嵌入式开发之hi3519---进程线程间的同步和互斥，条件变量、信号了、互斥锁等

sem_post 最安全

sem  有序，会卡顿 阻塞 

mutex  无序，不能同步

http://blog.chinaunix.net/uid-20671208-id-4935154.html

https://www.cnblogs.com/ngnetboy/p/3521547.html

http://www.jianshu.com/p/1e59f0970bf5 

http://blog.csdn.net/jenny8080/article/details/52094140