base/thread.h

// Copyright 2008, Google Inc.
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#ifndef BASE_THREAD_H_
#define BASE_THREAD_H_

#include <string>

#include "base/thread_local_storage.h"

class MessageLoop;

// Types that differ
#if defined(OS_WIN)
#include <wtypes.h>
typedef unsigned int ThreadId;
#elif defined(OS_POSIX)
typedef pthread_t ThreadId;
#endif

// A simple thread abstraction that establishes a MessageLoop on a new thread.
// The consumer uses the MessageLoop of the thread to cause code to execute on
// the thread.  When this object is destroyed the thread is terminated.  All
// pending tasks queued on the thread's message loop will run to completion
// before the thread is terminated.
//
class Thread {
 public:
  // Constructor.
  // name is a display string to identify the thread.
  explicit Thread(const char *name);

  // Destroys the thread, stopping it if necessary.
  //
  virtual ~Thread();

  // Starts the thread.  Returns true if the thread was successfully started;
  // otherwise, returns false.  Upon successful return, the message_loop()
  // getter will return non-null.
  //
  // Note: This function can't be called on Windows with the loader lock held;
  // i.e. during a DllMain, global object construction or destruction, atexit()
  // callback.
  bool Start();

  // Starts the thread. Behaves exactly like Start in addition to allow to
  // override the default process stack size. This is not the initial stack size
  // but the maximum stack size that thread is allowed to use.
  //
  // Note: This function can't be called on Windows with the loader lock held;
  // i.e. during a DllMain, global object construction or destruction, atexit()
  // callback.
  bool StartWithStackSize(size_t stack_size);

  // Signals the thread to exit and returns once the thread has exited.  After
  // this method returns, the Thread object is completely reset and may be used
  // as if it were newly constructed (i.e., Start may be called again).
  //
  // Stop may be called multiple times and is simply ignored if the thread is
  // already stopped.
  //
  // NOTE: This method is optional.  It is not strictly necessary to call this
  // method as the Thread's destructor will take care of stopping the thread if
  // necessary.
  //
  void Stop();

  // Signals the thread to exit in the near future.
  //
  // WARNING: This function is not meant to be commonly used. Use at your own
  // risk. Calling this function will cause message_loop() to become invalid in
  // the near future. This function was created to workaround a specific
  // deadlock on Windows with printer worker thread. In any other case, Stop()
  // should be used.
  //
  // StopSoon should not be called multiple times as it is risky to do so. It
  // could cause a timing issue in message_loop() access. Call Stop() to reset
  // the thread object once it is known that the thread has quit.
  void StopSoon();

  // Returns the message loop for this thread.  Use the MessageLoop's
  // PostTask methods to execute code on the thread.  This only returns
  // non-null after a successful call to Start.  After Stop has been called,
  // this will return NULL.
  //
  // NOTE: You must not call this MessageLoop's Quit method directly.  Use
  // the Thread's Stop method instead.
  //
  MessageLoop* message_loop() const {
    if (thread_id_)
      return message_loop_;
    return NULL;
  }

  // Set the name of this thread (for display in debugger too).
  const std::string &thread_name() { return name_; }

#if defined(OS_WIN)
  HANDLE thread_handle() { return thread_; }
#endif

  // Sets the thread name if a debugger is currently attached. Has no effect
  // otherwise. To set the name of the current thread, pass GetCurrentThreadId()
  // as the tid parameter.
  static void SetThreadName(const char* name, ThreadId tid);

 protected:
  // Called just prior to starting the message loop
  virtual void Init() { }

  // Called just after the message loop ends
  virtual void CleanUp() { }

  static void SetThreadWasQuitProperly(bool flag);
  static bool GetThreadWasQuitProperly();

 private:
#if defined(OS_WIN)
  static unsigned __stdcall ThreadFunc(void* param);
  // The thread's handle. Modified by the root thread.  
  HANDLE thread_;
#endif

  // The thread's id. Modified by the root thread. Set to 0 when the thread is
  // not ready to receive messages.
  ThreadId thread_id_;

  // The thread's message loop. Valid only while the thread is alive. Modified
  // by the created thread.
  MessageLoop* message_loop_;

  const std::string name_;

  static TLSSlot tls_index_;

  friend class ThreadQuitTask;

  DISALLOW_COPY_AND_ASSIGN(Thread);
};

#endif  // BASE_THREAD_H_