Fix the async free() and disconnect() functions

To make sure that these functions can also be called from functions
other than command callbacks, the flag IN_CALLBACK is introduced that
holds whether the context is currently executing a callback. If so,
redisAsyncFree() and redisAsyncDisconnect() should delegate their task
to the reply processor to avoid segfaults.

async.c

@@ -169,33 +169,19 @@ static void __redisAsyncFree(redisAsyncContext *ac) {
     redisFree(c);
 }
 
-/* Free's the async context. When REDIS_CONNECTED is set, it could only have
+/* Free the async context. When this function is called from a callback,
- * been called from a command callback so we need to let control return to
+ * control needs to be returned to redisProcessCallbacks() before actual
- * redisProcessCallbacks() before free'ing can continue.
+ * free'ing. To do so, a flag is set on the context which is picked up by
- *
+ * redisProcessCallbacks(). Otherwise, the context is immediately free'd. */
- * When REDIS_CONNECTED is not set, the first write event has not yet fired and
- * we can free immediately. */
 void redisAsyncFree(redisAsyncContext *ac) {
     redisContext *c = &(ac->c);
-    if (c->flags & REDIS_CONNECTED) {
+    if (c->flags & REDIS_IN_CALLBACK) {
         c->flags |= REDIS_FREEING;
     } else {
         __redisAsyncFree(ac);
     }
 }
 
-/* Tries to do a clean disconnect from Redis, meaning it stops new commands
- * from being issued, but tries to flush the output buffer and execute
- * callbacks for all remaining replies.
- *
- * This functions is generally called from within a callback, so the
- * processCallbacks function will pick up the flag when there are no
- * more replies. */
-void redisAsyncDisconnect(redisAsyncContext *ac) {
-    redisContext *c = &(ac->c);
-    c->flags |= REDIS_DISCONNECTING;
-}
-
 /* Helper function to make the disconnect happen and clean up. */
 static void __redisAsyncDisconnect(redisAsyncContext *ac) {
     redisContext *c = &(ac->c);
@@ -214,14 +200,32 @@ static void __redisAsyncDisconnect(redisAsyncContext *ac) {
 
         /* Execute pending callbacks with NULL reply. */
         while (__redisShiftCallback(&ac->replies,&cb) == REDIS_OK) {
-            if (cb.fn != NULL)
+            if (cb.fn != NULL) {
+                c->flags |= REDIS_IN_CALLBACK;
                 cb.fn(ac,NULL,cb.privdata);
+                c->flags &= ~REDIS_IN_CALLBACK;
+            }
         }
     }
 
     __redisAsyncFree(ac);
 }
 
+/* Tries to do a clean disconnect from Redis, meaning it stops new commands
+ * from being issued, but tries to flush the output buffer and execute
+ * callbacks for all remaining replies. When this function is called from a
+ * callback, there might be more replies and we can safely defer disconnecting
+ * to redisProcessCallbacks(). Otherwise, we can only disconnect immediately
+ * when there are no pending callbacks. */
+void redisAsyncDisconnect(redisAsyncContext *ac) {
+    redisContext *c = &(ac->c);
+    if (c->flags & REDIS_IN_CALLBACK || ac->replies.head != NULL) {
+        c->flags |= REDIS_DISCONNECTING;
+    } else {
+        __redisAsyncDisconnect(ac);
+    }
+}
+
 void redisProcessCallbacks(redisAsyncContext *ac) {
     redisContext *c = &(ac->c);
     redisCallback cb;
@@ -245,7 +249,9 @@ void redisProcessCallbacks(redisAsyncContext *ac) {
         /* Shift callback and execute it */
         assert(__redisShiftCallback(&ac->replies,&cb) == REDIS_OK);
         if (cb.fn != NULL) {
+            c->flags |= REDIS_IN_CALLBACK;
             cb.fn(ac,reply,cb.privdata);
+            c->flags &= ~REDIS_IN_CALLBACK;
 
             /* Proceed with free'ing when redisAsyncFree() was called. */
             if (c->flags & REDIS_FREEING) {

hiredis.h

@@ -68,6 +68,9 @@
  * up as soon as possible. */
 #define REDIS_FREEING 0x8
 
+/* Flag that is set when an async callback is executed. */
+#define REDIS_IN_CALLBACK 0x10
+
 #define REDIS_REPLY_STRING 1
 #define REDIS_REPLY_ARRAY 2
 #define REDIS_REPLY_INTEGER 3