From 2f4f2d0f274229fb82ca26614212ff12a3f77610 Mon Sep 17 00:00:00 2001
From: Artem Shvadskiy <ashvadskiy@cyngn.com>
Date: Mon, 9 May 2016 11:17:08 -0700
Subject: Update LookupProvider to new CallerInfoAPI spec

Change-Id: Icfd981473fdece5bf90016223909be54ee0f4b05
issue-id: DIALER-719 DIALER-724
(cherry picked from commit 13c6c99fa4799c3af18b45a4deaa9edbb6de04d0)
---
 .../contacts/common/util/SingletonHolder.java      | 93 ++++++++++++++++++++++
 1 file changed, 93 insertions(+)
 create mode 100644 src/com/android/contacts/common/util/SingletonHolder.java

(limited to 'src/com/android/contacts/common/util/SingletonHolder.java')

diff --git a/src/com/android/contacts/common/util/SingletonHolder.java b/src/com/android/contacts/common/util/SingletonHolder.java
new file mode 100644
index 00000000..c1a183d4
--- /dev/null
+++ b/src/com/android/contacts/common/util/SingletonHolder.java
@@ -0,0 +1,93 @@
+/*
+ * Copyright (C) 2016 The CyanogenMod Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
+ * in compliance with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software distributed under the License
+ * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
+ * or implied. See the License for the specific language governing permissions and limitations under
+ * the License.
+ */
+
+package com.android.contacts.common.util;
+
+/**
+ * Encapsulates a threadsafe singleton pattern.
+ *
+ * This class is designed to be used as a public constant, living within a class that has a private constructor.
+ * It defines a {@link #create(I)} method that will only ever be called once, upon the first call of {@link #get(I)}.
+ * That method is responsible for creating the actual singleton instance, and that instance will be returned for all
+ * future calls of {@link #get(I)}.
+ *
+ * Example:
+ * <code>
+ *     public class FooSingleton {
+ *         public static final SingletonHolder&lt;FooSingleton, ParamObject&gt; HOLDER =
+ *                 new SingletonHolder&lt;FooSingleton, ParamObject&gt;() {
+ *                     @Override
+ *                     protected FooSingleton create(ParamObject param) {
+ *                         return new FooSingleton(param);
+ *                     }
+ *                 };
+ *
+ *         private FooSingleton(ParamObject param) {
+ *
+ *         }
+ *     }
+ *
+ *     // somewhere else
+ *     FooSingleton.HOLDER.get(params).doStuff();
+ * </code>
+ * @param <E> The type of the class to hold as a singleton.
+ * @param <I> A parameter object to use during creation of the singleton object.
+ */
+public abstract class SingletonHolder<E, I> {
+    E mInstance;
+    final Object LOCK = new Object();
+
+    public E get(I initializer) {
+        if (null == mInstance) {
+            synchronized (LOCK) {
+                if (null == mInstance) {
+                    mInstance = create(initializer);
+                }
+            }
+        }
+
+        return mInstance;
+    }
+
+    protected abstract E create(I initializer);
+
+    /**
+     * Specialized version of {@link SingletonHolder} which will keep a count of referring
+     * objects, and clear the instance when all references have been removed.
+     *
+     * @param <E> The type of the class to hold as a singleton.
+     * @param <I> A parameter object to use during creation of the singleton object.
+     */
+    public static abstract class RefCountedSingletonHolder<E, I> extends SingletonHolder<E, I> {
+        private int mRefCount;
+
+        public E get(I initializer) {
+            synchronized (LOCK) {
+                mRefCount++;
+            }
+            return super.get(initializer);
+        }
+
+        public void release() {
+            synchronized (LOCK) {
+                if(--mRefCount == 0) {
+                    destroy(mInstance);
+                    mInstance = null;
+                }
+            }
+        }
+
+        protected abstract void destroy(E instance);
+    }
+}
-- 
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