New submission from STINNER Victor <[email protected]>:
When a thread gets a signal, SIGNAL_PENDING_SIGNALS() sets signals_pending to 1
and eval_breaker to 1. In this case, _PyEval_EvalFrameDefault() calls
handle_signals(), but since it's not the main thread, it does nothing and
signals_pending value remains 1. Moreover, eval_breaker value remains 1 which
means that the following code will be called before executing *each* bytecode
instruction.
if (_Py_atomic_load_relaxed(eval_breaker)) {
(...)
opcode = _Py_OPCODE(*next_instr);
if (opcode == SETUP_FINALLY || ...) {
...
}
if (_Py_atomic_load_relaxed(&ceval->signals_pending)) {
if (handle_signals(tstate) != 0) {
goto error;
}
}
if (_Py_atomic_load_relaxed(&ceval->pending.calls_to_do)) {
...
}
if (_Py_atomic_load_relaxed(&ceval->gil_drop_request)) {
...
}
if (tstate->async_exc != NULL) {
...
}
}
This is inefficient.
I'm working on a PR modifying SIGNAL_PENDING_SIGNALS() to not set eval_breaker
to 1 if the current thread is not the main thread.
----------
components: Interpreter Core
messages: 364580
nosy: vstinner
priority: normal
severity: normal
status: open
title: Inefficient sigal handling in multithreaded applications
versions: Python 3.9
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Python tracker <[email protected]>
<https://bugs.python.org/issue40010>
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