anmolnar commented on a change in pull request #831: ZOOKEEPER-3286: xid
wrap-around causes connection loss/segfault when hitting predefined XIDs
URL: https://github.com/apache/zookeeper/pull/831#discussion_r266710758
##########
File path: zookeeper-client/zookeeper-client-c/src/mt_adaptor.c
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@@ -502,13 +502,13 @@ int32_t fetch_and_add(volatile int32_t* operand, int
incr)
}
// make sure the static xid is initialized before any threads started
-__attribute__((constructor)) int32_t get_xid()
+int32_t get_xid()
{
- static int32_t xid = -1;
- if (xid == -1) {
- xid = time(0);
- }
- return fetch_and_add(&xid,1);
+ static int32_t xid = 1;
+
+ // The XID returned should not be negative to avoid collisions
+ // with reserved XIDs, such as AUTH_XID or SET_WATCHES_XID.
+ return fetch_and_add(&xid,1) & ~(1<<31);
Review comment:
I don't think there's anything wrong with using `0` as `xid`, but I would
stick to consistent behaviour between clients anyway.
So, I vote for option 2., but let's see what other people think.
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