lukijakirjoittajalukko

Lukijakirjoittajalukko, often translated as reader-writer lock or shared-exclusive lock, is a synchronization primitive used in computer science to manage concurrent access to a shared resource. It allows multiple threads or processes to read the resource simultaneously but restricts writing access to a single thread or process at a time.

The primary purpose of a lukijakirjoittajalukko is to improve performance in scenarios where reads are significantly more frequent than writes. By permitting concurrent reads, it avoids unnecessary blocking that would occur with a simple mutual exclusion lock (mutex). When a thread wishes to write to the resource, it must acquire an exclusive lock, which prevents any other threads, whether readers or writers, from accessing the resource until the write operation is complete and the lock is released.

There are typically two main operations associated with a lukijakirjoittajalukko: acquiring a read lock and acquiring a write lock. Acquiring a read lock is usually non-blocking if no write lock is held. Multiple threads can hold a read lock concurrently. Acquiring a write lock, however, is exclusive. If any read locks are held, a thread attempting to acquire a write lock will block until all read locks are released. Similarly, if a write lock is held, any thread attempting to acquire either a read or a write lock will block.

While effective for read-heavy workloads, lukijakirjoittajalukot can introduce potential issues such as writer starvation. If reads are extremely frequent, writers might have difficulty acquiring the exclusive lock, leading to delays in updates. Different implementations of lukijakirjoittajalukko may employ various strategies to mitigate such issues.