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// Copyright 2016 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "base/task/thread_pool/thread_pool_impl.h"
#include <algorithm>
#include <optional>
#include <string>
#include <string_view>
#include <utility>
#include "base/base_switches.h"
#include "base/command_line.h"
#include "base/compiler_specific.h"
#include "base/debug/leak_annotations.h"
#include "base/feature_list.h"
#include "base/functional/bind.h"
#include "base/functional/callback_helpers.h"
#include "base/message_loop/message_pump.h"
#include "base/message_loop/message_pump_type.h"
#include "base/metrics/field_trial_params.h"
#include "base/strings/string_util.h"
#include "base/system/sys_info.h"
#include "base/task/scoped_set_task_priority_for_current_thread.h"
#include "base/task/task_traits.h"
#include "base/task/thread_pool/pooled_parallel_task_runner.h"
#include "base/task/thread_pool/pooled_sequenced_task_runner.h"
#include "base/task/thread_pool/task.h"
#include "base/task/thread_pool/task_source.h"
#include "base/task/thread_pool/task_source_sort_key.h"
#include "base/task/thread_pool/thread_group_impl.h"
#include "base/task/thread_pool/worker_thread.h"
#include "base/thread_annotations.h"
#include "base/threading/platform_thread.h"
#include "base/time/time.h"
#include "build/build_config.h"
namespace base::internal {
namespace {
constexpr EnvironmentParams kForegroundPoolEnvironmentParams{
"Foreground", base::ThreadType::kDefault};
constexpr EnvironmentParams kUtilityPoolEnvironmentParams{
"Utility", base::ThreadType::kUtility};
constexpr EnvironmentParams kBackgroundPoolEnvironmentParams{
"Background", base::ThreadType::kBackground};
// Used for ThreadGroupProfiler to tag profiles collected for different thread
// groups.
enum ThreadGroupType { FOREGROUND = 0, UTILITY, BACKGROUND };
constexpr size_t kMaxBestEffortTasks = 2;
// Indicates whether BEST_EFFORT tasks are disabled by a command line switch.
bool HasDisableBestEffortTasksSwitch() {
// The CommandLine might not be initialized if ThreadPool is initialized in a
// dynamic library which doesn't have access to argc/argv.
return CommandLine::InitializedForCurrentProcess() &&
CommandLine::ForCurrentProcess()->HasSwitch(
switches::kDisableBestEffortTasks);
}
// A global variable that can be set from test fixtures while no
// ThreadPoolInstance is active. Global instead of being a member variable to
// avoid having to add a public API to ThreadPoolInstance::InitParams for this
// internal edge case.
bool g_synchronous_thread_start_for_testing = false;
} // namespace
ThreadPoolImpl::ThreadPoolImpl(std::string_view histogram_label)
: ThreadPoolImpl(histogram_label, std::make_unique<TaskTrackerImpl>()) {}
ThreadPoolImpl::ThreadPoolImpl(std::string_view histogram_label,
std::unique_ptr<TaskTrackerImpl> task_tracker,
bool use_background_threads)
: histogram_label_(histogram_label),
task_tracker_(std::move(task_tracker)),
single_thread_task_runner_manager_(task_tracker_->GetTrackedRef(),
&delayed_task_manager_),
has_disable_best_effort_switch_(HasDisableBestEffortTasksSwitch()),
tracked_ref_factory_(this) {
foreground_thread_group_ = std::make_unique<ThreadGroupImpl>(
histogram_label.empty()
? std::string()
: JoinString(
{histogram_label, kForegroundPoolEnvironmentParams.name_suffix},
"."),
kForegroundPoolEnvironmentParams.name_suffix,
kForegroundPoolEnvironmentParams.thread_type_hint,
ThreadGroupType::FOREGROUND, task_tracker_->GetTrackedRef(),
tracked_ref_factory_.GetTrackedRef());
if (CanUseBackgroundThreadTypeForWorkerThread()) {
background_thread_group_ = std::make_unique<ThreadGroupImpl>(
histogram_label.empty()
? std::string()
: JoinString({histogram_label,
kBackgroundPoolEnvironmentParams.name_suffix},
"."),
kBackgroundPoolEnvironmentParams.name_suffix,
use_background_threads
? kBackgroundPoolEnvironmentParams.thread_type_hint
: kForegroundPoolEnvironmentParams.thread_type_hint,
ThreadGroupType::BACKGROUND, task_tracker_->GetTrackedRef(),
tracked_ref_factory_.GetTrackedRef());
}
}
ThreadPoolImpl::~ThreadPoolImpl() {
#if DCHECK_IS_ON()
DCHECK(join_for_testing_returned_.IsSet());
#endif
// Reset thread groups to release held TrackedRefs, which block teardown.
foreground_thread_group_.reset();
utility_thread_group_.reset();
background_thread_group_.reset();
}
void ThreadPoolImpl::Start(const ThreadPoolInstance::InitParams& init_params,
WorkerThreadObserver* worker_thread_observer) {
DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
DCHECK(!started_);
// The max number of concurrent BEST_EFFORT tasks is |kMaxBestEffortTasks|,
// unless the max number of foreground threads is lower.
size_t max_best_effort_tasks =
std::min(kMaxBestEffortTasks, init_params.max_num_foreground_threads);
// Start the service thread. On platforms that support it (POSIX except NaCL
// SFI), the service thread runs a MessageLoopForIO which is used to support
// FileDescriptorWatcher in the scope in which tasks run.
ServiceThread::Options service_thread_options;
service_thread_options.message_pump_type =
#if (BUILDFLAG(IS_POSIX) && !BUILDFLAG(IS_NACL)) || BUILDFLAG(IS_FUCHSIA)
MessagePumpType::IO;
#else
MessagePumpType::DEFAULT;
#endif
CHECK(service_thread_.StartWithOptions(std::move(service_thread_options)));
if (g_synchronous_thread_start_for_testing) {
service_thread_.WaitUntilThreadStarted();
}
if (FeatureList::IsEnabled(kUseUtilityThreadGroup) &&
CanUseUtilityThreadTypeForWorkerThread()) {
utility_thread_group_ = std::make_unique<ThreadGroupImpl>(
histogram_label_.empty()
? std::string()
: JoinString(
{histogram_label_, kUtilityPoolEnvironmentParams.name_suffix},
"."),
kUtilityPoolEnvironmentParams.name_suffix,
kUtilityPoolEnvironmentParams.thread_type_hint,
ThreadGroupType::UTILITY, task_tracker_->GetTrackedRef(),
tracked_ref_factory_.GetTrackedRef());
foreground_thread_group_
->HandoffNonUserBlockingTaskSourcesToOtherThreadGroup(
utility_thread_group_.get());
}
// Update the CanRunPolicy based on |has_disable_best_effort_switch_|.
UpdateCanRunPolicy();
// Needs to happen after starting the service thread to get its task_runner().
auto service_thread_task_runner = service_thread_.task_runner();
delayed_task_manager_.Start(service_thread_task_runner);
single_thread_task_runner_manager_.Start(service_thread_task_runner,
worker_thread_observer);
ThreadGroup::WorkerEnvironment worker_environment;
switch (init_params.common_thread_pool_environment) {
case InitParams::CommonThreadPoolEnvironment::DEFAULT:
worker_environment = ThreadGroup::WorkerEnvironment::NONE;
break;
#if BUILDFLAG(IS_WIN)
case InitParams::CommonThreadPoolEnvironment::COM_MTA:
worker_environment = ThreadGroup::WorkerEnvironment::COM_MTA;
break;
#endif
}
size_t foreground_threads = init_params.max_num_foreground_threads;
size_t utility_threads = init_params.max_num_utility_threads;
// On platforms that can't use the background thread priority, best-effort
// tasks run in foreground pools. A cap is set on the number of best-effort
// tasks that can run in foreground pools to ensure that there is always
// room for incoming foreground tasks and to minimize the performance impact
// of best-effort tasks.
foreground_thread_group_.get()->Start(
foreground_threads, max_best_effort_tasks,
init_params.suggested_reclaim_time, service_thread_task_runner,
worker_thread_observer, worker_environment,
g_synchronous_thread_start_for_testing,
/*may_block_threshold=*/{});
if (utility_thread_group_) {
utility_thread_group_.get()->Start(
utility_threads, max_best_effort_tasks,
init_params.suggested_reclaim_time, service_thread_task_runner,
worker_thread_observer, worker_environment,
g_synchronous_thread_start_for_testing,
/*may_block_threshold=*/{});
}
if (background_thread_group_) {
background_thread_group_.get()->Start(
max_best_effort_tasks, max_best_effort_tasks,
init_params.suggested_reclaim_time, service_thread_task_runner,
worker_thread_observer, worker_environment,
g_synchronous_thread_start_for_testing,
/*may_block_threshold=*/{});
}
started_ = true;
}
bool ThreadPoolImpl::WasStarted() const {
DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
return started_;
}
bool ThreadPoolImpl::WasStartedUnsafe() const {
return TS_UNCHECKED_READ(started_);
}
void ThreadPoolImpl::BeginRestrictedTasks() {
foreground_thread_group_->SetMaxTasks(2);
if (utility_thread_group_) {
utility_thread_group_->SetMaxTasks(1);
}
if (background_thread_group_) {
background_thread_group_->SetMaxTasks(1);
}
}
void ThreadPoolImpl::EndRestrictedTasks() {
foreground_thread_group_->ResetMaxTasks();
if (utility_thread_group_) {
utility_thread_group_->ResetMaxTasks();
}
if (background_thread_group_) {
background_thread_group_->ResetMaxTasks();
}
}
bool ThreadPoolImpl::PostDelayedTask(const Location& from_here,
const TaskTraits& traits,
OnceClosure task,
TimeDelta delay) {
// Post |task| as part of a one-off single-task Sequence.
return PostTaskWithSequence(
Task(from_here, std::move(task), TimeTicks::Now(), delay,
MessagePump::GetLeewayIgnoringThreadOverride()),
MakeRefCounted<Sequence>(traits, nullptr,
TaskSourceExecutionMode::kParallel));
}
scoped_refptr<TaskRunner> ThreadPoolImpl::CreateTaskRunner(
const TaskTraits& traits) {
return MakeRefCounted<PooledParallelTaskRunner>(traits, this);
}
scoped_refptr<SequencedTaskRunner> ThreadPoolImpl::CreateSequencedTaskRunner(
const TaskTraits& traits) {
return MakeRefCounted<PooledSequencedTaskRunner>(traits, this);
}
scoped_refptr<SingleThreadTaskRunner>
ThreadPoolImpl::CreateSingleThreadTaskRunner(
const TaskTraits& traits,
SingleThreadTaskRunnerThreadMode thread_mode) {
return single_thread_task_runner_manager_.CreateSingleThreadTaskRunner(
traits, thread_mode);
}
#if BUILDFLAG(IS_WIN)
scoped_refptr<SingleThreadTaskRunner> ThreadPoolImpl::CreateCOMSTATaskRunner(
const TaskTraits& traits,
SingleThreadTaskRunnerThreadMode thread_mode) {
return single_thread_task_runner_manager_.CreateCOMSTATaskRunner(traits,
thread_mode);
}
#endif // BUILDFLAG(IS_WIN)
scoped_refptr<UpdateableSequencedTaskRunner>
ThreadPoolImpl::CreateUpdateableSequencedTaskRunner(const TaskTraits& traits) {
return MakeRefCounted<PooledSequencedTaskRunner>(traits, this);
}
scoped_refptr<SequencedTaskRunner>
ThreadPoolImpl::CreateSequencedTaskRunnerForResource(
const TaskTraits& traits,
const base::FilePath& path) {
AutoLock lock(sequences_for_resources_lock_);
auto iter = sequences_for_resources_.find(path);
if (iter != sequences_for_resources_.end()) {
// The sequence must use the same traits.
CHECK(iter->second->sequence()->traits() == traits);
return iter->second;
}
scoped_refptr<PooledSequencedTaskRunner> task_runner =
MakeRefCounted<PooledSequencedTaskRunner>(traits, this);
sequences_for_resources_[path] = task_runner;
return task_runner;
}
std::optional<TimeTicks> ThreadPoolImpl::NextScheduledRunTimeForTesting()
const {
if (task_tracker_->HasIncompleteTaskSourcesForTesting()) {
return TimeTicks::Now();
}
return delayed_task_manager_.NextScheduledRunTime();
}
void ThreadPoolImpl::ProcessRipeDelayedTasksForTesting() {
delayed_task_manager_.ProcessRipeTasks();
}
// static
void ThreadPoolImpl::SetSynchronousThreadStartForTesting(bool enabled) {
DCHECK(!ThreadPoolInstance::Get());
g_synchronous_thread_start_for_testing = enabled;
}
size_t ThreadPoolImpl::GetMaxConcurrentNonBlockedTasksWithTraitsDeprecated(
const TaskTraits& traits) const {
// This method does not support getting the maximum number of BEST_EFFORT
// tasks that can run concurrently in a pool.
DCHECK_NE(traits.priority(), TaskPriority::BEST_EFFORT);
return GetThreadGroupForTraits(traits)
->GetMaxConcurrentNonBlockedTasksDeprecated();
}
void ThreadPoolImpl::Shutdown() {
DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
// Cancels an internal service thread task. This must be done before stopping
// the service thread.
delayed_task_manager_.Shutdown();
// Stop() the ServiceThread before triggering shutdown. This ensures that no
// more delayed tasks or file descriptor watches will trigger during shutdown
// (preventing http://crbug.com/698140). None of these asynchronous tasks
// being guaranteed to happen anyways, stopping right away is valid behavior
// and avoids the more complex alternative of shutting down the service thread
// atomically during TaskTracker shutdown.
service_thread_.Stop();
task_tracker_->StartShutdown();
// Allow all tasks to run. Done after initiating shutdown to ensure that non-
// BLOCK_SHUTDOWN tasks don't get a chance to run and that BLOCK_SHUTDOWN
// tasks run with a normal thread priority.
UpdateCanRunPolicy();
// Ensures that there are enough background worker to run BLOCK_SHUTDOWN
// tasks.
// Shutdown must happen after service thread STOP as ThreadGroupProfiler
// destructor expects exclusive access to the instance during destruction.
foreground_thread_group_->OnShutdownStarted();
if (utility_thread_group_) {
utility_thread_group_->OnShutdownStarted();
}
if (background_thread_group_) {
background_thread_group_->OnShutdownStarted();
}
task_tracker_->CompleteShutdown();
}
void ThreadPoolImpl::FlushForTesting() {
task_tracker_->FlushForTesting();
}
void ThreadPoolImpl::FlushAsyncForTesting(OnceClosure flush_callback) {
task_tracker_->FlushAsyncForTesting(std::move(flush_callback));
}
void ThreadPoolImpl::JoinForTesting() {
#if DCHECK_IS_ON()
DCHECK(!join_for_testing_returned_.IsSet());
#endif
// Cancels an internal service thread task. This must be done before stopping
// the service thread.
delayed_task_manager_.Shutdown();
// The service thread must be stopped before the workers are joined, otherwise
// tasks scheduled by the DelayedTaskManager might be posted between joining
// those workers and stopping the service thread which will cause a CHECK. See
// https://crbug.com/771701.
service_thread_.Stop();
single_thread_task_runner_manager_.JoinForTesting();
foreground_thread_group_->JoinForTesting();
if (utility_thread_group_) {
utility_thread_group_->JoinForTesting(); // IN-TEST
}
if (background_thread_group_) {
background_thread_group_->JoinForTesting();
}
#if DCHECK_IS_ON()
join_for_testing_returned_.Set();
#endif
}
void ThreadPoolImpl::BeginFence() {
DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
++num_fences_;
UpdateCanRunPolicy();
}
void ThreadPoolImpl::EndFence() {
DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
DCHECK_GT(num_fences_, 0);
--num_fences_;
UpdateCanRunPolicy();
}
void ThreadPoolImpl::BeginBestEffortFence() {
DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
++num_best_effort_fences_;
UpdateCanRunPolicy();
}
void ThreadPoolImpl::EndBestEffortFence() {
DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
DCHECK_GT(num_best_effort_fences_, 0);
--num_best_effort_fences_;
UpdateCanRunPolicy();
}
void ThreadPoolImpl::BeginFizzlingBlockShutdownTasks() {
task_tracker_->BeginFizzlingBlockShutdownTasks();
}
void ThreadPoolImpl::EndFizzlingBlockShutdownTasks() {
task_tracker_->EndFizzlingBlockShutdownTasks();
}
bool ThreadPoolImpl::PostTaskWithSequenceNow(Task task,
scoped_refptr<Sequence> sequence) {
auto transaction = sequence->BeginTransaction();
const bool sequence_should_be_queued = transaction.WillPushImmediateTask();
RegisteredTaskSource task_source;
if (sequence_should_be_queued) {
task_source = task_tracker_->RegisterTaskSource(sequence);
// We shouldn't push |task| if we're not allowed to queue |task_source|.
if (!task_source) {
return false;
}
}
if (!task_tracker_->WillPostTaskNow(task, transaction.traits().priority())) {
return false;
}
transaction.PushImmediateTask(std::move(task));
if (task_source) {
const TaskTraits traits = transaction.traits();
GetThreadGroupForTraits(traits)->PushTaskSourceAndWakeUpWorkers(
{std::move(task_source), std::move(transaction)});
}
return true;
}
bool ThreadPoolImpl::PostTaskWithSequence(Task task,
scoped_refptr<Sequence> sequence) {
// Use CHECK instead of DCHECK to crash earlier. See http://crbug.com/711167
// for details.
CHECK(task.task);
DCHECK(sequence);
if (!task_tracker_->WillPostTask(&task, sequence->shutdown_behavior())) {
// `task`'s destructor may run sequence-affine code, so it must be leaked
// when `WillPostTask` returns false.
auto leak = std::make_unique<Task>(std::move(task));
ANNOTATE_LEAKING_OBJECT_PTR(leak.get());
leak.release();
return false;
}
if (task.delayed_run_time.is_null()) {
return PostTaskWithSequenceNow(std::move(task), std::move(sequence));
} else {
// It's safe to take a ref on this pointer since the caller must have a ref
// to the TaskRunner in order to post.
scoped_refptr<TaskRunner> task_runner = sequence->task_runner();
delayed_task_manager_.AddDelayedTask(
std::move(task),
BindOnce(
[](scoped_refptr<Sequence> sequence,
ThreadPoolImpl* thread_pool_impl, scoped_refptr<TaskRunner>,
Task task) {
thread_pool_impl->PostTaskWithSequenceNow(std::move(task),
std::move(sequence));
},
std::move(sequence), Unretained(this), std::move(task_runner)));
}
return true;
}
bool ThreadPoolImpl::ShouldYield(const TaskSource* task_source) {
const TaskPriority priority = task_source->priority_racy();
auto* const thread_group =
GetThreadGroupForTraits({priority, task_source->thread_policy()});
// A task whose priority changed and is now running in the wrong thread group
// should yield so it's rescheduled in the right one.
if (!thread_group->IsBoundToCurrentThread()) {
return true;
}
return GetThreadGroupForTraits({priority, task_source->thread_policy()})
->ShouldYield(task_source->GetSortKey());
}
bool ThreadPoolImpl::EnqueueJobTaskSource(
scoped_refptr<JobTaskSource> task_source) {
auto registered_task_source =
task_tracker_->RegisterTaskSource(std::move(task_source));
if (!registered_task_source) {
return false;
}
task_tracker_->WillEnqueueJob(
static_cast<JobTaskSource*>(registered_task_source.get()));
auto transaction = registered_task_source->BeginTransaction();
const TaskTraits traits = transaction.traits();
GetThreadGroupForTraits(traits)->PushTaskSourceAndWakeUpWorkers(
{std::move(registered_task_source), std::move(transaction)});
return true;
}
void ThreadPoolImpl::RemoveJobTaskSource(
scoped_refptr<JobTaskSource> task_source) {
auto transaction = task_source->BeginTransaction();
GetThreadGroupForTraits(transaction.traits())->RemoveTaskSource(*task_source);
}
void ThreadPoolImpl::UpdatePriority(scoped_refptr<TaskSource> task_source,
TaskPriority priority) {
auto transaction = task_source->BeginTransaction();
if (transaction.traits().priority() == priority) {
return;
}
if (transaction.traits().priority() == TaskPriority::BEST_EFFORT) {
DCHECK(transaction.traits().thread_policy_set_explicitly())
<< "A ThreadPolicy must be specified in the TaskTraits of an "
"UpdateableSequencedTaskRunner whose priority is increased from "
"BEST_EFFORT. See ThreadPolicy documentation.";
}
ThreadGroup* const old_thread_group =
GetThreadGroupForTraits(transaction.traits());
transaction.UpdatePriority(priority);
ThreadGroup* const new_thread_group =
GetThreadGroupForTraits(transaction.traits());
if (new_thread_group == old_thread_group) {
// |task_source|'s position needs to be updated within its current thread
// group.
old_thread_group->UpdateSortKey(std::move(transaction));
} else {
// |task_source| is changing thread groups; remove it from its current
// thread group and reenqueue it.
auto registered_task_source =
old_thread_group->RemoveTaskSource(*task_source);
if (registered_task_source) {
DCHECK(task_source);
new_thread_group->PushTaskSourceAndWakeUpWorkers(
{std::move(registered_task_source), std::move(transaction)});
}
}
}
void ThreadPoolImpl::UpdateJobPriority(scoped_refptr<TaskSource> task_source,
TaskPriority priority) {
UpdatePriority(std::move(task_source), priority);
}
const ThreadGroup* ThreadPoolImpl::GetThreadGroupForTraits(
const TaskTraits& traits) const {
return const_cast<ThreadPoolImpl*>(this)->GetThreadGroupForTraits(traits);
}
ThreadGroup* ThreadPoolImpl::GetThreadGroupForTraits(const TaskTraits& traits) {
if (traits.priority() == TaskPriority::BEST_EFFORT &&
traits.thread_policy() == ThreadPolicy::PREFER_BACKGROUND &&
background_thread_group_) {
return background_thread_group_.get();
}
if (traits.priority() <= TaskPriority::USER_VISIBLE &&
traits.thread_policy() == ThreadPolicy::PREFER_BACKGROUND &&
utility_thread_group_) {
return utility_thread_group_.get();
}
return foreground_thread_group_.get();
}
void ThreadPoolImpl::UpdateCanRunPolicy() {
DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
CanRunPolicy can_run_policy;
if ((num_fences_ == 0 && num_best_effort_fences_ == 0 &&
!has_disable_best_effort_switch_) ||
task_tracker_->HasShutdownStarted()) {
can_run_policy = CanRunPolicy::kAll;
} else if (num_fences_ != 0) {
can_run_policy = CanRunPolicy::kNone;
} else {
DCHECK(num_best_effort_fences_ > 0 || has_disable_best_effort_switch_);
can_run_policy = CanRunPolicy::kForegroundOnly;
}
task_tracker_->SetCanRunPolicy(can_run_policy);
foreground_thread_group_->DidUpdateCanRunPolicy();
if (utility_thread_group_) {
utility_thread_group_->DidUpdateCanRunPolicy();
}
if (background_thread_group_) {
background_thread_group_->DidUpdateCanRunPolicy();
}
single_thread_task_runner_manager_.DidUpdateCanRunPolicy();
}
} // namespace base::internal
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