Implement issue # 3255887 could CursorLoader offer...

...to throttle contentobserver-based requeries

Why yes, I guess it could.

This also reworks AsyncTaskLoader to not generate multiple
concurrent tasks if it is getting change notifications before
the last background task is complete.

And removes some of the old APIs that had been deprecated but
need to be gone for final release.

And fixes a few little problems with applying the wrong theme
in system code.

Change-Id: Ic7a665b666d0fb9d348e5f23595532191065884f

5 files changed, 180 insertions, 38 deletions

diff --git a/core/java/android/content/AsyncTaskLoader.java b/core/java/android/content/AsyncTaskLoader.java
index 01a2912..ec4e578 100644
--- a/core/java/android/content/AsyncTaskLoader.java
+++ b/core/java/android/content/AsyncTaskLoader.java
@@ -17,8 +17,13 @@
 package android.content;
 
 import android.os.AsyncTask;
+import android.os.Handler;
+import android.os.SystemClock;
 import android.util.Log;
+import android.util.TimeUtils;
 
+import java.io.FileDescriptor;
+import java.io.PrintWriter;
 import java.util.concurrent.ExecutionException;
 
 /**
@@ -30,14 +35,15 @@ public abstract class AsyncTaskLoader<D> extends Loader<D> {
 
     private static final String TAG = "AsyncTaskLoader";
 
-    final class LoadTask extends AsyncTask<Void, Void, D> {
+    final class LoadTask extends AsyncTask<Void, Void, D> implements Runnable {
 
-        private D result;
+        D result;
+        boolean waiting;
 
         /* Runs on a worker thread */
         @Override
         protected D doInBackground(Void... params) {
-            result = AsyncTaskLoader.this.loadInBackground();
+            result = AsyncTaskLoader.this.onLoadInBackground();
             return result;
         }
 
@@ -49,38 +55,91 @@ public abstract class AsyncTaskLoader<D> extends Loader<D> {
 
         @Override
         protected void onCancelled() {
-            AsyncTaskLoader.this.onCancelled(result);
+            AsyncTaskLoader.this.dispatchOnCancelled(this, result);
+        }
+
+        @Override
+        public void run() {
+            waiting = false;
+            AsyncTaskLoader.this.executePendingTask();
         }
     }
 
     volatile LoadTask mTask;
+    volatile LoadTask mCancellingTask;
+
+    long mUpdateThrottle;
+    long mLastLoadCompleteTime = -10000;
+    Handler mHandler;
 
     public AsyncTaskLoader(Context context) {
         super(context);
     }
 
+    /**
+     * Set amount to throttle updates by.  This is the minimum time from
+     * when the last {@link #onLoadInBackground()} call has completed until
+     * a new load is scheduled.
+     *
+     * @param delayMS Amount of delay, in milliseconds.
+     */
+    public void setUpdateThrottle(long delayMS) {
+        mUpdateThrottle = delayMS;
+        if (delayMS != 0) {
+            mHandler = new Handler();
+        }
+    }
+
     @Override
     protected void onForceLoad() {
         super.onForceLoad();
         cancelLoad();
         mTask = new LoadTask();
-        mTask.execute((Void[]) null);
+        executePendingTask();
     }
 
     /**
      * Attempt to cancel the current load task. See {@link AsyncTask#cancel(boolean)}
-     * for more info.
+     * for more info.  Must be called on the main thread of the process.
+     *
+     * <p>Cancelling is not an immediate operation, since the load is performed
+     * in a background thread.  If there is currently a load in progress, this
+     * method requests that the load be cancelled, and notes this is the case;
+     * once the background thread has completed its work its remaining state
+     * will be cleared.  If another load request comes in during this time,
+     * it will be held until the cancelled load is complete.
      *
-     * @return <tt>false</tt> if the task could not be canceled,
+     * @return Returns <tt>false</tt> if the task could not be cancelled,
      *         typically because it has already completed normally, or
-     *         because {@link #startLoading()} hasn't been called, and
-     *         <tt>true</tt> otherwise
+     *         because {@link #startLoading()} hasn't been called; returns
+     *         <tt>true</tt> otherwise.
      */
     public boolean cancelLoad() {
         if (mTask != null) {
-            boolean cancelled = mTask.cancel(false);
-            mTask = null;
-            return cancelled;
+            if (mCancellingTask != null) {
+                // There was a pending task already waiting for a previous
+                // one being canceled; just drop it.
+                if (mTask.waiting) {
+                    mTask.waiting = false;
+                    mHandler.removeCallbacks(mTask);
+                }
+                mTask = null;
+                return false;
+            } else if (mTask.waiting) {
+                // There is a task, but it is waiting for the time it should
+                // execute.  We can just toss it.
+                mTask.waiting = false;
+                mHandler.removeCallbacks(mTask);
+                mTask = null;
+                return false;
+            } else {
+                boolean cancelled = mTask.cancel(false);
+                if (cancelled) {
+                    mCancellingTask = mTask;
+                }
+                mTask = null;
+                return cancelled;
+            }
         }
         return false;
     }
@@ -92,32 +151,67 @@ public abstract class AsyncTaskLoader<D> extends Loader<D> {
     public void onCancelled(D data) {
     }
 
+    void executePendingTask() {
+        if (mCancellingTask == null && mTask != null) {
+            if (mTask.waiting) {
+                mTask.waiting = false;
+                mHandler.removeCallbacks(mTask);
+            }
+            if (mUpdateThrottle > 0) {
+                long now = SystemClock.uptimeMillis();
+                if (now < (mLastLoadCompleteTime+mUpdateThrottle)) {
+                    // Not yet time to do another load.
+                    mTask.waiting = true;
+                    mHandler.postAtTime(mTask, mLastLoadCompleteTime+mUpdateThrottle);
+                    return;
+                }
+            }
+            mTask.execute((Void[]) null);
+        }
+    }
+
+    void dispatchOnCancelled(LoadTask task, D data) {
+        onCancelled(data);
+        if (mCancellingTask == task) {
+            mLastLoadCompleteTime = SystemClock.uptimeMillis();
+            mCancellingTask = null;
+            executePendingTask();
+        }
+    }
+
     void dispatchOnLoadComplete(LoadTask task, D data) {
         if (mTask != task) {
-            onCancelled(data);
+            dispatchOnCancelled(task, data);
         } else {
+            mLastLoadCompleteTime = SystemClock.uptimeMillis();
             mTask = null;
             deliverResult(data);
         }
     }
 
     /**
+     */
+    public abstract D loadInBackground();
+
+    /**
      * Called on a worker thread to perform the actual load. Implementations should not deliver the
-     * results directly, but should return them from this method, which will eventually end up
-     * calling deliverResult on the UI thread. If implementations need to process
-     * the results on the UI thread they may override deliverResult and do so
+     * result directly, but should return them from this method, which will eventually end up
+     * calling {@link #deliverResult} on the UI thread. If implementations need to process
+     * the results on the UI thread they may override {@link #deliverResult} and do so
      * there.
      *
-     * @return the result of the load
+     * @return Implementations must return the result of their load operation.
      */
-    public abstract D loadInBackground();
+    protected D onLoadInBackground() {
+        return loadInBackground();
+    }
 
     /**
      * Locks the current thread until the loader completes the current load
      * operation. Returns immediately if there is no load operation running.
      * Should not be called from the UI thread.
      * <p>
-     * Used for testing.
+     * Use for testing only.  <b>Never</b> call this from a UI thread.
      */
     public void waitForLoader() {
         LoadTask task = mTask;
@@ -132,4 +226,25 @@ public abstract class AsyncTaskLoader<D> extends Loader<D> {
             }
         }
     }
+
+    @Override
+    public void dump(String prefix, FileDescriptor fd, PrintWriter writer, String[] args) {
+        super.dump(prefix, fd, writer, args);
+        if (mTask != null) {
+            writer.print(prefix); writer.print("mTask="); writer.print(mTask);
+                    writer.print(" waiting="); writer.println(mTask.waiting);
+        }
+        if (mCancellingTask != null) {
+            writer.print(prefix); writer.print("mCancellingTask="); writer.print(mCancellingTask);
+                    writer.print(" waiting="); writer.println(mCancellingTask.waiting);
+        }
+        if (mUpdateThrottle != 0) {
+            writer.print(prefix); writer.print("mUpdateThrottle=");
+                    TimeUtils.formatDuration(mUpdateThrottle, writer);
+                    writer.print(" mLastLoadCompleteTime=");
+                    TimeUtils.formatDuration(mLastLoadCompleteTime,
+                            SystemClock.uptimeMillis(), writer);
+                    writer.println();
+        }
+    }
 }
diff --git a/core/java/android/content/Context.java b/core/java/android/content/Context.java
index b128d31..227df21 100644
--- a/core/java/android/content/Context.java
+++ b/core/java/android/content/Context.java
@@ -227,6 +227,12 @@ public abstract class Context {
      */
     public abstract void setTheme(int resid);
 
+    /** @hide Needed for some internal implementation...  not public because
+     * you can't assume this actually means anything. */
+    public int getThemeResId() {
+        return 0;
+    }
+
     /**
      * Return the Theme object associated with this Context.
      */
diff --git a/core/java/android/content/ContextWrapper.java b/core/java/android/content/ContextWrapper.java
index f8928e4..545144e 100644
--- a/core/java/android/content/ContextWrapper.java
+++ b/core/java/android/content/ContextWrapper.java
@@ -106,6 +106,12 @@ public class ContextWrapper extends Context {
         mBase.setTheme(resid);
     }
 
+    /** @hide */
+    @Override
+    public int getThemeResId() {
+        return mBase.getThemeResId();
+    }
+
     @Override
     public Resources.Theme getTheme() {
         return mBase.getTheme();
diff --git a/core/java/android/content/CursorLoader.java b/core/java/android/content/CursorLoader.java
index 8ab0973..38ebaf2 100644
--- a/core/java/android/content/CursorLoader.java
+++ b/core/java/android/content/CursorLoader.java
@@ -55,7 +55,7 @@ public class CursorLoader extends AsyncTaskLoader<Cursor> {
      * Registers an observer to get notifications from the content provider
      * when the cursor needs to be refreshed.
      */
-    public void registerContentObserver(Cursor cursor, ContentObserver observer) {
+    void registerContentObserver(Cursor cursor, ContentObserver observer) {
         cursor.registerContentObserver(mObserver);
     }
 
diff --git a/core/java/android/content/Loader.java b/core/java/android/content/Loader.java
index ef81fe4..d63fe69 100644
--- a/core/java/android/content/Loader.java
+++ b/core/java/android/content/Loader.java
@@ -28,6 +28,13 @@ import java.io.PrintWriter;
  * they should monitor the source of their data and deliver new results when the contents
  * change.
  *
+ * <p><b>Note on threading:</b> Clients of loaders should as a rule perform
+ * any calls on to a Loader from the main thread of their process (that is,
+ * the thread the Activity callbacks and other things occur on).  Subclasses
+ * of Loader (such as {@link AsyncTaskLoader}) will often perform their work
+ * in a separate thread, but when delivering their results this too should
+ * be done on the main thread.</p>
+ *
  * <p>Subclasses generally must implement at least {@link #onStartLoading()},
  * {@link #onStopLoading()}, {@link #onForceLoad()}, and {@link #onReset()}.
  *
@@ -80,7 +87,7 @@ public class Loader<D> {
     /**
      * Sends the result of the load to the registered listener. Should only be called by subclasses.
      *
-     * Must be called from the UI thread.
+     * Must be called from the process's main thread.
      *
      * @param data the result of the load
      */
@@ -105,10 +112,11 @@ public class Loader<D> {
     }
 
     /**
-     * Registers a class that will receive callbacks when a load is complete. The callbacks will
-     * be called on the UI thread so it's safe to pass the results to widgets.
+     * Registers a class that will receive callbacks when a load is complete.
+     * The callback will be called on the process's main thread so it's safe to
+     * pass the results to widgets.
      *
-     * Must be called from the UI thread
+     * <p>Must be called from the process's main thread.
      */
     public void registerListener(int id, OnLoadCompleteListener<D> listener) {
         if (mListener != null) {
@@ -119,7 +127,9 @@ public class Loader<D> {
     }
 
     /**
-     * Must be called from the UI thread
+     * Remove a listener that was previously added with {@link #registerListener}.
+     *
+     * Must be called from the process's main thread.
      */
     public void unregisterListener(OnLoadCompleteListener<D> listener) {
         if (mListener == null) {
@@ -150,17 +160,19 @@ public class Loader<D> {
     }
 
     /**
-     * Starts an asynchronous load of the contacts list data. When the result is ready the callbacks
-     * will be called on the UI thread. If a previous load has been completed and is still valid
-     * the result may be passed to the callbacks immediately. The loader will monitor the source of
-     * the data set and may deliver future callbacks if the source changes. Calling
-     * {@link #stopLoading} will stop the delivery of callbacks.
+     * Starts an asynchronous load of the Loader's data. When the result
+     * is ready the callbacks will be called on the process's main thread.
+     * If a previous load has been completed and is still valid
+     * the result may be passed to the callbacks immediately.
+     * The loader will monitor the source of
+     * the data set and may deliver future callbacks if the source changes.
+     * Calling {@link #stopLoading} will stop the delivery of callbacks.
      *
      * <p>This updates the Loader's internal state so that
      * {@link #isStarted()} and {@link #isReset()} will return the correct
      * values, and then calls the implementation's {@link #onStartLoading()}.
      *
-     * <p>Must be called from the UI thread.
+     * <p>Must be called from the process's main thread.
      */
     public final void startLoading() {
         mStarted = true;
@@ -182,14 +194,15 @@ public class Loader<D> {
      * implementation's {@link #onForceLoad()}.  You generally should only call this
      * when the loader is started -- that is, {@link #isStarted()} returns true.
      *
-     * <p>Must be called from the UI thread.
+     * <p>Must be called from the process's main thread.
      */
-    public final void forceLoad() {
+    public void forceLoad() {
         onForceLoad();
     }
 
     /**
      * Subclasses must implement this to take care of requests to {@link #forceLoad()}.
+     * This will always be called from the process's main thread.
      */
     protected void onForceLoad() {
     }
@@ -206,9 +219,9 @@ public class Loader<D> {
      * {@link #isStarted()} will return the correct
      * value, and then calls the implementation's {@link #onStopLoading()}.
      *
-     * <p>Must be called from the UI thread.
+     * <p>Must be called from the process's main thread.
      */
-    public final void stopLoading() {
+    public void stopLoading() {
         mStarted = false;
         onStopLoading();
     }
@@ -217,6 +230,7 @@ public class Loader<D> {
      * Subclasses must implement this to take care of stopping their loader,
      * as per {@link #stopLoading()}.  This is not called by clients directly,
      * but as a result of a call to {@link #stopLoading()}.
+     * This will always be called from the process's main thread.
      */
     protected void onStopLoading() {
     }
@@ -231,9 +245,9 @@ public class Loader<D> {
      * {@link #isStarted()} and {@link #isReset()} will return the correct
      * values, and then calls the implementation's {@link #onReset()}.
      *
-     * <p>Must be called from the UI thread.
+     * <p>Must be called from the process's main thread.
      */
-    public final void reset() {
+    public void reset() {
         onReset();
         mReset = true;
         mStarted = false;
@@ -244,6 +258,7 @@ public class Loader<D> {
      * Subclasses must implement this to take care of resetting their loader,
      * as per {@link #reset()}.  This is not called by clients directly,
      * but as a result of a call to {@link #reset()}.
+     * This will always be called from the process's main thread.
      */
     protected void onReset() {
     }
@@ -265,7 +280,7 @@ public class Loader<D> {
      * if so, it simply calls {@link #forceLoad()}; otherwise, it sets a flag
      * so that {@link #takeContentChanged()} returns true.
      *
-     * <p>Must be called from the UI thread.
+     * <p>Must be called from the process's main thread.
      */
     public void onContentChanged() {
         if (mStarted) {