进程是程序在一个数据集合上运行的过程，进程是并发进行的，也即系统中的多个进程轮流的占用处理器运行。

　　我们把若干个进程都能进行访问和修改的那些变量称为公共变量。由于进程是并发执行的，所以，如果对进程访问公共变量不加限制，那么就会产生“与时间有关”的错误，即进程执行后，所得到的结果与访问公共变量的时间有关。为了防止这类错误，系统必须要用同步机构来控制进程对公共变量的访问。一般说，同步机构是由若干条语句——同步原语——所组成。本试验要求学生模拟PV操作同步机构的实现，模拟进程的并发执行，了解进程并发执行时同步机构的作用。

-process is a procedure in the data set to run the process, the process is conducted with the system that is the rotation process more than the occupier runs. We have a number of process can visit and revision of those variables as public variables. As the process is complicated by the implementation, so if the right to visit public process variables without restrictions, it will have a "Time" is wrong, the implementation process, the results obtained with the public to visit the variables of time. To prevent such mistakes, the system must be used to control synchronization process bodies for public variables visit. In general, synchronous bodies of a number of statements -- synchronization primitives -- composed. This experiment simulated PV require students to simultaneously ope