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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 <memory>
#include <string>
#include <type_traits>
#if defined(WEBRTC_POSIX)
#include <pthread.h>
#include "rtc_base/constructor_magic.h"
#include "rtc_base/location.h"
#include "rtc_base/message_handler.h"
#include "rtc_base/message_queue.h"
#include "rtc_base/platform_thread_types.h"
#include "rtc_base/socket_server.h"
#include "rtc_base/thread_annotations.h"
#if defined(WEBRTC_WIN)
#include "rtc_base/win32.h"
namespace rtc {
class Thread;
namespace rtc_thread_internal {
template <class FunctorT>
class SingleMessageHandlerWithFunctor final : public MessageHandler {
explicit SingleMessageHandlerWithFunctor(FunctorT&& functor)
: functor_(std::forward<FunctorT>(functor)) {}
void OnMessage(Message* msg) override {
delete this;
~SingleMessageHandlerWithFunctor() override {}
typename std::remove_reference<FunctorT>::type functor_;
} // namespace rtc_thread_internal
class ThreadManager {
static const int kForever = -1;
// Singleton, constructor and destructor are private.
static ThreadManager* Instance();
Thread* CurrentThread();
void SetCurrentThread(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();
bool IsMainThread();
#if defined(WEBRTC_POSIX)
pthread_key_t key_;
#if defined(WEBRTC_WIN)
const DWORD key_;
// The thread to potentially autowrap.
const PlatformThreadRef main_thread_ref_;
struct _SendMessage {
_SendMessage() {}
Thread* thread;
Message msg;
bool* ready;
class Runnable {
virtual ~Runnable() {}
virtual void Run(Thread* thread) = 0;
Runnable() {}
class RTC_LOCKABLE Thread : public MessageQueue {
// The default constructor should not be used because it hides whether or
// not a socket server will be associated with the thread. Most instances
// of Thread do actually not need one, so please use either of the Create*
// methods to construct an instance of Thread.
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().
~Thread() override;
static std::unique_ptr<Thread> CreateWithSocketServer();
static std::unique_ptr<Thread> Create();
static Thread* Current();
// Used to catch performance regressions. Use this to disallow blocking calls
// (Invoke) 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 {
Thread* const thread_;
const bool previous_state_;
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(const std::string& name, const void* obj);
// Starts the execution of the thread.
bool Start(Runnable* runnable = nullptr);
// 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 MessageQueue 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();
virtual void Send(const Location& posted_from,
MessageHandler* phandler,
uint32_t id = 0,
MessageData* pdata = nullptr);
// Convenience method to invoke a functor on another thread. Caller must
// provide the |ReturnT| template argument, which cannot (easily) be deduced.
// Uses Send() internally, which blocks the current thread until execution
// is complete.
// Ex: bool result = thread.Invoke<bool>(RTC_FROM_HERE,
// &MyFunctionReturningBool);
// NOTE: This function can only be called when synchronous calls are allowed.
// See ScopedDisallowBlockingCalls for details.
// NOTE: Blocking invokes are DISCOURAGED, consider if what you're doing can
// be achieved with PostTask() and callbacks instead.
template <class ReturnT, class FunctorT>
ReturnT Invoke(const Location& posted_from, FunctorT&& functor) {
FunctorMessageHandler<ReturnT, FunctorT> handler(
InvokeInternal(posted_from, &handler);
return handler.MoveResult();
// Posts a task to invoke the functor on |this| thread asynchronously, i.e.
// without blocking the thread that invoked PostTask(). Ownership of |functor|
// is passed and destroyed on |this| thread after it is invoked.
// Requirements of FunctorT:
// - FunctorT is movable.
// - FunctorT implements "T operator()()" or "T operator()() const" for some T
// (if T is not void, the return value is discarded on |this| thread).
// - FunctorT has a public destructor that can be invoked from |this| thread
// after operation() has been invoked.
// - The functor must not cause the thread to quit before PostTask() is done.
// Example - Calling a class method:
// class Foo {
// public:
// void DoTheThing();
// };
// Foo foo;
// thread->PostTask(RTC_FROM_HERE, Bind(&Foo::DoTheThing, &foo));
// Example - Calling a lambda function:
// thread->PostTask(RTC_FROM_HERE,
// [&x, &y] { x.TrackComputations(y.Compute()); });
template <class FunctorT>
void PostTask(const Location& posted_from, FunctorT&& functor) {
new rtc_thread_internal::SingleMessageHandlerWithFunctor<FunctorT>(
// This DCHECK guarantees that the post was successful.
// Post() doesn't say whether it succeeded, but it will only fail if the
// thread is quitting. DCHECKing that the thread is not quitting *after*
// posting might yield some false positives (where the thread did in fact
// quit, but only after posting), but if we have false positives here then
// we have a race condition anyway.
// TODO( When Post() returns a bool we can
// DCHECK the result instead of inferring success from IsQuitting().
// From MessageQueue
bool IsProcessingMessagesForTesting() override;
void Clear(MessageHandler* phandler,
uint32_t id = MQID_ANY,
MessageList* removed = nullptr) override;
void ReceiveSends() 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); }
// Sets the per-thread allow-blocking-calls flag to true, sidestepping the
// invariants upheld by DisallowBlockingCalls() and
// ScopedDisallowBlockingCalls. Must be called on this thread.
void DEPRECATED_AllowBlockingCalls() { SetAllowBlockingCalls(true); }
// 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;
struct ThreadInit {
Thread* thread;
Runnable* runnable;
// 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();
// Processes received "Send" requests. If |source| is not null, only requests
// from |source| are processed, otherwise, all requests are processed.
void ReceiveSendsFromThread(const Thread* source);
// If |source| is not null, pops the first "Send" message from |source| in
// |sendlist_|, otherwise, pops the first "Send" message of |sendlist_|.
// The caller must lock |crit_| before calling.
// Returns true if there is such a message.
bool PopSendMessageFromThread(const Thread* source, _SendMessage* msg);
void InvokeInternal(const Location& posted_from, MessageHandler* handler);
std::list<_SendMessage> sendlist_;
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;
// AutoThread automatically installs itself at construction
// uninstalls at destruction, if a Thread object is
// _not already_ associated with the current OS thread.
class AutoThread : public Thread {
~AutoThread() override;
// 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;
rtc::Thread* old_thread_;
} // namespace rtc
#endif // RTC_BASE_THREAD_H_