From 9f5b96225885f927727a57b6123d8550d6c373bb Mon Sep 17 00:00:00 2001

From: Johan Klokkhammer Helsing <johan.helsing@qt.io>

Date: Tue, 15 Oct 2019 09:51:43 +0200

Subject: [PATCH] Client: Fix 100ms freeze when applications do not swap after deliverUpdateRequest

[ChangeLog][QPA plugin] Fixed a 100 ms freeze that would occur if applications

did not draw after receiving a deliverUpdateRequest().

QtQuick does this at the start of animations. This should get rid of those

backingstore warnings (and also remove a 100ms freeze before animations start

in those instances).

Fixes: QTBUG-76813

Change-Id: Id366bf4a14f402fa44530ae46e7b66d9988c14f6

Reviewed-by: Paul Olav Tvete <paul.tvete@qt.io>

Reviewed-by: John Brooks <john.brooks@qt.io>

---

diff --git a/src/client/qwaylandwindow.cpp b/src/client/qwaylandwindow.cpp

index ae26ba0..8d34afd 100644

--- a/src/client/qwaylandwindow.cpp

+++ b/src/client/qwaylandwindow.cpp

@@ -1105,25 +1105,6 @@

 void QWaylandWindow::timerEvent(QTimerEvent *event)

 {

-    if (event->timerId() == mFallbackUpdateTimerId) {

-        killTimer(mFallbackUpdateTimerId);

-        mFallbackUpdateTimerId = -1;

-        qCDebug(lcWaylandBackingstore) << "mFallbackUpdateTimer timed out";

-

-        if (!isExposed()) {

-            qCDebug(lcWaylandBackingstore) << "Fallback update timer: Window not exposed,"

-                                           << "not delivering update request.";

-            return;

-        }

-

-        if (mWaitingForUpdate && hasPendingUpdateRequest() && !mWaitingForFrameCallback) {

-            qCWarning(lcWaylandBackingstore) << "Delivering update request through fallback timer,"

-                                             << "may not be in sync with display";

-            deliverUpdateRequest();

-        }

-    }

-

-

     if (mFrameCallbackTimerId.testAndSetOrdered(event->timerId(), -1)) {

         killTimer(event->timerId());

         qCDebug(lcWaylandBackingstore) << "Didn't receive frame callback in time, window should now be inexposed";

@@ -1135,6 +1116,7 @@

 void QWaylandWindow::requestUpdate()

 {

+    qCDebug(lcWaylandBackingstore) << "requestUpdate";

     Q_ASSERT(hasPendingUpdateRequest()); // should be set by QPA

     // If we have a frame callback all is good and will be taken care of there

@@ -1142,20 +1124,17 @@

         return;

     // If we've already called deliverUpdateRequest(), but haven't seen any attach+commit/swap yet

-    if (mWaitingForUpdate) {

-        // Ideally, we should just have returned here, but we're not guaranteed that the client

-        // will actually update, so start this timer to deliver another request update after a while

-        // *IF* the client doesn't update.

-        int fallbackTimeout = 100;

-        mFallbackUpdateTimerId = startTimer(fallbackTimeout);

-        return;

-    }

+    // This is a somewhat redundant behavior and might indicate a bug in the calling code, so log

+    // here so we can get this information when debugging update/frame callback issues.

+    // Continue as nothing happened, though.

+    if (mWaitingForUpdate)

+        qCDebug(lcWaylandBackingstore) << "requestUpdate called twice without committing anything";

     // Some applications (such as Qt Quick) depend on updates being delivered asynchronously,

     // so use invokeMethod to delay the delivery a bit.

     QMetaObject::invokeMethod(this, [this] {

         // Things might have changed in the meantime

-        if (hasPendingUpdateRequest() && !mWaitingForUpdate && !mWaitingForFrameCallback)

+        if (hasPendingUpdateRequest() && !mWaitingForFrameCallback)

             deliverUpdateRequest();

     }, Qt::QueuedConnection);

 }

@@ -1165,6 +1144,7 @@

 // Can be called from the render thread (without locking anything) so make sure to not make races in this method.

 void QWaylandWindow::handleUpdate()

 {

+    qCDebug(lcWaylandBackingstore) << "handleUpdate" << QThread::currentThread();

     // TODO: Should sync subsurfaces avoid requesting frame callbacks?

     QReadLocker lock(&mSurfaceLock);

     if (!isInitialized())

@@ -1175,15 +1155,6 @@

         mFrameCallback = nullptr;

     }

-    if (mFallbackUpdateTimerId != -1) {

-        // Ideally, we would stop the fallback timer here, but since we're on another thread,

-        // it's not allowed. Instead we set mFallbackUpdateTimer to -1 here, so we'll just

-        // ignore it if it times out before it's cleaned up by the invokeMethod call.

-        int id = mFallbackUpdateTimerId;

-        mFallbackUpdateTimerId = -1;

-        QMetaObject::invokeMethod(this, [this, id] { killTimer(id); }, Qt::QueuedConnection);

-    }

-

     mFrameCallback = frame();

     wl_callback_add_listener(mFrameCallback, &QWaylandWindow::callbackListener, this);

     mWaitingForFrameCallback = true;

@@ -1203,6 +1174,7 @@

 void QWaylandWindow::deliverUpdateRequest()

 {

+    qCDebug(lcWaylandBackingstore) << "deliverUpdateRequest";

     mWaitingForUpdate = true;

     QPlatformWindow::deliverUpdateRequest();

 }

diff --git a/src/client/qwaylandwindow_p.h b/src/client/qwaylandwindow_p.h

index b03d92e..e4a1124 100644

--- a/src/client/qwaylandwindow_p.h

+++ b/src/client/qwaylandwindow_p.h

@@ -232,7 +232,6 @@

     // True when we have called deliverRequestUpdate, but the client has not yet attached a new buffer

     bool mWaitingForUpdate = false;

-    int mFallbackUpdateTimerId = -1; // Started when waiting for app to commit

     QMutex mResizeLock;

     bool mWaitingToApplyConfigure = false;