MediaCaptureDevicesDispatcher: Disable getDefaultScreenId on X11

Not needed and triggers race condition.

Task-number: QTBUG-69007
Change-Id: Id57ba527387e5dbe44a8dd6c5a49e7278403ce64
Reviewed-by: Michal Klocek <michal.klocek@qt.io>

1 files changed, 10 insertions, 1 deletions

diff --git a/src/core/media_capture_devices_dispatcher.cpp b/src/core/media_capture_devices_dispatcher.cpp
index 87fe543b1..7f521dd10 100644
--- a/src/core/media_capture_devices_dispatcher.cpp
+++ b/src/core/media_capture_devices_dispatcher.cpp
@@ -123,7 +123,16 @@ std::unique_ptr<content::MediaStreamUI> getDevicesForDesktopCapture(content::Med
 
 content::DesktopMediaID getDefaultScreenId()
 {
-#if BUILDFLAG(ENABLE_WEBRTC)
+    // While this function is executing another thread may also want to create a
+    // DesktopCapturer [1]. Unfortunately, creating a DesktopCapturer is not
+    // thread safe on X11 due to the use of webrtc::XErrorTrap. It's safe to
+    // disable this code on X11 since we don't actually need to create a
+    // DesktopCapturer to get the screen id anyway
+    // (ScreenCapturerLinux::GetSourceList always returns 0 as the id).
+    //
+    // [1]: webrtc::InProcessVideoCaptureDeviceLauncher::DoStartDesktopCaptureOnDeviceThread
+
+#if BUILDFLAG(ENABLE_WEBRTC) && !defined(USE_X11)
     // Source id patterns are different across platforms.
     // On Linux, the hardcoded value "0" is used.
     // On Windows, the screens are enumerated consecutively in increasing order from 0.