linux thread的joinable和detached屬性

linux的thread有兩種屬性，分別是

joinable和detached。

我們看下man對於pthread_create說明裏的notes部分：

A thread may either be joinable or detached.  If a thread is joinable, then another thread can call pthread_join(3) to wait  for  the
       thread  to terminate and fetch its exit status.  Only when a terminated joinable thread has been joined are the last of its resources
       released back to the system.  When a detached thread terminates, its resources are automatically released back to the system:

這兩者的區別在於，joinable的thread只有被別的線程執行pthread_join，資源才能被系統回收，另外可以獲取該線程的退出碼。

detached的thread在退出時，如thread_exit，資源會自動被系統回收。

默認創建的thread都是joinable的，除非在thread_create裏特殊指定，或者在thread運行後執行thread_detach，就可以變爲detached線程。