don't use object sharing inside I/O threads, as a fix for a well known instability of VM introduced with the new object sharing code

1 files changed, 9 insertions, 2 deletions

diff --git a/src/object.c b/src/object.c
index 772637ce0..25567e2ac 100644
--- a/src/object.c
+++ b/src/object.c
@@ -213,8 +213,15 @@ robj *tryObjectEncoding(robj *o) {
     /* Check if we can represent this string as a long integer */
     if (isStringRepresentableAsLong(s,&value) == REDIS_ERR) return o;
 
-    /* Ok, this object can be encoded */
-    if (value >= 0 && value < REDIS_SHARED_INTEGERS) {
+    /* Ok, this object can be encoded...
+     *
+     * Can I use a shared object? Only if the object is inside a given
+     * range and if this is the main thread, sinc when VM is enabled we
+     * have the constraint that I/O thread should only handle non-shared
+     * objects, in order to avoid race conditions (we don't have per-object
+     * locking). */
+    if (value >= 0 && value < REDIS_SHARED_INTEGERS &&
+        pthread_equal(pthread_self(),server.mainthread)) {
         decrRefCount(o);
         incrRefCount(shared.integers[value]);
         return shared.integers[value];