critical resource
critical resource A resource that can only be in use by at most one process at any one time. A common example is a section of code that deals with the allocation or release of a shared resource, where it is imperative that no more than one process at a time is allowed to alter the data that defines which processes have been allocated parts of the resource.
Where several asynchronous processes are required to coordinate their access to a critical resource, they do so by controlled access to a semaphore. A process wishing to access the resource issues a P operation that inspects the value of the semaphore; the value indicates whether or not any other process has access to the critical resource. If some other process is using the resource then the process issuing the P operation will be suspended. A process issues a V operation when it has finished using the critical resource. The V operation can never cause suspension of the issuing process but by operating on the value of the semaphore may allow some other cooperating process to commence operation.
Where several asynchronous processes are required to coordinate their access to a critical resource, they do so by controlled access to a semaphore. A process wishing to access the resource issues a P operation that inspects the value of the semaphore; the value indicates whether or not any other process has access to the critical resource. If some other process is using the resource then the process issuing the P operation will be suspended. A process issues a V operation when it has finished using the critical resource. The V operation can never cause suspension of the issuing process but by operating on the value of the semaphore may allow some other cooperating process to commence operation.
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