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gh-116522: Refactor _PyThreadState_DeleteExcept (#117131)

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Split `_PyThreadState_DeleteExcept` into two functions:

- `_PyThreadState_RemoveExcept` removes all thread states other than one
  passed as an argument. It returns the removed thread states as a
  linked list.

- `_PyThreadState_DeleteList` deletes those dead thread states. It may
  call destructors, so we want to "start the world" before calling
  `_PyThreadState_DeleteList` to avoid potential deadlocks.
This commit is contained in:
Sam Gross 2024-03-21 14:21:02 -04:00 • committed by GitHub
parent 50369e6c34
commit 1f72fb5447
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5 changed files with 41 additions and 23 deletions
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39
Python/pystate.c
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@ -1763,15 +1763,17 @@ PyThreadState_DeleteCurrent(void)
}
/*
* Delete all thread states except the one passed as argument.
* Note that, if there is a current thread state, it *must* be the one
* passed as argument. Also, this won't touch any other interpreters
* than the current one, since we don't know which thread state should
* be kept in those other interpreters.
*/
void
_PyThreadState_DeleteExcept(PyThreadState *tstate)
// Unlinks and removes all thread states from `tstate->interp`, with the
// exception of the one passed as an argument. However, it does not delete
// these thread states. Instead, it returns the removed thread states as a
// linked list.
//
// Note that if there is a current thread state, it *must* be the one
// passed as argument. Also, this won't touch any interpreters other
// than the current one, since we don't know which thread state should
// be kept in those other interpreters.
PyThreadState *
_PyThreadState_RemoveExcept(PyThreadState *tstate)
{
assert(tstate != NULL);
PyInterpreterState *interp = tstate->interp;
@ -1783,8 +1785,7 @@ _PyThreadState_DeleteExcept(PyThreadState *tstate)
HEAD_LOCK(runtime);
/* Remove all thread states, except tstate, from the linked list of
thread states. This will allow calling PyThreadState_Clear()
without holding the lock. */
thread states. */
PyThreadState *list = interp->threads.head;
if (list == tstate) {
list = tstate->next;
@ -1799,11 +1800,19 @@ _PyThreadState_DeleteExcept(PyThreadState *tstate)
interp->threads.head = tstate;
HEAD_UNLOCK(runtime);
_PyEval_StartTheWorldAll(runtime);
return list;
}
// Deletes the thread states in the linked list `list`.
//
// This is intended to be used in conjunction with _PyThreadState_RemoveExcept.
void
_PyThreadState_DeleteList(PyThreadState *list)
{
// The world can't be stopped because we PyThreadState_Clear() can
// call destructors.
assert(!_PyRuntime.stoptheworld.world_stopped);
/* Clear and deallocate all stale thread states. Even if this
executes Python code, we should be safe since it executes
in the current thread, not one of the stale threads. */
PyThreadState *p, *next;
for (p = list; p; p = next) {
next = p->next;