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android / platform / art / 4bedb38 / . / runtime / thread_list.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 "thread_list.h"
#define ATRACE_TAG ATRACE_TAG_DALVIK
#include <backtrace/BacktraceMap.h>
#include <cutils/trace.h>
#include <dirent.h>
#include <ScopedLocalRef.h>
#include <ScopedUtfChars.h>
#include <sys/types.h>
#include <unistd.h>
#include <sstream>
#include "base/histogram-inl.h"
#include "base/mutex-inl.h"
#include "base/time_utils.h"
#include "base/timing_logger.h"
#include "debugger.h"
#include "gc/collector/concurrent_copying.h"
#include "jni_internal.h"
#include "lock_word.h"
#include "monitor.h"
#include "scoped_thread_state_change.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 {
static constexpr uint64_t kLongThreadSuspendThreshold = MsToNs(5);
static constexpr uint64_t kThreadSuspendTimeoutMs = 30 * 1000; // 30s.
// 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;
ThreadList::ThreadList()
: suspend_all_count_(0),
debug_suspend_all_count_(0),
unregistering_count_(0),
suspend_all_historam_("suspend all histogram", 16, 64),
long_suspend_(false) {
CHECK(Monitor::IsValidLockWord(LockWord::FromThinLockId(kMaxThreadId, 1, 0U)));
}
ThreadList::~ThreadList() {
ATRACE_BEGIN(__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) {
ATRACE_BEGIN("DetachCurrentThread");
Runtime::Current()->DetachCurrentThread();
ATRACE_END();
}
ATRACE_BEGIN("WaitForOtherNonDaemonThreadsToExit");
WaitForOtherNonDaemonThreadsToExit();
ATRACE_END();
// 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.
ATRACE_BEGIN("WaitForGcToComplete");
heap->WaitForGcToComplete(gc::kGcCauseBackground, Thread::Current());
ATRACE_END();
// TODO: there's an unaddressed race here where a thread may attach during shutdown, see
// Thread::Init.
ATRACE_BEGIN("SuspendAllDaemonThreads");
SuspendAllDaemonThreads();
ATRACE_END();
ATRACE_END();
}
bool ThreadList::Contains(Thread* thread) {
return find(list_.begin(), list_.end(), thread) != list_.end();
}
bool ThreadList::Contains(pid_t tid) {
for (const auto& thread : list_) {
if (thread->GetTid() == tid) {
return true;
}
}
return false;
}
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.
}
}
Dump(os);
DumpUnattachedThreads(os);
}
static void DumpUnattachedThread(std::ostream& os, pid_t tid) 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);
DumpKernelStack(os, tid, " kernel: ", false);
// TODO: Reenable this when the native code in system_server can handle it.
// Currently "adb shell kill -3 `pid system_server`" will cause it to exit.
if (false) {
DumpNativeStack(os, tid, nullptr, " native: ");
}
os << "\n";
}
void ThreadList::DumpUnattachedThreads(std::ostream& os) {
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) {
bool contains;
{
MutexLock mu(self, *Locks::thread_list_lock_);
contains = Contains(tid);
}
if (!contains) {
DumpUnattachedThread(os, tid);
}
}
}
closedir(d);
}
// Dump checkpoint timeout in milliseconds. Larger amount on the host, as dumping will invoke
// addr2line when available.
static constexpr uint32_t kDumpWaitTimeout = kIsTargetBuild ? 10000 : 20000;
// A closure used by Thread::Dump.
class DumpCheckpoint FINAL : public Closure {
public:
explicit DumpCheckpoint(std::ostream* os)
: os_(os), barrier_(0), backtrace_map_(BacktraceMap::Create(GetTid())) {}
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();
std::ostringstream local_os;
{
ScopedObjectAccess soa(self);
thread->Dump(local_os, backtrace_map_.get());
}
local_os << "\n";
{
// Use the logging lock to ensure serialization when writing to the common ostream.
MutexLock mu(self, *Locks::logging_lock_);
*os_ << local_os.str();
}
barrier_.Pass(self);
}
void WaitForThreadsToRunThroughCheckpoint(size_t threads_running_checkpoint) {
Thread* self = Thread::Current();
ScopedThreadStateChange tsc(self, kWaitingForCheckPointsToRun);
bool timed_out = barrier_.Increment(self, threads_running_checkpoint, kDumpWaitTimeout);
if (timed_out) {
// Avoid a recursive abort.
LOG((kIsDebugBuild && (gAborting == 0)) ? FATAL : 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_;
};
void ThreadList::Dump(std::ostream& os) {
{
MutexLock mu(Thread::Current(), *Locks::thread_list_lock_);
os << "DALVIK THREADS (" << list_.size() << "):\n";
}
DumpCheckpoint checkpoint(&os);
size_t threads_running_checkpoint = RunCheckpoint(&checkpoint);
if (threads_running_checkpoint != 0) {
checkpoint.WaitForThreadsToRunThroughCheckpoint(threads_running_checkpoint);
}
}
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() {
Runtime* runtime = Runtime::Current();
std::ostringstream ss;
ss << "Thread suspend timeout\n";
Locks::mutator_lock_->Dump(ss);
ss << "\n";
runtime->GetThreadList()->Dump(ss);
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.
static void ThreadSuspendSleep(useconds_t delay_us) {
if (delay_us == 0) {
sched_yield();
} else {
usleep(delay_us);
}
}
size_t ThreadList::RunCheckpoint(Closure* checkpoint_function) {
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 suspend 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) {
while (true) {
if (thread->RequestCheckpoint(checkpoint_function)) {
// This thread will run its checkpoint some time in the near future.
break;
} else {
// We are probably suspended, try to make sure that we stay suspended.
// The thread switched back to runnable.
if (thread->GetState() == kRunnable) {
// Spurious fail, try again.
continue;
}
thread->ModifySuspendCount(self, +1, nullptr, false);
suspended_count_modified_threads.push_back(thread);
break;
}
}
}
}
}
// 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) {
if (!thread->IsSuspended()) {
if (ATRACE_ENABLED()) {
std::ostringstream oss;
thread->ShortDump(oss);
ATRACE_BEGIN((std::string("Waiting for suspension of thread ") + oss.str()).c_str());
}
// Busy wait until the thread is suspended.
const uint64_t start_time = NanoTime();
do {
ThreadSuspendSleep(kThreadSuspendInitialSleepUs);
} while (!thread->IsSuspended());
const uint64_t total_delay = NanoTime() - start_time;
// Shouldn't need to wait for longer than 1000 microseconds.
constexpr uint64_t kLongWaitThreshold = MsToNs(1);
ATRACE_END();
if (UNLIKELY(total_delay > kLongWaitThreshold)) {
LOG(WARNING) << "Long wait of " << PrettyDuration(total_delay) << " for "
<< *thread << " suspension!";
}
}
// We know for sure that the thread is suspended at this point.
checkpoint_function->Run(thread);
{
MutexLock mu2(self, *Locks::thread_suspend_count_lock_);
thread->ModifySuspendCount(self, -1, nullptr, false);
}
}
{
// 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;
}
// Request that a checkpoint function be run on all active (non-suspended)
// threads. Returns the number of successful requests.
size_t ThreadList::RunCheckpointOnRunnableThreads(Closure* checkpoint_function) {
Thread* self = Thread::Current();
Locks::mutator_lock_->AssertNotExclusiveHeld(self);
Locks::thread_list_lock_->AssertNotHeld(self);
Locks::thread_suspend_count_lock_->AssertNotHeld(self);
CHECK_NE(self->GetState(), kRunnable);
size_t count = 0;
{
// Call a checkpoint function for each non-suspended thread.
MutexLock mu(self, *Locks::thread_list_lock_);
MutexLock mu2(self, *Locks::thread_suspend_count_lock_);
for (const auto& thread : list_) {
if (thread != self) {
if (thread->RequestCheckpoint(checkpoint_function)) {
// This thread will run its checkpoint some time in the near future.
count++;
}
}
}
}
// Return the number of threads that will run the checkpoint function.
return count;
}
// 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) {
TimingLogger::ScopedTiming split("ThreadListFlip", collector->GetTimings());
const uint64_t start_time = NanoTime();
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(), kRunnable);
SuspendAllInternal(self, self, nullptr);
// Run the flip callback for the collector.
Locks::mutator_lock_->ExclusiveLock(self);
flip_callback->Run(self);
Locks::mutator_lock_->ExclusiveUnlock(self);
collector->RegisterPause(NanoTime() - start_time);
// Resume runnable threads.
std::vector<Thread*> runnable_threads;
std::vector<Thread*> other_threads;
{
MutexLock mu(self, *Locks::thread_list_lock_);
MutexLock mu2(self, *Locks::thread_suspend_count_lock_);
--suspend_all_count_;
for (const auto& thread : list_) {
if (thread == self) {
continue;
}
// Set the flip function for both runnable and suspended threads
// because Thread::DumpState/DumpJavaStack() (invoked by a
// checkpoint) may cause the flip function to be run for a
// runnable/suspended thread before a runnable threads runs it
// for itself or we run it for a suspended thread below.
thread->SetFlipFunction(thread_flip_visitor);
if (thread->IsSuspendedAtSuspendCheck()) {
// The thread will resume right after the broadcast.
thread->ModifySuspendCount(self, -1, nullptr, false);
runnable_threads.push_back(thread);
} else {
other_threads.push_back(thread);
}
}
Thread::resume_cond_->Broadcast(self);
}
// Run the closure on the other threads and let them resume.
{
ReaderMutexLock mu(self, *Locks::mutator_lock_);
for (const auto& thread : other_threads) {
Closure* flip_func = thread->GetFlipFunction();
if (flip_func != nullptr) {
flip_func->Run(thread);
}
}
// Run it for self.
thread_flip_visitor->Run(self);
}
// Resume other threads.
{
MutexLock mu2(self, *Locks::thread_suspend_count_lock_);
for (const auto& thread : other_threads) {
thread->ModifySuspendCount(self, -1, nullptr, false);
}
Thread::resume_cond_->Broadcast(self);
}
return runnable_threads.size() + 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...";
}
ATRACE_BEGIN("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, kThreadSuspendTimeoutMs, 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 kThreadSuspendTimeoutMs seconds.
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);
}
ATRACE_END();
ATRACE_BEGIN((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.
// Debugger thread might be set to kRunnable for a short period of time after the
// SuspendAllInternal. This is safe because it will be set back to suspended state before
// the SuspendAll returns.
void ThreadList::SuspendAllInternal(Thread* self,
Thread* ignore1,
Thread* ignore2,
bool debug_suspend) {
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(), 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_;
if (debug_suspend)
++debug_suspend_all_count_;
pending_threads.StoreRelaxed(list_.size() - num_ignored);
// 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;
while (true) {
if (LIKELY(thread->ModifySuspendCount(self, +1, &pending_threads, debug_suspend))) {
break;
} else {
// Failure means the list of active_suspend_barriers is full, we should release the
// thread_suspend_count_lock_ (to avoid deadlock) and wait till the target thread has
// executed Thread::PassActiveSuspendBarriers(). Note that we could not simply wait for
// the thread to change to a suspended state, because it might need to run checkpoint
// function before the state change, which also needs thread_suspend_count_lock_.
// This is very unlikely to happen since more than kMaxSuspendBarriers threads need to
// execute SuspendAllInternal() simultaneously, and target thread stays in kRunnable
// in the mean time.
Locks::thread_suspend_count_lock_->ExclusiveUnlock(self);
NanoSleep(100000);
Locks::thread_suspend_count_lock_->ExclusiveLock(self);
}
}
// 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.FetchAndSubSequentiallyConsistent(1);
}
}
}
// 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(true, CLOCK_MONOTONIC, 10000, 0, &wait_timeout);
#endif
while (true) {
int32_t cur_val = pending_threads.LoadRelaxed();
if (LIKELY(cur_val > 0)) {
#if ART_USE_FUTEXES
if (futex(pending_threads.Address(), FUTEX_WAIT, cur_val, &wait_timeout, nullptr, 0) != 0) {
// EAGAIN and EINTR both indicate a spurious failure, try again from the beginning.
if ((errno != EAGAIN) && (errno != EINTR)) {
if (errno == ETIMEDOUT) {
LOG(kIsDebugBuild ? FATAL : ERROR) << "Unexpected time out during suspend all.";
} else {
PLOG(FATAL) << "futex wait failed for SuspendAllInternal()";
}
}
} else {
cur_val = pending_threads.LoadRelaxed();
CHECK_EQ(cur_val, 0);
break;
}
#else
// Spin wait. This is likely to be slow, but on most architecture ART_USE_FUTEXES is set.
#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";
}
ATRACE_END();
ATRACE_BEGIN("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;
}
thread->ModifySuspendCount(self, -1, nullptr, false);
}
// 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);
}
ATRACE_END();
if (self != nullptr) {
VLOG(threads) << *self << " ResumeAll complete";
} else {
VLOG(threads) << "Thread[null] ResumeAll complete";
}
}
void ThreadList::Resume(Thread* thread, bool for_debugger) {
// This assumes there was an ATRACE_BEGIN when we suspended the thread.
ATRACE_END();
Thread* self = Thread::Current();
DCHECK_NE(thread, self);
VLOG(threads) << "Resume(" << reinterpret_cast<void*>(thread) << ") starting..."
<< (for_debugger ? " (debugger)" : "");
{
// To check Contains.
MutexLock mu(self, *Locks::thread_list_lock_);
// To check IsSuspended.
MutexLock mu2(self, *Locks::thread_suspend_count_lock_);
DCHECK(thread->IsSuspended());
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;
}
thread->ModifySuspendCount(self, -1, nullptr, for_debugger);
}
{
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";
}
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,
bool request_suspension,
bool debug_suspension,
bool* timed_out) {
const uint64_t start_time = NanoTime();
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.
suspended_thread->ModifySuspendCount(soa.Self(), -1, nullptr, debug_suspension);
}
ThreadSuspendByPeerWarning(self, 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.
continue;
}
CHECK(suspended_thread == nullptr);
suspended_thread = thread;
suspended_thread->ModifySuspendCount(self, +1, nullptr, debug_suspension);
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 (ATRACE_ENABLED()) {
std::string name;
thread->GetThreadName(name);
ATRACE_BEGIN(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 >= MsToNs(kThreadSuspendTimeoutMs)) {
ThreadSuspendByPeerWarning(self, FATAL, "Thread suspension timed out", peer);
if (suspended_thread != nullptr) {
CHECK_EQ(suspended_thread, thread);
suspended_thread->ModifySuspendCount(soa.Self(), -1, nullptr, debug_suspension);
}
*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) << "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,
bool debug_suspension,
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(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;
}
thread->ModifySuspendCount(self, +1, nullptr, debug_suspension);
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 (ATRACE_ENABLED()) {
std::string name;
thread->GetThreadName(name);
ATRACE_BEGIN(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 >= MsToNs(kThreadSuspendTimeoutMs)) {
ThreadSuspendByThreadIdWarning(WARNING, "Thread suspension timed out", thread_id);
if (suspended_thread != nullptr) {
thread->ModifySuspendCount(soa.Self(), -1, nullptr, debug_suspension);
}
*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 thin_lock_id) {
Thread* self = Thread::Current();
MutexLock mu(self, *Locks::thread_list_lock_);
for (const auto& thread : list_) {
if (thread->GetThreadId() == thin_lock_id) {
CHECK(thread == self || thread->IsSuspended());
return thread;
}
}
return nullptr;
}
void ThreadList::SuspendAllForDebugger() {
Thread* self = Thread::Current();
Thread* debug_thread = Dbg::GetDebugThread();
VLOG(threads) << *self << " SuspendAllForDebugger starting...";
SuspendAllInternal(self, self, debug_thread, true);
// Block on the mutator lock until all Runnable threads release their share of access then
// immediately unlock again.
#if HAVE_TIMED_RWLOCK
// Timeout if we wait more than 30 seconds.
if (!Locks::mutator_lock_->ExclusiveLockWithTimeout(self, 30 * 1000, 0)) {
UnsafeLogFatalForThreadSuspendAllTimeout();
} else {
Locks::mutator_lock_->ExclusiveUnlock(self);
}
#else
Locks::mutator_lock_->ExclusiveLock(self);
Locks::mutator_lock_->ExclusiveUnlock(self);
#endif
// Disabled for the following race condition:
// Thread 1 calls SuspendAllForDebugger, gets preempted after pulsing the mutator lock.
// Thread 2 calls SuspendAll and SetStateUnsafe (perhaps from Dbg::Disconnected).
// Thread 1 fails assertion that all threads are suspended due to thread 2 being in a runnable
// state (from SetStateUnsafe).
// AssertThreadsAreSuspended(self, self, debug_thread);
VLOG(threads) << *self << " SuspendAllForDebugger complete";
}
void ThreadList::SuspendSelfForDebugger() {
Thread* const self = Thread::Current();
self->SetReadyForDebugInvoke(true);
// The debugger thread must not suspend itself due to debugger activity!
Thread* debug_thread = Dbg::GetDebugThread();
CHECK(self != debug_thread);
CHECK_NE(self->GetState(), kRunnable);
Locks::mutator_lock_->AssertNotHeld(self);
// The debugger may have detached while we were executing an invoke request. In that case, we
// must not suspend ourself.
DebugInvokeReq* pReq = self->GetInvokeReq();
const bool skip_thread_suspension = (pReq != nullptr && !Dbg::IsDebuggerActive());
if (!skip_thread_suspension) {
// Collisions with other suspends aren't really interesting. We want
// to ensure that we're the only one fiddling with the suspend count
// though.
MutexLock mu(self, *Locks::thread_suspend_count_lock_);
self->ModifySuspendCount(self, +1, nullptr, true);
CHECK_GT(self->GetSuspendCount(), 0);
VLOG(threads) << *self << " self-suspending (debugger)";
} else {
// We must no longer be subject to debugger suspension.
MutexLock mu(self, *Locks::thread_suspend_count_lock_);
CHECK_EQ(self->GetDebugSuspendCount(), 0) << "Debugger detached without resuming us";
VLOG(threads) << *self << " not self-suspending because debugger detached during invoke";
}
// If the debugger requested an invoke, we need to send the reply and clear the request.
if (pReq != nullptr) {
Dbg::FinishInvokeMethod(pReq);
self->ClearDebugInvokeReq();
pReq = nullptr; // object has been deleted, clear it for safety.
}
// Tell JDWP that we've completed suspension. The JDWP thread can't
// tell us to resume before we're fully asleep because we hold the
// suspend count lock.
Dbg::ClearWaitForEventThread();
{
MutexLock mu(self, *Locks::thread_suspend_count_lock_);
while (self->GetSuspendCount() != 0) {
Thread::resume_cond_->Wait(self);
if (self->GetSuspendCount() != 0) {
// The condition was signaled but we're still suspended. This
// can happen when we suspend then resume all threads to
// update instrumentation or compute monitor info. This can
// also happen if the debugger lets go while a SIGQUIT thread
// dump event is pending (assuming SignalCatcher was resumed for
// just long enough to try to grab the thread-suspend lock).
VLOG(jdwp) << *self << " still suspended after undo "
<< "(suspend count=" << self->GetSuspendCount() << ", "
<< "debug suspend count=" << self->GetDebugSuspendCount() << ")";
}
}
CHECK_EQ(self->GetSuspendCount(), 0);
}
self->SetReadyForDebugInvoke(false);
VLOG(threads) << *self << " self-reviving (debugger)";
}
void ThreadList::ResumeAllForDebugger() {
Thread* self = Thread::Current();
Thread* debug_thread = Dbg::GetDebugThread();
VLOG(threads) << *self << " ResumeAllForDebugger starting...";
// Threads can't resume if we exclusively hold the mutator lock.
Locks::mutator_lock_->AssertNotExclusiveHeld(self);
{
MutexLock thread_list_mu(self, *Locks::thread_list_lock_);
{
MutexLock suspend_count_mu(self, *Locks::thread_suspend_count_lock_);
// Update global suspend all state for attaching threads.
DCHECK_GE(suspend_all_count_, debug_suspend_all_count_);
if (debug_suspend_all_count_ > 0) {
--suspend_all_count_;
--debug_suspend_all_count_;
} else {
// We've been asked to resume all threads without being asked to
// suspend them all before. That may happen if a debugger tries
// to resume some suspended threads (with suspend count == 1)
// at once with a VirtualMachine.Resume command. Let's print a
// warning.
LOG(WARNING) << "Debugger attempted to resume all threads without "
<< "having suspended them all before.";
}
// Decrement everybody's suspend count (except our own).
for (const auto& thread : list_) {
if (thread == self || thread == debug_thread) {
continue;
}
if (thread->GetDebugSuspendCount() == 0) {
// This thread may have been individually resumed with ThreadReference.Resume.
continue;
}
VLOG(threads) << "requesting thread resume: " << *thread;
thread->ModifySuspendCount(self, -1, nullptr, true);
}
}
}
{
MutexLock mu(self, *Locks::thread_suspend_count_lock_);
Thread::resume_cond_->Broadcast(self);
}
VLOG(threads) << *self << " ResumeAllForDebugger complete";
}
void ThreadList::UndoDebuggerSuspensions() {
Thread* self = Thread::Current();
VLOG(threads) << *self << " UndoDebuggerSuspensions starting";
{
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_ -= debug_suspend_all_count_;
debug_suspend_all_count_ = 0;
// Update running threads.
for (const auto& thread : list_) {
if (thread == self || thread->GetDebugSuspendCount() == 0) {
continue;
}
thread->ModifySuspendCount(self, -thread->GetDebugSuspendCount(), nullptr, true);
}
}
{
MutexLock mu(self, *Locks::thread_suspend_count_lock_);
Thread::resume_cond_->Broadcast(self);
}
VLOG(threads) << "UndoDebuggerSuspensions(" << *self << ") complete";
}
void ThreadList::WaitForOtherNonDaemonThreadsToExit() {
Thread* self = Thread::Current();
Locks::mutator_lock_->AssertNotHeld(self);
while (true) {
{
// No more threads can be born after we start to shutdown.
MutexLock mu(self, *Locks::runtime_shutdown_lock_);
CHECK(Runtime::Current()->IsShuttingDownLocked());
CHECK_EQ(Runtime::Current()->NumberOfThreadsBeingBorn(), 0U);
}
MutexLock mu(self, *Locks::thread_list_lock_);
// 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::SuspendAllDaemonThreads() {
Thread* self = Thread::Current();
MutexLock mu(self, *Locks::thread_list_lock_);
{ // Tell all the daemons it's time to suspend.
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) {
thread->ModifySuspendCount(self, +1, nullptr, false);
}
}
}
// Give the threads a chance to suspend, complaining if they're slow.
bool have_complained = false;
for (int i = 0; i < 10; ++i) {
usleep(200 * 1000);
bool all_suspended = true;
for (const auto& thread : list_) {
if (thread != self && thread->GetState() == kRunnable) {
if (!have_complained) {
LOG(WARNING) << "daemon thread not yet suspended: " << *thread;
have_complained = true;
}
all_suspended = false;
}
}
if (all_suspended) {
return;
}
}
LOG(ERROR) << "suspend all daemons failed";
}
void ThreadList::Register(Thread* self) {
DCHECK_EQ(self, Thread::Current());
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_);
CHECK_GE(suspend_all_count_, debug_suspend_all_count_);
// 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 = debug_suspend_all_count_; delta > 0; delta--) {
self->ModifySuspendCount(self, +1, nullptr, true);
}
for (int delta = suspend_all_count_ - debug_suspend_all_count_; delta > 0; delta--) {
self->ModifySuspendCount(self, +1, nullptr, false);
}
CHECK(!Contains(self));
list_.push_back(self);
if (kUseReadBarrier) {
// Initialize according to the state of the CC collector.
bool is_gc_marking =
Runtime::Current()->GetHeap()->ConcurrentCopyingCollector()->IsMarking();
self->SetIsGcMarking(is_gc_marking);
bool weak_ref_access_enabled =
Runtime::Current()->GetHeap()->ConcurrentCopyingCollector()->IsWeakRefAccessEnabled();
self->SetWeakRefAccessEnabled(weak_ref_access_enabled);
}
}
void ThreadList::Unregister(Thread* self) {
DCHECK_EQ(self, Thread::Current());
CHECK_NE(self->GetState(), 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;
}
}
// 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 __ANDROID__
__get_tls()[TLS_SLOT_ART_THREAD_SELF] = nullptr;
#else
CHECK_PTHREAD_CALL(pthread_setspecific, (Thread::pthread_key_self_, nullptr), "detach self");
#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::VisitRoots(RootVisitor* visitor) const {
MutexLock mu(Thread::Current(), *Locks::thread_list_lock_);
for (const auto& thread : list_) {
thread->VisitRoots(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";
return 0;
}
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