Callbacks pended by `Py_AddPendingCall` will never be invoked if the main thread doesn't release GIL
@markshannon 已经在做这个了。
开始于 2022年8月23日。
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描述
According to the Py_AddPendingCall's document (https://docs.python.org/3/c-api/init.html#c.Py_AddPendingCall), a pended callback function should be invoked when:
It will be called asynchronously with respect to normally running Python code, but with both these conditions met:
- on a bytecode boundary;
- with the main thread holding the global interpreter lock.
So if the main thread is processing an endless loop like:
while True:
pass
A callback pended from another thread by Py_AddPendingCall should still be able to be invoked.
It works in Python 3.8.13, but doesn't work in Python 3.9.13. In 3.9.13, the callback pended by Py_AddPendingCall will never be invoked in this case.
The root cause may be here: https://github.com/python/cpython/pull/19091/files#diff-c22186367cbe20233e843261998dc027ae5f1f8c0d2e778abfa454ae74cc59deL152-L153. After this change, pending a callback from a non-main thread will not set the ceval2->eval_breaker to be true. So when the main thread is trapped in an endless loop and keeps holding GIL, pending callbacks will never be invoked.
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