You have C extension code in that you want to execute concurrently with other threads

in the Python interpreter. To do this, you need to release and reacquire the global in‐

terpreter lock (GIL).

In C extension code, the GIL can be released and reacquired by inserting the following

macros in the code:

#include "Python.h"

PyObject *pyfunc(PyObject *self, PyObject *args) {

The GIL can only safely be released if you can guarantee that no Python C API functions

will be executed in the C code. Typical examples where the GIL might be released are

in computationally intensive code that performs calculations on C arrays (e.g., in ex‐

tensions such as numpy) or in code where blocking I/O operations are going to be per‐

formed (e.g., reading or writing on a file descriptor).

While the GIL is released, other Python threads are allowed to execute in the interpreter.

The Py_END_ALLOW_THREADS macro blocks execution until the calling threads reacquires

the GIL in the interpreter.