex*> all_mutexes_guard;
// All created mutexes guarded by all_mutexes_guard_.
std::set<BaseMutex*>* all_mutexes;
AllMutexData() : all_mutexes(nullptr) {}
};
static struct AllMutexData gAllMutexData[kAllMutexDataSize];
struct DumpStackLastTimeTLSData : public art::TLSData {
explicit DumpStackLastTimeTLSData(uint64_t last_dump_time_ms)
: last_dump_time_ms_(last_dump_time_ms) {}
std::atomic<uint64_t> last_dump_time_ms_;
};
#if ART_USE_FUTEXES
static bool ComputeRelativeTimeSpec(timespec* result_ts, const timespec& lhs, const timespec& rhs) {
const int32_t one_sec = 1000 * 1000 * 1000; // one second in nanoseconds.
result_ts->tv_sec = lhs.tv_sec - rhs.tv_sec;
result_ts->tv_nsec = lhs.tv_nsec - rhs.tv_nsec;
if (result_ts->tv_nsec < 0) {
result_ts->tv_sec--;
result_ts->tv_nsec += one_sec;
} else if (result_ts->tv_nsec > one_sec) {
result_ts->tv_sec++;
result_ts->tv_nsec -= one_sec;
}
return result_ts->tv_sec < 0;
}
#endif
#if ART_USE_FUTEXES
// If we wake up from a futex wake, and the runtime disappeared while we were asleep,
// it's important to stop in our tracks before we touch deallocated memory.
static inline void SleepIfRuntimeDeleted(Thread* self) {
if (self != nullptr) {
JNIEnvExt* const env = self->GetJniEnv();
if (UNLIKELY(env != nullptr && env->IsRuntimeDeleted())) {
DCHECK(self->IsDaemon());
// If the runtime has been deleted, then we cannot proceed. Just sleep forever. This may
// occur for user daemon threads that get a spurious wakeup. This occurs for test 132 with
// --host and --gdb.
// After we wake up, the runtime may have been shutdown, which means that this condition may
// have been deleted. It is not safe to retry the wait.
SleepForever();
}
}
}
#else
// We should be doing this for pthreads to, but it seems to be impossible for something
// like a condition variable wait. Thus we don't bother trying.
#endif
// Wait for an amount of time that roughly increases in the argument i.
// Spin for small arguments and yield/sleep for longer ones.
static void BackOff(uint32_t i) {
static constexpr uint32_t kSpinMax = 10;
static constexpr uint32_t kYieldMax = 20;
if (i <= kSpinMax) {
// TODO: Esp. in very latency-sensitive cases, consider replacing this with an explicit
// test-and-test-and-set loop in the caller. Possibly skip entirely on a uniprocessor.
volatile uint32_t x = 0;
const uint32_t spin_count = 10 * i;
for (uint32_t spin = 0; spin < spin_count; ++spin) {
++x; // Volatile; hence should not be optimized away.
}
// TODO: Consider adding x86 PAUSE and/or ARM YIELD here.
} else if (i <= kYieldMax) {
sched_yield();
} else {
NanoSleep(1000ull * (i - kYieldMax));
}
}
// Wait until pred(testLoc->load(std::memory_order_relaxed)) holds, or until a
// short time interval, on the order of kernel context-switch time, passes.
// Return true if the predicate test succeeded, false if we timed out.
template<typename Pred>
static inline bool WaitBrieflyFor(AtomicInteger* testLoc, Thread* self, Pred pred) {
// TODO: Tune these parameters correctly. BackOff(3) should take on the order of 100 cycles. So
// this should result in retrying <= 10 times, usually waiting around 100 cycles each. The
// maximum delay should be significantly less than the expected futex() context switch time, so
// there should be little danger of this worsening things appreciably. If the lock was only
// held briefly by a running thread, this should help immensely.
static constexpr uint32_t kMaxBackOff = 3; // Should probably be <= kSpinMax above.
static constexpr uint32_t kMaxIters = 50;
JNIEnvExt* const env = self == nullptr ? nullptr : self->GetJniEnv();
for (uint32_t i = 1; i <= kMaxIters; ++i) {
BackOff(std::min(i, kMaxBackOff));
if (pred(testLoc->load(std::memory_order_relaxed))) {
return true;
}
if (UNLIKELY(env != nullptr && env->IsRuntimeDeleted())) {
// This returns true once we've started shutting down. We then try to reach a quiescent
// state as soon as possible to avoid touching data that may be deallocated by the shutdown
// process. It currently relies on a timeout.
return false;
}
}
return false;
}
class ScopedAllMutexesLock final {
public:
explicit ScopedAllMutexesLock(const BaseMutex* mutex) : mutex_(mutex) {
for (uint32_t i = 0;
!gAllMutexData->all_mutexes_guard.CompareAndSetWeakAcquire(nullptr, mutex);
++i) {
BackOff(i);
}
}
~ScopedAllMutexesLock() {
DCHECK_EQ(gAllMutexData->all_mutexes_guard.load(std::memory_order_relaxed), mutex_);
gAllMutexData->all_mutexes_guard.store(nullptr, std::memory_order_release);
}
private:
const BaseMutex* const mutex_;
};
// Scoped class that generates events at the beginning and end of lock contention.
class ScopedContentionRecorder final : public ValueObject {
public:
ScopedContentionRecorder(BaseMutex* mutex, uint64_t blocked_tid, uint64_t owner_tid)
: mutex_(kLogLockContentions ? mutex : nullptr),
blocked_tid_(kLogLockContentions ? blocked_tid : 0),
owner_tid_(kLogLockContentions ? owner_tid : 0),
start_nano_time_(kLogLockContentions ? NanoTime() : 0) {
if (ATraceEnabled()) {
std::string msg = StringPrintf("Lock contention on %s (owner tid: %" PRIu64 ")",
mutex->GetName(), owner_tid);
ATraceBegin(msg.c_str());
}
}
~ScopedContentionRecorder() {
ATraceEnd();
if (kLogLockContentions) {
uint64_t end_nano_time = NanoTime();
mutex_->RecordContention(blocked_tid_, owner_tid_, end_nano_time - start_nano_time_);
}
}
private:
BaseMutex* const mutex_;
const uint64_t blocked_tid_;
const uint64_t owner_tid_;
const uint64_t start_nano_time_;
};
BaseMutex::BaseMutex(const char* name, LockLevel level)
: name_(name),
level_(level),
should_respond_to_empty_checkpoint_request_(false) {
if (kLogLockContentions) {
ScopedAllMutexesLock mu(this);
std::set<BaseMutex*>** all_mutexes_ptr = &gAllMutexData->all_mutexes;
if (*all_mutexes_ptr == nullptr) {
// We leak the global set of all mutexes to avoid ordering issues in global variable
// construction/destruction.
*all_mutexes_ptr = new std::set<BaseMutex*>();
}
(*all_mutexes_ptr)->insert(this);
}
}
BaseMutex::~BaseMutex() {
if (kLogLockContentions) {
ScopedAllMutexesLock mu(this);
gAllMutexData->all_mutexes->erase(this);
}
}
void BaseMutex::DumpAll(std::ostream& os) {
if (kLogLockContentions) {
os << "Mutex logging:\n";
ScopedAllMutexesLock mu(reinterpret_cast<const BaseMutex*>(-1));
std::set<BaseMutex*>* all_mutexes = gAllMutexData->all_mutexes;
if (all_mutexes == nullptr) {
// No mutexes have been created yet during at startup.
return;
}
os << "(Contended)\n";
for (const BaseMutex* mutex : *all_mutexes) {
if (mutex->HasEverContended()) {
mutex->Dump(os);
os << "\n";
}
}
os << "(Never contented)\n";
for (const BaseMutex* mutex : *all_mutexes) {
if (!mutex->HasEverContended()) {
mutex->Dump(os);
os << "\n";
}
}
}
}
void BaseMutex::CheckSafeToWait(Thread* self) {
if (self == nullptr) {
CheckUnattachedThread(level_);
return;
}
if (kDebugLocking) {
CHECK(self->GetHeldMutex(level_) == this || level_ == kMonitorLock)
<< "Waiting on unacquired mutex: " << name_;
bool bad_mutexes_held = false;
std::string error_msg;
for (int i = kLockLevelCount - 1; i >= 0; --i) {
if (i != level_) {
BaseMutex* held_mutex = self->GetHeldMutex(static_cast<LockLevel>(i));
// We allow the thread to wait even if the user_code_suspension_lock_ is held so long. This
// just means that gc or some other internal process is suspending the thread while it is
// trying to suspend some other thread. So long as the current thread is not being suspended
// by a SuspendReason::kForUserCode (which needs the user_code_suspension_lock_ to clear)
// this is fine. This is needed due to user_code_suspension_lock_ being the way untrusted
// code interacts with suspension. One holds the lock to prevent user-code-suspension from
// occurring. Since this is only initiated from user-supplied native-code this is safe.
if (held_mutex == Locks::user_code_suspension_lock_) {
// No thread safety analysis is fine since we have both the user_code_suspension_lock_
// from the line above and the ThreadSuspendCountLock since it is our level_. We use this
// lambda to avoid having to annotate the whole function as NO_THREAD_SAFETY_ANALYSIS.
auto is_suspending_for_user_code = [self]() NO_THREAD_SAFETY_ANALYSIS {
return self->GetUserCodeSuspendCount() != 0;
};
if (is_suspending_for_user_code()) {
std::ostringstream oss;
oss << "Holding \"" << held_mutex->name_ << "\" "
<< "(level " << LockLevel(i) << ") while performing wait on "
<< "\"" << name_ << "\" (level " << level_ << ") "
<< "with SuspendReason::kForUserCode pending suspensions";
error_msg = oss.str();
LOG(ERROR) << error_msg;
bad_mutexes_held = true;
}
} else if (held_mutex != nullptr) {
std::ostringstream oss;
oss << "Holding \"" << held_mutex->name_ << "\" "
<< "(level " << LockLevel(i) << ") while performing wait on "
<< "\"" << name_ << "\" (level " << level_ << ")";
error_msg = oss.str();
LOG(ERROR) << error_msg;
bad_mutexes_held = true;
}
}
}
if (gAborting == 0) { // Avoid recursive aborts.
CHECK(!bad_mutexes_held) << error_msg;
}
}
}
void BaseMutex::ContentionLogData::AddToWaitTime(uint64_t value) {
if (kLogLockContentions) {
// Atomically add value to wait_time.
wait_time.fetch_add(value, std::memory_order_seq_cst);
}
}
void BaseMutex::RecordContention(uint64_t blocked_tid,
uint64_t owner_tid,
uint64_t nano_time_blocked) {
if (kLogLockContentions) {
ContentionLogData* data = contention_log_data_;
++(data->contention_count);
data->AddToWaitTime(nano_time_blocked);
ContentionLogEntry* log = data->contention_log;
// This code is intentionally racy as it is only used for diagnostics.
int32_t slot = data->cur_content_log_entry.load(std::memory_order_relaxed);
if (log[slot].blocked_tid == blocked_tid &&
log[slot].owner_tid == blocked_tid) {
++log[slot].count;
} else {
uint32_t new_slot;
do {
slot = data->cur_content_log_entry.load(std::memory_order_relaxed);
new_slot = (slot + 1) % kContentionLogSize;
} while (!data->cur_content_log_entry.CompareAndSetWeakRelaxed(slot, new_slot));
log[new_slot].blocked_tid = blocked_tid;
log[new_slot].owner_tid = owner_tid;
log[new_slot].count.store(1, std::memory_order_relaxed);
}
}
}
void BaseMutex::DumpContention(std::ostream& os) const {
if (kLogLockContentions) {
const ContentionLogData* data = contention_log_data_;
const ContentionLogEntry* log = data->contention_log;
uint64_t wait_time = data->wait_time.load(std::memory_order_relaxed);
uint32_t contention_count = data->contention_count.load(std::memory_order_relaxed);
if (contention_count == 0) {
os << "never contended";
} else {
os << "contended " << contention_count
<< " total wait of contender " << PrettyDuration(wait_time)
<< " average " << PrettyDuration(wait_time / contention_count);
SafeMap<uint64_t, size_t> most_common_blocker;
SafeMap<uint64_t, size_t> most_common_blocked;
for (size_t i = 0; i < kContentionLogSize; ++i) {
uint64_t blocked_tid = log[i].blocked_tid;
uint64_t owner_tid = log[i].owner_tid;
uint32_t count = log[i].count.load(std::memory_order_relaxed);
if (count > 0) {
auto it = most_common_blocked.find(blocked_tid);
if (it != most_common_blocked.end()) {
most_common_blocked.Overwrite(blocked_tid, it->second + count);
} else {
most_common_blocked.Put(blocked_tid, count);
}
it = most_common_blocker.find(owner_tid);
if (it != most_common_blocker.end()) {
most_common_blocker.Overwrite(owner_tid, it->second + count);
} else {
most_common_blocker.Put(owner_tid, count);
}
}
}
uint64_t max_tid = 0;
size_t max_tid_count = 0;
for (const auto& pair : most_common_blocked) {
if (pair.second > max_tid_count) {
max_tid = pair.first;
max_tid_count = pair.second;
}
}
if (max_tid != 0) {
os << " sample shows most blocked tid=" << max_tid;
}
max_tid = 0;
max_tid_count = 0;
for (const auto& pair : most_common_blocker) {
if (pair.second > max_tid_count) {
max_tid = pair.first;
max_tid_count = pair.second;
}
}
if (max_tid != 0) {
os << " sample shows tid=" << max_tid << " owning during this time";
}
}
}
}
Mutex::Mutex(const char* name, LockLevel level, bool recursive)
: BaseMutex(name, level), exclusive_owner_(0), recursion_count_(0), recursive_(recursive) {
#if ART_USE_FUTEXES
DCHECK_EQ(0, state_and_contenders_.load(std::memory_order_relaxed));
#else
CHECK_MUTEX_CALL(pthread_mutex_init, (&mutex_, nullptr));
#endif
}
// Helper to allow checking shutdown while locking for thread safety.
static bool IsSafeToCallAbortSafe() {
MutexLock mu(Thread::Current(), *Locks::runtime_shutdown_lock_);
return Locks::IsSafeToCallAbortRacy();
}
Mutex::~Mutex() {
bool safe_to_call_abort = Locks::IsSafeToCallAbortRacy();
#if ART_USE_FUTEXES
if (state_and_contenders_.load(std::memory_order_relaxed) != 0) {
LOG(safe_to_call_abort ? FATAL : WARNING)
<< "destroying mutex with owner or contenders. Owner:" << GetExclusiveOwnerTid();
} else {
if (GetExclusiveOwnerTid() != 0) {
LOG(safe_to_call_abort ? FATAL : WARNING)
<< "unexpectedly found an owner on unlocked mutex " << name_;
}
}
#else
// We can't use CHECK_MUTEX_CALL here because on shutdown a suspended daemon thread
// may still be using locks.
int rc = pthread_mutex_destroy(&mutex_);
if (rc != 0) {
errno = rc;
PLOG(safe_to_call_abort ? FATAL : WARNING)
<< "pthread_mutex_destroy failed for " << name_;
}
#endif
}
void Mutex::ExclusiveLock(Thread* self) {
DCHECK(self == nullptr || self == Thread::Current());
if (kDebugLocking && !recursive_) {
AssertNotHeld(self);
}
if (!recursive_ || !IsExclusiveHeld(self)) {
#if ART_USE_FUTEXES
bool done = false;
do {
int32_t cur_state = state_and_contenders_.load(std::memory_order_relaxed);
if (LIKELY((cur_state & kHeldMask) == 0) /* lock not held */) {
done = state_and_contenders_.CompareAndSetWeakAcquire(cur_state, cur_state | kHeldMask);
} else {
// Failed to acquire, hang up.
ScopedContentionRecorder scr(this, SafeGetTid(self), GetExclusiveOwnerTid());
// Empirically, it appears important to spin again each time through the loop; if we
// bother to go to sleep and wake up, we should be fairly persistent in trying for the
// lock.
if (!WaitBrieflyFor(&state_and_contenders_, self,
[](int32_t v) { return (v & kHeldMask) == 0; })) {
// Increment contender count. We can't create enough threads for this to overflow.
increment_contenders();
// Make cur_state again reflect the expected value of state_and_contenders.
cur_state += kContenderIncrement;
if (UNLIKELY(should_respond_to_empty_checkpoint_request_)) {
self->CheckEmptyCheckpointFromMutex();
}
uint64_t wait_start_ms = enable_monitor_timeout_ ? MilliTime() : 0;
uint64_t try_times = 0;
do {
timespec timeout_ts;
timeout_ts.tv_sec = 0;
timeout_ts.tv_nsec = Runtime::Current()->GetMonitorTimeoutNs();
if (futex(state_and_contenders_.Address(), FUTEX_WAIT_PRIVATE, cur_state,
enable_monitor_timeout_ ? &timeout_ts : nullptr , nullptr, 0) != 0) {
// We only went to sleep after incrementing and contenders and checking that the
// lock is still held by someone else. EAGAIN and EINTR both indicate a spurious
// failure, try again from the beginning. We don't use TEMP_FAILURE_RETRY so we can
// intentionally retry to acquire the lock.
if ((errno != EAGAIN) && (errno != EINTR)) {
if (errno == ETIMEDOUT) {
try_times++;
if (try_times <= kMonitorTimeoutTryMax) {
DumpStack(self, wait_start_ms, try_times);
}
} else {
PLOG(FATAL) << "futex wait failed for " << name_;
}
}
}
SleepIfRuntimeDeleted(self);
// Retry until not held. In heavy contention situations we otherwise get redundant
// futex wakeups as a result of repeatedly decrementing and incrementing contenders.
cur_state = state_and_contenders_.load(std::memory_order_relaxed);
} while ((cur_state & kHeldMask) != 0);
decrement_contenders();
}
}
} while (!done);
// Confirm that lock is now held.
DCHECK_NE(state_and_contenders_.load(std::memory_order_relaxed) & kHeldMask, 0);
#else
CHECK_MUTEX_CALL(pthread_mutex_lock, (&mutex_));
#endif
DCHECK_EQ(GetExclusiveOwnerTid(), 0) << " my tid = " << SafeGetTid(self)
<< " recursive_ = " << recursive_;
exclusive_owner_.store(SafeGetTid(self), std::memory_order_relaxed);
RegisterAsLocked(self);
}
recursion_count_++;
if (kDebugLocking) {
CHECK(recursion_count_ == 1 || recursive_) << "Unexpected recursion count on mutex: "
<< name_ << " " << recursion_count_;
AssertHeld(self);
}
}
void Mutex::DumpStack(Thread* self, uint64_t wait_start_ms, uint64_t try_times) {
ScopedObjectAccess soa(self);
Locks::thread_list_lock_->ExclusiveLock(self);
std::string owner_stack_dump;
pid_t owner_tid = GetExclusiveOwnerTid();
Thread *owner = Runtime::Current()->GetThreadList()->FindThreadByTid(owner_tid);
if (owner != nullptr) {
if (IsDumpFrequent(owner, try_times)) {
Locks::thread_list_lock_->ExclusiveUnlock(self);
LOG(WARNING) << "Contention with tid " << owner_tid << ", monitor id " << monitor_id_;
return;
}
struct CollectStackTrace : public Closure {
void Run(art::Thread* thread) override
REQUIRES_SHARED(art::Locks::mutator_lock_) {
if (IsDumpFrequent(thread)) {
return;
}
DumpStackLastTimeTLSData* tls_data =
reinterpret_cast<DumpStackLastTimeTLSData*>(thread->GetCustomTLS(kLastDumpStackTime));
if (tls_data == nullptr) {
thread->SetCustomTLS(kLastDumpStackTime, new DumpStackLastTimeTLSData(MilliTime()));
} else {
tls_data->last_dump_time_ms_.store(MilliTime());
}
thread->DumpJavaStack(oss);
}
std::ostringstream oss;
};
CollectStackTrace owner_trace;
owner->RequestSynchronousCheckpoint(&owner_trace);
owner_stack_dump = owner_trace.oss.str();
uint64_t wait_ms = MilliTime() - wait_start_ms;
LOG(WARNING) << "Monitor contention with tid " << owner_tid << ", wait time: " << wait_ms
<< "ms, monitor id: " << monitor_id_
<< "\nPerfMonitor owner thread(" << owner_tid << ") stack is:\n"
<< owner_stack_dump;
} else {
Locks::thread_list_lock_->ExclusiveUnlock(self);
}
}
bool Mutex::IsDumpFrequent(Thread* thread, uint64_t try_times) {
uint64_t last_dump_time_ms = 0;
DumpStackLastTimeTLSData* tls_data =
reinterpret_cast<DumpStackLastTimeTLSData*>(thread->GetCustomTLS(kLastDumpStackTime));
if (tls_data != nullptr) {
last_dump_time_ms = tls_data->last_dump_time_ms_.load();
}
uint64_t interval = MilliTime() - last_dump_time_ms;
if (interval < kIntervalMillis * try_times) {
return true;
} else {
return false;
}
}
bool Mutex::ExclusiveTryLock(Thread* self) {
DCHECK(self == nullptr || self == Thread::Current());
if (kDebugLocking && !recursive_) {
AssertNotHeld(self);
}
if (!recursive_ || !IsExclusiveHeld(self)) {
#if ART_USE_FUTEXES
bool done = false;
do {
int32_t cur_state = state_and_contenders_.load(std::memory_order_relaxed);
if ((cur_state & kHeldMask) == 0) {
// Change state to held and impose load/store ordering appropriate for lock acquisition.
done = state_and_contenders_.CompareAndSetWeakAcquire(cur_state, cur_state | kHeldMask);
} else {
return false;
}
} while (!done);
DCHECK_NE(state_and_contenders_.load(std::memory_order_relaxed) & kHeldMask, 0);
#else
int result = pthread_mutex_trylock(&mutex_);
if (result == EBUSY) {
return false;
}
if (result != 0) {
errno = result;
PLOG(FATAL) << "pthread_mutex_trylock failed for " << name_;
}
#endif
DCHECK_EQ(GetExclusiveOwnerTid(), 0);
exclusive_owner_.store(SafeGetTid(self), std::memory_order_relaxed);
RegisterAsLocked(self);
}
recursion_count_++;
if (kDebugLocking) {
CHECK(recursion_count_ == 1 || recursive_) << "Unexpected recursion count on mutex: "
<< name_ << " " << recursion_count_;
AssertHeld(self);
}
return true;
}
bool Mutex::ExclusiveTryLockWithSpinning(Thread* self) {
// Spin a small number of times, since this affects our ability to respond to suspension
// requests. We spin repeatedly only if the mutex repeatedly becomes available and unavailable
// in rapid succession, and then we will typically not spin for the maximal period.
const int kMaxSpins = 5;
for (int i = 0; i < kMaxSpins; ++i) {
if (ExclusiveTryLock(self)) {
return true;
}
#if ART_USE_FUTEXES
if (!WaitBrieflyFor(&state_and_contenders_, self,
[](int32_t v) { return (v & kHeldMask) == 0; })) {
return false;
}
#endif
}
return ExclusiveTryLock(self);
}
#if ART_USE_FUTEXES
void Mutex::ExclusiveLockUncontendedFor(Thread* new_owner) {
DCHECK_EQ(level_, kMonitorLock);
DCHECK(!recursive_);
state_and_contenders_.store(kHeldMask, std::memory_order_relaxed);
recursion_count_ = 1;
exclusive_owner_.store(SafeGetTid(new_owner), std::memory_order_relaxed);
// Don't call RegisterAsLocked(). It wouldn't register anything anyway. And
// this happens as we're inflating a monitor, which doesn't logically affect
// held "locks"; it effectively just converts a thin lock to a mutex. By doing
// this while the lock is already held, we're delaying the acquisition of a
// logically held mutex, which can introduce bogus lock order violations.
}
void Mutex::ExclusiveUnlockUncontended() {
DCHECK_EQ(level_, kMonitorLock);
state_and_contenders_.store(0, std::memory_order_relaxed);
recursion_count_ = 0;
exclusive_owner_.store(0 /* pid */, std::memory_order_relaxed);
// Skip RegisterAsUnlocked(), which wouldn't do anything anyway.
}
#endif // ART_USE_FUTEXES
void Mutex::ExclusiveUnlock(Thread* self) {
if (kIsDebugBuild && self != nullptr && self != Thread::Current()) {
std::string name1 = "<null>";
std::string name2 = "<null>";
if (self != nullptr) {
self->GetThreadName(name1);
}
if (Thread::Current() != nullptr) {
Thread::Current()->GetThreadName(name2);
}
LOG(FATAL) << GetName() << " level=" << level_ << " self=" << name1
<< " Thread::Current()=" << name2;
}
AssertHeld(self);
DCHECK_NE(GetExclusiveOwnerTid(), 0);
recursion_count_--;
if (!recursive_ || recursion_count_ == 0) {
if (kDebugLocking) {
CHECK(recursion_count_ == 0 || recursive_) << "Unexpected recursion count on mutex: "
<< name_ << " " << recursion_count_;
}
RegisterAsUnlocked(self);
#if ART_USE_FUTEXES
bool done = false;
do {
int32_t cur_state = state_and_contenders_.load(std::memory_order_relaxed);
if (LIKELY((cur_state & kHeldMask) != 0)) {
// We're no longer the owner.
exclusive_owner_.store(0 /* pid */, std::memory_order_relaxed);
// Change state to not held and impose load/store ordering appropriate for lock release.
uint32_t new_state = cur_state & ~kHeldMask; // Same number of contenders.
done = state_and_contenders_.CompareAndSetWeakRelease(cur_state, new_state);
if (LIKELY(done)) { // Spurious fail or waiters changed ?
if (UNLIKELY(new_state != 0) /* have contenders */) {
futex(state_and_contenders_.Address(), FUTEX_WAKE_PRIVATE, kWakeOne,
nullptr, nullptr, 0);
}
// We only do a futex wait after incrementing contenders and verifying the lock was
// still held. If we didn't see waiters, then there couldn't have been any futexes
// waiting on this lock when we did the CAS. New arrivals after that cannot wait for us,
// since the futex wait call would see the lock available and immediately return.
}
} else {
// Logging acquires the logging lock, avoid infinite recursion in that case.
if (this != Locks::logging_lock_) {
LOG(FATAL) << "Unexpected state_ in unlock " << cur_state << " for " << name_;
} else {
LogHelper::LogLineLowStack(__FILE__,
__LINE__,
::android::base::FATAL_WITHOUT_ABORT,
StringPrintf("Unexpected state_ %d in unlock for %s",
cur_state, name_).c_str());
_exit(1);
}
}
} while (!done);
#else
exclusive_owner_.store(0 /* pid */, std::memory_order_relaxed);
CHECK_MUTEX_CALL(pthread_mutex_unlock, (&mutex_));
#endif
}
}
void Mutex::Dump(std::ostream& os) const {
os << (recursive_ ? "recursive " : "non-recursive ")
<< name_
<< " level=" << static_cast<int>(level_)
<< " rec=" << recursion_count_
<< " owner=" << GetExclusiveOwnerTid() << " ";
DumpContention(os);
}
std::ostream& operator<<(std::ostream& os, const Mutex& mu) {
mu.Dump(os);
return os;
}
void Mutex::WakeupToRespondToEmptyCheckpoint() {
#if ART_USE_FUTEXES
// Wake up all the waiters so they will respond to the emtpy checkpoint.
DCHECK(should_respond_to_empty_checkpoint_request_);
if (UNLIKELY(get_contenders() != 0)) {
futex(state_and_contenders_.Address(), FUTEX_WAKE_PRIVATE, kWakeAll, nullptr, nullptr, 0);
}
#else
LOG(FATAL) << "Non futex case isn't supported.";
#endif
}
ReaderWriterMutex::ReaderWriterMutex(const char* name, LockLevel level)
: BaseMutex(name, level)
#if ART_USE_FUTEXES
, state_(0), exclusive_owner_(0), num_contenders_(0)
#endif
{
#if !ART_USE_FUTEXES
CHECK_MUTEX_CALL(pthread_rwlock_init, (&rwlock_, nullptr));
#endif
}
ReaderWriterMutex::~ReaderWriterMutex() {
#if ART_USE_FUTEXES
CHECK_EQ(state_.load(std::memory_order_relaxed), 0);
CHECK_EQ(GetExclusiveOwnerTid(), 0);
CHECK_EQ(num_contenders_.load(std::memory_order_relaxed), 0);
#else
// We can't use CHECK_MUTEX_CALL here because on shutdown a suspended daemon thread
// may still be using locks.
int rc = pthread_rwlock_destroy(&rwlock_);
if (rc != 0) {
errno = rc;
bool is_safe_to_call_abort = IsSafeToCallAbortSafe();
PLOG(is_safe_to_call_abort ? FATAL : WARNING) << "pthread_rwlock_destroy failed for " << name_;
}
#endif
}
void ReaderWriterMutex::ExclusiveLock(Thread* self) {
DCHECK(self == nullptr || self == Thread::Current());
AssertNotExclusiveHeld(self);
#if ART_USE_FUTEXES
bool done = false;
do {
int32_t cur_state = state_.load(std::memory_order_relaxed);
if (LIKELY(cur_state == 0)) {
// Change state from 0 to -1 and impose load/store ordering appropriate for lock acquisition.
done = state_.CompareAndSetWeakAcquire(0 /* cur_state*/, -1 /* new state */);
} else {
// Failed to acquire, hang up.
ScopedContentionRecorder scr(this, SafeGetTid(self), GetExclusiveOwnerTid());
if (!WaitBrieflyFor(&state_, self, [](int32_t v) { return v == 0; })) {
num_contenders_.fetch_add(1);
if (UNLIKELY(should_respond_to_empty_checkpoint_request_)) {
self->CheckEmptyCheckpointFromMutex();
}
if (futex(state_.Address(), FUTEX_WAIT_PRIVATE, cur_state, nullptr, nullptr, 0) != 0) {
// EAGAIN and EINTR both indicate a spurious failure, try again from the beginning.
// We don't use TEMP_FAILURE_RETRY so we can intentionally retry to acquire the lock.
if ((errno != EAGAIN) && (errno != EINTR)) {
PLOG(FATAL) << "futex wait failed for " << name_;
}
}
SleepIfRuntimeDeleted(self);
num_contenders_.fetch_sub(1);
}
}
} while (!done);
DCHECK_EQ(state_.load(std::memory_order_relaxed), -1);
#else
CHECK_MUTEX_CALL(pthread_rwlock_wrlock, (&rwlock_));
#endif
DCHECK_EQ(GetExclusiveOwnerTid(), 0);
exclusive_owner_.store(SafeGetTid(self), std::memory_order_relaxed);
RegisterAsLocked(self);
AssertExclusiveHeld(self);
}
void ReaderWriterMutex::ExclusiveUnlock(Thread* self) {
DCHECK(self == nullptr || self == Thread::Current());
AssertExclusiveHeld(self);
RegisterAsUnlocked(self);
DCHECK_NE(GetExclusiveOwnerTid(), 0);
#if ART_USE_FUTEXES
bool done = false;
do {
int32_t cur_state = state_.load(std::memory_order_relaxed);
if (LIKELY(cur_state == -1)) {
// We're no longer the owner.
exclusive_owner_.store(0 /* pid */, std::memory_order_relaxed);
// Change state from -1 to 0 and impose load/store ordering appropriate for lock release.
// Note, the num_contenders_ load below musn't reorder before the CompareAndSet.
done = state_.CompareAndSetWeakSequentiallyConsistent(-1 /* cur_state*/, 0 /* new state */);
if (LIKELY(done)) { // Weak CAS may fail spuriously.
// Wake any waiters.
if (UNLIKELY(num_contenders_.load(std::memory_order_seq_cst) > 0)) {
futex(state_.Address(), FUTEX_WAKE_PRIVATE, kWakeAll, nullptr, nullptr, 0);
}
}
} else {
LOG(FATAL) << "Unexpected state_:" << cur_state << " for " << name_;
}
} while (!done);
#else
exclusive_owner_.store(0 /* pid */, std::memory_order_relaxed);
CHECK_MUTEX_CALL(pthread_rwlock_unlock, (&rwlock_));
#endif
}
#if HAVE_TIMED_RWLOCK
bool ReaderWriterMutex::ExclusiveLockWithTimeout(Thread* self, int64_t ms, int32_t ns) {
DCHECK(self == nullptr || self == Thread::Current());
#if ART_USE_FUTEXES
bool done = false;
timespec end_abs_ts;
InitTimeSpec(true, CLOCK_MONOTONIC, ms, ns, &end_abs_ts);
do {
int32_t cur_state = state_.load(std::memory_order_relaxed);
if (cur_state == 0) {
// Change state from 0 to -1 and impose load/store ordering appropriate for lock acquisition.
done = state_.CompareAndSetWeakAcquire(0 /* cur_state */, -1 /* new state */);
} else {
// Failed to acquire, hang up.
timespec now_abs_ts;
InitTimeSpec(true, CLOCK_MONOTONIC, 0, 0, &now_abs_ts);
timespec rel_ts;
if (ComputeRelativeTimeSpec(&rel_ts, end_abs_ts, now_abs_ts)) {
return false; // Timed out.
}
ScopedContentionRecorder scr(this, SafeGetTid(self), GetExclusiveOwnerTid());
if (!WaitBrieflyFor(&state_, self, [](int32_t v) { return v == 0; })) {
num_contenders_.fetch_add(1);
if (UNLIKELY(should_respond_to_empty_checkpoint_request_)) {
self->CheckEmptyCheckpointFromMutex();
}
if (futex(state_.Address(), FUTEX_WAIT_PRIVATE, cur_state, &rel_ts, nullptr, 0) != 0) {
if (errno == ETIMEDOUT) {
num_contenders_.fetch_sub(1);
return false; // Timed out.
} else if ((errno != EAGAIN) && (errno != EINTR)) {
// EAGAIN and EINTR both indicate a spurious failure,
// recompute the relative time out from now and try again.
// We don't use TEMP_FAILURE_RETRY so we can recompute rel_ts;
PLOG(FATAL) << "timed futex wait failed for " << name_;
}
}
SleepIfRuntimeDeleted(self);
num_contenders_.fetch_sub(1);
}
}
} while (!done);
#else
timespec ts;
InitTimeSpec(true, CLOCK_REALTIME, ms, ns, &ts);
int result = pthread_rwlock_timedwrlock(&rwlock_, &ts);
if (result == ETIMEDOUT) {
return false;
}
if (result != 0) {
errno = result;
PLOG(FATAL) << "pthread_rwlock_timedwrlock failed for " << name_;
}
#endif
exclusive_owner_.store(SafeGetTid(self), std::memory_order_relaxed);
RegisterAsLocked(self);
AssertSharedHeld(self);
return true;
}
#endif
#if ART_USE_FUTEXES
void ReaderWriterMutex::HandleSharedLockContention(Thread* self, int32_t cur_state) {
// Owner holds it exclusively, hang up.
ScopedContentionRecorder scr(this, SafeGetTid(self), GetExclusiveOwnerTid());
if (!WaitBrieflyFor(&state_, self, [](int32_t v) { return v >= 0; })) {
num_contenders_.fetch_add(1);
if (UNLIKELY(should_respond_to_empty_checkpoint_request_)) {
self->CheckEmptyCheckpointFromMutex();
}
if (futex(state_.Address(), FUTEX_WAIT_PRIVATE, cur_state, nullptr, nullptr, 0) != 0) {
if (errno != EAGAIN && errno != EINTR) {
PLOG(FATAL) << "futex wait failed for " << name_;
}
}
SleepIfRuntimeDeleted(self);
num_contenders_.fetch_sub(1);
}
}
#endif
bool ReaderWriterMutex::SharedTryLock(Thread* self) {
DCHECK(self == nullptr || self == Thread::Current());
#if ART_USE_FUTEXES
bool done = false;
do {
int32_t cur_state = state_.load(std::memory_order_relaxed);
if (cur_state >= 0) {
// Add as an extra reader and impose load/store ordering appropriate for lock acquisition.
done = state_.CompareAndSetWeakAcquire(cur_state, cur_state + 1);
} else {
// Owner holds it exclusively.
return false;
}
} while (!done);
#else
int result = pthread_rwlock_tryrdlock(&rwlock_);
if (result == EBUSY) {
return false;
}
if (result != 0) {
errno = result;
PLOG(FATAL) << "pthread_mutex_trylock failed for " << name_;
}
#endif
RegisterAsLocked(self);
AssertSharedHeld(self);
return true;
}
bool ReaderWriterMutex::IsSharedHeld(const Thread* self) const {
DCHECK(self == nullptr || self == Thread::Current());
bool result;
if (UNLIKELY(self == nullptr)) { // Handle unattached threads.
result = IsExclusiveHeld(self); // TODO: a better best effort here.
} else {
result = (self->GetHeldMutex(level_) == this);
}
return result;
}
void ReaderWriterMutex::Dump(std::ostream& os) const {
os << name_
<< " level=" << static_cast<int>(level_)
<< " owner=" << GetExclusiveOwnerTid()
#if ART_USE_FUTEXES
<< " state=" << state_.load(std::memory_order_seq_cst)
<< " num_contenders=" << num_contenders_.load(std::memory_order_seq_cst)
#endif
<< " ";
DumpContention(os);
}
std::ostream& operator<<(std::ostream& os, const ReaderWriterMutex& mu) {
mu.Dump(os);
return os;
}
std::ostream& operator<<(std::ostream& os, const MutatorMutex& mu) {
mu.Dump(os);
return os;
}
void ReaderWriterMutex::WakeupToRespondToEmptyCheckpoint() {
#if ART_USE_FUTEXES
// Wake up all the waiters so they will respond to the emtpy checkpoint.
DCHECK(should_respond_to_empty_checkpoint_request_);
if (UNLIKELY(num_contenders_.load(std::memory_order_relaxed) > 0)) {
futex(state_.Address(), FUTEX_WAKE_PRIVATE, kWakeAll, nullptr, nullptr, 0);
}
#else
LOG(FATAL) << "Non futex case isn't supported.";
#endif
}
ConditionVariable::ConditionVariable(const char* name, Mutex& guard)
: name_(name), guard_(guard) {
#if ART_USE_FUTEXES
DCHECK_EQ(0, sequence_.load(std::memory_order_relaxed));
num_waiters_ = 0;
#else
pthread_condattr_t cond_attrs;
CHECK_MUTEX_CALL(pthread_condattr_init, (&cond_attrs));
#if !defined(__APPLE__)
// Apple doesn't have CLOCK_MONOTONIC or pthread_condattr_setclock.
CHECK_MUTEX_CALL(pthread_condattr_setclock, (&cond_attrs, CLOCK_MONOTONIC));
#endif
CHECK_MUTEX_CALL(pthread_cond_init, (&cond_, &cond_attrs));
#endif
}
ConditionVariable::~ConditionVariable() {
#if ART_USE_FUTEXES
if (num_waiters_!= 0) {
bool is_safe_to_call_abort = IsSafeToCallAbortSafe();
LOG(is_safe_to_call_abort ? FATAL : WARNING)
<< "ConditionVariable::~ConditionVariable for " << name_
<< " called with " << num_waiters_ << " waiters.";
}
#else
// We can't use CHECK_MUTEX_CALL here because on shutdown a suspended daemon thread
// may still be using condition variables.
int rc = pthread_cond_destroy(&cond_);
if (rc != 0) {
errno = rc;
bool is_safe_to_call_abort = IsSafeToCallAbortSafe();
PLOG(is_safe_to_call_abort ? FATAL : WARNING) << "pthread_cond_destroy failed for " << name_;
}
#endif
}
void ConditionVariable::Broadcast(Thread* self) {
DCHECK(self == nullptr || self == Thread::Current());
// TODO: enable below, there's a race in thread creation that causes false failures currently.
// guard_.AssertExclusiveHeld(self);
DCHECK_EQ(guard_.GetExclusiveOwnerTid(), SafeGetTid(self));
#if ART_USE_FUTEXES
RequeueWaiters(std::numeric_limits<int32_t>::max());
#else
CHECK_MUTEX_CALL(pthread_cond_broadcast, (&cond_));
#endif
}
#if ART_USE_FUTEXES
void ConditionVariable::RequeueWaiters(int32_t count) {
if (num_waiters_ > 0) {
sequence_++; // Indicate a signal occurred.
// Move waiters from the condition variable's futex to the guard's futex,
// so that they will be woken up when the mutex is released.
bool done = futex(sequence_.Address(),
FUTEX_REQUEUE_PRIVATE,
/* Threads to wake */ 0,
/* Threads to requeue*/ reinterpret_cast<const timespec*>(count),
guard_.state_and_contenders_.Address(),
0) != -1;
if (!done && errno != EAGAIN && errno != EINTR) {
PLOG(FATAL) << "futex requeue failed for " << name_;
}
}
}
#endif
void ConditionVariable::Signal(Thread* self) {
DCHECK(self == nullptr || self == Thread::Current());
guard_.AssertExclusiveHeld(self);
#if ART_USE_FUTEXES
RequeueWaiters(1);
#else
CHECK_MUTEX_CALL(pthread_cond_signal, (&cond_));
#endif
}
void ConditionVariable::Wait(Thread* self) {
guard_.CheckSafeToWait(self);
WaitHoldingLocks(self);
}
void ConditionVariable::WaitHoldingLocks(Thread* self) {
DCHECK(self == nullptr || self == Thread::Current());
guard_.AssertExclusiveHeld(self);
unsigned int old_recursion_count = guard_.recursion_count_;
#if ART_USE_FUTEXES
num_waiters_++;
// Ensure the Mutex is contended so that requeued threads are awoken.
guard_.increment_contenders();
guard_.recursion_count_ = 1;
int32_t cur_sequence = sequence_.load(std::memory_order_relaxed);
guard_.ExclusiveUnlock(self);
if (futex(sequence_.Address(), FUTEX_WAIT_PRIVATE, cur_sequence, nullptr, nullptr, 0) != 0) {
// Futex failed, check it is an expected error.
// EAGAIN == EWOULDBLK, so we let the caller try again.
// EINTR implies a signal was sent to this thread.
if ((errno != EINTR) && (errno != EAGAIN)) {
PLOG(FATAL) << "futex wait failed for " << name_;
}
}
SleepIfRuntimeDeleted(self);
guard_.ExclusiveLock(self);
CHECK_GT(num_waiters_, 0);
num_waiters_--;
// We awoke and so no longer require awakes from the guard_'s unlock.
CHECK_GT(guard_.get_contenders(), 0);
guard_.decrement_contenders();
#else
pid_t old_owner = guard_.GetExclusiveOwnerTid();
guard_.exclusive_owner_.store(0 /* pid */, std::memory_order_relaxed);
guard_.recursion_count_ = 0;
CHECK_MUTEX_CALL(pthread_cond_wait, (&cond_, &guard_.mutex_));
guard_.exclusive_owner_.store(old_owner, std::memory_order_relaxed);
#endif
guard_.recursion_count_ = old_recursion_count;
}
bool ConditionVariable::TimedWait(Thread* self, int64_t ms, int32_t ns) {
DCHECK(self == nullptr || self == Thread::Current());
bool timed_out = false;
guard_.AssertExclusiveHeld(self);
guard_.CheckSafeToWait(self);
unsigned int old_recursion_count = guard_.recursion_count_;
#if ART_USE_FUTEXES
timespec rel_ts;
InitTimeSpec(false, CLOCK_REALTIME, ms, ns, &rel_ts);
num_waiters_++;
// Ensure the Mutex is contended so that requeued threads are awoken.
guard_.increment_contenders();
guard_.recursion_count_ = 1;
int32_t cur_sequence = sequence_.load(std::memory_order_relaxed);
guard_.ExclusiveUnlock(self);
if (futex(sequence_.Address(), FUTEX_WAIT_PRIVATE, cur_sequence, &rel_ts, nullptr, 0) != 0) {
if (errno == ETIMEDOUT) {
// Timed out we're done.
timed_out = true;
} else if ((errno == EAGAIN) || (errno == EINTR)) {
// A signal or ConditionVariable::Signal/Broadcast has come in.
} else {
PLOG(FATAL) << "timed futex wait failed for " << name_;
}
}
SleepIfRuntimeDeleted(self);
guard_.ExclusiveLock(self);
CHECK_GT(num_waiters_, 0);
num_waiters_--;
// We awoke and so no longer require awakes from the guard_'s unlock.
CHECK_GT(guard_.get_contenders(), 0);
guard_.decrement_contenders();
#else
#if !defined(__APPLE__)
int clock = CLOCK_MONOTONIC;
#else
int clock = CLOCK_REALTIME;
#endif
pid_t old_owner = guard_.GetExclusiveOwnerTid();
guard_.exclusive_owner_.store(0 /* pid */, std::memory_order_relaxed);
guard_.recursion_count_ = 0;
timespec ts;
InitTimeSpec(true, clock, ms, ns, &ts);
int rc;
while ((rc = pthread_cond_timedwait(&cond_, &guard_.mutex_, &ts)) == EINTR) {
continue;
}
if (rc == ETIMEDOUT) {
timed_out = true;
} else if (rc != 0) {
errno = rc;
PLOG(FATAL) << "TimedWait failed for " << name_;
}
guard_.exclusive_owner_.store(old_owner, std::memory_order_relaxed);
#endif
guard_.recursion_count_ = old_recursion_count;
return timed_out;
}
} // namespace art
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