Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit 6aef7931 authored by Phil Weaver's avatar Phil Weaver
Browse files

Protect a11y against multi-threaded UIs 

It seems that the accessibility event dispatch is very
susceptible to multi-threaded UIs. This CL tries to handle
that situation gracefully. I'm thinking in P I can throw
an exception when events are dispatched on the wrong
thread, but it seems late to introduce such a behavior in O.

Bug: 62201606
Test: Ran a11y cts and unit tests.
Change-Id: I50b857667d8c3ae51a085afb15acefccbef4b762
parent df99c779

core/java/android/view/ViewRootImpl.java

+24 −3
Original line number Diff line number Diff line
@@ -7874,9 +7874,14 @@ public final class ViewRootImpl implements ViewParent, 


        @Override

        public void run() {

            // mSource may be changed in calls below.

            // Protect against re-entrant code and attempt to do the right thing in the case that

            // we're multithreaded.

            View source = mSource;

            mSource = null;

            if (source == null) {

                Log.e(TAG, "Accessibility content change has no source");

                return;

            }

            // The accessibility may be turned off while we were waiting so check again.

            if (AccessibilityManager.getInstance(mContext).isEnabled()) {

                mLastEventTimeMillis = SystemClock.uptimeMillis();
@@ -7893,6 +7898,22 @@ public final class ViewRootImpl implements ViewParent, 
        }



        public void runOrPost(View source, int changeType) {

            if (mHandler.getLooper() != Looper.myLooper()) {

                CalledFromWrongThreadException e = new CalledFromWrongThreadException("Only the "

                        + "original thread that created a view hierarchy can touch its views.");

                // TODO: Throw the exception

                Log.e(TAG, "Accessibility content change on non-UI thread. Future Android "

                        + "versions will throw an exception.", e);

                // Attempt to recover. This code does not eliminate the thread safety issue, but

                // it should force any issues to happen near the above log.

                mHandler.removeCallbacks(this);

                if (mSource != null) {

                    // Dispatch whatever was pending. It's still possible that the runnable started

                    // just before we removed the callbacks, and bad things will happen, but at

                    // least they should happen very close to the logged error.

                    run();

                }

            }

            if (mSource != null) {

                // If there is no common predecessor, then mSource points to

                // a removed view, hence in this case always prefer the source.
@@ -7909,12 +7930,12 @@ public final class ViewRootImpl implements ViewParent, 
            if (timeSinceLastMillis >= minEventIntevalMillis) {

                removeCallbacksAndRun();

            } else {

                mSource.postDelayed(this, minEventIntevalMillis - timeSinceLastMillis);

                mHandler.postDelayed(this, minEventIntevalMillis - timeSinceLastMillis);

            }

        }



        public void removeCallbacksAndRun() {

            mSource.removeCallbacks(this);

            mHandler.removeCallbacks(this);

            run();

        }

    }