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      1 /*
      2  * Copyright (C) 2013 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *      http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 
     17 package com.android.documentsui;
     18 
     19 import android.os.AsyncTask;
     20 
     21 import com.android.internal.annotations.GuardedBy;
     22 
     23 import java.lang.ref.WeakReference;
     24 import java.util.ArrayList;
     25 import java.util.HashMap;
     26 import java.util.concurrent.Executor;
     27 import java.util.concurrent.LinkedBlockingQueue;
     28 
     29 public class ProviderExecutor extends Thread implements Executor {
     30 
     31     @GuardedBy("sExecutors")
     32     private static HashMap<String, ProviderExecutor> sExecutors = new HashMap<>();
     33 
     34     public static ProviderExecutor forAuthority(String authority) {
     35         synchronized (sExecutors) {
     36             ProviderExecutor executor = sExecutors.get(authority);
     37             if (executor == null) {
     38                 executor = new ProviderExecutor();
     39                 executor.setName("ProviderExecutor: " + authority);
     40                 executor.start();
     41                 sExecutors.put(authority, executor);
     42             }
     43             return executor;
     44         }
     45     }
     46 
     47     public interface Preemptable {
     48         void preempt();
     49     }
     50 
     51     private final LinkedBlockingQueue<Runnable> mQueue = new LinkedBlockingQueue<Runnable>();
     52 
     53     private final ArrayList<WeakReference<Preemptable>> mPreemptable = new ArrayList<>();
     54 
     55     private void preempt() {
     56         synchronized (mPreemptable) {
     57             int count = 0;
     58             for (WeakReference<Preemptable> ref : mPreemptable) {
     59                 final Preemptable p = ref.get();
     60                 if (p != null) {
     61                     count++;
     62                     p.preempt();
     63                 }
     64             }
     65             mPreemptable.clear();
     66         }
     67     }
     68 
     69     /**
     70      * Execute the given task. If given task is not {@link Preemptable}, it will
     71      * preempt all outstanding preemptable tasks.
     72      */
     73     public <P> void execute(AsyncTask<P, ?, ?> task, P... params) {
     74         if (task instanceof Preemptable) {
     75             synchronized (mPreemptable) {
     76                 mPreemptable.add(new WeakReference<Preemptable>((Preemptable) task));
     77             }
     78             task.executeOnExecutor(mNonPreemptingExecutor, params);
     79         } else {
     80             task.executeOnExecutor(this, params);
     81         }
     82     }
     83 
     84     private Executor mNonPreemptingExecutor = new Executor() {
     85         @Override
     86         public void execute(Runnable command) {
     87             assert(command != null);
     88             mQueue.add(command);
     89         }
     90     };
     91 
     92     @Override
     93     public void execute(Runnable command) {
     94         preempt();
     95         assert(command != null);
     96         mQueue.add(command);
     97     }
     98 
     99     @Override
    100     public void run() {
    101         while (true) {
    102             try {
    103                 final Runnable command = mQueue.take();
    104                 command.run();
    105             } catch (InterruptedException e) {
    106                 // That was weird; let's go look for more tasks.
    107             }
    108         }
    109     }
    110 }
    111