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In computer science, a semaphore is a variable or abstract data type used to control access to a common resource by multiple threads and avoid critical section problems in a concurrent system such as a multitasking operating system. Semaphores are a type of synchronization primitive. A trivial semaphore is a plain variable that is changed (for ...
The resource semaphore can be locked by both the writer and the reader in their entry section. They are only able to do so after first locking the readtry semaphore, which can only be done by one of them at a time. It will then take control over the resource as soon as the current reader is done reading and lock all future readers out.
In the Solaris implementation of condition variables, a spurious wakeup may occur without the condition being assigned if the process is signaled; the wait system call aborts and returns EINTR. [2] The Linux p-thread implementation of condition variables guarantees that it will not do that. [3] [4]
Semaphores are signalling mechanisms which can allow one or more threads/processors to access a section. A Semaphore has a flag which has a certain fixed value associated with it and each time a thread wishes to access the section, it decrements the flag. Similarly, when the thread leaves the section, the flag is incremented.
The monitor is an object that contains variables buffer, head, tail and count to realize a circular buffer, the condition variables nonempty and nonfull for synchronization and the methods append and remove to access the bounded buffer. The monitor operation wait corresponds to the semaphore operation P or acquire, signal corresponds to V or ...
In computer science, a readers–writer (single-writer lock, [1] a multi-reader lock, [2] a push lock, [3] or an MRSW lock) is a synchronization primitive that solves one of the readers–writers problems.
There are several possible solutions, but all solutions require a mutex, which ensures that only one of the participants can change state at once.The barber must acquire the room status mutex before checking for customers and release it when they begin either to sleep or cut hair; a customer must acquire it before entering the shop and release it once they are sitting in a waiting room or ...
By carefully controlling which variables are modified inside and outside the critical section, concurrent access to the shared variable are prevented. A critical section is typically used when a multi-threaded program must update multiple related variables without a separate thread making conflicting changes to that data.