[Spice-devel] [PATCH v7 06/14] usbredir: Spawn a different thread for device redirection flow

[Dmitry Fleytman]

From: Kirill Moizik <kmoizik at redhat.com>

On Windows when using usbdk, opening and closing USB device handle,
i.e. calling libusb_open()/libusb_unref_device() can block for a few
seconds (3-5 second more specifically on patch author's HW).

libusb_open() is called by spice_usbredir_channel_open_device().

libusb_unref_device() is called implicitly via
usbredirhost_set_device(..., NULL) from
spice_usbredir_channel_disconnect_device().

Both these calls happen on the main thread. If it blocks,
this causes the UI to freeze.

This commit makes sure libusb_open() is called from a different
thread to avoid blocking the mainloop when usbdk is used.

Following commits also move usbredirhost_set_device(..., NULL) call
to separate threads.

Since this commit introduces additional execution contexts running in
parallel to the main thread there are thread safety concerns to be secured.
Mainly there are 3 types of objects accessed by newly introduced threads:
  1. libusb contexts
  2. usbredir context
  3. redirection channels

Fortunately libusb accesses are either thread safe or already
performed by a separate thread and protected by locks as needed.

As for channels and usbredir, in order to achieve thread safety
additional locks were introduced by previous patches
in preparation to adding asynchronous contexts:

1. Channel objects data accesses from different threads protected with a
   new lock (device_connect_mutex);
2. Handling usbredir messages protected by the same new lock in order to
   ensure there are no messages processing flows in progress when device gets
   connected or disconnected.

Signed-off-by: Kirill Moizik <kmoizik at redhat.com>
Signed-off-by: Dmitry Fleytman <dfleytma at redhat.com>
---
 src/channel-usbredir.c | 40 ++++++++++++++++++++++++++++++----------
 1 file changed, 30 insertions(+), 10 deletions(-)

diff --git a/src/channel-usbredir.c b/src/channel-usbredir.c
index 9491f60..b33122a 100644
--- a/src/channel-usbredir.c
+++ b/src/channel-usbredir.c
@@ -313,6 +313,30 @@ static void spice_usbredir_channel_open_acl_cb(
 }
 #endif
 
+#ifndef USE_POLKIT
+static void
+_open_device_async_cb(GSimpleAsyncResult *simple,
+                      GObject *object,
+                      GCancellable *cancellable)
+{
+    GError *err = NULL;
+    SpiceUsbredirChannel *channel = SPICE_USBREDIR_CHANNEL(object);
+    SpiceUsbredirChannelPrivate *priv = channel->priv;
+
+    spice_usbredir_channel_lock(channel);
+
+    if (!spice_usbredir_channel_open_device(channel, &err)) {
+        g_simple_async_result_take_error(simple, err);
+        libusb_unref_device(priv->device);
+        priv->device = NULL;
+        g_boxed_free(spice_usb_device_get_type(), priv->spice_device);
+        priv->spice_device = NULL;
+    }
+
+    spice_usbredir_channel_unlock(channel);
+}
+#endif
+
 G_GNUC_INTERNAL
 void spice_usbredir_channel_connect_device_async(
                                           SpiceUsbredirChannel *channel,
@@ -324,9 +348,6 @@ void spice_usbredir_channel_connect_device_async(
 {
     SpiceUsbredirChannelPrivate *priv = channel->priv;
     GSimpleAsyncResult *result;
-#if ! USE_POLKIT
-    GError *err = NULL;
-#endif
 
     g_return_if_fail(SPICE_IS_USBREDIR_CHANNEL(channel));
     g_return_if_fail(device != NULL);
@@ -370,13 +391,12 @@ void spice_usbredir_channel_connect_device_async(
                                   channel);
     return;
 #else
-    if (!spice_usbredir_channel_open_device(channel, &err)) {
-        g_simple_async_result_take_error(result, err);
-        libusb_unref_device(priv->device);
-        priv->device = NULL;
-        g_boxed_free(spice_usb_device_get_type(), priv->spice_device);
-        priv->spice_device = NULL;
-    }
+    g_simple_async_result_run_in_thread(result,
+                                        _open_device_async_cb,
+                                        G_PRIORITY_DEFAULT,
+                                        cancellable);
+    g_object_unref(result);
+    return;
 #endif
 
 done:
-- 
2.5.0