实现UP、DOWN原语

产生3个进程：

两个进程模拟需要进入临界区的用户进程。

当需要进入临界区时，显示：“进程x请求进入临界区…”，同时向管理进程提出申请；

申请返回，表示进入了临界区。在临界区中等待一段随机时间，并显示：“进程x正在临界区…”；

当时间结束，显示：“进程x退出临界区…”,同时向管理进程提出退出申请；

当申请返回，显示：“进程x已退出临界区。”

一个进程作为原语的管理进程，接受其他进程的临界区进入请求：

如果允许进入，则根据DOWN 原语的操作步骤设置相应变量，然后返回；

如果不允许进入，则进入循环等待，直到允许为止；

退出时模拟UP 操作。

进程间通信可以采用信号、消息传递、管道或网络通信方式。

-achieve UP, DOWN original language have three processes : process simulation of two critical needs for access to the users in the process. When the need to access critical areas, revealed : "The process of x request to enter the critical areas ...", and also to the management process applications; applied to return, entered a critical area. In the critical area to wait for a certain period of time random, and that : "the process of x is the critical area ..."; When the time ended, showed : "x withdraw from the process of critical areas ...", and also to withdraw from the process management applications; When applied to return, showing : "x process has been critical to withdraw from the area." a process as the original language of the management proce