bpo-31976: Fix race condition when flushing a file is slow. (#4331)
diff --git a/Modules/_io/bufferedio.c b/Modules/_io/bufferedio.c
index edc4ba5..1ae7a70 100644
--- a/Modules/_io/bufferedio.c
+++ b/Modules/_io/bufferedio.c
@@ -347,9 +347,10 @@
}
#define IS_CLOSED(self) \
+ (!self->buffer || \
(self->fast_closed_checks \
? _PyFileIO_closed(self->raw) \
- : buffered_closed(self))
+ : buffered_closed(self)))
#define CHECK_CLOSED(self, error_msg) \
if (IS_CLOSED(self)) { \
@@ -1971,14 +1972,17 @@
Py_off_t offset;
CHECK_INITIALIZED(self)
- if (IS_CLOSED(self)) {
- PyErr_SetString(PyExc_ValueError, "write to closed file");
- return NULL;
- }
if (!ENTER_BUFFERED(self))
return NULL;
+ /* Issue #31976: Check for closed file after acquiring the lock. Another
+ thread could be holding the lock while closing the file. */
+ if (IS_CLOSED(self)) {
+ PyErr_SetString(PyExc_ValueError, "write to closed file");
+ goto error;
+ }
+
/* Fast path: the data to write can be fully buffered. */
if (!VALID_READ_BUFFER(self) && !VALID_WRITE_BUFFER(self)) {
self->pos = 0;