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二进制信号量或互斥量

操作系统IT知识信号量

在计算信号量时, 未提供互斥, 因为我们拥有在关键部分同时执行的一组线程。
但是, Binary Semaphore严格提供互斥。在这里, 关键部分中最多只能有1个进程, 而不是关键部分中有1个以上的可用插槽。信号量只能有两个值, 即0或1。
【二进制信号量或互斥量】让我们看一下二进制信号量的编程实现。

StructBsemaphore{ enum Value(0, 1); //value is enumerated data type which can only have two values 0 or 1. Queue type L; }/* L contains all PCBs corresponding to process Blocked while processing down operation unsuccessfully. */ Down (Bsemaphore S) { if (s.value =http://www.srcmini.com/= 1) // if a slot is available in the //critical section then let the process enter in the queue. {S.value = 0; // initialize the value to 0 so that no other process can read it as 1. } else {put the process (PCB) in S.L; //if no slot is available //then let the process wait in the blocked queue. sleep(); }}Up (Bsemaphore S) { if (S.L is empty) //an empty blocked processes list implies that no process //has ever tried to get enter in the critical section. {S.Value =1; } else {Select a process from S.L; Wakeup(); // if it is not empty then wake the first process of the blocked queue. } }

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