block/backup: deal with zero detection

[qemu.git] / iothread.c

diff --git a/iothread.c b/iothread.c
index 6fa87876e026d978c723f072f9d82fb1e9259ce9..7130be58e3e6c83640b7cf03b233c5069568e25b 100644 (file)
--- a/iothread.c
+++ b/iothread.c
@@ -53,12 +53,25 @@ static void *iothread_run(void *opaque)
     IOThread *iothread = opaque;
 
     rcu_register_thread();
-
+    /*
+     * g_main_context_push_thread_default() must be called before anything
+     * in this new thread uses glib.
+     */
+    g_main_context_push_thread_default(iothread->worker_context);
     my_iothread = iothread;
     iothread->thread_id = qemu_get_thread_id();
     qemu_sem_post(&iothread->init_done_sem);
 
     while (iothread->running) {
+        /*
+         * Note: from functional-wise the g_main_loop_run() below can
+         * already cover the aio_poll() events, but we can't run the
+         * main loop unconditionally because explicit aio_poll() here
+         * is faster than g_main_loop_run() when we do not need the
+         * gcontext at all (e.g., pure block layer iothreads).  In
+         * other words, when we want to run the gcontext with the
+         * iothread we need to pay some performance for functionality.
+         */
         aio_poll(iothread->ctx, true);
 
         /*
@@ -66,21 +79,11 @@ static void *iothread_run(void *opaque)
          * changed in previous aio_poll()
          */
         if (iothread->running && atomic_read(&iothread->run_gcontext)) {
-            GMainLoop *loop;
-
-            g_main_context_push_thread_default(iothread->worker_context);
-            iothread->main_loop =
-                g_main_loop_new(iothread->worker_context, TRUE);
-            loop = iothread->main_loop;
-
             g_main_loop_run(iothread->main_loop);
-            iothread->main_loop = NULL;
-            g_main_loop_unref(loop);
-
-            g_main_context_pop_thread_default(iothread->worker_context);
         }
     }
 
+    g_main_context_pop_thread_default(iothread->worker_context);
     rcu_unregister_thread();
     return NULL;
 }
@@ -141,6 +144,8 @@ static void iothread_instance_finalize(Object *obj)
     if (iothread->worker_context) {
         g_main_context_unref(iothread->worker_context);
         iothread->worker_context = NULL;
+        g_main_loop_unref(iothread->main_loop);
+        iothread->main_loop = NULL;
     }
     qemu_sem_destroy(&iothread->init_done_sem);
 }
@@ -153,6 +158,7 @@ static void iothread_init_gcontext(IOThread *iothread)
     source = aio_get_g_source(iothread_get_aio_context(iothread));
     g_source_attach(source, iothread->worker_context);
     g_source_unref(source);
+    iothread->main_loop = g_main_loop_new(iothread->worker_context, TRUE);
 }
 
 static void iothread_complete(UserCreatable *obj, Error **errp)