rtc_base/thread.h

/*
 *  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.
 */

#ifndef RTC_BASE_THREAD_H_
#define RTC_BASE_THREAD_H_

#include <algorithm>
#include <list>
#include <memory>
#include <string>
#include <utility>
#include <vector>

#if defined(WEBRTC_POSIX)
#include <pthread.h>
#endif
#include "rtc_base/constructormagic.h"
#include "rtc_base/messagequeue.h"
#include "rtc_base/platform_thread_types.h"
#include "rtc_base/thread_checker.h"

#if defined(WEBRTC_WIN)
#include "rtc_base/win32.h"
#endif

namespace rtc {

class Thread;

class ThreadManager {
 public:
  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();

 private:
  ThreadManager();
  ~ThreadManager();

#if defined(WEBRTC_POSIX)
  pthread_key_t key_;
#endif

#if defined(WEBRTC_WIN)
  const DWORD key_;
#endif

  // The thread to potentially autowrap.
  const PlatformThreadRef main_thread_ref_;

  RTC_DISALLOW_COPY_AND_ASSIGN(ThreadManager);
};

struct _SendMessage {
  _SendMessage() {}
  Thread *thread;
  Message msg;
  bool *ready;
};

class Runnable {
 public:
  virtual ~Runnable() {}
  virtual void Run(Thread* thread) = 0;

 protected:
  Runnable() {}

 private:
  RTC_DISALLOW_COPY_AND_ASSIGN(Runnable);
};

// WARNING! SUBCLASSES MUST CALL Stop() IN THEIR DESTRUCTORS!  See ~Thread().

class RTC_LOCKABLE Thread : public MessageQueue {
 public:
  // DEPRECATED.
  // 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.
  Thread();

  explicit Thread(SocketServer* ss);
  explicit Thread(std::unique_ptr<SocketServer> ss);

  // NOTE: ALL SUBCLASSES OF Thread MUST CALL Stop() IN THEIR DESTRUCTORS (or
  // 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 {
   public:
    ScopedDisallowBlockingCalls();
    ~ScopedDisallowBlockingCalls();
   private:
    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.
  template <class ReturnT, class FunctorT>
  ReturnT Invoke(const Location& posted_from, FunctorT&& functor) {
    FunctorMessageHandler<ReturnT, FunctorT> handler(
        std::forward<FunctorT>(functor));
    InvokeInternal(posted_from, &handler);
    return handler.MoveResult();
  }

  // From MessageQueue
  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(); }

  // Sets the per-thread allow-blocking-calls flag and returns the previous
  // value. Must be called on this thread.
  bool SetAllowBlockingCalls(bool allow);

  // 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();

 protected:
  // 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;

 private:
  struct ThreadInit {
    Thread* thread;
    Runnable* runnable;
  };

#if defined(WEBRTC_WIN)
  static DWORD WINAPI PreRun(LPVOID context);
#else
  static void *PreRun(void *pv);
#endif

  // 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_;

  // Used to check access to unguarded thread control state variables and ensure
  // that control functions are called on the right thread.
  // The |thread_checker_| might represent a 'parent' thread from which
  // Start()/Stop() are called or it could represent the worker thread itself in
  // case the thread is wrapped since the functions that modified the control
  // state will in this case be called from that thread.
  ThreadChecker thread_checker_;

#if defined(WEBRTC_POSIX)
  pthread_t thread_ RTC_ACCESS_ON(thread_checker_) = 0;
#endif

#if defined(WEBRTC_WIN)
  HANDLE thread_ RTC_ACCESS_ON(thread_checker_) = nullptr;
  DWORD thread_id_ RTC_ACCESS_ON(thread_checker_) = 0;
#endif

  // 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;

  RTC_DISALLOW_COPY_AND_ASSIGN(Thread);
};

// 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 {
 public:
  AutoThread();
  ~AutoThread() override;

 private:
  RTC_DISALLOW_COPY_AND_ASSIGN(AutoThread);
};

// 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 {
 public:
  explicit AutoSocketServerThread(SocketServer* ss);
  ~AutoSocketServerThread() override;

 private:
  rtc::Thread* old_thread_;

  RTC_DISALLOW_COPY_AND_ASSIGN(AutoSocketServerThread);
};

}  // namespace rtc

#endif  // RTC_BASE_THREAD_H_