Topic Notes: Process Synchronization - Courses

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CS 322 Operating Systems Spring 2008provide semaphores through system calls. We will examine their implementation in this contextsoon.Given semaphores, we can create a much simpler solution to the critical section problem for nprocesses:• Shared datasemaphore mutex=1;• <strong>Process</strong> P iwhile (1) {wait(mutex);/* critical section */signal(mutex);}/* non-critical section */The semaphore provides the mutual exclusion for sure, and should satify progress, but dependingon the implementation of semaphores, may or may not provide bounded waiting.A semaphore implementation might look like this:struct semaphore {int value;proclist L;};• block operation suspends the calling process, removes it from consideration by the scheduler• wakeup(P) resumes execution of suspended process P , puts it back into consideration• wait(S):S.value--;if (S.value < 0) {add this process to S.L;block;}14
CS 322 Operating Systems Spring 2008• signal(S):S.value++;if (S.value
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Topic Notes: Process Synchronization - Courses

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