The Global interpreter lock(GIL) is a mechanism in CPython implementation to ensure only one thread is running at a time. This means that even if we use threads to try to speed up our programs’ runtime, this will not work because, in the end, the interpreter will block that two or more threads will be executed in parallel.
As the name suggests, the GIL is a locker that a thread gets when it starts and releases at some moment. There is only one locker, so two threads cannot get it simultaneously. As a result, our program with threads will be slower than the same program without threads because of the time to create threads and not take advantage of them. However, this is true only for CPU bound problems, which requires a large amount of CPU time to process, like inverse matrix. For I/O bound problems, CPython releases the locker as soon as an I/O call happens. We still have only one thread running at once on the CPU, but now, a thread does not block other threads while waiting for the I/O result.
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