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course/14-mutexes/exercises/5-rw_mutex/readme.md

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+# RW Mutex
+
+The standard library also exposes a [sync.RWMutex](https://golang.org/pkg/sync/#RWMutex)
+
+In addition to these methods:
+
+* [Lock()](https://golang.org/pkg/sync/#Mutex.Lock)
+* [Unlock()](https://golang.org/pkg/sync/#Mutex.Unlock)
+
+The `sync.RWMutex` also has these methods:
+
+* [RLock()](https://golang.org/pkg/sync/#RWMutex.RLock)
+* [RUnlock()](https://golang.org/pkg/sync/#RWMutex.RUnlock)
+
+The `sync.RWMutex` can help with performance if we have a read-intensive process. Many goroutines can safely read from the map at the same time (multiple `Rlock()` calls can happen simultaneously). However, only one goroutine can hold a `Lock()` and all `RLock()`'s will also be excluded.
+
+## Assignment
+
+Let's update our same code from the last assignment, but this time we can speed it up by allowing readers to read from the map concurrently.
+
+Update the `val` method to only lock the mutex for *reading*. Notice that if you run the code with a write lock it will block forever.