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Commit 19f88e9f authored by Mark Fasheh's avatar Mark Fasheh
Browse files

Avoid races between nextMessage() and stackHasMessages() 

Always check if the stack is draining before we exit stackHasMessages().
 - This will ensure that next has put any pending messages into the
   priority queues before we search them.

Bug: 396569494
Flag: EXEMPT - bugfix
Test: atest MessageQueueTest
Change-Id: If3259e13060baae4125a4977519a7f08390f79cb
parent 318fcc18

core/java/android/os/CombinedMessageQueue/MessageQueue.java

+6 −15
Original line number Diff line number Diff line
@@ -2563,10 +2563,6 @@ public final class MessageQueue { 
            return mMessage.when;

        }



        boolean isRemovedFromStack() {

            return mRemovedFromStackValue;

        }



        boolean removeFromStack() {

            return sRemovedFromStack.compareAndSet(this, false, true);

        }
@@ -2919,16 +2915,10 @@ public final class MessageQueue { 
        StateNode bottom = getStateNode(top);



        /*

         * If the top node is a state node, there are no reachable messages.

         * If it's anything other than Active, we can quit as we know that next() is not

         * consuming items.

         * If the top node is Active then we know that next() is currently consuming items.

         * In that case we should wait next() has drained the stack.

         * If the top node is a state node, there are no reachable messages. We should still

         * wait for next to complete draining the stack.

         */

        if (top == bottom) {

            if (bottom != sStackStateActive) {

                return false;

            }

            waitForDrainCompleted();

            return false;

        }
@@ -2957,7 +2947,7 @@ public final class MessageQueue { 
                        }

                    }

                } else {

                    return true;

                    break;

                }

            }
@@ -2967,16 +2957,17 @@ public final class MessageQueue { 
                if (DEBUG) {

                    Log.d(TAG_C, "stackHasMessages next() is walking the stack, we must re-sample");

                }

                waitForDrainCompleted();

                break;

            }

            if (!n.isMessageNode()) {

                /* We reached the end of the stack */

                return found;

                break;

            }

            p = (MessageNode) n;

        }



        waitForDrainCompleted();



        return found;

    }