[DO NOT MERGE] Delay SharedPreferences.apply() by 50 ms

... so that multiple applies can be combined into a single write.

Do do this I replaces the executor in the QueuedWork by a more Android-y
handler.

Test: Ran shared preferences CTS tests. Looked at log and saw a lot of
      skipped writes

Bug: 33385963
Bug: 30662828

Change-Id: I8f33df717be7091532930ccf6ca8c48940e4edd4
(cherry picked from commit 3349644872d9b769f4e2d0ec1b91d368a552ff8d)

3 files changed, 167 insertions, 56 deletions

diff --git a/core/java/android/app/QueuedWork.java b/core/java/android/app/QueuedWork.java
index 6ee478059171..0ae85056da56 100644
--- a/core/java/android/app/QueuedWork.java
+++ b/core/java/android/app/QueuedWork.java
@@ -16,86 +16,197 @@
 
 package android.app;
 
-import java.util.concurrent.ConcurrentLinkedQueue;
-import java.util.concurrent.ExecutorService;
-import java.util.concurrent.Executors;
+import android.os.Handler;
+import android.os.HandlerThread;
+import android.os.Looper;
+import android.os.Message;
+import android.os.Process;
+import android.util.Log;
+
+import com.android.internal.annotations.GuardedBy;
+
+import java.util.LinkedList;
 
 /**
- * Internal utility class to keep track of process-global work that's
- * outstanding and hasn't been finished yet.
+ * Internal utility class to keep track of process-global work that's outstanding and hasn't been
+ * finished yet.
+ *
+ * New work will be {@link #queue queued}.
  *
- * This was created for writing SharedPreference edits out
- * asynchronously so we'd have a mechanism to wait for the writes in
- * Activity.onPause and similar places, but we may use this mechanism
- * for other things in the future.
+ * It is possible to add 'finisher'-runnables that are {@link #waitToFinish guaranteed to be run}.
+ * This is used to make sure the work has been finished.
+ *
+ * This was created for writing SharedPreference edits out asynchronously so we'd have a mechanism
+ * to wait for the writes in Activity.onPause and similar places, but we may use this mechanism for
+ * other things in the future.
+ *
+ * The queued asynchronous work is performed on a separate, dedicated thread.
  *
  * @hide
  */
 public class QueuedWork {
+    private static final String LOG_TAG = QueuedWork.class.getSimpleName();
+
+    /** Delay for delayed runnables */
+    private static final long DELAY = 50;
 
-    // The set of Runnables that will finish or wait on any async
-    // activities started by the application.
-    private static final ConcurrentLinkedQueue<Runnable> sPendingWorkFinishers =
-            new ConcurrentLinkedQueue<Runnable>();
+    /** Lock for this class */
+    private static final Object sLock = new Object();
 
-    private static ExecutorService sSingleThreadExecutor = null; // lazy, guarded by class
+    /** Finishers {@link #addFinisher added} and not yet {@link #removeFinisher removed} */
+    @GuardedBy("sLock")
+    private static final LinkedList<Runnable> sFinishers = new LinkedList<>();
+
+    /** {@link #getHandler() Lazily} created handler */
+    @GuardedBy("sLock")
+    private static Handler sHandler = null;
+
+    /** Work queued via {@link #queue} */
+    @GuardedBy("sLock")
+    private static final LinkedList<Runnable> sWork = new LinkedList<>();
+
+    /** If new work can be delayed or not */
+    @GuardedBy("sLock")
+    private static boolean sCanDelay = true;
 
     /**
-     * Returns a single-thread Executor shared by the entire process,
-     * creating it if necessary.
+     * Lazily create a handler on a separate thread.
+     *
+     * @return the handler
      */
-    public static ExecutorService singleThreadExecutor() {
-        synchronized (QueuedWork.class) {
-            if (sSingleThreadExecutor == null) {
-                // TODO: can we give this single thread a thread name?
-                sSingleThreadExecutor = Executors.newSingleThreadExecutor();
+    private static Handler getHandler() {
+        synchronized (sLock) {
+            if (sHandler == null) {
+                HandlerThread handlerThread = new HandlerThread("queued-work-looper",
+                        Process.THREAD_PRIORITY_BACKGROUND);
+                handlerThread.start();
+
+                sHandler = new QueuedWorkHandler(handlerThread.getLooper());
             }
-            return sSingleThreadExecutor;
+            return sHandler;
         }
     }
 
     /**
-     * Add a runnable to finish (or wait for) a deferred operation
-     * started in this context earlier.  Typically finished by e.g.
-     * an Activity#onPause.  Used by SharedPreferences$Editor#startCommit().
+     * Add a finisher-runnable to wait for {@link #queue asynchronously processed work}.
+     *
+     * Used by SharedPreferences$Editor#startCommit().
      *
-     * Note that this doesn't actually start it running.  This is just
-     * a scratch set for callers doing async work to keep updated with
-     * what's in-flight.  In the common case, caller code
-     * (e.g. SharedPreferences) will pretty quickly call remove()
-     * after an add().  The only time these Runnables are run is from
-     * waitToFinish(), below.
+     * Note that this doesn't actually start it running.  This is just a scratch set for callers
+     * doing async work to keep updated with what's in-flight. In the common case, caller code
+     * (e.g. SharedPreferences) will pretty quickly call remove() after an add(). The only time
+     * these Runnables are run is from {@link #waitToFinish}.
+     *
+     * @param finisher The runnable to add as finisher
      */
-    public static void add(Runnable finisher) {
-        sPendingWorkFinishers.add(finisher);
+    public static void addFinisher(Runnable finisher) {
+        synchronized (sLock) {
+            sFinishers.add(finisher);
+        }
     }
 
-    public static void remove(Runnable finisher) {
-        sPendingWorkFinishers.remove(finisher);
+    /**
+     * Remove a previously {@link #addFinisher added} finisher-runnable.
+     *
+     * @param finisher The runnable to remove.
+     */
+    public static void removeFinisher(Runnable finisher) {
+        synchronized (sLock) {
+            sFinishers.remove(finisher);
+        }
     }
 
     /**
-     * Finishes or waits for async operations to complete.
-     * (e.g. SharedPreferences$Editor#startCommit writes)
+     * Trigger queued work to be processed immediately. The queued work is processed on a separate
+     * thread asynchronous. While doing that run and process all finishers on this thread. The
+     * finishers can be implemented in a way to check weather the queued work is finished.
      *
-     * Is called from the Activity base class's onPause(), after
-     * BroadcastReceiver's onReceive, after Service command handling,
-     * etc.  (so async work is never lost)
+     * Is called from the Activity base class's onPause(), after BroadcastReceiver's onReceive,
+     * after Service command handling, etc. (so async work is never lost)
      */
     public static void waitToFinish() {
-        Runnable toFinish;
-        while ((toFinish = sPendingWorkFinishers.poll()) != null) {
-            toFinish.run();
+        Handler handler = getHandler();
+
+        synchronized (sLock) {
+            if (handler.hasMessages(QueuedWorkHandler.MSG_RUN)) {
+                // Force the delayed work to be processed now
+                handler.removeMessages(QueuedWorkHandler.MSG_RUN);
+                handler.sendEmptyMessage(QueuedWorkHandler.MSG_RUN);
+            }
+
+            // We should not delay any work as this might delay the finishers
+            sCanDelay = false;
+        }
+
+        try {
+            while (true) {
+                Runnable finisher;
+
+                synchronized (sLock) {
+                    finisher = sFinishers.poll();
+                }
+
+                if (finisher == null) {
+                    break;
+                }
+
+                finisher.run();
+            }
+        } finally {
+            sCanDelay = true;
+        }
+    }
+
+    /**
+     * Queue a work-runnable for processing asynchronously.
+     *
+     * @param work The new runnable to process
+     * @param shouldDelay If the message should be delayed
+     */
+    public static void queue(Runnable work, boolean shouldDelay) {
+        Handler handler = getHandler();
+
+        synchronized (sLock) {
+            sWork.add(work);
+
+            if (shouldDelay && sCanDelay) {
+                handler.sendEmptyMessageDelayed(QueuedWorkHandler.MSG_RUN, DELAY);
+            } else {
+                handler.sendEmptyMessage(QueuedWorkHandler.MSG_RUN);
+            }
         }
     }
-    
+
     /**
-     * Returns true if there is pending work to be done.  Note that the
-     * result is out of data as soon as you receive it, so be careful how you
-     * use it.
+     * @return True iff there is any {@link #queue async work queued}.
      */
     public static boolean hasPendingWork() {
-        return !sPendingWorkFinishers.isEmpty();
+        synchronized (sLock) {
+            return !sWork.isEmpty();
+        }
+    }
+
+    private static class QueuedWorkHandler extends Handler {
+        static final int MSG_RUN = 1;
+
+        QueuedWorkHandler(Looper looper) {
+            super(looper);
+        }
+
+        public void handleMessage(Message msg) {
+            if (msg.what == MSG_RUN) {
+                LinkedList<Runnable> work;
+
+                synchronized (sWork) {
+                    work = (LinkedList<Runnable>) sWork.clone();
+                    sWork.clear();
+
+                    // Remove all msg-s as all work will be processed now
+                    removeMessages(MSG_RUN);
+                }
+
+                work.forEach(Runnable::run);
+            }
+        }
     }
-    
 }
diff --git a/core/java/android/app/SharedPreferencesImpl.java b/core/java/android/app/SharedPreferencesImpl.java
index f273cd8670f0..59434331b36a 100644
--- a/core/java/android/app/SharedPreferencesImpl.java
+++ b/core/java/android/app/SharedPreferencesImpl.java
@@ -379,12 +379,12 @@ final class SharedPreferencesImpl implements SharedPreferences {
                     }
                 };
 
-            QueuedWork.add(awaitCommit);
+            QueuedWork.addFinisher(awaitCommit);
 
             Runnable postWriteRunnable = new Runnable() {
                     public void run() {
                         awaitCommit.run();
-                        QueuedWork.remove(awaitCommit);
+                        QueuedWork.removeFinisher(awaitCommit);
                     }
                 };
 
@@ -557,10 +557,10 @@ final class SharedPreferencesImpl implements SharedPreferences {
         }
 
         if (DEBUG) {
-            Log.d(TAG, "added " + mcr.memoryStateGeneration + " -> " + mFile.getName());
+            Log.d(TAG, "queued " + mcr.memoryStateGeneration + " -> " + mFile.getName());
         }
 
-        QueuedWork.singleThreadExecutor().execute(writeToDiskRunnable);
+        QueuedWork.queue(writeToDiskRunnable, !isFromSyncCommit);
     }
 
     private static FileOutputStream createFileOutputStream(File file) {
diff --git a/core/java/android/content/BroadcastReceiver.java b/core/java/android/content/BroadcastReceiver.java
index a7a86158edee..68c25ef5bd06 100644
--- a/core/java/android/content/BroadcastReceiver.java
+++ b/core/java/android/content/BroadcastReceiver.java
@@ -211,16 +211,16 @@ public abstract class BroadcastReceiver {
                     // of the list to finish the broadcast, so we don't block this
                     // thread (which may be the main thread) to have it finished.
                     //
-                    // Note that we don't need to use QueuedWork.add() with the
+                    // Note that we don't need to use QueuedWork.addFinisher() with the
                     // runnable, since we know the AM is waiting for us until the
                     // executor gets to it.
-                    QueuedWork.singleThreadExecutor().execute( new Runnable() {
+                    QueuedWork.queue(new Runnable() {
                         @Override public void run() {
                             if (ActivityThread.DEBUG_BROADCAST) Slog.i(ActivityThread.TAG,
                                     "Finishing broadcast after work to component " + mToken);
                             sendFinished(mgr);
                         }
-                    });
+                    }, false);
                 } else {
                     if (ActivityThread.DEBUG_BROADCAST) Slog.i(ActivityThread.TAG,
                             "Finishing broadcast to component " + mToken);