Since semaphores can have a count associated with them, they are usually made use of when multiple threads cooperatively need to achieve an objective. Consider this example:- We have a thread(A) that needs information from two databases before proceeding. The access to these two DBs is controlled by two separate threads(B,C). These two threads have a message processing loop and anybody desirous of their service needs to post a message into their message queue. Our first thread initialises a semaphore S with init(S,-1). It then posts a DBData ...

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Semaphore programming, Semaphore programming - Semaphores today, Semaphore programming - Example of Usage of Semaphore, Semaphore programming - C# Semaphore

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Lock computer science, Lock computer science - Types, Lock computer science - Implementation, Lock computer science - Granularity, Lock computer science - Database locks

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Locks typically require hardware support for efficient implementation. This usually takes the form of one or more atomic instructions such as "test-and-set", "fetch-and-add" or "compare-and-swap". These instructions allow a single process to test if the lock is free, and if free, acquire the lock in a single atomic operation. Uniprocessor architectures have the option of using uninterruptable sequences of instructions, using special instructions or instruction prefixes to disable interrupts temporarily, but this technique does not wor ...

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Lock computer science, Lock computer science - Types, Lock computer science - Implementation, Lock computer science - Granularity, Lock computer science - Database locks

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An important property of a lock is its granularity. The granularity is a measure of the amount of data the lock is protecting. In general, choosing a coarse granularity (a small number of locks, each protecting a large segment of data) results in less overhead when a single process is accessing the protected data, but worse performance when multiple processes are running concurrently. This is because of increased lock contention: the more coarse the lock, the higher the likelihood that the lock will stop an unrelated process from proc ...

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Lock computer science, Lock computer science - Types, Lock computer science - Implementation, Lock computer science - Granularity, Lock computer science - Database locks

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In databases, locks can be used as a means of ensuring transaction synchronisity. i.e. when making transaction processing concurrent (interleaving transactions), using 2-phased locks ensures that the concurrent execution of the transaction turns out equivalent to some serial ordering of the transaction. However, deadlocks become an unfortunate side-effect of locking in databases. Deadlocks are either prevented by pre-determining the locking order between transactions or are detected using waits-for graphs. An alternate to locking for database synchronisity while avoiding deadlocks involves the ...

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Lock computer science, Lock computer science - Types, Lock computer science - Implementation, Lock computer science - Granularity, Lock computer science - Database locks

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Threaded programs usually use synchronisation primitives provided by a high-level programming environment such as Java, or an API such as POSIX pthreads or Win32. Primitives such as mutexes and semaphores are provided to synchronize access to resources from parallel threads of execution. These primitives are usually implemented with the memory barriers required to provide the expected memory visibility semantics. When using ...

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Memory barrier, Memory barrier - An illustrative example, Memory barrier - Low-level architecture-specific primitives, Memory barrier - Threaded programming and memory visibility, Memory barrier - Out-of-order execution versus compiler reordering optimisations

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Dijkstra studied theoretical physics at the University of Leiden, but he quickly realized he was more interested in programming than physics. He worked as a research fellow for Burroughs Corporation in the early 1970s. He worked at the Eindhoven University of Technology in the Netherlands and later held the Schlumberger Centennial Chair in Computer Sciences at the University of Texas at Austin, in the United States. He retired in 2000. Among his contributions to computer science is the shortest path-algorithm, also known as Dijkstra's algorithm, and the semaphore construct, for coordi ...

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Edsger Dijkstra, Edsger Dijkstra - Life, Edsger Dijkstra - Pronunciation

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The Join Java extension introduces three new language constucts: Join methods Asynchronous methods Order class modifiers for determining the order that patterns are matched Concurrency expression in most popular programming languages is still quite low level and based on constructs such as semaphores and monitors, that have not changed in twenty years. Libraries that are emerging (such as the Java concurrency library JSR-166) show that programmers demand that higher-level concurrency semantics be ...

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Join Java, Join Java - Language characteristics, Join Java - Join methods, Join Java - Ordering modifiers, Join Java - Asynchronous methods, Join Java - Related languages

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The traditional approach to multi-threaded programming is to use locks to synchronize access to shared resources. Synchronization primitives such as mutexes, semaphores, and critical sections are all mechanisms by which a programmer can ensure that certain sections of code do not execute concurrently if doing so would corrupt shared memory structures. If one thread attempts to acquire a lock that is already held by an ...

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Non-blocking synchronization, Non-blocking synchronization - Motivation, Non-blocking synchronization - Implementation, Non-blocking synchronization - Wait-freedom, Non-blocking synchronization - Lock-freedom, Non-blocking synchronization - Obstruction-freedom, Non-blocking synchronization - Resources

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1.TR.6 -- 100BaseFX -- 100BaseTX -- 100BaseT -- 100BaseVG -- 100VG-AnyLAN -- 10base2 -- 10base5 -- 10baseT -- 120 reset -- 16-bit -- 16-bit application -- 16550 UART -- 1NF -- 1TBS -- 2.PAK -- 20-Gate programming language -- 20-GATE -- 28-bit -- 2B1D -- 2B1Q -- 2D -- 2NF -- 3-tier (computing) -- 32-bit application -- 32-bit -- 320xx microprocessor -- 320xx -- 386BSD -- 386SPART.PAR -- 3Com Corporation -- 3DO -- 3D computer graphics -- 3GL -- 3NF -- 3Station -- 4.2BSD -- 404 error -- 431A -- 473L Query programming language -- 486SX -- 4GL -- 4NF -- 51forth programming language -- 56 kbit/s ...

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List of computing topics, List of computing topics - 0–9, List of computing topics - A, List of computing topics - B, List of computing topics - C, List of computing topics - D, List of computing topics - E, List of computing topics - F, List of computing topics - G, List of computing topics - H, List of computing topics - I, List of computing topics - J, List of computing topics - K, List of computing topics - L, List of computing topics - M, List of computing topics - N, List of computing topics - O, List of computing topics - P, List of computing topics - Q, List of computing topics - R, List of computing topics - S, List of computing topics - T, List of computing topics - U, List of computing topics - V, List of computing topics - W, List of computing topics - X, List of computing topics - Y, List of computing topics - Z

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