Readers–writer lock

<p>In <a href="/facts/Computer_science/lN3pEyPz">computer science</a>, a readers–writer (single-writer lock, a multi-reader lock, a push lock, or an MRSW lock) is a <a href="/facts/Synchronization_(computer_science)/n7ID76uM">synchronization</a> primitive that solves one of the <a href="/facts/Readers%25E2%2580%2593writers_problem/cGtVXQaU">readers–writers problems</a>. An RW lock allows <a href="/facts/Concurrency_control/JWnmhVd5">concurrent</a> access for read-only operations, whereas write operations require exclusive access. This means that multiple threads can read the data in parallel but an exclusive <a href="/facts/Lock_(computer_science)/e3a9gnJT">lock</a> is needed for writing or modifying data. When a writer is writing the data, all other writers and readers will be blocked until the writer is finished writing. A common use might be to control access to a data structure in memory that cannot be updated <a href="/facts/Atomicity_(programming)/u3pnNCvs">atomically</a> and is invalid (and should not be read by another thread) until the update is complete.
</p><p>Readers–writer locks are usually constructed on top of <a href="/facts/Mutex/e3a9gnJT">mutexes</a> and <a href="/facts/Condition_variable/g2zfRatV">condition variables</a>, or on top of <a href="/facts/Semaphore_(programming)/BrE1W4Je">semaphores</a>.
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Readers–writer lock open-in-new

Readers–writer lock