printf("thread = %d\n",pthread_kill(thread_id,0));

上述用法，在未對一個pthread_t執行pthread_create前呼叫pthread_kill，會出現Segmentation fault

google上摘錄如下解釋：

pthread_t is not a thread ID, or a numeric index. It is an opaque type. Making up values can result in a crash.

On Linux NPTL, pthread_t is used as a pointer:

int
__pthread_kill (threadid, signo)pthread_t threadid;int signo;{struct pthread *pd =(struct pthread *) threadid;

It should be fairly clear where things are going wrong already :) Note that this pointerness is also an implementation detail - the older Linuxthreads implementation used numeric indices into a table, and there you could indeed make up TIDs and not expect things to crash.

You need to be tracking thread life and death yourself. A pthread_t is valid until you call pthread_join on it successfully. If you want to test whether a valid pthread_t is alive, call pthread_tryjoin_np on it; if it returns EBUSY, the thread is alive. If the function succeeds, the pthread_t is no longer valid

You could, of course, implement your own tracking system - create a table somewhere of liveness, a system for handing out TIDs, and passing them into newly created threads. Have each thread mark itself as dead prior to exiting (perhaps using pthread_cleanup_push so you handle thread cancellation and pthread_exit), and detach the thread so you don't need to join it (using pthread_detach). Now you have explicit control of your thread-death reporting.