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From GitBox <...@apache.org>
Subject [GitHub] [zookeeper] anmolnar commented on a change in pull request #831: ZOOKEEPER-3286: xid wrap-around causes connection loss/segfault when hitting predefined XIDs
Date Mon, 11 Mar 2019 22:06:37 GMT
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_r264450447
 
 

 ##########
 File path: zookeeper-client/zookeeper-client-c/src/st_adaptor.c
 ##########
 @@ -77,11 +77,11 @@ int32_t inc_ref_counter(zhandle_t* zh,int i)
 
 int32_t get_xid()
 {
-    static int32_t xid = -1;
-    if (xid == -1) {
-        xid = time(0);
-    }
-    return xid++;
+    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 xid++ & ~(1<<31);
 
 Review comment:
   I'm not a C expert, but I believe C coders generally prefer magic bitwise operations to
gain performance.

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