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      1 /*
      2  * Copyright (C) 2016 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 static com.android.documentsui.base.Shared.VERBOSE;
     20 
     21 import android.annotation.MainThread;
     22 import android.annotation.Nullable;
     23 import android.util.Log;
     24 
     25 import com.android.documentsui.base.Shared;
     26 import com.android.documentsui.selection.BandController;
     27 
     28 /**
     29  * A lock used by {@link DirectoryLoader} and {@link BandController} to ensure refresh is blocked
     30  * while Band Selection is active.
     31  */
     32 public final class DirectoryReloadLock {
     33     private static final String TAG = "DirectoryReloadLock";
     34 
     35     private int mPauseCount = 0;
     36     private @Nullable Runnable mCallback;
     37 
     38     /**
     39      * Increment the block count by 1
     40      */
     41     @MainThread
     42     public void block() {
     43         Shared.checkMainLoop();
     44         mPauseCount++;
     45         if (VERBOSE) Log.v(TAG, "Block count increments to " + mPauseCount + ".");
     46     }
     47 
     48     /**
     49      * Decrement the block count by 1; If no other object is trying to block and there exists some
     50      * callback, that callback will be run
     51      */
     52     @MainThread
     53     public void unblock() {
     54         Shared.checkMainLoop();
     55         assert(mPauseCount > 0);
     56         mPauseCount--;
     57         if (VERBOSE) Log.v(TAG, "Block count decrements to " + mPauseCount + ".");
     58         if (mPauseCount == 0 && mCallback != null) {
     59             mCallback.run();
     60             mCallback = null;
     61         }
     62     }
     63 
     64     /**
     65      * Attempts to run the given Runnable if not-blocked, or else the Runnable is set to be ran next
     66      * (replacing any previous set Runnables).
     67      */
     68     public void tryUpdate(Runnable update) {
     69         if (mPauseCount == 0) {
     70             update.run();
     71         } else {
     72             mCallback = update;
     73         }
     74     }
     75 }
     76