Fix an issue that I noticed in autoservice while mmichelson and I were debugging

a different problem.  I noticed that it was theoretically possible for two threads
to attempt to start the autoservice thread at the same time.  This change makes the
process of starting the autoservice thread, thread-safe.


git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.4@115990 65c4cc65-6c06-0410-ace0-fbb531ad65f3

main/autoservice.c

@@ -201,25 +201,29 @@ int ast_autoservice_start(struct ast_channel *chan)
 	ast_channel_unlock(chan);
 
 	AST_LIST_LOCK(&aslist);
-	if (AST_LIST_EMPTY(&aslist))
+
+	if (AST_LIST_EMPTY(&aslist) && asthread != AST_PTHREADT_NULL) {
 		ast_cond_signal(&as_cond);
+	}
+
 	AST_LIST_INSERT_HEAD(&aslist, as, list);
-	AST_LIST_UNLOCK(&aslist);
 
 	if (asthread == AST_PTHREADT_NULL) { /* need start the thread */
 		if (ast_pthread_create_background(&asthread, NULL, autoservice_run, NULL)) {
 			ast_log(LOG_WARNING, "Unable to create autoservice thread :(\n");
 			/* There will only be a single member in the list at this point,
 			   the one we just added. */
-			AST_LIST_LOCK(&aslist);
 			AST_LIST_REMOVE(&aslist, as, list);
-			AST_LIST_UNLOCK(&aslist);
 			free(as);
+			asthread = AST_PTHREADT_NULL;
 			res = -1;
-		} else
+		} else {
 			pthread_kill(asthread, SIGURG);
+		}
 	}
 
+	AST_LIST_UNLOCK(&aslist);
+
 	return res;
 }