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Commit 05d42ad0 authored by Garfield Tan's avatar Garfield Tan
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Ensure long wait time for the first item in PersisterQueue 

Unit tests revealed a race condition where mNextWriteTime set in the
first PersisterQueue#addItem() can be overwritten by
PersisterQueue#processNextItem() if the item is added quickly after
starting the writer thread. This could defeat the overall purpose of
having a long wait to avoid competing with critical resources system
boots need.

Bug: 402243483
Test: atest --iterations 20 PersisterQueueTests
Flag: EXEMPT bug fix
Change-Id: I6ca44618999aca4674d6a8fbc5e02592dd25169a
parent 0fa17c84

services/core/java/com/android/server/wm/PersisterQueue.java

+7 −4
Original line number Diff line number Diff line
@@ -232,8 +232,12 @@ class PersisterQueue { 
        final WriteQueueItem item;

        synchronized (this) {

            if (mNextWriteTime != FLUSH_QUEUE) {

                // The next write we don't have to wait so long.

                mNextWriteTime = SystemClock.uptimeMillis() + mInterWriteDelayMs;

                // mNextWriteTime can be mPreTaskDelayMs from the time when the first item is added

                // before the writer thread enters this synchronized block for the first time. In

                // other cases, mNextWriteTime is the time when the last item was processed and we

                // don't need to wait so long to process the next task if the queue isn't empty.

                mNextWriteTime =

                    Math.max(mNextWriteTime, SystemClock.uptimeMillis() + mInterWriteDelayMs);

                if (DEBUG) {

                    Slog.d(TAG, "Next write time may be in " + mInterWriteDelayMs

                            + " msec. (" + mNextWriteTime + ")");
@@ -252,8 +256,7 @@ class PersisterQueue { 
                }

                if (DEBUG) Slog.d(TAG, "LazyTaskWriter: waiting indefinitely.");

                wait();

                // Invariant: mNextWriteTime is either FLUSH_QUEUE or PRE_WRITE_DELAY_MS

                // from now.

                // Invariant: mNextWriteTime is either FLUSH_QUEUE or mPreTaskDelayMs from now.

            }

            item = mWriteQueue.remove(0);