Treat document thumbnails as preemptable.

When a more important request comes along, preempt all outstanding
thumbnail requests.

Bug: 11317901
Change-Id: I164fc8d804bb9c471e6da3f8127228043b3ca482

2 files changed, 58 insertions, 6 deletions

diff --git a/packages/DocumentsUI/src/com/android/documentsui/DirectoryFragment.java b/packages/DocumentsUI/src/com/android/documentsui/DirectoryFragment.java
index 1f3901c..fa8bc9d 100644
--- a/packages/DocumentsUI/src/com/android/documentsui/DirectoryFragment.java
+++ b/packages/DocumentsUI/src/com/android/documentsui/DirectoryFragment.java
@@ -76,6 +76,7 @@ import android.widget.TextView;
 import android.widget.Toast;
 
 import com.android.documentsui.DocumentsActivity.State;
+import com.android.documentsui.ProviderExecutor.Preemptable;
 import com.android.documentsui.RecentsProvider.StateColumns;
 import com.android.documentsui.model.DocumentInfo;
 import com.android.documentsui.model.RootInfo;
@@ -528,7 +529,7 @@ public class DirectoryFragment extends Fragment {
             if (iconThumb != null) {
                 final ThumbnailAsyncTask oldTask = (ThumbnailAsyncTask) iconThumb.getTag();
                 if (oldTask != null) {
-                    oldTask.reallyCancel();
+                    oldTask.preempt();
                     iconThumb.setTag(null);
                 }
             }
@@ -794,7 +795,7 @@ public class DirectoryFragment extends Fragment {
 
             final ThumbnailAsyncTask oldTask = (ThumbnailAsyncTask) iconThumb.getTag();
             if (oldTask != null) {
-                oldTask.reallyCancel();
+                oldTask.preempt();
                 iconThumb.setTag(null);
             }
 
@@ -818,7 +819,7 @@ public class DirectoryFragment extends Fragment {
                     final ThumbnailAsyncTask task = new ThumbnailAsyncTask(
                             uri, iconMime, iconThumb, mThumbSize);
                     iconThumb.setTag(task);
-                    task.executeOnExecutor(ProviderExecutor.forAuthority(docAuthority));
+                    ProviderExecutor.forAuthority(docAuthority).execute(task);
                 }
             }
 
@@ -988,7 +989,8 @@ public class DirectoryFragment extends Fragment {
         }
     }
 
-    private static class ThumbnailAsyncTask extends AsyncTask<Uri, Void, Bitmap> {
+    private static class ThumbnailAsyncTask extends AsyncTask<Uri, Void, Bitmap>
+            implements Preemptable {
         private final Uri mUri;
         private final ImageView mIconMime;
         private final ImageView mIconThumb;
@@ -1004,7 +1006,8 @@ public class DirectoryFragment extends Fragment {
             mSignal = new CancellationSignal();
         }
 
-        public void reallyCancel() {
+        @Override
+        public void preempt() {
             cancel(false);
             mSignal.cancel();
         }
diff --git a/packages/DocumentsUI/src/com/android/documentsui/ProviderExecutor.java b/packages/DocumentsUI/src/com/android/documentsui/ProviderExecutor.java
index 2105cb4..f94aebd 100644
--- a/packages/DocumentsUI/src/com/android/documentsui/ProviderExecutor.java
+++ b/packages/DocumentsUI/src/com/android/documentsui/ProviderExecutor.java
@@ -16,10 +16,15 @@
 
 package com.android.documentsui;
 
+import android.os.AsyncTask;
+
 import com.android.internal.annotations.GuardedBy;
 import com.android.internal.util.Preconditions;
+import com.google.android.collect.Lists;
 import com.google.android.collect.Maps;
 
+import java.lang.ref.WeakReference;
+import java.util.ArrayList;
 import java.util.HashMap;
 import java.util.concurrent.Executor;
 import java.util.concurrent.LinkedBlockingQueue;
@@ -29,7 +34,7 @@ public class ProviderExecutor extends Thread implements Executor {
     @GuardedBy("sExecutors")
     private static HashMap<String, ProviderExecutor> sExecutors = Maps.newHashMap();
 
-    public static Executor forAuthority(String authority) {
+    public static ProviderExecutor forAuthority(String authority) {
         synchronized (sExecutors) {
             ProviderExecutor executor = sExecutors.get(authority);
             if (executor == null) {
@@ -42,10 +47,54 @@ public class ProviderExecutor extends Thread implements Executor {
         }
     }
 
+    public interface Preemptable {
+        void preempt();
+    }
+
     private final LinkedBlockingQueue<Runnable> mQueue = new LinkedBlockingQueue<Runnable>();
 
+    private final ArrayList<WeakReference<Preemptable>> mPreemptable = Lists.newArrayList();
+
+    private void preempt() {
+        synchronized (mPreemptable) {
+            int count = 0;
+            for (WeakReference<Preemptable> ref : mPreemptable) {
+                final Preemptable p = ref.get();
+                if (p != null) {
+                    count++;
+                    p.preempt();
+                }
+            }
+            mPreemptable.clear();
+        }
+    }
+
+    /**
+     * Execute the given task. If given task is not {@link Preemptable}, it will
+     * preempt all outstanding preemptable tasks.
+     */
+    public <P> void execute(AsyncTask<P, ?, ?> task, P... params) {
+        if (task instanceof Preemptable) {
+            synchronized (mPreemptable) {
+                mPreemptable.add(new WeakReference<Preemptable>((Preemptable) task));
+            }
+            task.executeOnExecutor(mNonPreemptingExecutor, params);
+        } else {
+            task.executeOnExecutor(this, params);
+        }
+    }
+
+    private Executor mNonPreemptingExecutor = new Executor() {
+        @Override
+        public void execute(Runnable command) {
+            Preconditions.checkNotNull(command);
+            mQueue.add(command);
+        }
+    };
+
     @Override
     public void execute(Runnable command) {
+        preempt();
         Preconditions.checkNotNull(command);
         mQueue.add(command);
     }