1 files changed, 51 insertions, 5 deletions

diff --git a/chardev/char-io.c b/chardev/char-io.c
index 4451128cba..dab77b112e 100644
--- a/chardev/char-io.c
+++ b/chardev/char-io.c
@@ -33,6 +33,7 @@ typedef struct IOWatchPoll {
     IOCanReadHandler *fd_can_read;
     GSourceFunc fd_read;
     void *opaque;
+    GMainContext *context;
 } IOWatchPoll;
 
 static IOWatchPoll *io_watch_poll_from_source(GSource *source)
@@ -50,28 +51,59 @@ static gboolean io_watch_poll_prepare(GSource *source,
         return FALSE;
     }
 
+    /*
+     * We do not register the QIOChannel watch as a child GSource.
+     * The 'prepare' function on the parent GSource will be
+     * skipped if a child GSource's 'prepare' function indicates
+     * readiness. We need this prepare function be guaranteed
+     * to run on *every* iteration of the main loop, because
+     * it is critical to ensure we remove the QIOChannel watch
+     * if 'fd_can_read' indicates the frontend cannot receive
+     * more data.
+     */
     if (now_active) {
         iwp->src = qio_channel_create_watch(
             iwp->ioc, G_IO_IN | G_IO_ERR | G_IO_HUP | G_IO_NVAL);
         g_source_set_callback(iwp->src, iwp->fd_read, iwp->opaque, NULL);
-        g_source_add_child_source(source, iwp->src);
-        g_source_unref(iwp->src);
+        g_source_attach(iwp->src, iwp->context);
     } else {
-        g_source_remove_child_source(source, iwp->src);
+        g_source_destroy(iwp->src);
+        g_source_unref(iwp->src);
         iwp->src = NULL;
     }
     return FALSE;
 }
 
+static gboolean io_watch_poll_check(GSource *source)
+{
+    return FALSE;
+}
+
 static gboolean io_watch_poll_dispatch(GSource *source, GSourceFunc callback,
                                        gpointer user_data)
 {
-    return G_SOURCE_CONTINUE;
+    abort();
+}
+
+static void io_watch_poll_finalize(GSource *source)
+{
+    /*
+     * Due to a glib bug, removing the last reference to a source
+     * inside a finalize callback causes recursive locking (and a
+     * deadlock).  This is not a problem inside other callbacks,
+     * including dispatch callbacks, so we call io_remove_watch_poll
+     * to remove this source.  At this point, iwp->src must
+     * be NULL, or we would leak it.
+     */
+    IOWatchPoll *iwp = io_watch_poll_from_source(source);
+    assert(iwp->src == NULL);
 }
 
 static GSourceFuncs io_watch_poll_funcs = {
     .prepare = io_watch_poll_prepare,
+    .check = io_watch_poll_check,
     .dispatch = io_watch_poll_dispatch,
+    .finalize = io_watch_poll_finalize,
 };
 
 GSource *io_add_watch_poll(Chardev *chr,
@@ -91,6 +123,7 @@ GSource *io_add_watch_poll(Chardev *chr,
     iwp->ioc = ioc;
     iwp->fd_read = (GSourceFunc) fd_read;
     iwp->src = NULL;
+    iwp->context = context;
 
     name = g_strdup_printf("chardev-iowatch-%s", chr->label);
     g_source_set_name((GSource *)iwp, name);
@@ -101,10 +134,23 @@ GSource *io_add_watch_poll(Chardev *chr,
     return (GSource *)iwp;
 }
 
+static void io_remove_watch_poll(GSource *source)
+{
+    IOWatchPoll *iwp;
+
+    iwp = io_watch_poll_from_source(source);
+    if (iwp->src) {
+        g_source_destroy(iwp->src);
+        g_source_unref(iwp->src);
+        iwp->src = NULL;
+    }
+    g_source_destroy(&iwp->parent);
+}
+
 void remove_fd_in_watch(Chardev *chr)
 {
     if (chr->gsource) {
-        g_source_destroy(chr->gsource);
+        io_remove_watch_poll(chr->gsource);
         chr->gsource = NULL;
     }
 }