gh-116908: Only write to _pending_calls.calls_to_do with atomic operations (#117044)

swtaarrs · web-flow · commit 9221ef2d8cb7 · 2024-03-20T11:18:26.000-04:00
These writes to `pending-&gt;calls_to_do` need to be atomic, because other threads
can read (atomically) from `calls_to_do` without holding `pending-&gt;mutex`.
diff --git a/Python/ceval_gil.c b/Python/ceval_gil.c
@@ -671,7 +671,7 @@ _push_pending_call(struct _pending_calls *pending,
     pending->calls[i].flags = flags;
     pending->last = j;
     assert(pending->calls_to_do < NPENDINGCALLS);
-    pending->calls_to_do++;
+    _Py_atomic_add_int32(&pending->calls_to_do, 1);
     return 0;
 }
 
@@ -701,7 +701,7 @@ _pop_pending_call(struct _pending_calls *pending,
         pending->calls[i] = (struct _pending_call){0};
         pending->first = (i + 1) % NPENDINGCALLS;
         assert(pending->calls_to_do > 0);
-        pending->calls_to_do--;
+        _Py_atomic_add_int32(&pending->calls_to_do, -1);
     }
 }
 

Original file line number	Diff line number	Diff line change
`@@ -671,7 +671,7 @@ _push_pending_call(struct _pending_calls *pending,`
`671`	`671`	`pending->calls[i].flags = flags;`
`672`	`672`	`pending->last = j;`
`673`	`673`	`assert(pending->calls_to_do < NPENDINGCALLS);`
`674`		`- pending->calls_to_do++;`
	`674`	`+ _Py_atomic_add_int32(&pending->calls_to_do, 1);`
`675`	`675`	`return 0;`
`676`	`676`	`}`
`677`	`677`
`@@ -701,7 +701,7 @@ _pop_pending_call(struct _pending_calls *pending,`
`701`	`701`	`pending->calls[i] = (struct _pending_call){0};`
`702`	`702`	`pending->first = (i + 1) % NPENDINGCALLS;`
`703`	`703`	`assert(pending->calls_to_do > 0);`
`704`		`- pending->calls_to_do--;`
	`704`	`+ _Py_atomic_add_int32(&pending->calls_to_do, -1);`
`705`	`705`	`}`
`706`	`706`	`}`
`707`	`707`