android上Bionic不支持pthread_cancel等函数

谷歌在Bionic中没有实现pthread_cancel、pthread_testcancel的函数主要出于线程安全性以及其他api实现简洁性等方面考虑。官方的说法如下：

pthread_cancel():

   pthread_cancel() will *not* be supported in Bionic, because doing this would
   involve making the C library significantly bigger for very little benefit.

   Consider that:

     - A proper implementation must insert pthread cancellation checks in a lot
       of different places of the C library. And conformance is very difficult
       to test properly.

     - A proper implementation must also clean up resources, like releasing
       memory, or unlocking mutexes, properly if the cancellation happens in a
       complex function (e.g. inside gethostbyname() or fprintf() + complex
       formatting rules). This tends to slow down the path of many functions.

     - pthread cancellation cannot stop all threads: e.g. it can't do anything
       against an infinite loop

     - pthread cancellation itself has short-comings and isn't very portable
       (see http://advogato.org/person/slamb/diary.html?start=49 for
example).

   All of this is contrary to the Bionic design goals. If your code depends on
   thread cancellation, please consider alternatives.

   Note however that Bionic does implement pthread_cleanup_push() and
   pthread_cleanup_pop(), which can be used to handle cleanups that happen when
   a thread voluntarily exits through pthread_exit() or returning from its
   main function.

杀死线程的功能肯定是要用的，解决的方法大概有两种：

1.主进程中设标志，线程查询标志，被置位后调用pthread_exit()退出；

2.用pthread_kill()代替，如这位哥们所述http://www.rosoo.net/a/201112/15523.html，安全性很差

其他pthread相关资料：

http://www.cnblogs.com/lijunamneg/archive/2013/01/25/2877211.html

http://my.oschina.net/u/178323/blog/32535