Lock Convoy

In computer science, a lock convoy is a performance problem that can occur when using locks for concurrency control in a multithreaded application.

A lock convoy occurs when multiple threads of equal priority contend repeatedly for the same lock. Unlike deadlock and livelock situations, the threads in a lock convoy do progress; however, each time a thread attempts to acquire the lock and fails, it relinquishes the remainder of its scheduling quantum and forces a context switch. The overhead of repeated context switches and underutilization of scheduling quanta degrade overall performance.

Lock convoys often occur when concurrency control primitives such as critical sections serialize access to a commonly used resource, such as a memory heap or a thread pool. They can sometimes be addressed by using non-locking alternatives such as lock-free algorithms or by altering the relative priorities of the contending threads.