PyGILState_Release(): If we need to delete the TLS entry for this thread,

that must be done under protection of the GIL, for reasons explained in
new comments.

diff --git a/Python/pystate.c b/Python/pystate.c
index ba9be971b8d200af5591eddcbfe19243bdf55180..703ce482001c3c1bd218ad819a2ddd1ee2c3fc50 100644 (file)
--- a/Python/pystate.c
+++ b/Python/pystate.c
@@ -472,24 +472,31 @@ PyGILState_Release(PyGILState_STATE oldstate)
        assert(tcur->gilstate_counter >= 0); /* illegal counter value */
 
        /* If we are about to destroy this thread-state, we must
-          clear it while the lock is held, as destructors may run
-       */
+        * clear it while the lock is held, as destructors may run.
+        * In addition, we have to delete out TLS entry, which is keyed
+        * by thread id, while the GIL is held:  the thread calling us may
+        * go away, and a new thread may be created with the same thread
+        * id.  If we don't delete our TLS until after the GIL is released,
+        * that new thread may manage to insert a TLS value with the same
+        * thread id as ours, and then we'd erroneously delete it.
+        */
        if (tcur->gilstate_counter == 0) {
                /* can't have been locked when we created it */
                assert(oldstate == PyGILState_UNLOCKED);
                PyThreadState_Clear(tcur);
+               /* Delete this thread from our TLS */
+               PyThread_delete_key_value(autoTLSkey);
        }
 
        /* Release the lock if necessary */
        if (oldstate == PyGILState_UNLOCKED)
                PyEval_ReleaseThread(tcur);
 
-       /* Now complete destruction of the thread if necessary */
-       if (tcur->gilstate_counter == 0) {
-               /* Delete this thread from our TLS */
-               PyThread_delete_key_value(autoTLSkey);
-               /* Delete the thread-state */
+       /* Now complete destruction of the thread if necessary.  This
+        * couldn't be done before PyEval_ReleaseThread() because
+        * PyThreadState_Delete doesn't allow deleting the current thread.
+        */
+       if (tcur->gilstate_counter == 0)
                PyThreadState_Delete(tcur);
-       }
 }
 #endif /* WITH_THREAD */