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Dispatch Semaphores are objects that allow a client to permit only a certain number of tasks to execute concurrently. Libdispatch comes with its own object model, OS Object, that is partially compatible with the Objective-C model. As a result, its objects can be bridged toll-free to ObjC objects. [17]
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 ...
semaphore: In computer science, particularly in operating systems, a semaphore is a variable or abstract data type that is used for controlling access, by multiple processes, to a common resource in a parallel programming or a multi user environment.
To enter a critical section, a thread must obtain a semaphore, which it releases on leaving the section. Other threads are prevented from entering the critical section at the same time as the original thread, but are free to gain control of the CPU and execute other code, including other critical sections that are protected by different semaphores.
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Semaphore (lit. ' apparatus for signalling ' ; from Ancient Greek σῆμα ( sêma ) 'mark, sign, token' and Greek -φόρος ( -phóros ) 'bearer, carrier') [ 1 ] is the use of an apparatus to create a visual signal transmitted over distance.
In computing, a memory barrier, also known as a membar, memory fence or fence instruction, is a type of barrier instruction that causes a central processing unit (CPU) or compiler to enforce an ordering constraint on memory operations issued before and after the barrier instruction.
In computer science, deadlock prevention algorithms are used in concurrent programming when multiple processes must acquire more than one shared resource.If two or more concurrent processes obtain multiple resources indiscriminately, a situation can occur where each process has a resource needed by another process.