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* Copyright 2004 The WebRTC Project Authors. All rights reserved.
* Use of this source code is governed by a BSD-style license
* that can be found in the LICENSE file in the root of the source
* tree. An additional intellectual property rights grant can be found
* in the file PATENTS. All contributing project authors may
* be found in the AUTHORS file in the root of the source tree.
#include <stdint.h>
#include <list>
#include <map>
#include <memory>
#include <queue>
#include <set>
#include <string>
#include <type_traits>
#include <utility>
#include <vector>
#include "absl/strings/string_view.h"
#if defined(WEBRTC_POSIX)
#include <pthread.h>
#include "absl/base/attributes.h"
#include "absl/functional/any_invocable.h"
#include "api/function_view.h"
#include "api/location.h"
#include "api/task_queue/task_queue_base.h"
#include "api/units/time_delta.h"
#include "rtc_base/checks.h"
#include "rtc_base/platform_thread_types.h"
#include "rtc_base/socket_server.h"
#include "rtc_base/synchronization/mutex.h"
#include "rtc_base/system/rtc_export.h"
#include "rtc_base/thread_annotations.h"
#if defined(WEBRTC_WIN)
#include "rtc_base/win32.h"
// Counts how many `Thread::BlockingCall` are made from within a scope and logs
// the number of blocking calls at the end of the scope.
rtc::Thread::ScopedCountBlockingCalls blocked_call_count_printer( \
[func = __func__](uint32_t actual_block, uint32_t could_block) { \
auto total = actual_block + could_block; \
if (total) { \
RTC_LOG(LS_WARNING) << "Blocking " << func << ": total=" << total \
<< " (actual=" << actual_block \
<< ", could=" << could_block << ")"; \
} \
// Adds an RTC_DCHECK_LE that checks that the number of blocking calls are
// less than or equal to a specific value. Use to avoid regressing in the
// number of blocking thread calls.
// Note: Use of this macro, requires RTC_LOG_THREAD_BLOCK_COUNT() to be called
// first.
do { \
blocked_call_count_printer.set_minimum_call_count_for_callback(x + 1); \
RTC_DCHECK_LE(blocked_call_count_printer.GetTotalBlockedCallCount(), x); \
} while (0)
namespace rtc {
class Thread;
class RTC_EXPORT ThreadManager {
static const int kForever = -1;
// Singleton, constructor and destructor are private.
static ThreadManager* Instance();
static void Add(Thread* message_queue);
static void Remove(Thread* message_queue);
// For testing purposes, for use with a simulated clock.
// Ensures that all message queues have processed delayed messages
// up until the current point in time.
static void ProcessAllMessageQueuesForTesting();
Thread* CurrentThread();
void SetCurrentThread(Thread* thread);
// Allows changing the current thread, this is intended for tests where we
// want to simulate multiple threads running on a single physical thread.
void ChangeCurrentThreadForTest(Thread* thread);
// Returns a thread object with its thread_ ivar set
// to whatever the OS uses to represent the thread.
// If there already *is* a Thread object corresponding to this thread,
// this method will return that. Otherwise it creates a new Thread
// object whose wrapped() method will return true, and whose
// handle will, on Win32, be opened with only synchronization privileges -
// if you need more privilegs, rather than changing this method, please
// write additional code to adjust the privileges, or call a different
// factory method of your own devising, because this one gets used in
// unexpected contexts (like inside browser plugins) and it would be a
// shame to break it. It is also conceivable on Win32 that we won't even
// be able to get synchronization privileges, in which case the result
// will have a null handle.
Thread* WrapCurrentThread();
void UnwrapCurrentThread();
// Registers that a Send operation is to be performed between `source` and
// `target`, while checking that this does not cause a send cycle that could
// potentially cause a deadlock.
void RegisterSendAndCheckForCycles(Thread* source, Thread* target);
ThreadManager(const ThreadManager&) = delete;
ThreadManager& operator=(const ThreadManager&) = delete;
void SetCurrentThreadInternal(Thread* thread);
void AddInternal(Thread* message_queue);
void RemoveInternal(Thread* message_queue);
void ProcessAllMessageQueuesInternal();
void RemoveFromSendGraph(Thread* thread) RTC_EXCLUSIVE_LOCKS_REQUIRED(crit_);
// This list contains all live Threads.
std::vector<Thread*> message_queues_ RTC_GUARDED_BY(crit_);
webrtc::Mutex crit_;
// Represents all thread seand actions by storing all send targets per thread.
// This is used by RegisterSendAndCheckForCycles. This graph has no cycles
// since we will trigger a CHECK failure if a cycle is introduced.
std::map<Thread*, std::set<Thread*>> send_graph_ RTC_GUARDED_BY(crit_);
#if defined(WEBRTC_POSIX)
pthread_key_t key_;
#if defined(WEBRTC_WIN)
const DWORD key_;
class RTC_LOCKABLE RTC_EXPORT Thread : public webrtc::TaskQueueBase {
static const int kForever = -1;
// Create a new Thread and optionally assign it to the passed
// SocketServer. Subclasses that override Clear should pass false for
// init_queue and call DoInit() from their constructor to prevent races
// with the ThreadManager using the object while the vtable is still
// being created.
explicit Thread(SocketServer* ss);
explicit Thread(std::unique_ptr<SocketServer> ss);
// Constructors meant for subclasses; they should call DoInit themselves and
// pass false for `do_init`, so that DoInit is called only on the fully
// instantiated class, which avoids a vptr data race.
Thread(SocketServer* ss, bool do_init);
Thread(std::unique_ptr<SocketServer> ss, bool do_init);
// guarantee Stop() is explicitly called before the subclass is destroyed).
// This is required to avoid a data race between the destructor modifying the
// vtable, and the Thread::PreRun calling the virtual method Run().
// DoDestroy() IN THEIR DESTRUCTORS! This is required to avoid a data race
// between the destructor modifying the vtable, and the ThreadManager
// calling Clear on the object from a different thread.
~Thread() override;
Thread(const Thread&) = delete;
Thread& operator=(const Thread&) = delete;
static std::unique_ptr<Thread> CreateWithSocketServer();
static std::unique_ptr<Thread> Create();
static Thread* Current();
// Used to catch performance regressions. Use this to disallow BlockingCall
// for a given scope. If a synchronous call is made while this is in
// effect, an assert will be triggered.
// Note that this is a single threaded class.
class ScopedDisallowBlockingCalls {
ScopedDisallowBlockingCalls(const ScopedDisallowBlockingCalls&) = delete;
ScopedDisallowBlockingCalls& operator=(const ScopedDisallowBlockingCalls&) =
Thread* const thread_;
const bool previous_state_;
class ScopedCountBlockingCalls {
ScopedCountBlockingCalls(std::function<void(uint32_t, uint32_t)> callback);
ScopedCountBlockingCalls(const ScopedDisallowBlockingCalls&) = delete;
ScopedCountBlockingCalls& operator=(const ScopedDisallowBlockingCalls&) =
uint32_t GetBlockingCallCount() const;
uint32_t GetCouldBeBlockingCallCount() const;
uint32_t GetTotalBlockedCallCount() const;
void set_minimum_call_count_for_callback(uint32_t minimum) {
min_blocking_calls_for_callback_ = minimum;
Thread* const thread_;
const uint32_t base_blocking_call_count_;
const uint32_t base_could_be_blocking_call_count_;
// The minimum number of blocking calls required in order to issue the
// result_callback_. This is used by RTC_DCHECK_BLOCK_COUNT_NO_MORE_THAN to
// tame log spam.
// By default we always issue the callback, regardless of callback count.
uint32_t min_blocking_calls_for_callback_ = 0;
std::function<void(uint32_t, uint32_t)> result_callback_;
uint32_t GetBlockingCallCount() const;
uint32_t GetCouldBeBlockingCallCount() const;
SocketServer* socketserver();
// Note: The behavior of Thread has changed. When a thread is stopped,
// futher Posts and Sends will fail. However, any pending Sends and *ready*
// Posts (as opposed to unexpired delayed Posts) will be delivered before
// Get (or Peek) returns false. By guaranteeing delivery of those messages,
// we eliminate the race condition when an MessageHandler and Thread
// may be destroyed independently of each other.
virtual void Quit();
virtual bool IsQuitting();
virtual void Restart();
// Not all message queues actually process messages (such as SignalThread).
// In those cases, it's important to know, before posting, that it won't be
// Processed. Normally, this would be true until IsQuitting() is true.
virtual bool IsProcessingMessagesForTesting();
// Amount of time until the next message can be retrieved
virtual int GetDelay();
bool empty() const { return size() == 0u; }
size_t size() const {
webrtc::MutexLock lock(&mutex_);
return messages_.size() + delayed_messages_.size();
bool IsCurrent() const;
// Sleeps the calling thread for the specified number of milliseconds, during
// which time no processing is performed. Returns false if sleeping was
// interrupted by a signal (POSIX only).
static bool SleepMs(int millis);
// Sets the thread's name, for debugging. Must be called before Start().
// If `obj` is non-null, its value is appended to `name`.
const std::string& name() const { return name_; }
bool SetName(absl::string_view name, const void* obj);
// Sets the expected processing time in ms. The thread will write
// log messages when Dispatch() takes more time than this.
// Default is 50 ms.
void SetDispatchWarningMs(int deadline);
// Starts the execution of the thread.
bool Start();
// Tells the thread to stop and waits until it is joined.
// Never call Stop on the current thread. Instead use the inherited Quit
// function which will exit the base Thread without terminating the
// underlying OS thread.
virtual void Stop();
// By default, Thread::Run() calls ProcessMessages(kForever). To do other
// work, override Run(). To receive and dispatch messages, call
// ProcessMessages occasionally.
virtual void Run();
// Convenience method to invoke a functor on another thread.
// Blocks the current thread until execution is complete.
// Ex: thread.BlockingCall([&] { result = MyFunctionReturningBool(); });
// NOTE: This function can only be called when synchronous calls are allowed.
// See ScopedDisallowBlockingCalls for details.
// NOTE: Blocking calls are DISCOURAGED, consider if what you're doing can
// be achieved with PostTask() and callbacks instead.
void BlockingCall(
FunctionView<void()> functor,
const webrtc::Location& location = webrtc::Location::Current()) {
BlockingCallImpl(std::move(functor), location);
template <typename Functor,
typename ReturnT = std::invoke_result_t<Functor>,
typename = typename std::enable_if_t<!std::is_void_v<ReturnT>>>
ReturnT BlockingCall(
Functor&& functor,
const webrtc::Location& location = webrtc::Location::Current()) {
ReturnT result;
BlockingCall([&] { result = std::forward<Functor>(functor)(); }, location);
return result;
// Allows BlockingCall to specified `thread`. Thread never will be
// dereferenced and will be used only for reference-based comparison, so
// instance can be safely deleted. If NDEBUG is defined and RTC_DCHECK_IS_ON
// is undefined do nothing.
void AllowInvokesToThread(Thread* thread);
// If NDEBUG is defined and RTC_DCHECK_IS_ON is undefined do nothing.
void DisallowAllInvokes();
// Returns true if `target` was allowed by AllowInvokesToThread() or if no
// calls were made to AllowInvokesToThread and DisallowAllInvokes. Otherwise
// returns false.
// If NDEBUG is defined and RTC_DCHECK_IS_ON is undefined always returns
// true.
bool IsInvokeToThreadAllowed(rtc::Thread* target);
// From TaskQueueBase
void Delete() override;
// ProcessMessages will process I/O and dispatch messages until:
// 1) cms milliseconds have elapsed (returns true)
// 2) Stop() is called (returns false)
bool ProcessMessages(int cms);
// Returns true if this is a thread that we created using the standard
// constructor, false if it was created by a call to
// ThreadManager::WrapCurrentThread(). The main thread of an application
// is generally not owned, since the OS representation of the thread
// obviously exists before we can get to it.
// You cannot call Start on non-owned threads.
bool IsOwned();
// Expose private method IsRunning() for tests.
// DANGER: this is a terrible public API. Most callers that might want to
// call this likely do not have enough control/knowledge of the Thread in
// question to guarantee that the returned value remains true for the duration
// of whatever code is conditionally executing because of the return value!
bool RunningForTest() { return IsRunning(); }
// These functions are public to avoid injecting test hooks. Don't call them
// outside of tests.
// This method should be called when thread is created using non standard
// method, like derived implementation of rtc::Thread and it can not be
// started by calling Start(). This will set started flag to true and
// owned to false. This must be called from the current thread.
bool WrapCurrent();
void UnwrapCurrent();
// Sets the per-thread allow-blocking-calls flag to false; this is
// irrevocable. Must be called on this thread.
void DisallowBlockingCalls() { SetAllowBlockingCalls(false); }
class CurrentThreadSetter : CurrentTaskQueueSetter {
explicit CurrentThreadSetter(Thread* thread)
: CurrentTaskQueueSetter(thread),
previous_(manager_->CurrentThread()) {
~CurrentThreadSetter() { manager_->ChangeCurrentThreadForTest(previous_); }
rtc::ThreadManager* const manager_;
rtc::Thread* const previous_;
// DelayedMessage goes into a priority queue, sorted by trigger time. Messages
// with the same trigger time are processed in num_ (FIFO) order.
struct DelayedMessage {
bool operator<(const DelayedMessage& dmsg) const {
return (dmsg.run_time_ms < run_time_ms) ||
((dmsg.run_time_ms == run_time_ms) &&
(dmsg.message_number < message_number));
int64_t delay_ms; // for debugging
int64_t run_time_ms;
// Monotonicaly incrementing number used for ordering of messages
// targeted to execute at the same time.
uint32_t message_number;
// std::priority_queue doesn't allow to extract elements, but functor
// is move-only and thus need to be changed when pulled out of the
// priority queue. That is ok because `functor` doesn't affect operator<
mutable absl::AnyInvocable<void() &&> functor;
// TaskQueueBase implementation.
void PostTaskImpl(absl::AnyInvocable<void() &&> task,
const PostTaskTraits& traits,
const webrtc::Location& location) override;
void PostDelayedTaskImpl(absl::AnyInvocable<void() &&> task,
webrtc::TimeDelta delay,
const PostDelayedTaskTraits& traits,
const webrtc::Location& location) override;
virtual void BlockingCallImpl(FunctionView<void()> functor,
const webrtc::Location& location);
// Perform initialization, subclasses must call this from their constructor
// if false was passed as init_queue to the Thread constructor.
void DoInit();
// Perform cleanup; subclasses must call this from the destructor,
// and are not expected to actually hold the lock.
void DoDestroy() RTC_EXCLUSIVE_LOCKS_REQUIRED(mutex_);
void WakeUpSocketServer();
// Same as WrapCurrent except that it never fails as it does not try to
// acquire the synchronization access of the thread. The caller should never
// call Stop() or Join() on this thread.
void SafeWrapCurrent();
// Blocks the calling thread until this thread has terminated.
void Join();
static void AssertBlockingIsAllowedOnCurrentThread();
friend class ScopedDisallowBlockingCalls;
static const int kSlowDispatchLoggingThreshold = 50; // 50 ms
// Get() will process I/O until:
// 1) A task is available (returns it)
// 2) cmsWait seconds have elapsed (returns empty task)
// 3) Stop() is called (returns empty task)
absl::AnyInvocable<void() &&> Get(int cmsWait);
void Dispatch(absl::AnyInvocable<void() &&> task);
// Sets the per-thread allow-blocking-calls flag and returns the previous
// value. Must be called on this thread.
bool SetAllowBlockingCalls(bool allow);
#if defined(WEBRTC_WIN)
static DWORD WINAPI PreRun(LPVOID context);
static void* PreRun(void* pv);
// ThreadManager calls this instead WrapCurrent() because
// ThreadManager::Instance() cannot be used while ThreadManager is
// being created.
// The method tries to get synchronization rights of the thread on Windows if
// `need_synchronize_access` is true.
bool WrapCurrentWithThreadManager(ThreadManager* thread_manager,
bool need_synchronize_access);
// Return true if the thread is currently running.
bool IsRunning();
// Called by the ThreadManager when being set as the current thread.
void EnsureIsCurrentTaskQueue();
// Called by the ThreadManager when being unset as the current thread.
void ClearCurrentTaskQueue();
std::queue<absl::AnyInvocable<void() &&>> messages_ RTC_GUARDED_BY(mutex_);
std::priority_queue<DelayedMessage> delayed_messages_ RTC_GUARDED_BY(mutex_);
uint32_t delayed_next_num_ RTC_GUARDED_BY(mutex_);
uint32_t blocking_call_count_ RTC_GUARDED_BY(this) = 0;
uint32_t could_be_blocking_call_count_ RTC_GUARDED_BY(this) = 0;
std::vector<Thread*> allowed_threads_ RTC_GUARDED_BY(this);
bool invoke_policy_enabled_ RTC_GUARDED_BY(this) = false;
mutable webrtc::Mutex mutex_;
bool fInitialized_;
bool fDestroyed_;
std::atomic<int> stop_;
// The SocketServer might not be owned by Thread.
SocketServer* const ss_;
// Used if SocketServer ownership lies with `this`.
std::unique_ptr<SocketServer> own_ss_;
std::string name_;
// TODO(tommi): Add thread checks for proper use of control methods.
// Ideally we should be able to just use PlatformThread.
#if defined(WEBRTC_POSIX)
pthread_t thread_ = 0;
#if defined(WEBRTC_WIN)
HANDLE thread_ = nullptr;
DWORD thread_id_ = 0;
// Indicates whether or not ownership of the worker thread lies with
// this instance or not. (i.e. owned_ == !wrapped).
// Must only be modified when the worker thread is not running.
bool owned_ = true;
// Only touched from the worker thread itself.
bool blocking_calls_allowed_ = true;
friend class ThreadManager;
int dispatch_warning_ms_ RTC_GUARDED_BY(this) = kSlowDispatchLoggingThreshold;
// AutoThread automatically installs itself at construction
// uninstalls at destruction, if a Thread object is
// _not already_ associated with the current OS thread.
// NOTE: *** This class should only be used by tests ***
class AutoThread : public Thread {
~AutoThread() override;
AutoThread(const AutoThread&) = delete;
AutoThread& operator=(const AutoThread&) = delete;
// AutoSocketServerThread automatically installs itself at
// construction and uninstalls at destruction. If a Thread object is
// already associated with the current OS thread, it is temporarily
// disassociated and restored by the destructor.
class AutoSocketServerThread : public Thread {
explicit AutoSocketServerThread(SocketServer* ss);
~AutoSocketServerThread() override;
AutoSocketServerThread(const AutoSocketServerThread&) = delete;
AutoSocketServerThread& operator=(const AutoSocketServerThread&) = delete;
rtc::Thread* old_thread_;
} // namespace rtc
#endif // RTC_BASE_THREAD_H_