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      1 /*
      2  * Copyright (C) 2007 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 android.database.sqlite;
     18 
     19 import java.io.Closeable;
     20 
     21 /**
     22  * An object created from a SQLiteDatabase that can be closed.
     23  *
     24  * This class implements a primitive reference counting scheme for database objects.
     25  */
     26 public abstract class SQLiteClosable implements Closeable {
     27     private int mReferenceCount = 1;
     28 
     29     /**
     30      * Called when the last reference to the object was released by
     31      * a call to {@link #releaseReference()} or {@link #close()}.
     32      */
     33     protected abstract void onAllReferencesReleased();
     34 
     35     /**
     36      * Called when the last reference to the object was released by
     37      * a call to {@link #releaseReferenceFromContainer()}.
     38      *
     39      * @deprecated Do not use.
     40      */
     41     @Deprecated
     42     protected void onAllReferencesReleasedFromContainer() {
     43         onAllReferencesReleased();
     44     }
     45 
     46     /**
     47      * Acquires a reference to the object.
     48      *
     49      * @throws IllegalStateException if the last reference to the object has already
     50      * been released.
     51      */
     52     public void acquireReference() {
     53         synchronized(this) {
     54             if (mReferenceCount <= 0) {
     55                 throw new IllegalStateException(
     56                         "attempt to re-open an already-closed object: " + this);
     57             }
     58             mReferenceCount++;
     59         }
     60     }
     61 
     62     /**
     63      * Releases a reference to the object, closing the object if the last reference
     64      * was released.
     65      *
     66      * @see #onAllReferencesReleased()
     67      */
     68     public void releaseReference() {
     69         boolean refCountIsZero = false;
     70         synchronized(this) {
     71             refCountIsZero = --mReferenceCount == 0;
     72         }
     73         if (refCountIsZero) {
     74             onAllReferencesReleased();
     75         }
     76     }
     77 
     78     /**
     79      * Releases a reference to the object that was owned by the container of the object,
     80      * closing the object if the last reference was released.
     81      *
     82      * @see #onAllReferencesReleasedFromContainer()
     83      * @deprecated Do not use.
     84      */
     85     @Deprecated
     86     public void releaseReferenceFromContainer() {
     87         boolean refCountIsZero = false;
     88         synchronized(this) {
     89             refCountIsZero = --mReferenceCount == 0;
     90         }
     91         if (refCountIsZero) {
     92             onAllReferencesReleasedFromContainer();
     93         }
     94     }
     95 
     96     /**
     97      * Releases a reference to the object, closing the object if the last reference
     98      * was released.
     99      *
    100      * Calling this method is equivalent to calling {@link #releaseReference}.
    101      *
    102      * @see #releaseReference()
    103      * @see #onAllReferencesReleased()
    104      */
    105     public void close() {
    106         releaseReference();
    107     }
    108 }
    109