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Commit d2731127 authored by Mark Fasheh's avatar Mark Fasheh
Browse files

Message: Don't use sentinel for target 

This breaks the check for a barrier (target == null).

Normally we wouldn't care but DeliQueue.nextMessage() can race with remove.
When this happens, we have no way of making a distinction between
a barrier node and a deleted barrier node. Additionally this makes
debugging nextMessage much easier.

Bug: 421623328
Flag: EXEMPT - bugfix
Test: atest CtsOsTestCasesRavenwood:MessageQueueTest#testSyncBarriersWakeup -- --abi x86_64
Change-Id: Ib7497343104b1173acf7942cc16cbe1a7a4dfa02
parent aed1a7f1

core/java/android/os/Handler.java

+0 −17
Original line number Diff line number Diff line
@@ -330,23 +330,6 @@ public class Handler { 
        return new Handler(looper, callback, true);

    }



    /**

     * Create a new Handler with all reference fields explicitly provided. This is intended to be

     * used for creating a Handler sentinel object.

     */

    private Handler(Looper looper, MessageQueue queue, Callback callback) {

        mLooper = looper;

        mQueue = queue;

        mCallback = callback;

        mAsynchronous = false;

        mIsShared = false;

    }



    /** @hide */

    static Handler createSentinelHandler() {

        return new Handler(null, null, null);

    }



    /** @hide */

    @UnsupportedAppUsage(maxTargetSdk = Build.VERSION_CODES.R, trackingBug = 170729553)

    @NonNull

core/java/android/os/Message.java

+1 −5
Original line number Diff line number Diff line
@@ -419,7 +419,6 @@ public final class Message implements Parcelable { 
    // Sentinel values used to clear reference fields with a valid 'null' value, to avoid grabbing a

    // removed message when matching for 'null' in these fields.

    private static final Object NULL_OBJECT = new Object();

    private static final Handler NULL_HANDLER = Handler.createSentinelHandler();

    private static final Runnable NULL_RUNNABLE = () -> {};



    /**
@@ -433,7 +432,6 @@ public final class Message implements Parcelable { 
        replyTo = null;

        sendingThreadName = null;

        data = null;

        target = NULL_HANDLER;

        callback = NULL_RUNNABLE;

    }
@@ -479,9 +477,7 @@ public final class Message implements Parcelable { 
     * worry about yours conflicting with other handlers.

     */

    public Handler getTarget() {

        // We assign this first to avoid a data race that could potentially expose NULL_HANDLER.

        final Handler ret = target;

        return ret == NULL_HANDLER ? null : ret;

        return target;

    }



    /**