如何在Mac OS X下调试死锁？

Question

我正在把一个音频播放器移植到Mac环境下。它在Windows上运行得很好，但在Mac上却不行。当我用播放器播放音乐时，出现了不可预测的死锁。现在我只能获取到挂起进程的线程堆栈信息。以下是我得到的调用堆栈：

Sampling process 1808 for 1 seconds with 1 millisecond of run time between samples
Sampling completed, processing symbols...
Analysis of sampling Python (pid 1808) every 1 millisecond
Call graph:
    785 Thread_32664   DispatchQueue_1: com.apple.main-thread  (serial)
      785 0x1ea9
        785 0x1f82
          785 Py_Main
            785 PyRun_SimpleFileExFlags
              785 PyRun_FileExFlags
                785 PyEval_EvalCode
                  785 PyEval_EvalCodeEx
                    785 PyEval_EvalFrameEx
                      785 time_sleep
                        785 select
                          785 select$DARWIN_EXTSN$NOCANCEL
    785 Thread_32672   DispatchQueue_2: com.apple.libdispatch-manager  (serial)
      785 start_wqthread
        785 _pthread_wqthread
          785 _dispatch_worker_thread2
            785 _dispatch_queue_invoke
              785 _dispatch_mgr_invoke
                785 kevent
    785 Thread_32679
      785 thread_start
        785 _pthread_start
          785 CAPThread::Entry(CAPThread*)
            785 HP_IOThread::ThreadEntry(HP_IOThread*)
              785 HP_IOThread::WorkLoop()
                785 HP_IOThread::PerformIO(AudioTimeStamp const&, double)
                  785 IOA_Device::CallIOProcs(AudioTimeStamp const&, AudioTimeStamp const&, AudioTimeStamp const&)
                    785 HP_IOProc::Call(AudioTimeStamp const&, AudioTimeStamp const&, AudioBufferList const*, AudioTimeStamp const&, AudioBufferList*)
                      785 BASS_ChannelIsSliding
                        785 MPEnterCriticalRegion
                          785 TSWaitOnConditionTimedRelative
                            785 TSWaitOnCondition
                              785 pthread_cond_wait$UNIX2003
                                785 _pthread_cond_wait
                                  785 __semwait_signal
    785 Thread_32680
      785 0xa4fffad
        785 dict_repr
          785 0x1307ccd
            785 MPEnterCriticalRegion
              785 TSWaitOnConditionTimedRelative
                785 TSWaitOnCondition
                  785 pthread_cond_wait$UNIX2003
                    785 _pthread_cond_wait
                      785 __semwait_signal
    785 Thread_32681
      785 MPEnterCriticalRegion
        785 TSWaitOnConditionTimedRelative
          785 TSWaitOnCondition
            785 pthread_cond_wait$UNIX2003
              785 _pthread_cond_wait
                785 __semwait_signal
    785 Thread_36905
      785 start_wqthread
        785 _pthread_wqthread
          785 __workq_kernreturn

Total number in stack (recursive counted multiple, when >=5):

Sort by top of stack, same collapsed (when >= 5):
        __semwait_signal        2355
        __workq_kernreturn        785
        kevent        785
        select$DARWIN_EXTSN$NOCANCEL        785
Sample analysis of process 1808 written to file /dev/stdout

我只能知道一些线程在等待其他线程，但我不知道它们在等待什么锁，也不知道是谁在等待。我的问题是，如何在Mac环境下调试这个死锁问题呢？

Answer 1

调试多线程应用程序本身就很困难。一个简单（可能有点过于简单）的办法是把你所有关于锁的获取、阻塞和释放事件都写到一个日志文件里。这种方法并没有什么特别针对OS X的地方，但我在类似的问题上用过，效果不错。