RwLock in std::sync

A reader-writer lock

This type of lock allows a number of readers or at most one writer at any point in time. The write portion of this lock typically allows modification of the underlying data (exclusive access) and the read portion of this lock typically allows for read-only access (shared access).

In comparison, a Mutex does not distinguish between readers or writers that acquire the lock, therefore blocking any threads waiting for the lock to become available. An RwLock will allow any number of readers to acquire the lock as long as a writer is not holding the lock.

The priority policy of the lock is dependent on the underlying operating system’s implementation, and this type does not guarantee that any particular policy will be used. In particular, a writer which is waiting to acquire the lock in write might or might not block concurrent calls to read, e.g.:

The type parameter T represents the data that this lock protects. It is required that T satisfies Send to be shared across threads and Sync to allow concurrent access through readers. The RAII guards returned from the locking methods implement Deref (and DerefMut for the write methods) to allow access to the content of the lock.

An RwLock, like Mutex, will become poisoned on a panic. Note, however, that an RwLock may only be poisoned if a panic occurs while it is locked exclusively (write mode). If a panic occurs in any reader, then the lock will not be poisoned.