[queuedwork] Avoid blocking on thread creation

Never create a HandlerThread just to then see that its queue is empty.
Reduces exposure to priority inversions.

Bug: 263820216

Change-Id: Id8db19b56a690c4eae88386554fa060d40e0b012

1 files changed, 23 insertions, 11 deletions

diff --git a/core/java/android/app/QueuedWork.java b/core/java/android/app/QueuedWork.java
index edf0a46b1433..6a114f908a22 100644
--- a/core/java/android/app/QueuedWork.java
+++ b/core/java/android/app/QueuedWork.java
@@ -114,6 +114,22 @@ public class QueuedWork {
     }
 
     /**
+     * Remove all Messages from the Handler with the given code.
+     *
+     * This method intentionally avoids creating the Handler if it doesn't
+     * already exist.
+     */
+    private static void handlerRemoveMessages(int what) {
+        synchronized (sLock) {
+            if (sHandler == null) {
+                // Nothing to remove
+                return;
+            }
+            getHandler().removeMessages(what);
+        }
+    }
+
+    /**
      * Add a finisher-runnable to wait for {@link #queue asynchronously processed work}.
      *
      * Used by SharedPreferences$Editor#startCommit().
@@ -156,17 +172,13 @@ public class QueuedWork {
         long startTime = System.currentTimeMillis();
         boolean hadMessages = false;
 
-        Handler handler = getHandler();
-
         synchronized (sLock) {
-            if (handler.hasMessages(QueuedWorkHandler.MSG_RUN)) {
-                // Delayed work will be processed at processPendingWork() below
-                handler.removeMessages(QueuedWorkHandler.MSG_RUN);
-
-                if (DEBUG) {
-                    hadMessages = true;
-                    Log.d(LOG_TAG, "waiting");
-                }
+            if (DEBUG) {
+                hadMessages = getHandler().hasMessages(QueuedWorkHandler.MSG_RUN);
+            }
+            handlerRemoveMessages(QueuedWorkHandler.MSG_RUN);
+            if (DEBUG && hadMessages) {
+                Log.d(LOG_TAG, "waiting");
             }
 
             // We should not delay any work as this might delay the finishers
@@ -257,7 +269,7 @@ public class QueuedWork {
                 sWork = new LinkedList<>();
 
                 // Remove all msg-s as all work will be processed now
-                getHandler().removeMessages(QueuedWorkHandler.MSG_RUN);
+                handlerRemoveMessages(QueuedWorkHandler.MSG_RUN);
             }
 
             if (work.size() > 0) {