What is the Python Global Interpreter Lock (GIL)

The Python Global Interpreter Lock (GIL) is a mutex that protects access to Python objects, preventing multiple threads from executing Python bytecode at once. This means that even in a multi-threaded program, only one thread can execute Python code at a time. The GIL's primary purpose is to ensure thread safety when accessing Python objects, but it can also be a hindrance to multi-threaded performance in CPU-bound programs.

When a thread acquires the GIL, it can execute Python code until it releases the GIL or is preempted by the interpreter. For I/O-bound programs, this may not be an issue, but for CPU-bound processes, the GIL can be a significant bottleneck in performance, as it prevents true parallel execution of threads.

Example

# This is a Python example demonstrating the effect of GIL import threading counter = 0 def increment(): global counter for _ in range(100000): counter += 1 threads = [] for i in range(10): thread = threading.Thread(target=increment) threads.append(thread) thread.start() for thread in threads: thread.join() print(counter) # Expected output: 1000000

Python Global Interpreter Lock GIL Multi-threading Performance Bottleneck

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