summaryrefslogtreecommitdiffstats
path: root/Python
diff options
context:
space:
mode:
authorTim Peters <tim.peters@gmail.com>2004-10-10 01:58:44 (GMT)
committerTim Peters <tim.peters@gmail.com>2004-10-10 01:58:44 (GMT)
commit263091e38835bb96d06928ea56e4db73c1d2b7c1 (patch)
tree718d13932945cf9b630e643d61e4f27ff02cab39 /Python
parent5c14e6498a9ca90f482d9d70c6df92d508aa8ff9 (diff)
downloadcpython-263091e38835bb96d06928ea56e4db73c1d2b7c1.zip
cpython-263091e38835bb96d06928ea56e4db73c1d2b7c1.tar.gz
cpython-263091e38835bb96d06928ea56e4db73c1d2b7c1.tar.bz2
find_key(): This routine wasn't thread-correct, and accounts for the
release-build failures noted in bug 1041645. This is a critical bugfix. I'm not going to backport it, though (no time).
Diffstat (limited to 'Python')
-rw-r--r--Python/thread.c22
1 files changed, 17 insertions, 5 deletions
diff --git a/Python/thread.c b/Python/thread.c
index b1ddf53..4c0edfb 100644
--- a/Python/thread.c
+++ b/Python/thread.c
@@ -209,6 +209,15 @@ static int nkeys = 0; /* PyThread_create_key() hands out nkeys+1 next */
* So when value==NULL, this acts like a pure lookup routine, and when
* value!=NULL, this acts like dict.setdefault(), returning an existing
* mapping if one exists, else creating a new mapping.
+ *
+ * Caution: this used to be too clever, trying to hold keymutex only
+ * around the "p->next = keyhead; keyhead = p" pair. That allowed
+ * another thread to mutate the list, via key deletion, concurrent with
+ * find_key() crawling over the list. Hilarity ensued. For example, when
+ * the for-loop here does "p = p->next", p could end up pointing at a
+ * record that PyThread_delete_key_value() was concurrently free()'ing.
+ * That could lead to anything, from failing to find a key that exists, to
+ * segfaults. Now we lock the whole routine.
*/
static struct key *
find_key(int key, void *value)
@@ -216,22 +225,25 @@ find_key(int key, void *value)
struct key *p;
long id = PyThread_get_thread_ident();
+ PyThread_acquire_lock(keymutex, 1);
for (p = keyhead; p != NULL; p = p->next) {
if (p->id == id && p->key == key)
- return p;
+ goto Done;
+ }
+ if (value == NULL) {
+ assert(p == NULL);
+ goto Done;
}
- if (value == NULL)
- return NULL;
p = (struct key *)malloc(sizeof(struct key));
if (p != NULL) {
p->id = id;
p->key = key;
p->value = value;
- PyThread_acquire_lock(keymutex, 1);
p->next = keyhead;
keyhead = p;
- PyThread_release_lock(keymutex);
}
+ Done:
+ PyThread_release_lock(keymutex);
return p;
}