Global Interpreter Lock (abbr. GIL) is a mutual exclusion lock held by a programming language interpreter thread to avoid sharing code that is not thread-safe with other threads. There is always one GIL for one interpreter process. Usage of a Global Interpreter Lock in a language effectively limits concurrency of a single interpreter process with multiple threads -- there is no or very little increase in speed when running the process on a multiprocessor machine. The reasons of employing such a lock include:
- increased speed of single-threaded programs (no necessity to acquire or release locks on all data structures separately)
- easy integration of C libraries that usually are not thread-safe.
Applications written in languages with a GIL have to use separate processes (i.e. interpreters) to achieve full concurrency, as each interpreter has its own GIL. Languages that implement a Global Interpreter Lock are, among others:
