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Commit e2c336e7 authored by Robert Carr's avatar Robert Carr
Browse files

ViewRootImpl: Add P2P sync primitive 

Expose consumeNextDraw from ViewRootImpl to enable
one-off sync between two ViewRoots.

Bug: 201046726
Test: Existing tests pass
Change-Id: Iaf30830dc529eac83276a76d1908a06d12175b00
parent 7122b1ee

core/java/android/view/ViewRootImpl.java

+43 −0
Original line number Diff line number Diff line
@@ -211,6 +211,7 @@ import java.io.PrintWriter; 
import java.io.StringWriter;

import java.lang.ref.WeakReference;

import java.util.ArrayList;

import java.util.function.Consumer;

import java.util.HashSet;

import java.util.LinkedList;

import java.util.List;
@@ -742,6 +743,8 @@ public final class ViewRootImpl implements ViewParent, 
     */

    private long mRtLastAttemptedDrawFrameNum = 0;



    private Consumer<SurfaceControl.Transaction> mBLASTDrawConsumer;



    private HashSet<ScrollCaptureCallback> mRootScrollCaptureCallbacks;



    private long mScrollCaptureRequestTimeout = SCROLL_CAPTURE_REQUEST_TIMEOUT_MILLIS;
@@ -3252,6 +3255,9 @@ public final class ViewRootImpl implements ViewParent, 
        }



        boolean cancelDraw = mAttachInfo.mTreeObserver.dispatchOnPreDraw() || !isViewVisible;

        if (mBLASTDrawConsumer != null) {

            useBlastSync = true;

        }



        if (!cancelDraw) {

            if (mPendingTransitions != null && mPendingTransitions.size() > 0) {
@@ -3966,6 +3972,9 @@ public final class ViewRootImpl implements ViewParent, 
            Log.d(mTag, "Creating frameCompleteCallback");

        }



        final Consumer<SurfaceControl.Transaction> blastSyncConsumer = mBLASTDrawConsumer;

        mBLASTDrawConsumer = null;



        mAttachInfo.mThreadedRenderer.setFrameCompleteCallback(() -> {

            long frameNr = mBlastBufferQueue.getLastAcquiredFrameNum();

            if (DEBUG_BLAST) {
@@ -3991,6 +4000,9 @@ public final class ViewRootImpl implements ViewParent, 
            mHandler.postAtFrontOfQueue(() -> {

                if (useBlastSync) {

                    mSurfaceChangedTransaction.merge(tmpTransaction);

                    if (blastSyncConsumer != null) {

                        blastSyncConsumer.accept(mSurfaceChangedTransaction);

                    }

                }



                if (reportNextDraw) {
@@ -10417,4 +10429,35 @@ public final class ViewRootImpl implements ViewParent, 
            listener.onBufferTransformHintChanged(hint);

        }

    }



    /**

     * Redirect the next draw of this ViewRoot (from the UI thread perspective)

     * to the passed in consumer. This can be used to create P2P synchronization

     * between ViewRoot's however it comes with many caveats.

     *

     * 1. You MUST consume the transaction, by either applying it immediately or

     *    merging it in to another transaction. The threading model doesn't

     *    allow you to hold in the passed transaction.

     * 2. If you merge it in to another transaction, this ViewRootImpl will be

     *    paused until you finally apply that transaction and it receives

     *    the callback from SF. If you lose track of the transaction you will

     *    ANR the app.

     * 3. Only one person can consume the transaction at a time, if you already

     *    have a pending consumer for this frame, the function will return false

     * 4. Someone else may have requested to consume the next frame, in which case

     *    this function will return false and you will not receive a callback.

     * 5. This function does not trigger drawing so even if it returns true you

     *    may not receive a callback unless there is some other UI thread work

     *    to trigger drawing. If it returns true, and a draw occurs, the callback

     *    will be called (Though again watch out for the null transaction case!)

     * 6. This function must be called on the UI thread. The consumer will likewise

     *    be called on the UI thread.

     */

    public boolean consumeNextDraw(Consumer<SurfaceControl.Transaction> consume) {

       if (mBLASTDrawConsumer != null) {

           return false;

       }

       mBLASTDrawConsumer = consume;

       return true;

   }

}