信号量又称为信号灯，它是用来协调不同进程间的数据对象的，而最主要的应用是前一节的共享内存方式的进程间通信。本质上，信号量是一个计数器，它用来记录对某个资源（如共享内存）的存取状况。一般说来，为了获得共享资源，进程需要执行下列操作：-volume also known as signal lights, it is used to coordinate different processes of the data object, but the most important application of a pre-shared memory approach inter-process communication. In essence, the signal level is a counter, it is used to record a pair of resources (such as shared memory) access conditions. Generally, in order to access shared resources, the process requires the following :