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gh-120837: Update _Py_DumpExtensionModules to be async-signal-safe #121051

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merged 8 commits into from
Jun 27, 2024
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gh-120837: Update _Py_DumpExtensionModules to be async-signal-safe #121051

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gh-120837: Update _Py_DumpExtensionModules to be async-signal-safe
corona10 Jun 26, 2024
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nit
corona10 Jun 26, 2024
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fix
corona10 Jun 26, 2024
e7f24af
Address code review
corona10 Jun 27, 2024
ed9bb3b
Address code review
corona10 Jun 27, 2024
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nit
corona10 Jun 27, 2024
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Address code review
corona10 Jun 27, 2024
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Address code review
corona10 Jun 27, 2024
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39 changes: 37 additions & 2 deletions Python/pylifecycle.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2897,6 +2897,31 @@ fatal_error_exit(int status)
}
}

static inline int
acquire_dict_lock_for_dump(PyObject *obj) {
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#ifdef Py_GIL_DISABLED
PyMutex *mutex = &obj->ob_mutex;
if (_PyMutex_LockTimed(mutex, 0, 0) == PY_LOCK_ACQUIRED) {
return 0;
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}
return -1;
#else
return 0;
#endif
}

static inline void
release_dict_lock_for_dump(PyObject *obj) {
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#ifdef Py_GIL_DISABLED
PyMutex *mutex = &obj->ob_mutex;
uint8_t expected = _Py_LOCKED;
// We can not call PyMutex_Unlock because it's not async-signal-safe.
// So not to wake up other threads, we just use a simple CAS in here.
_Py_atomic_compare_exchange_uint8(&mutex->_bits, &expected, _Py_UNLOCKED);
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Do we have to run for loop to prevent CAS failure?

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I think this should be a _Py_atomic_store_uint8(&mutex->_bits, _Py_UNLOCKED)

#else
return;
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The #else return; doesn't do anything. I would delete it, but up to you.

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Done!

#endif
}

// Dump the list of extension modules of sys.modules, excluding stdlib modules
// (sys.stdlib_module_names), into fd file descriptor.
Expand Down Expand Up @@ -2924,13 +2949,18 @@ _Py_DumpExtensionModules(int fd, PyInterpreterState *interp)
PyObject *stdlib_module_names = NULL;
if (interp->sysdict != NULL) {
pos = 0;
while (PyDict_Next(interp->sysdict, &pos, &key, &value)) {
if (acquire_dict_lock_for_dump(interp->sysdict) < 0) {
// If we cannot acquire the lock, just don't dump the list of extension modules.
return;
}
while (_PyDict_Next(interp->sysdict, &pos, &key, &value, NULL)) {
if (PyUnicode_Check(key)
&& PyUnicode_CompareWithASCIIString(key, "stdlib_module_names") == 0) {
stdlib_module_names = value;
break;
}
}
release_dict_lock_for_dump(interp->sysdict);
}
// If we failed to get sys.stdlib_module_names or it's not a frozenset,
// don't exclude stdlib modules.
Expand All @@ -2942,7 +2972,11 @@ _Py_DumpExtensionModules(int fd, PyInterpreterState *interp)
int header = 1;
Py_ssize_t count = 0;
pos = 0;
while (PyDict_Next(modules, &pos, &key, &value)) {
if (acquire_dict_lock_for_dump(modules) < 0) {
// If we cannot acquire the lock, just don't dump the list of extension modules.
return;
}
while (_PyDict_Next(modules, &pos, &key, &value, NULL)) {
if (!PyUnicode_Check(key)) {
continue;
}
Expand Down Expand Up @@ -2983,6 +3017,7 @@ _Py_DumpExtensionModules(int fd, PyInterpreterState *interp)
_Py_DumpASCII(fd, key);
count++;
}
release_dict_lock_for_dump(modules);

if (count) {
PUTS(fd, " (total: ");
Expand Down
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