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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"
#include <unistd.h>
#include "debugger.h"
#include "scoped_heap_lock.h"
#include "scoped_thread_list_lock.h"
namespace art {
ThreadList::ThreadList()
: thread_list_lock_("thread list lock", kThreadListLock),
thread_start_cond_("thread_start_cond_"),
thread_exit_cond_("thread_exit_cond_"),
thread_suspend_count_lock_("thread suspend count lock", kThreadSuspendCountLock),
thread_suspend_count_cond_("thread_suspend_count_cond_") {
VLOG(threads) << "Default stack size: " << Runtime::Current()->GetDefaultStackSize() / KB << "KiB";
}
ThreadList::~ThreadList() {
// Detach the current thread if necessary.
if (Contains(Thread::Current())) {
Runtime::Current()->DetachCurrentThread();
}
WaitForNonDaemonThreadsToExit();
SuspendAllDaemonThreads();
}
bool ThreadList::Contains(Thread* thread) {
return find(list_.begin(), list_.end(), thread) != list_.end();
}
pid_t ThreadList::GetLockOwner() {
return thread_list_lock_.GetOwner();
}
void ThreadList::Dump(std::ostream& os) {
ScopedThreadListLock thread_list_lock;
DumpLocked(os);
}
void ThreadList::DumpLocked(std::ostream& os) {
os << "DALVIK THREADS (" << list_.size() << "):\n";
for (It it = list_.begin(), end = list_.end(); it != end; ++it) {
(*it)->Dump(os);
os << "\n";
}
}
void ThreadList::ModifySuspendCount(Thread* thread, int delta, bool for_debugger) {
#ifndef NDEBUG
DCHECK(delta == -1 || delta == +1 || delta == -thread->debug_suspend_count_)
<< delta << " " << thread->debug_suspend_count_ << " " << *thread;
DCHECK_GE(thread->suspend_count_, thread->debug_suspend_count_) << *thread;
#endif
if (delta == -1 && thread->suspend_count_ <= 0) {
// This can happen if you attach a thread during a GC.
LOG(WARNING) << *thread << " suspend count already zero";
return;
}
thread->suspend_count_ += delta;
if (for_debugger) {
thread->debug_suspend_count_ += delta;
}
}
void ThreadList::FullSuspendCheck(Thread* thread) {
CHECK(thread != NULL);
CHECK_GE(thread->suspend_count_, 0);
MutexLock mu(thread_suspend_count_lock_);
if (thread->suspend_count_ == 0) {
return;
}
VLOG(threads) << *thread << " self-suspending";
{
ScopedThreadStateChange tsc(thread, Thread::kSuspended);
while (thread->suspend_count_ != 0) {
/*
* Wait for wakeup signal, releasing lock. The act of releasing
* and re-acquiring the lock provides the memory barriers we
* need for correct behavior on SMP.
*/
thread_suspend_count_cond_.Wait(thread_suspend_count_lock_);
}
CHECK_EQ(thread->suspend_count_, 0);
}
VLOG(threads) << *thread << " self-reviving";
}
void ThreadList::SuspendAll(bool for_debugger) {
Thread* self = Thread::Current();
VLOG(threads) << *self << " SuspendAll starting..." << (for_debugger ? " (debugger)" : "");
CHECK_EQ(self->GetState(), Thread::kRunnable);
ScopedThreadListLock thread_list_lock;
Thread* debug_thread = Dbg::GetDebugThread();
{
// Increment everybody's suspend count (except our own).
MutexLock mu(thread_suspend_count_lock_);
for (It it = list_.begin(), end = list_.end(); it != end; ++it) {
Thread* thread = *it;
if (thread == self || (for_debugger && thread == debug_thread)) {
continue;
}
VLOG(threads) << "requesting thread suspend: " << *thread;
ModifySuspendCount(thread, +1, for_debugger);
}
}
/*
* Wait for everybody in kRunnable state to stop. Other states
* indicate the code is either running natively or sleeping quietly.
* Any attempt to transition back to kRunnable will cause a check
* for suspension, so it should be impossible for anything to execute
* interpreted code or modify objects (assuming native code plays nicely).
*
* It's also okay if the thread transitions to a non-kRunnable state.
*
* Note we released the thread_suspend_count_lock_ before getting here,
* so if another thread is fiddling with its suspend count (perhaps
* self-suspending for the debugger) it won't block while we're waiting
* in here.
*/
for (It it = list_.begin(), end = list_.end(); it != end; ++it) {
Thread* thread = *it;
if (thread == self || (for_debugger && thread == debug_thread)) {
continue;
}
thread->WaitUntilSuspended();
VLOG(threads) << "thread suspended: " << *thread;
}
VLOG(threads) << *self << " SuspendAll complete";
}
void ThreadList::Suspend(Thread* thread, bool for_debugger) {
DCHECK(thread != Thread::Current());
thread_list_lock_.AssertHeld();
// TODO: add another thread_suspend_lock_ to avoid GC/debugger races.
VLOG(threads) << "Suspend(" << *thread << ") starting..." << (for_debugger ? " (debugger)" : "");
if (!Contains(thread)) {
return;
}
{
MutexLock mu(thread_suspend_count_lock_);
ModifySuspendCount(thread, +1, for_debugger);
}
thread->WaitUntilSuspended();
VLOG(threads) << "Suspend(" << *thread << ") complete";
}
void ThreadList::SuspendSelfForDebugger() {
Thread* self = Thread::Current();
// The debugger thread must not suspend itself due to debugger activity!
Thread* debug_thread = Dbg::GetDebugThread();
CHECK(debug_thread != NULL);
CHECK(self != debug_thread);
// 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(thread_suspend_count_lock_);
ModifySuspendCount(self, +1, true);
// Suspend ourselves.
CHECK_GT(self->suspend_count_, 0);
self->SetState(Thread::kSuspended);
VLOG(threads) << *self << " self-suspending (debugger)";
// 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();
while (self->suspend_count_ != 0) {
thread_suspend_count_cond_.Wait(thread_suspend_count_lock_);
if (self->suspend_count_ != 0) {
// The condition was signaled but we're still suspended. This
// can 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).
LOG(DEBUG) << *self << " still suspended after undo "
<< "(suspend count=" << self->suspend_count_ << ")";
}
}
CHECK_EQ(self->suspend_count_, 0);
self->SetState(Thread::kRunnable);
VLOG(threads) << *self << " self-reviving (debugger)";
}
void ThreadList::ResumeAll(bool for_debugger) {
Thread* self = Thread::Current();
VLOG(threads) << *self << " ResumeAll starting" << (for_debugger ? " (debugger)" : "");
// Decrement the suspend counts for all threads. No need for atomic
// writes, since nobody should be moving until we decrement the count.
// We do need to hold the thread list because of JNI attaches.
{
ScopedThreadListLock thread_list_lock;
Thread* debug_thread = Dbg::GetDebugThread();
MutexLock mu(thread_suspend_count_lock_);
for (It it = list_.begin(), end = list_.end(); it != end; ++it) {
Thread* thread = *it;
if (thread == self || (for_debugger && thread == debug_thread)) {
continue;
}
ModifySuspendCount(thread, -1, for_debugger);
}
}
// Broadcast a notification to all suspended threads, some or all of
// which may choose to wake up. No need to wait for them.
{
VLOG(threads) << *self << " ResumeAll waking others";
MutexLock mu(thread_suspend_count_lock_);
thread_suspend_count_cond_.Broadcast();
}
VLOG(threads) << *self << " ResumeAll complete";
}
void ThreadList::Resume(Thread* thread, bool for_debugger) {
DCHECK(thread != Thread::Current());
if (!for_debugger) { // The debugger is very naughty. See Dbg::InvokeMethod.
thread_list_lock_.AssertHeld();
}
VLOG(threads) << "Resume(" << *thread << ") starting..." << (for_debugger ? " (debugger)" : "");
{
MutexLock mu(thread_suspend_count_lock_);
if (!Contains(thread)) {
return;
}
ModifySuspendCount(thread, -1, for_debugger);
}
{
VLOG(threads) << "Resume(" << *thread << ") waking others";
MutexLock mu(thread_suspend_count_lock_);
thread_suspend_count_cond_.Broadcast();
}
VLOG(threads) << "Resume(" << *thread << ") complete";
}
void ThreadList::RunWhileSuspended(Thread* thread, void (*callback)(void*), void* arg) { // NOLINT
DCHECK(thread != NULL);
Thread* self = Thread::Current();
if (thread != self) {
Suspend(thread);
}
callback(arg);
if (thread != self) {
Resume(thread);
}
}
void ThreadList::UndoDebuggerSuspensions() {
Thread* self = Thread::Current();
VLOG(threads) << *self << " UndoDebuggerSuspensions starting";
{
ScopedThreadListLock thread_list_lock;
MutexLock mu(thread_suspend_count_lock_);
for (It it = list_.begin(), end = list_.end(); it != end; ++it) {
Thread* thread = *it;
if (thread == self || thread->debug_suspend_count_ == 0) {
continue;
}
ModifySuspendCount(thread, -thread->debug_suspend_count_, true);
}
}
{
MutexLock mu(thread_suspend_count_lock_);
thread_suspend_count_cond_.Broadcast();
}
VLOG(threads) << "UndoDebuggerSuspensions(" << *self << ") complete";
}
void ThreadList::Register() {
Thread* self = Thread::Current();
VLOG(threads) << "ThreadList::Register() " << *self << "\n" << Dumpable<Thread>(*self);
ScopedThreadListLock thread_list_lock;
CHECK(!Contains(self));
list_.push_back(self);
}
void ThreadList::Unregister() {
Thread* self = Thread::Current();
VLOG(threads) << "ThreadList::Unregister() " << *self;
// 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.
self->Destroy();
{
// Remove this thread from the list.
ScopedThreadListLock thread_list_lock;
CHECK(Contains(self));
list_.remove(self);
// Delete the Thread* and release the thin lock id.
uint32_t thin_lock_id = self->thin_lock_id_;
delete self;
ReleaseThreadId(thin_lock_id);
}
// Clear the TLS data, so that the underlying native thread is recognizably detached.
// (It may wish to reattach later.)
CHECK_PTHREAD_CALL(pthread_setspecific, (Thread::pthread_key_self_, NULL), "detach self");
// Signal that a thread just detached.
thread_exit_cond_.Signal();
}
void ThreadList::ForEach(void (*callback)(Thread*, void*), void* context) {
thread_list_lock_.AssertHeld();
for (It it = list_.begin(), end = list_.end(); it != end; ++it) {
callback(*it, context);
}
}
void ThreadList::VisitRoots(Heap::RootVisitor* visitor, void* arg) const {
ScopedThreadListLock thread_list_lock;
for (It it = list_.begin(), end = list_.end(); it != end; ++it) {
(*it)->VisitRoots(visitor, arg);
}
}
/*
* Tell a new thread it's safe to start.
*
* We must hold the thread list lock before messing with another thread.
* In the general case we would also need to verify that the new thread was
* still in the thread list, but in our case the thread has not started
* executing user code and therefore has not had a chance to exit.
*
* We move it to kVmWait, and it then shifts itself to kRunning, which
* comes with a suspend-pending check. We do this after
*/
void ThreadList::SignalGo(Thread* child) {
Thread* self = Thread::Current();
CHECK(child != self);
{
ScopedThreadListLock thread_list_lock;
VLOG(threads) << *self << " waiting for child " << *child << " to be in thread list...";
// We wait for the child to tell us that it's in the thread list.
while (child->GetState() != Thread::kStarting) {
thread_start_cond_.Wait(thread_list_lock_);
}
}
// If we switch out of runnable and then back in, we know there's no pending suspend.
self->SetState(Thread::kVmWait);
self->SetState(Thread::kRunnable);
// Tell the child that it's safe: it will see any future suspend request.
ScopedThreadListLock thread_list_lock;
VLOG(threads) << *self << " telling child " << *child << " it's safe to proceed...";
child->SetState(Thread::kVmWait);
thread_start_cond_.Broadcast();
}
void ThreadList::WaitForGo() {
Thread* self = Thread::Current();
DCHECK(Contains(self));
{
ScopedThreadListLock thread_list_lock;
// Tell our parent that we're in the thread list.
VLOG(threads) << *self << " telling parent that we're now in thread list...";
self->SetState(Thread::kStarting);
thread_start_cond_.Broadcast();
// Wait until our parent tells us there's no suspend still pending
// from before we were on the thread list.
VLOG(threads) << *self << " waiting for parent's go-ahead...";
while (self->GetState() != Thread::kVmWait) {
thread_start_cond_.Wait(thread_list_lock_);
}
}
// Enter the runnable state. We know that any pending suspend will affect us now.
VLOG(threads) << *self << " entering runnable state...";
// Lock and unlock the heap lock. This ensures that if there was a GC in progress when we
// started, we wait until it's over. Which means that if there's now another GC pending, our
// suspend count is non-zero, so switching to the runnable state will suspend us.
// TODO: find a better solution!
{
ScopedHeapLock heap_lock;
}
self->SetState(Thread::kRunnable);
}
bool ThreadList::AllThreadsAreDaemons() {
for (It it = list_.begin(), end = list_.end(); it != end; ++it) {
// TODO: there's a race here with thread exit that's being worked around by checking if the peer
// is null.
if ((*it)->GetPeer() != NULL && !(*it)->IsDaemon()) {
return false;
}
}
return true;
}
void ThreadList::WaitForNonDaemonThreadsToExit() {
ScopedThreadListLock thread_list_lock;
while (!AllThreadsAreDaemons()) {
thread_exit_cond_.Wait(thread_list_lock_);
}
}
void ThreadList::SuspendAllDaemonThreads() {
ScopedThreadListLock thread_list_lock;
// Tell all the daemons it's time to suspend. (At this point, we know
// all threads are daemons.)
{
MutexLock mu(thread_suspend_count_lock_);
for (It it = list_.begin(), end = list_.end(); it != end; ++it) {
Thread* thread = *it;
++thread->suspend_count_;
}
}
// 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 (It it = list_.begin(), end = list_.end(); it != end; ++it) {
Thread* thread = *it;
if (thread->GetState() == Thread::kRunnable) {
if (!have_complained) {
LOG(WARNING) << "daemon thread not yet suspended: " << *thread;
have_complained = true;
}
all_suspended = false;
}
}
if (all_suspended) {
return;
}
}
}
uint32_t ThreadList::AllocThreadId() {
ScopedThreadListLock thread_list_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(uint32_t id) {
thread_list_lock_.AssertHeld();
--id; // Zero is reserved to mean "invalid".
DCHECK(allocated_ids_[id]) << id;
allocated_ids_.reset(id);
}
} // namespace art