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Editing: semaphore.md
--- title: Semaphore permalink: /semaphore --- [Semaphores](https://en.wikipedia.org/wiki/Semaphore_%28programming%29) are another synchronization primitive in addition to [mutual exclusion](./mutex.md). Instead of providing exclusive access to a single party, they provide access to a limited set of N parties at the same time. This makes them great to control concurrency, e.g. limiting an HTTP client to X concurrent requests, so the HTTP server doesn't get overwhelmed. Similar to [`Mutex`](./mutex.md), `Lock` instances can be acquired using `Semaphore::acquire()`. Please refer to the `Mutex` documentation for additional usage documentation, as they're basically equivalent except for the fact that `Mutex` is always a `Semaphore` with a count of exactly one party. In many cases you can use [concurrent iterators](./concurrent-iterator.md) instead of directly using a `Semaphore`.
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