/*
* 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 "thread_list.h"
#include <dirent.h>
#include <sys/types.h>
#include <unistd.h>
#include <sstream>
#include <vector>
#include "android-base/stringprintf.h"
#include "backtrace/BacktraceMap.h"
#include "nativehelper/scoped_local_ref.h"
#include "nativehelper/scoped_utf_chars.h"
#include "base/aborting.h"
#include "base/histogram-inl.h"
#include "base/mutex-inl.h"
#include "base/systrace.h"
#include "base/time_utils.h"
#include "base/timing_logger.h"
#include "debugger.h"
#include "gc/collector/concurrent_copying.h"
#include "gc/gc_pause_listener.h"
#include "gc/heap.h"
#include "gc/reference_processor.h"
#include "gc_root.h"
#include "jni/jni_internal.h"
#include "lock_word.h"
#include "monitor.h"
#include "native_stack_dump.h"
#include "scoped_thread_state_change-inl.h"
#include "thread.h"
#include "trace.h"
#include "well_known_classes.h"
#if ART_USE_FUTEXES
#include "linux/futex.h"
#include "sys/syscall.h"
#ifndef SYS_futex
#define SYS_futex __NR_futex
#endif
#endif // ART_USE_FUTEXES
namespace art {
using android::base::StringPrintf;
static constexpr uint64_t kLongThreadSuspendThreshold = MsToNs(5);
// Use 0 since we want to yield to prevent blocking for an unpredictable amount of time.
static constexpr useconds_t kThreadSuspendInitialSleepUs = 0;
static constexpr useconds_t kThreadSuspendMaxYieldUs = 3000;
static constexpr useconds_t kThreadSuspendMaxSleepUs = 5000;
// Whether we should try to dump the native stack of unattached threads. See commit ed8b723 for
// some history.
static constexpr bool kDumpUnattachedThreadNativeStackForSigQuit = true;
ThreadList::ThreadList(uint64_t thread_suspend_timeout_ns)
: suspend_all_count_(0),
unregistering_count_(0),
suspend_all_historam_("suspend all histogram", 16, 64),
long_suspend_(false),
shut_down_(false),
thread_suspend_timeout_ns_(thread_suspend_timeout_ns),
empty_checkpoint_barrier_(new Barrier(0)) {
CHECK(Monitor::IsValidLockWord(LockWord::FromThinLockId(kMaxThreadId, 1, 0U)));
}
ThreadList::~ThreadList() {
CHECK(shut_down_);
}
void ThreadList::ShutDown() {
ScopedTrace trace(__PRETTY_FUNCTION__);
// Detach the current thread if necessary. If we failed to start, there might not be any threads.
// We need to detach the current thread here in case there's another thread waiting to join with
// us.
bool contains = false;
Thread* self = Thread::Current();
{
MutexLock mu(self, *Locks::thread_list_lock_);
contains = Contains(self);
}
if (contains) {
Runtime::Current()->DetachCurrentThread();
}
WaitForOtherNonDaemonThreadsToExit();
// Disable GC and wait for GC to complete in case there are still daemon threads doing
// allocations.
gc::Heap* const heap = Runtime::Current()->GetHeap();
heap->DisableGCForShutdown();
// In case a GC is in progress, wait for it to finish.
heap->WaitForGcToComplete(gc::kGcCauseBackground, Thread::Current());
// TODO: there's an unaddressed race here where a thread may attach during shutdown, see
// Thread::Init.
SuspendAllDaemonThreadsForShutdown();
shut_down_ = true;
}
bool ThreadList::Contains(Thread* thread) {
return find(list_.begin(), list_.end(), thread) != list_.end();
}
pid_t ThreadList::GetLockOwner() {
return Locks::thread_list_lock_->GetExclusiveOwnerTid();
}
void ThreadList::DumpNativeStacks(std::ostream& os) {
MutexLock mu(Thread::Current(), *Locks::thread_list_lock_);
std::unique_ptr<BacktraceMap> map(BacktraceMap::Create(getpid()));
for (const auto& thread : list_) {
os << "DUMPING THREAD " << thread->GetTid() << "\n";
DumpNativeStack(os, thread->GetTid(), map.get(), "\t");
os << "\n";
}
}
void ThreadList::DumpForSigQuit(std::ostream& os) {
{
ScopedObjectAccess soa(Thread::Current());
// Only print if we have samples.
if (suspend_all_historam_.SampleSize() > 0) {
Histogram<uint64_t>::CumulativeData data;
suspend_all_historam_.CreateHistogram(&data);
suspend_all_historam_.PrintConfidenceIntervals(os, 0.99, data); // Dump time to suspend.
}
}
bool dump_native_stack = Runtime::Current()->GetDumpNativeStackOnSigQuit();
Dump(os, dump_native_stack);
DumpUnattachedThreads(os, dump_native_stack && kDumpUnattachedThreadNativeStackForSigQuit);
}
static void DumpUnattachedThread(std::ostream& os, pid_t tid, bool dump_native_stack)
NO_THREAD_SAFETY_ANALYSIS {
// TODO: No thread safety analysis as DumpState with a null thread won't access fields, should
// refactor DumpState to avoid skipping analysis.
Thread::DumpState(os, nullptr, tid);
if (dump_native_stack) {
DumpNativeStack(os, tid, nullptr, " native: ");
}
os << std::endl;
}
void ThreadList::DumpUnattachedThreads(std::ostream& os, bool dump_native_stack) {
DIR* d = opendir("/proc/self/task");
if (!d) {
return;
}
Thread* self = Thread::Current();
dirent* e;
while ((e = readdir(d)) != nullptr) {
char* end;
pid_t tid = strtol(e->d_name, &end, 10);
if (!*end) {
Thread* thread;
{
MutexLock mu(self, *Locks::thread_list_lock_);
thread = FindThreadByTid(tid);
}
if (thread == nullptr) {
DumpUnattachedThread(os, tid, dump_native_stack);
}
}
}
closedir(d);
}
// Dump checkpoint timeout in milliseconds. Larger amount on the target, since the device could be
// overloaded with ANR dumps.
static constexpr uint32_t kDumpWaitTimeout = kIsTargetBuild ? 100000 : 20000;
// A closure used by Thread::Dump.
class DumpCheckpoint final : public Closure {
public:
DumpCheckpoint(std::ostream* os, bool dump_native_stack)
: os_(os),
// Avoid verifying count in case a thread doesn't end up passing through the barrier.
// This avoids a SIGABRT that would otherwise happen in the destructor.
barrier_(0, /*verify_count_on_shutdown=*/false),
backtrace_map_(dump_native_stack ? BacktraceMap::Create(getpid()) : nullptr),
dump_native_stack_(dump_native_stack) {
if (backtrace_map_ != nullptr) {
backtrace_map_->SetSuffixesToIgnore(std::vector<std::string> { "oat", "odex" });
}
}
void Run(Thread* thread) override {
// Note thread and self may not be equal if thread was already suspended at the point of the
// request.
Thread* self = Thread::Current();
CHECK(self != nullptr);
std::ostringstream local_os;
{
ScopedObjectAccess soa(self);
thread->Dump(local_os, dump_native_stack_, backtrace_map_.get());
}
{
// Use the logging lock to ensure serialization when writing to the common ostream.
MutexLock mu(self, *Locks::logging_lock_);
*os_ << local_os.str() << std::endl;
}
barrier_.Pass(self);
}
void WaitForThreadsToRunThroughCheckpoint(size_t threads_running_checkpoint) {
Thread* self = Thread::Current();
ScopedThreadStateChange tsc(self, ThreadState::kWaitingForCheckPointsToRun);
bool timed_out = barrier_.Increment(self, threads_running_checkpoint, kDumpWaitTimeout);
if (timed_out) {
// Avoid a recursive abort.
LOG((kIsDebugBuild && (gAborting == 0)) ? ::android::base::FATAL : ::android::base::ERROR)
<< "Unexpected time out during dump checkpoint.";
}
}
private:
// The common stream that will accumulate all the dumps.
std::ostream* const os_;
// The barrier to be passed through and for the requestor to wait upon.
Barrier barrier_;
// A backtrace map, so that all threads use a shared info and don't reacquire/parse separately.
std::unique_ptr<BacktraceMap> backtrace_map_;
// Whether we should dump the native stack.
const bool dump_native_stack_;
};
void ThreadList::Dump(std::ostream& os, bool dump_native_stack) {
Thread* self = Thread::Current();
{
MutexLock mu(self, *Locks::thread_list_lock_);
os << "DALVIK THREADS (" << list_.size() << "):\n";
}
if (self != nullptr) {
DumpCheckpoint checkpoint(&os, dump_native_stack);
size_t threads_running_checkpoint;
{
// Use SOA to prevent deadlocks if multiple threads are calling Dump() at the same time.
ScopedObjectAccess soa(self);
threads_running_checkpoint = RunCheckpoint(&checkpoint);
}
if (threads_running_checkpoint != 0) {
checkpoint.WaitForThreadsToRunThroughCheckpoint(threads_running_checkpoint);
}
} else {
DumpUnattachedThreads(os, dump_native_stack);
}
}
void ThreadList::AssertThreadsAreSuspended(Thread* self, Thread* ignore1, Thread* ignore2) {
MutexLock mu(self, *Locks::thread_list_lock_);
MutexLock mu2(self, *Locks::thread_suspend_count_lock_);
for (const auto& thread : list_) {
if (thread != ignore1 && thread != ignore2) {
CHECK(thread->IsSuspended())
<< "\nUnsuspended thread: <<" << *thread << "\n"
<< "self: <<" << *Thread::Current();
}
}
}
#if HAVE_TIMED_RWLOCK
// Attempt to rectify locks so that we dump thread list with required locks before exiting.
NO_RETURN static void UnsafeLogFatalForThreadSuspendAllTimeout() {
// Increment gAborting before doing the thread list dump since we don't want any failures from
// AssertThreadSuspensionIsAllowable in cases where thread suspension is not allowed.
// See b/69044468.
++gAborting;
Runtime* runtime = Runtime::Current();
std::ostringstream ss;
ss << "Thread suspend timeout\n";
Locks::mutator_lock_->Dump(ss);
ss << "\n";
runtime->GetThreadList()->Dump(ss);
--gAborting;
LOG(FATAL) << ss.str();
exit(0);
}
#endif
// Unlike suspending all threads where we can wait to acquire the mutator_lock_, suspending an
// individual thread requires polling. delay_us is the requested sleep wait. If delay_us is 0 then
// we use sched_yield instead of calling usleep.
// Although there is the possibility, here and elsewhere, that usleep could return -1 and
// errno = EINTR, there should be no problem if interrupted, so we do not check.
static void ThreadSuspendSleep(useconds_t delay_us) {
if (delay_us == 0) {
sched_yield();
} else {
usleep(delay_us);
}
}
size_t ThreadList::RunCheckpoint(Closure* checkpoint_function, Closure* callback) {
Thread* self = Thread::Current();
Locks::mutator_lock_->AssertNotExclusiveHeld(self);
Locks::thread_list_lock_->AssertNotHeld(self);
Locks::thread_suspend_count_lock_->AssertNotHeld(self);
std::vector<Thread*> suspended_count_modified_threads;
size_t count = 0;
{
// Call a checkpoint function for each thread, threads which are suspended get their checkpoint
// manually called.
MutexLock mu(self, *Locks::thread_list_lock_);
MutexLock mu2(self, *Locks::thread_suspend_count_lock_);
count = list_.size();
for (const auto& thread : list_) {
if (thread != self) {
bool requested_suspend = false;
while (true) {
if (thread->RequestCheckpoint(checkpoint_function)) {
// This thread will run its checkpoint some time in the near future.
if (requested_suspend) {
// The suspend request is now unnecessary.
bool updated =
thread->ModifySuspendCount(self, -1, nullptr, SuspendReason::kInternal);
DCHECK(updated);
requested_suspend = false;
}
break;
} else {
// The thread is probably suspended, try to make sure that it stays suspended.
if (thread->GetState() == ThreadState::kRunnable) {
// Spurious fail, try again.
continue;
}
if (!requested_suspend) {
bool updated =
thread->ModifySuspendCount(self, +1, nullptr, SuspendReason::kInternal);
DCHECK(updated);
requested_suspend = true;
if (thread->IsSuspended()) {
break;
}
// The thread raced us to become Runnable. Try to RequestCheckpoint() again.
} else {
// The thread previously raced our suspend request to become Runnable but
// since it is suspended again, it must honor that suspend request now.
DCHECK(thread->IsSuspended());
break;
}
}
}
if (requested_suspend) {
suspended_count_modified_threads.push_back(thread);
}
}
}
// Run the callback to be called inside this critical section.
if (callback != nullptr) {
callback->Run(self);
}
}
// Run the checkpoint on ourself while we wait for threads to suspend.
checkpoint_function->Run(self);
// Run the checkpoint on the suspended threads.
for (const auto& thread : suspended_count_modified_threads) {
// We know for sure that the thread is suspended at this point.
DCHECK(thread->IsSuspended());
checkpoint_function->Run(thread);
{
MutexLock mu2(self, *Locks::thread_suspend_count_lock_);
bool updated = thread->ModifySuspendCount(self, -1, nullptr, SuspendReason::kInternal);
DCHECK(updated);
}
}
{
// Imitate ResumeAll, threads may be waiting on Thread::resume_cond_ since we raised their
// suspend count. Now the suspend_count_ is lowered so we must do the broadcast.
MutexLock mu2(self, *Locks::thread_suspend_count_lock_);
Thread::resume_cond_->Broadcast(self);
}
return count;
}
void ThreadList::RunEmptyCheckpoint() {
Thread* self = Thread::Current();
Locks::mutator_lock_->AssertNotExclusiveHeld(self);
Locks::thread_list_lock_->AssertNotHeld(self);
Locks::thread_suspend_count_lock_->AssertNotHeld(self);
std::vector<uint32_t> runnable_thread_ids;
size_t count = 0;
Barrier* barrier = empty_checkpoint_barrier_.get();
barrier->Init(self, 0);
{
MutexLock mu(self, *Locks::thread_list_lock_);
MutexLock mu2(self, *Locks::thread_suspend_count_lock_);
for (Thread* thread : list_) {
if (thread != self) {
while (true) {
if (thread->RequestEmptyCheckpoint()) {
// This thread will run an empty checkpoint (decrement the empty checkpoint barrier)
// some time in the near future.
++count;
if (kIsDebugBuild) {
runnable_thread_ids.push_back(thread->GetThreadId());
}
break;
}
if (thread->GetState() != ThreadState::kRunnable) {
// It's seen suspended, we are done because it must not be in the middle of a mutator
// heap access.
break;
}
}
}
}
}
// Wake up the threads blocking for weak ref access so that they will respond to the empty
// checkpoint request. Otherwise we will hang as they are blocking in the kRunnable state.
Runtime::Current()->GetHeap()->GetReferenceProcessor()->BroadcastForSlowPath(self);
Runtime::Current()->BroadcastForNewSystemWeaks(/*broadcast_for_checkpoint=*/true);
{
ScopedThreadStateChange tsc(self, ThreadState::kWaitingForCheckPointsToRun);
uint64_t total_wait_time = 0;
bool first_iter = true;
while (true) {
// Wake up the runnable threads blocked on the mutexes that another thread, which is blocked
// on a weak ref access, holds (indirectly blocking for weak ref access through another thread
// and a mutex.) This needs to be done periodically because the thread may be preempted
// between the CheckEmptyCheckpointFromMutex call and the subsequent futex wait in
// Mutex::ExclusiveLock, etc. when the wakeup via WakeupToRespondToEmptyCheckpoint
// arrives. This could cause a *very rare* deadlock, if not repeated. Most of the cases are
// handled in the first iteration.
for (BaseMutex* mutex : Locks::expected_mutexes_on_weak_ref_access_) {
mutex->WakeupToRespondToEmptyCheckpoint();
}
static constexpr uint64_t kEmptyCheckpointPeriodicTimeoutMs = 100; // 100ms
static constexpr uint64_t kEmptyCheckpointTotalTimeoutMs = 600 * 1000; // 10 minutes.
size_t barrier_count = first_iter ? count : 0;
first_iter = false; // Don't add to the barrier count from the second iteration on.
bool timed_out = barrier->Increment(self, barrier_count, kEmptyCheckpointPeriodicTimeoutMs);
if (!timed_out) {
break; // Success
}
// This is a very rare case.
total_wait_time += kEmptyCheckpointPeriodicTimeoutMs;
if (kIsDebugBuild && total_wait_time > kEmptyCheckpointTotalTimeoutMs) {
std::ostringstream ss;
ss << "Empty checkpoint timeout\n";
ss << "Barrier count " << barrier->GetCount(self) << "\n";
ss << "Runnable thread IDs";
for (uint32_t tid : runnable_thread_ids) {
ss << " " << tid;
}
ss << "\n";
Locks::mutator_lock_->Dump(ss);
ss << "\n";
LOG(FATAL_WITHOUT_ABORT) << ss.str();
// Some threads in 'runnable_thread_ids' are probably stuck. Try to dump their stacks.
// Avoid using ThreadList::Dump() initially because it is likely to get stuck as well.
{
ScopedObjectAccess soa(self);
MutexLock mu1(self, *Locks::thread_list_lock_);
for (Thread* thread : GetList()) {
uint32_t tid = thread->GetThreadId();
bool is_in_runnable_thread_ids =
std::find(runnable_thread_ids.begin(), runnable_thread_ids.end(), tid) !=
runnable_thread_ids.end();
if (is_in_runnable_thread_ids &&
thread->ReadFlag(ThreadFlag::kEmptyCheckpointRequest)) {
// Found a runnable thread that hasn't responded to the empty checkpoint request.
// Assume it's stuck and safe to dump its stack.
thread->Dump(LOG_STREAM(FATAL_WITHOUT_ABORT),
/*dump_native_stack=*/ true,
/*backtrace_map=*/ nullptr,
/*force_dump_stack=*/ true);
}
}
}
LOG(FATAL_WITHOUT_ABORT)
<< "Dumped runnable threads that haven't responded to empty checkpoint.";
// Now use ThreadList::Dump() to dump more threads, noting it may get stuck.
Dump(LOG_STREAM(FATAL_WITHOUT_ABORT));
LOG(FATAL) << "Dumped all threads.";
}
}
}
}
// A checkpoint/suspend-all hybrid to switch thread roots from
// from-space to to-space refs. Used to synchronize threads at a point
// to mark the initiation of marking while maintaining the to-space
// invariant.
size_t ThreadList::FlipThreadRoots(Closure* thread_flip_visitor,
Closure* flip_callback,
gc::collector::GarbageCollector* collector,
gc::GcPauseListener* pause_listener) {
TimingLogger::ScopedTiming split("ThreadListFlip", collector->GetTimings());
Thread* self = Thread::Current();
Locks::mutator_lock_->AssertNotHeld(self);
Locks::thread_list_lock_->AssertNotHeld(self);
Locks::thread_suspend_count_lock_->AssertNotHeld(self);
CHECK_NE(self->GetState(), ThreadState::kRunnable);
collector->GetHeap()->ThreadFlipBegin(self); // Sync with JNI critical calls.
// ThreadFlipBegin happens before we suspend all the threads, so it does not count towards the
// pause.
const uint64_t suspend_start_time = NanoTime();
SuspendAllInternal(self, self, nullptr);
if (pause_listener != nullptr) {
pause_listener->StartPause();
}
// Run the flip callback for the collector.
Locks::mutator_lock_->ExclusiveLock(self);
suspend_all_historam_.AdjustAndAddValue(NanoTime() - suspend_start_time);
flip_callback->Run(self);
Locks::mutator_lock_->ExclusiveUnlock(self);
collector->RegisterPause(NanoTime() - suspend_start_time);
if (pause_listener != nullptr) {
pause_listener->EndPause();
}
// Resume runnable threads.
size_t runnable_thread_count = 0;
std::vector<Thread*> other_threads;
{
TimingLogger::ScopedTiming split2("ResumeRunnableThreads", collector->GetTimings());
MutexLock mu(self, *Locks::thread_list_lock_);
MutexLock mu2(self, *Locks::thread_suspend_count_lock_);
--suspend_all_count_;
for (Thread* thread : list_) {
// Set the flip function for all threads because once we start resuming any threads,
// they may need to run the flip function on behalf of other threads, even this one.
thread->SetFlipFunction(thread_flip_visitor);
if (thread == self) {
continue;
}
// Resume early the threads that were runnable but are suspended just for this thread flip or
// about to transition from non-runnable (eg. kNative at the SOA entry in a JNI function) to
// runnable (both cases waiting inside Thread::TransitionFromSuspendedToRunnable), or waiting
// for the thread flip to end at the JNI critical section entry (kWaitingForGcThreadFlip),
ThreadState state = thread->GetState();
if ((state == ThreadState::kWaitingForGcThreadFlip || thread->IsTransitioningToRunnable()) &&
thread->GetSuspendCount() == 1) {
// The thread will resume right after the broadcast.
bool updated = thread->ModifySuspendCount(self, -1, nullptr, SuspendReason::kInternal);
DCHECK(updated);
++runnable_thread_count;
} else {
other_threads.push_back(thread);
}
}
Thread::resume_cond_->Broadcast(self);
}
collector->GetHeap()->ThreadFlipEnd(self);
// Try to run the closure on the other threads.
{
TimingLogger::ScopedTiming split3("FlipOtherThreads", collector->GetTimings());
ReaderMutexLock mu(self, *Locks::mutator_lock_);
for (Thread* thread : other_threads) {
thread->EnsureFlipFunctionStarted(self);
DCHECK(!thread->ReadFlag(ThreadFlag::kPendingFlipFunction));
}
// Try to run the flip function for self.
self->EnsureFlipFunctionStarted(self);
DCHECK(!self->ReadFlag(ThreadFlag::kPendingFlipFunction));
}
// Resume other threads.
{
TimingLogger::ScopedTiming split4("ResumeOtherThreads", collector->GetTimings());
MutexLock mu2(self, *Locks::thread_suspend_count_lock_);
for (const auto& thread : other_threads) {
bool updated = thread->ModifySuspendCount(self, -1, nullptr, SuspendReason::kInternal);
DCHECK(updated);
}
Thread::resume_cond_->Broadcast(self);
}
return runnable_thread_count + other_threads.size() + 1; // +1 for self.
}
void ThreadList::SuspendAll(const char* cause, bool long_suspend) {
Thread* self = Thread::Current();
if (self != nullptr) {
VLOG(threads) << *self << " SuspendAll for " << cause << " starting...";
} else {
VLOG(threads) << "Thread[null] SuspendAll for " << cause << " starting...";
}
{
ScopedTrace trace("Suspending mutator threads");
const uint64_t start_time = NanoTime();
SuspendAllInternal(self, self);
// All threads are known to have suspended (but a thread may still own the mutator lock)
// Make sure this thread grabs exclusive access to the mutator lock and its protected data.
#if HAVE_TIMED_RWLOCK
while (true) {
if (Locks::mutator_lock_->ExclusiveLockWithTimeout(self,
NsToMs(thread_suspend_timeout_ns_),
0)) {
break;
} else if (!long_suspend_) {
// Reading long_suspend without the mutator lock is slightly racy, in some rare cases, this
// could result in a thread suspend timeout.
// Timeout if we wait more than thread_suspend_timeout_ns_ nanoseconds.
UnsafeLogFatalForThreadSuspendAllTimeout();
}
}
#else
Locks::mutator_lock_->ExclusiveLock(self);
#endif
long_suspend_ = long_suspend;
const uint64_t end_time = NanoTime();
const uint64_t suspend_time = end_time - start_time;
suspend_all_historam_.AdjustAndAddValue(suspend_time);
if (suspend_time > kLongThreadSuspendThreshold) {
LOG(WARNING) << "Suspending all threads took: " << PrettyDuration(suspend_time);
}
if (kDebugLocking) {
// Debug check that all threads are suspended.
AssertThreadsAreSuspended(self, self);
}
}
ATraceBegin((std::string("Mutator threads suspended for ") + cause).c_str());
if (self != nullptr) {
VLOG(threads) << *self << " SuspendAll complete";
} else {
VLOG(threads) << "Thread[null] SuspendAll complete";
}
}
// Ensures all threads running Java suspend and that those not running Java don't start.
void ThreadList::SuspendAllInternal(Thread* self,
Thread* ignore1,
Thread* ignore2,
SuspendReason reason) {
Locks::mutator_lock_->AssertNotExclusiveHeld(self);
Locks::thread_list_lock_->AssertNotHeld(self);
Locks::thread_suspend_count_lock_->AssertNotHeld(self);
if (kDebugLocking && self != nullptr) {
CHECK_NE(self->GetState(), ThreadState::kRunnable);
}
// First request that all threads suspend, then wait for them to suspend before
// returning. This suspension scheme also relies on other behaviour:
// 1. Threads cannot be deleted while they are suspended or have a suspend-
// request flag set - (see Unregister() below).
// 2. When threads are created, they are created in a suspended state (actually
// kNative) and will never begin executing Java code without first checking
// the suspend-request flag.
// The atomic counter for number of threads that need to pass the barrier.
AtomicInteger pending_threads;
uint32_t num_ignored = 0;
if (ignore1 != nullptr) {
++num_ignored;
}
if (ignore2 != nullptr && ignore1 != ignore2) {
++num_ignored;
}
{
MutexLock mu(self, *Locks::thread_list_lock_);
MutexLock mu2(self, *Locks::thread_suspend_count_lock_);
// Update global suspend all state for attaching threads.
++suspend_all_count_;
pending_threads.store(list_.size() - num_ignored, std::memory_order_relaxed);
// Increment everybody's suspend count (except those that should be ignored).
for (const auto& thread : list_) {
if (thread == ignore1 || thread == ignore2) {
continue;
}
VLOG(threads) << "requesting thread suspend: " << *thread;
bool updated = thread->ModifySuspendCount(self, +1, &pending_threads, reason);
DCHECK(updated);
// Must install the pending_threads counter first, then check thread->IsSuspend() and clear
// the counter. Otherwise there's a race with Thread::TransitionFromRunnableToSuspended()
// that can lead a thread to miss a call to PassActiveSuspendBarriers().
if (thread->IsSuspended()) {
// Only clear the counter for the current thread.
thread->ClearSuspendBarrier(&pending_threads);
pending_threads.fetch_sub(1, std::memory_order_seq_cst);
}
}
}
// Wait for the barrier to be passed by all runnable threads. This wait
// is done with a timeout so that we can detect problems.
#if ART_USE_FUTEXES
timespec wait_timeout;
InitTimeSpec(false, CLOCK_MONOTONIC, NsToMs(thread_suspend_timeout_ns_), 0, &wait_timeout);
#endif
const uint64_t start_time = NanoTime();
while (true) {
int32_t cur_val = pending_threads.load(std::memory_order_relaxed);
if (LIKELY(cur_val > 0)) {
#if ART_USE_FUTEXES
if (futex(pending_threads.Address(), FUTEX_WAIT_PRIVATE, cur_val, &wait_timeout, nullptr, 0)
!= 0) {
if ((errno == EAGAIN) || (errno == EINTR)) {
// EAGAIN and EINTR both indicate a spurious failure, try again from the beginning.
continue;
}
if (errno == ETIMEDOUT) {
const uint64_t wait_time = NanoTime() - start_time;
MutexLock mu(self, *Locks::thread_list_lock_);
MutexLock mu2(self, *Locks::thread_suspend_count_lock_);
std::ostringstream oss;
for (const auto& thread : list_) {
if (thread == ignore1 || thread == ignore2) {
continue;
}
if (!thread->IsSuspended()) {
oss << std::endl << "Thread not suspended: " << *thread;
}
}
LOG(kIsDebugBuild ? ::android::base::FATAL : ::android::base::ERROR)
<< "Timed out waiting for threads to suspend, waited for "
<< PrettyDuration(wait_time)
<< oss.str();
} else {
PLOG(FATAL) << "futex wait failed for SuspendAllInternal()";
}
} // else re-check pending_threads in the next iteration (this may be a spurious wake-up).
#else
// Spin wait. This is likely to be slow, but on most architecture ART_USE_FUTEXES is set.
UNUSED(start_time);
#endif
} else {
CHECK_EQ(cur_val, 0);
break;
}
}
}
void ThreadList::ResumeAll() {
Thread* self = Thread::Current();
if (self != nullptr) {
VLOG(threads) << *self << " ResumeAll starting";
} else {
VLOG(threads) << "Thread[null] ResumeAll starting";
}
ATraceEnd();
ScopedTrace trace("Resuming mutator threads");
if (kDebugLocking) {
// Debug check that all threads are suspended.
AssertThreadsAreSuspended(self, self);
}
long_suspend_ = false;
Locks::mutator_lock_->ExclusiveUnlock(self);
{
MutexLock mu(self, *Locks::thread_list_lock_);
MutexLock mu2(self, *Locks::thread_suspend_count_lock_);
// Update global suspend all state for attaching threads.
--suspend_all_count_;
// Decrement the suspend counts for all threads.
for (const auto& thread : list_) {
if (thread == self) {
continue;
}
bool updated = thread->ModifySuspendCount(self, -1, nullptr, SuspendReason::kInternal);
DCHECK(updated);
}
// Broadcast a notification to all suspended threads, some or all of
// which may choose to wake up. No need to wait for them.
if (self != nullptr) {
VLOG(threads) << *self << " ResumeAll waking others";
} else {
VLOG(threads) << "Thread[null] ResumeAll waking others";
}
Thread::resume_cond_->Broadcast(self);
}
if (self != nullptr) {
VLOG(threads) << *self << " ResumeAll complete";
} else {
VLOG(threads) << "Thread[null] ResumeAll complete";
}
}
bool ThreadList::Resume(Thread* thread, SuspendReason reason) {
// This assumes there was an ATraceBegin when we suspended the thread.
ATraceEnd();
Thread* self = Thread::Current();
DCHECK_NE(thread, self);
VLOG(threads) << "Resume(" << reinterpret_cast<void*>(thread) << ") starting..." << reason;
{
// To check Contains.
MutexLock mu(self, *Locks::thread_list_lock_);
// To check IsSuspended.
MutexLock mu2(self, *Locks::thread_suspend_count_lock_);
if (UNLIKELY(!thread->IsSuspended())) {
LOG(ERROR) << "Resume(" << reinterpret_cast<void*>(thread)
<< ") thread not suspended";
return false;
}
if (!Contains(thread)) {
// We only expect threads within the thread-list to have been suspended otherwise we can't
// stop such threads from delete-ing themselves.
LOG(ERROR) << "Resume(" << reinterpret_cast<void*>(thread)
<< ") thread not within thread list";
return false;
}
if (UNLIKELY(!thread->ModifySuspendCount(self, -1, nullptr, reason))) {
LOG(ERROR) << "Resume(" << reinterpret_cast<void*>(thread)
<< ") could not modify suspend count.";
return false;
}
}
{
VLOG(threads) << "Resume(" << reinterpret_cast<void*>(thread) << ") waking others";
MutexLock mu(self, *Locks::thread_suspend_count_lock_);
Thread::resume_cond_->Broadcast(self);
}
VLOG(threads) << "Resume(" << reinterpret_cast<void*>(thread) << ") complete";
return true;
}
static void ThreadSuspendByPeerWarning(Thread* self,
LogSeverity severity,
const char* message,
jobject peer) {
JNIEnvExt* env = self->GetJniEnv();
ScopedLocalRef<jstring>
scoped_name_string(env, static_cast<jstring>(env->GetObjectField(
peer, WellKnownClasses::java_lang_Thread_name)));
ScopedUtfChars scoped_name_chars(env, scoped_name_string.get());
if (scoped_name_chars.c_str() == nullptr) {
LOG(severity) << message << ": " << peer;
env->ExceptionClear();
} else {
LOG(severity) << message << ": " << peer << ":" << scoped_name_chars.c_str();
}
}
Thread* ThreadList::SuspendThreadByPeer(jobject peer,
SuspendReason reason,
bool* timed_out) {
bool request_suspension = true;
const uint64_t start_time = NanoTime();
int self_suspend_count = 0;
useconds_t sleep_us = kThreadSuspendInitialSleepUs;
*timed_out = false;
Thread* const self = Thread::Current();
Thread* suspended_thread = nullptr;
VLOG(threads) << "SuspendThreadByPeer starting";
while (true) {
Thread* thread;
{
// Note: this will transition to runnable and potentially suspend. We ensure only one thread
// is requesting another suspend, to avoid deadlock, by requiring this function be called
// holding Locks::thread_list_suspend_thread_lock_. Its important this thread suspend rather
// than request thread suspension, to avoid potential cycles in threads requesting each other
// suspend.
ScopedObjectAccess soa(self);
MutexLock thread_list_mu(self, *Locks::thread_list_lock_);
thread = Thread::FromManagedThread(soa, peer);
if (thread == nullptr) {
if (suspended_thread != nullptr) {
MutexLock suspend_count_mu(self, *Locks::thread_suspend_count_lock_);
// If we incremented the suspend count but the thread reset its peer, we need to
// re-decrement it since it is shutting down and may deadlock the runtime in
// ThreadList::WaitForOtherNonDaemonThreadsToExit.
bool updated = suspended_thread->ModifySuspendCount(soa.Self(),
-1,
nullptr,
reason);
DCHECK(updated);
}
ThreadSuspendByPeerWarning(self,
::android::base::WARNING,
"No such thread for suspend",
peer);
return nullptr;
}
if (!Contains(thread)) {
CHECK(suspended_thread == nullptr);
VLOG(threads) << "SuspendThreadByPeer failed for unattached thread: "
<< reinterpret_cast<void*>(thread);
return nullptr;
}
VLOG(threads) << "SuspendThreadByPeer found thread: " << *thread;
{
MutexLock suspend_count_mu(self, *Locks::thread_suspend_count_lock_);
if (request_suspension) {
if (self->GetSuspendCount() > 0) {
// We hold the suspend count lock but another thread is trying to suspend us. Its not
// safe to try to suspend another thread in case we get a cycle. Start the loop again
// which will allow this thread to be suspended.
++self_suspend_count;
continue;
}
CHECK(suspended_thread == nullptr);
suspended_thread = thread;
bool updated = suspended_thread->ModifySuspendCount(self, +1, nullptr, reason);
DCHECK(updated);
request_suspension = false;
} else {
// If the caller isn't requesting suspension, a suspension should have already occurred.
CHECK_GT(thread->GetSuspendCount(), 0);
}
// IsSuspended on the current thread will fail as the current thread is changed into
// Runnable above. As the suspend count is now raised if this is the current thread
// it will self suspend on transition to Runnable, making it hard to work with. It's simpler
// to just explicitly handle the current thread in the callers to this code.
CHECK_NE(thread, self) << "Attempt to suspend the current thread for the debugger";
// If thread is suspended (perhaps it was already not Runnable but didn't have a suspend
// count, or else we've waited and it has self suspended) or is the current thread, we're
// done.
if (thread->IsSuspended()) {
VLOG(threads) << "SuspendThreadByPeer thread suspended: " << *thread;
if (ATraceEnabled()) {
std::string name;
thread->GetThreadName(name);
ATraceBegin(StringPrintf("SuspendThreadByPeer suspended %s for peer=%p", name.c_str(),
peer).c_str());
}
return thread;
}
const uint64_t total_delay = NanoTime() - start_time;
if (total_delay >= thread_suspend_timeout_ns_) {
if (suspended_thread == nullptr) {
ThreadSuspendByPeerWarning(self,
::android::base::FATAL,
"Failed to issue suspend request",
peer);
} else {
CHECK_EQ(suspended_thread, thread);
LOG(WARNING) << "Suspended thread state_and_flags: "
<< suspended_thread->StateAndFlagsAsHexString()
<< ", self_suspend_count = " << self_suspend_count;
// Explicitly release thread_suspend_count_lock_; we haven't held it for long, so
// seeing threads blocked on it is not informative.
Locks::thread_suspend_count_lock_->Unlock(self);
ThreadSuspendByPeerWarning(self,
::android::base::FATAL,
"Thread suspension timed out",
peer);
}
UNREACHABLE();
} else if (sleep_us == 0 &&
total_delay > static_cast<uint64_t>(kThreadSuspendMaxYieldUs) * 1000) {
// We have spun for kThreadSuspendMaxYieldUs time, switch to sleeps to prevent
// excessive CPU usage.
sleep_us = kThreadSuspendMaxYieldUs / 2;
}
}
// Release locks and come out of runnable state.
}
VLOG(threads) << "SuspendThreadByPeer waiting to allow thread chance to suspend";
ThreadSuspendSleep(sleep_us);
// This may stay at 0 if sleep_us == 0, but this is WAI since we want to avoid using usleep at
// all if possible. This shouldn't be an issue since time to suspend should always be small.
sleep_us = std::min(sleep_us * 2, kThreadSuspendMaxSleepUs);
}
}
static void ThreadSuspendByThreadIdWarning(LogSeverity severity,
const char* message,
uint32_t thread_id) {
LOG(severity) << StringPrintf("%s: %d", message, thread_id);
}
Thread* ThreadList::SuspendThreadByThreadId(uint32_t thread_id,
SuspendReason reason,
bool* timed_out) {
const uint64_t start_time = NanoTime();
useconds_t sleep_us = kThreadSuspendInitialSleepUs;
*timed_out = false;
Thread* suspended_thread = nullptr;
Thread* const self = Thread::Current();
CHECK_NE(thread_id, kInvalidThreadId);
VLOG(threads) << "SuspendThreadByThreadId starting";
while (true) {
{
// Note: this will transition to runnable and potentially suspend. We ensure only one thread
// is requesting another suspend, to avoid deadlock, by requiring this function be called
// holding Locks::thread_list_suspend_thread_lock_. Its important this thread suspend rather
// than request thread suspension, to avoid potential cycles in threads requesting each other
// suspend.
ScopedObjectAccess soa(self);
MutexLock thread_list_mu(self, *Locks::thread_list_lock_);
Thread* thread = nullptr;
for (const auto& it : list_) {
if (it->GetThreadId() == thread_id) {
thread = it;
break;
}
}
if (thread == nullptr) {
CHECK(suspended_thread == nullptr) << "Suspended thread " << suspended_thread
<< " no longer in thread list";
// There's a race in inflating a lock and the owner giving up ownership and then dying.
ThreadSuspendByThreadIdWarning(::android::base::WARNING,
"No such thread id for suspend",
thread_id);
return nullptr;
}
VLOG(threads) << "SuspendThreadByThreadId found thread: " << *thread;
DCHECK(Contains(thread));
{
MutexLock suspend_count_mu(self, *Locks::thread_suspend_count_lock_);
if (suspended_thread == nullptr) {
if (self->GetSuspendCount() > 0) {
// We hold the suspend count lock but another thread is trying to suspend us. Its not
// safe to try to suspend another thread in case we get a cycle. Start the loop again
// which will allow this thread to be suspended.
continue;
}
bool updated = thread->ModifySuspendCount(self, +1, nullptr, reason);
DCHECK(updated);
suspended_thread = thread;
} else {
CHECK_EQ(suspended_thread, thread);
// If the caller isn't requesting suspension, a suspension should have already occurred.
CHECK_GT(thread->GetSuspendCount(), 0);
}
// IsSuspended on the current thread will fail as the current thread is changed into
// Runnable above. As the suspend count is now raised if this is the current thread
// it will self suspend on transition to Runnable, making it hard to work with. It's simpler
// to just explicitly handle the current thread in the callers to this code.
CHECK_NE(thread, self) << "Attempt to suspend the current thread for the debugger";
// If thread is suspended (perhaps it was already not Runnable but didn't have a suspend
// count, or else we've waited and it has self suspended) or is the current thread, we're
// done.
if (thread->IsSuspended()) {
if (ATraceEnabled()) {
std::string name;
thread->GetThreadName(name);
ATraceBegin(StringPrintf("SuspendThreadByThreadId suspended %s id=%d",
name.c_str(), thread_id).c_str());
}
VLOG(threads) << "SuspendThreadByThreadId thread suspended: " << *thread;
return thread;
}
const uint64_t total_delay = NanoTime() - start_time;
if (total_delay >= thread_suspend_timeout_ns_) {
ThreadSuspendByThreadIdWarning(::android::base::WARNING,
"Thread suspension timed out",
thread_id);
if (suspended_thread != nullptr) {
bool updated = thread->ModifySuspendCount(soa.Self(), -1, nullptr, reason);
DCHECK(updated);
}
*timed_out = true;
return nullptr;
} else if (sleep_us == 0 &&
total_delay > static_cast<uint64_t>(kThreadSuspendMaxYieldUs) * 1000) {
// We have spun for kThreadSuspendMaxYieldUs time, switch to sleeps to prevent
// excessive CPU usage.
sleep_us = kThreadSuspendMaxYieldUs / 2;
}
}
// Release locks and come out of runnable state.
}
VLOG(threads) << "SuspendThreadByThreadId waiting to allow thread chance to suspend";
ThreadSuspendSleep(sleep_us);
sleep_us = std::min(sleep_us * 2, kThreadSuspendMaxSleepUs);
}
}
Thread* ThreadList::FindThreadByThreadId(uint32_t thread_id) {
for (const auto& thread : list_) {
if (thread->GetThreadId() == thread_id) {
return thread;
}
}
return nullptr;
}
Thread* ThreadList::FindThreadByTid(int tid) {
for (const auto& thread : list_) {
if (thread->GetTid() == tid) {
return thread;
}
}
return nullptr;
}
void ThreadList::WaitForOtherNonDaemonThreadsToExit(bool check_no_birth) {
ScopedTrace trace(__PRETTY_FUNCTION__);
Thread* self = Thread::Current();
Locks::mutator_lock_->AssertNotHeld(self);
while (true) {
Locks::runtime_shutdown_lock_->Lock(self);
if (check_no_birth) {
// No more threads can be born after we start to shutdown.
CHECK(Runtime::Current()->IsShuttingDownLocked());
CHECK_EQ(Runtime::Current()->NumberOfThreadsBeingBorn(), 0U);
} else {
if (Runtime::Current()->NumberOfThreadsBeingBorn() != 0U) {
// Awkward. Shutdown_cond_ is private, but the only live thread may not be registered yet.
// Fortunately, this is used mostly for testing, and not performance-critical.
Locks::runtime_shutdown_lock_->Unlock(self);
usleep(1000);
continue;
}
}
MutexLock mu(self, *Locks::thread_list_lock_);
Locks::runtime_shutdown_lock_->Unlock(self);
// Also wait for any threads that are unregistering to finish. This is required so that no
// threads access the thread list after it is deleted. TODO: This may not work for user daemon
// threads since they could unregister at the wrong time.
bool done = unregistering_count_ == 0;
if (done) {
for (const auto& thread : list_) {
if (thread != self && !thread->IsDaemon()) {
done = false;
break;
}
}
}
if (done) {
break;
}
// Wait for another thread to exit before re-checking.
Locks::thread_exit_cond_->Wait(self);
}
}
void ThreadList::SuspendAllDaemonThreadsForShutdown() {
ScopedTrace trace(__PRETTY_FUNCTION__);
Thread* self = Thread::Current();
size_t daemons_left = 0;
{
// Tell all the daemons it's time to suspend.
MutexLock mu(self, *Locks::thread_list_lock_);
MutexLock mu2(self, *Locks::thread_suspend_count_lock_);
for (const auto& thread : list_) {
// This is only run after all non-daemon threads have exited, so the remainder should all be
// daemons.
CHECK(thread->IsDaemon()) << *thread;
if (thread != self) {
bool updated = thread->ModifySuspendCount(self, +1, nullptr, SuspendReason::kInternal);
DCHECK(updated);
++daemons_left;
}
// We are shutting down the runtime, set the JNI functions of all the JNIEnvs to be
// the sleep forever one.
thread->GetJniEnv()->SetFunctionsToRuntimeShutdownFunctions();
}
}
if (daemons_left == 0) {
// No threads left; safe to shut down.
return;
}
// There is not a clean way to shut down if we have daemons left. We have no mechanism for
// killing them and reclaiming thread stacks. We also have no mechanism for waiting until they
// have truly finished touching the memory we are about to deallocate. We do the best we can with
// timeouts.
//
// If we have any daemons left, wait until they are (a) suspended and (b) they are not stuck
// in a place where they are about to access runtime state and are not in a runnable state.
// We attempt to do the latter by just waiting long enough for things to
// quiesce. Examples: Monitor code or waking up from a condition variable.
//
// Give the threads a chance to suspend, complaining if they're slow. (a)
bool have_complained = false;
static constexpr size_t kTimeoutMicroseconds = 2000 * 1000;
static constexpr size_t kSleepMicroseconds = 1000;
bool all_suspended = false;
for (size_t i = 0; !all_suspended && i < kTimeoutMicroseconds / kSleepMicroseconds; ++i) {
bool found_running = false;
{
MutexLock mu(self, *Locks::thread_list_lock_);
for (const auto& thread : list_) {
if (thread != self && thread->GetState() == ThreadState::kRunnable) {
if (!have_complained) {
LOG(WARNING) << "daemon thread not yet suspended: " << *thread;
have_complained = true;
}
found_running = true;
}
}
}
if (found_running) {
// Sleep briefly before checking again. Max total sleep time is kTimeoutMicroseconds.
usleep(kSleepMicroseconds);
} else {
all_suspended = true;
}
}
if (!all_suspended) {
// We can get here if a daemon thread executed a fastnative native call, so that it
// remained in runnable state, and then made a JNI call after we called
// SetFunctionsToRuntimeShutdownFunctions(), causing it to permanently stay in a harmless
// but runnable state. See b/147804269 .
LOG(WARNING) << "timed out suspending all daemon threads";
}
// Assume all threads are either suspended or somehow wedged.
// Wait again for all the now "suspended" threads to actually quiesce. (b)
static constexpr size_t kDaemonSleepTime = 400'000;
usleep(kDaemonSleepTime);
std::list<Thread*> list_copy;
{
MutexLock mu(self, *Locks::thread_list_lock_);
// Half-way through the wait, set the "runtime deleted" flag, causing any newly awoken
// threads to immediately go back to sleep without touching memory. This prevents us from
// touching deallocated memory, but it also prevents mutexes from getting released. Thus we
// only do this once we're reasonably sure that no system mutexes are still held.
for (const auto& thread : list_) {
DCHECK(thread == self || !all_suspended || thread->GetState() != ThreadState::kRunnable);
// In the !all_suspended case, the target is probably sleeping.
thread->GetJniEnv()->SetRuntimeDeleted();
// Possibly contended Mutex acquisitions are unsafe after this.
// Releasing thread_list_lock_ is OK, since it can't block.
}
}
// Finally wait for any threads woken before we set the "runtime deleted" flags to finish
// touching memory.
usleep(kDaemonSleepTime);
#if defined(__has_feature)
#if __has_feature(address_sanitizer) || __has_feature(hwaddress_sanitizer)
// Sleep a bit longer with -fsanitize=address, since everything is slower.
usleep(2 * kDaemonSleepTime);
#endif
#endif
// At this point no threads should be touching our data structures anymore.
}
void ThreadList::Register(Thread* self) {
DCHECK_EQ(self, Thread::Current());
CHECK(!shut_down_);
if (VLOG_IS_ON(threads)) {
std::ostringstream oss;
self->ShortDump(oss); // We don't hold the mutator_lock_ yet and so cannot call Dump.
LOG(INFO) << "ThreadList::Register() " << *self << "\n" << oss.str();
}
// Atomically add self to the thread list and make its thread_suspend_count_ reflect ongoing
// SuspendAll requests.
MutexLock mu(self, *Locks::thread_list_lock_);
MutexLock mu2(self, *Locks::thread_suspend_count_lock_);
// Modify suspend count in increments of 1 to maintain invariants in ModifySuspendCount. While
// this isn't particularly efficient the suspend counts are most commonly 0 or 1.
for (int delta = suspend_all_count_; delta > 0; delta--) {
bool updated = self->ModifySuspendCount(self, +1, nullptr, SuspendReason::kInternal);
DCHECK(updated);
}
CHECK(!Contains(self));
list_.push_back(self);
if (kUseReadBarrier) {
gc::collector::ConcurrentCopying* const cc =
Runtime::Current()->GetHeap()->ConcurrentCopyingCollector();
// Initialize according to the state of the CC collector.
self->SetIsGcMarkingAndUpdateEntrypoints(cc->IsMarking());
if (cc->IsUsingReadBarrierEntrypoints()) {
self->SetReadBarrierEntrypoints();
}
self->SetWeakRefAccessEnabled(cc->IsWeakRefAccessEnabled());
}
}
void ThreadList::Unregister(Thread* self) {
DCHECK_EQ(self, Thread::Current());
CHECK_NE(self->GetState(), ThreadState::kRunnable);
Locks::mutator_lock_->AssertNotHeld(self);
VLOG(threads) << "ThreadList::Unregister() " << *self;
{
MutexLock mu(self, *Locks::thread_list_lock_);
++unregistering_count_;
}
// Any time-consuming destruction, plus anything that can call back into managed code or
// suspend and so on, must happen at this point, and not in ~Thread. The self->Destroy is what
// causes the threads to join. It is important to do this after incrementing unregistering_count_
// since we want the runtime to wait for the daemon threads to exit before deleting the thread
// list.
self->Destroy();
// If tracing, remember thread id and name before thread exits.
Trace::StoreExitingThreadInfo(self);
uint32_t thin_lock_id = self->GetThreadId();
while (true) {
// Remove and delete the Thread* while holding the thread_list_lock_ and
// thread_suspend_count_lock_ so that the unregistering thread cannot be suspended.
// Note: deliberately not using MutexLock that could hold a stale self pointer.
{
MutexLock mu(self, *Locks::thread_list_lock_);
if (!Contains(self)) {
std::string thread_name;
self->GetThreadName(thread_name);
std::ostringstream os;
DumpNativeStack(os, GetTid(), nullptr, " native: ", nullptr);
LOG(ERROR) << "Request to unregister unattached thread " << thread_name << "\n" << os.str();
break;
} else {
MutexLock mu2(self, *Locks::thread_suspend_count_lock_);
if (!self->IsSuspended()) {
list_.remove(self);
break;
}
}
}
// In the case where we are not suspended yet, sleep to leave other threads time to execute.
// This is important if there are realtime threads. b/111277984
usleep(1);
// We failed to remove the thread due to a suspend request, loop and try again.
}
delete self;
// Release the thread ID after the thread is finished and deleted to avoid cases where we can
// temporarily have multiple threads with the same thread id. When this occurs, it causes
// problems in FindThreadByThreadId / SuspendThreadByThreadId.
ReleaseThreadId(nullptr, thin_lock_id);
// Clear the TLS data, so that the underlying native thread is recognizably detached.
// (It may wish to reattach later.)
#ifdef __BIONIC__
__get_tls()[TLS_SLOT_ART_THREAD_SELF] = nullptr;
#else
CHECK_PTHREAD_CALL(pthread_setspecific, (Thread::pthread_key_self_, nullptr), "detach self");
Thread::self_tls_ = nullptr;
#endif
// Signal that a thread just detached.
MutexLock mu(nullptr, *Locks::thread_list_lock_);
--unregistering_count_;
Locks::thread_exit_cond_->Broadcast(nullptr);
}
void ThreadList::ForEach(void (*callback)(Thread*, void*), void* context) {
for (const auto& thread : list_) {
callback(thread, context);
}
}
void ThreadList::VisitRootsForSuspendedThreads(RootVisitor* visitor) {
Thread* const self = Thread::Current();
std::vector<Thread*> threads_to_visit;
// Tell threads to suspend and copy them into list.
{
MutexLock mu(self, *Locks::thread_list_lock_);
MutexLock mu2(self, *Locks::thread_suspend_count_lock_);
for (Thread* thread : list_) {
bool suspended = thread->ModifySuspendCount(self, +1, nullptr, SuspendReason::kInternal);
DCHECK(suspended);
if (thread == self || thread->IsSuspended()) {
threads_to_visit.push_back(thread);
} else {
bool resumed = thread->ModifySuspendCount(self, -1, nullptr, SuspendReason::kInternal);
DCHECK(resumed);
}
}
}
// Visit roots without holding thread_list_lock_ and thread_suspend_count_lock_ to prevent lock
// order violations.
for (Thread* thread : threads_to_visit) {
thread->VisitRoots(visitor, kVisitRootFlagAllRoots);
}
// Restore suspend counts.
{
MutexLock mu2(self, *Locks::thread_suspend_count_lock_);
for (Thread* thread : threads_to_visit) {
bool updated = thread->ModifySuspendCount(self, -1, nullptr, SuspendReason::kInternal);
DCHECK(updated);
}
}
}
void ThreadList::VisitRoots(RootVisitor* visitor, VisitRootFlags flags) const {
MutexLock mu(Thread::Current(), *Locks::thread_list_lock_);
for (const auto& thread : list_) {
thread->VisitRoots(visitor, flags);
}
}
void ThreadList::VisitReflectiveTargets(ReflectiveValueVisitor *visitor) const {
MutexLock mu(Thread::Current(), *Locks::thread_list_lock_);
for (const auto& thread : list_) {
thread->VisitReflectiveTargets(visitor);
}
}
uint32_t ThreadList::AllocThreadId(Thread* self) {
MutexLock mu(self, *Locks::allocated_thread_ids_lock_);
for (size_t i = 0; i < allocated_ids_.size(); ++i) {
if (!allocated_ids_[i]) {
allocated_ids_.set(i);
return i + 1; // Zero is reserved to mean "invalid".
}
}
LOG(FATAL) << "Out of internal thread ids";
UNREACHABLE();
}
void ThreadList::ReleaseThreadId(Thread* self, uint32_t id) {
MutexLock mu(self, *Locks::allocated_thread_ids_lock_);
--id; // Zero is reserved to mean "invalid".
DCHECK(allocated_ids_[id]) << id;
allocated_ids_.reset(id);
}
ScopedSuspendAll::ScopedSuspendAll(const char* cause, bool long_suspend) {
Runtime::Current()->GetThreadList()->SuspendAll(cause, long_suspend);
}
ScopedSuspendAll::~ScopedSuspendAll() {
Runtime::Current()->GetThreadList()->ResumeAll();
}
} // namespace art