浙江大学操作系统课件（Operating System Concepts）CH07.pptVIP

Chapter 7: Process Synchronization进程同步 7.1 Background 背景 7.2 The Critical-Section Problem 临界区问题 7.3 Synchronization Hardware 同步的硬件实现. 7.4 Semaphores 信号量 7.5 Classical Problems of Synchronization 经典同步问题 7.6 Critical Regions 临界区 7.7 Monitors 管程 7.8 OS Synchronization 操作系统的同步机制 7.9 Atomic Transactions 自动事务处理 7.1 Background背景 Concurrent access to shared data may result in data inconsistency. 对共享数据的并发访问可能导致数据的不一致性 Maintaining data consistency requires mechanisms to ensure the orderly execution of cooperating processes. 要保持数据的一致性，就需要一种保证并发进程的正确执行顺序的机制 Background (Cont.) Shared-memory solution to bounded-butter problem (Chapter 4) allows at most n – 1 items in buffer at the same time. A solution, where all N buffers are used is not simple. 第4章中解决有界缓冲区问题的共享内存方法在类数据count 上将一起竞争条件 Suppose that we modify the producer-consumer code by adding a variable counter, initialized to 0 and incremented each time a new item is added to the buffer Bounded-Buffer Shared data #define BUFFER_SIZE 10 typedef struct { . . . } item; item buffer[BUFFER_SIZE]; int in = 0; int out = 0; int counter = 0; Bounded-Buffer (Cont.-1) Producer process item nextProduced; while (1) { while (counter == BUFFER_SIZE) ; /* do nothing */ buffer[in] = nextProduced; in = (in + 1) % BUFFER_SIZE; counter++; } Bounded-Buffer (Cont.-2) Consumer process item nextConsumed; while (1) { while (counter == 0) ; /* do nothing */ nextConsumed = buffer[out]; out = (out + 1) % BUFFER_SIZE; counter--; } Bounded Buffer (Cont.-3) The statementscounter++;counter--;must be performed atomically. Atomic ope