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Commit b95efc2c authored by Mark Fasheh's avatar Mark Fasheh
Browse files

MessageStack: add quitting sentinel node 

We use the timestamp of the quitting message to tell
DeliQueue whether it should remove all messages or just
remove messages past a given time ("removeAllFutureMessages").

Test: atest android.os.MessageStackTest
Bug: 421623328
Flag: EXEMPT new data structure isn't used yet; usages will be flagged.
Change-Id: I7caf36e9a5fc1efec1be7f733b4b2d7f2f176f92
parent ab70951a

core/java/android/os/MessageStack.java

+61 −4
Original line number Diff line number Diff line
@@ -41,7 +41,7 @@ public final class MessageStack { 
    private final MessageHeap mAsyncHeap = new MessageHeap();



    // This points to the most-recently processed message. Comparison with mTopValue will indicate

    // whether some messages still need to be processed.

    // whether some messages still need to be processed. This value excludes the quitting sentinel.

    private Message mLooperProcessed = null;



    static {
@@ -56,17 +56,65 @@ public final class MessageStack { 
        }

    }



    private static final Object QUITTING_NODE_OBJ = new Object();



    private boolean isQuittingMessage(Message m) {

        return m != null && m.obj == QUITTING_NODE_OBJ;

    }



    /**

     * Pushes a message onto the top of the stack with a CAS.

     * @return true if successfully pushed; false if the stack is quitting.

     */

    public void pushMessage(Message m) {

        // TODO: This should fail if the current top value is the shutdown sentinel.

    public boolean pushMessage(Message m) {

        Message current;

        do {

            current = mTopValue;

            if (isQuittingMessage(current)) {

                return false;

            }

            m.next = current;

        } while (!sTop.weakCompareAndSetRelease(this, current, m));

        return true;

    }



    /**

     * Pushes a quitting message onto the top of the stack.

     * After this call no more messages can be pushed onto the stack.

     * @return true if pushed, false if there was already a quitting message

     */

    public boolean pushQuitting(long when) {

        Message quittingMsg = Message.obtain();

        quittingMsg.obj = QUITTING_NODE_OBJ;

        quittingMsg.when = when;

        /* Should never go into the heap, initialize idx to an impossible value */

        quittingMsg.heapIndex = -1;

        final boolean ret = pushMessage(quittingMsg);

        if (!ret) {

            quittingMsg.recycleUnchecked();

        }



        return ret;

    }



    /**

     * Query if we are in a quitting state.

     * @return true if we have a quitting message on top of the stack.

     */

    public boolean isQuitting() {

        return isQuittingMessage((Message) sTop.getAcquire(this));

    }



    /**

     * Gets timestamp of quitting message.

     * @return timestamp, or throws an exception if no quitting message exists.

     */

    public long getQuittingTimestamp() throws IllegalStateException {

        Message m = (Message) sTop.getAcquire(this);

        if (!isQuittingMessage(m)) {

            throw new IllegalStateException();

        }

        return m.when;

    }



    /**
@@ -80,7 +128,8 @@ public final class MessageStack { 


        while (current != null) {

            // Check that the message hasn't already been removed or processed elsewhere.

            if (!current.isRemoved()

            if (!isQuittingMessage(current)

                    && !current.isRemoved()

                    && compare.compareMessage(current, h, what, object, r, when)

                    && current.markRemoved()) {

                if (firstRemoved == null) {
@@ -107,6 +156,14 @@ public final class MessageStack { 
     */

    public void heapSweep() {

        Message current = (Message) sTop.getAcquire(this);



        if (current != null && isQuittingMessage(current)) {

            if (current.next != null) {

                current.next.prev = current;

            }

            current = current.next;

        }



        Message prevLooperProcessed = mLooperProcessed;

        mLooperProcessed = current;

core/tests/coretests/src/android/os/MessageStackTest.java

+20 −0
Original line number Diff line number Diff line
@@ -17,7 +17,9 @@ 
package android.os;



import static org.junit.Assert.assertEquals;

import static org.junit.Assert.assertFalse;

import static org.junit.Assert.assertNull;

import static org.junit.Assert.assertTrue;



import androidx.test.runner.AndroidJUnit4;
@@ -45,6 +47,24 @@ public final class MessageStackTest { 
        assertEquals(10, stack.sizeForTest());

    }



    /**

     * Verify quitting state

     */

    @Test

    public void testQuitting() {

        MessageStack stack = new MessageStack();

        for (int i = 0; i < 10; i++) {

            stack.pushMessage(new Message());

        }



        assertFalse(stack.isQuitting());



        stack.pushQuitting(42);

        assertFalse(stack.pushMessage(new Message()));

        assertTrue(stack.isQuitting());

        assertEquals(stack.getQuittingTimestamp(), 42);

    }



    /**

     * Verify heap size after sweeping messages from a MessageStack.

     */