@@ -0,0 +1,5 @@
+At Python exit, sometimes a thread holding the GIL can wait forever for a
+thread (usually a daemon thread) which requested to drop the GIL, whereas
+the thread already exited. To fix the race condition, the thread which
+requested the GIL drop now resets its request before exiting. Issue
+discovered and analyzed by Mingliang ZHAO. Patch by Victor Stinner.
@@ -239,6 +239,7 @@ take_gil(PyThreadState *tstate)
         goto _ready;
     }
 
+    int drop_requested = 0;
     while (_Py_atomic_load_relaxed(&gil->locked)) {
         unsigned long saved_switchnum = gil->switch_number;
 
@@ -254,11 +255,21 @@ take_gil(PyThreadState *tstate)
         {
             if (tstate_must_exit(tstate)) {
                 MUTEX_UNLOCK(gil->mutex);
+                // gh-96387: If the loop requested a drop request in a previous
+                // iteration, reset the request. Otherwise, drop_gil() can
+                // block forever waiting for the thread which exited. Drop
+                // requests made by other threads are also reset: these threads
+                // may have to request again a drop request (iterate one more
+                // time).
+                if (drop_requested) {
+                    RESET_GIL_DROP_REQUEST(interp);
+                }
                 PyThread_exit_thread();
             }
             assert(is_tstate_valid(tstate));
 
             SET_GIL_DROP_REQUEST(interp);
+            drop_requested = 1;
         }
     }
Original file line number	Diff line number	Diff line change
`@@ -239,6 +239,7 @@ take_gil(PyThreadState *tstate)`
`239`	`239`	`goto _ready;`
`240`	`240`	`}`
`241`	`241`
	`242`	`+ int drop_requested = 0;`
`242`	`243`	`while (_Py_atomic_load_relaxed(&gil->locked)) {`
`243`	`244`	`unsigned long saved_switchnum = gil->switch_number;`
`244`	`245`
`@@ -254,11 +255,21 @@ take_gil(PyThreadState *tstate)`
`254`	`255`	`{`
`255`	`256`	`if (tstate_must_exit(tstate)) {`
`256`	`257`	`MUTEX_UNLOCK(gil->mutex);`
	`258`	`+ // gh-96387: If the loop requested a drop request in a previous`
	`259`	`+ // iteration, reset the request. Otherwise, drop_gil() can`
	`260`	`+ // block forever waiting for the thread which exited. Drop`
	`261`	`+ // requests made by other threads are also reset: these threads`
	`262`	`+ // may have to request again a drop request (iterate one more`
	`263`	`+ // time).`
	`264`	`+ if (drop_requested) {`
	`265`	`+ RESET_GIL_DROP_REQUEST(interp);`
	`266`	`+ }`
`257`	`267`	`PyThread_exit_thread();`
`258`	`268`	`}`
`259`	`269`	`assert(is_tstate_valid(tstate));`
`260`	`270`
`261`	`271`	`SET_GIL_DROP_REQUEST(interp);`
	`272`	`+ drop_requested = 1;`
`262`	`273`	`}`
`263`	`274`	`}`
`264`	`275`