调用speak线程：

cancel时死锁堆栈：

* thread #1, queue = 'com.apple.main-thread', stop reason = signal SIGSTOP

  * frame #0: 0x0000000182e7c0f0 libsystem_kernel.dylib`__psynch_cvwait + 8

    frame #1: 0x0000000182f92ce4 libsystem_pthread.dylib`_pthread_cond_wait$VARIANT$mp + 640

    frame #2: 0x0000000102467b28 TheLittleKing`BDS_TTS::Threads::Synchronization::AppConditionMutex::lockWhenNotFlags(this=0x00000001c40f4d80, flags=2) at AppConditionMutex.cpp:124 [opt]

    frame #3: 0x000000010240d9fc TheLittleKing`::-[BDSSpeechSynthesizer cancel](self=0x00000001c41e7a00, _cmd=) at BDSSpeechSynthesizer.mm:1538 [opt]

    frame #4: 0x00000001024001cc TheLittleKing`-[LKChatManager stopSpeeking](self=, _cmd=) at LKChatManager.m:274 [opt]