linux下是这样定义的：
在linux的实现中pthread_t被定义为 "unsigned long int",参考http://condor.depaul.edu/glancast/443class/docs/pthreads.html
Windows下这样定义：
1 /*
2 * Generic handle type - intended to extend uniqueness beyond
3 * that available with a simple pointer. It should scale for either
4 * IA-32 or IA-64.
5 */
6 typedef struct {
7 void * p; /* Pointer to actual object */
8 unsigned int x; /* Extra information - reuse count etc */
9 } ptw32_handle_t;
10 typedef ptw32_handle_t pthread_t;