/
AbstractLazyInitializer.java
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/
AbstractLazyInitializer.java
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/*
* Copyright 2020 Google LLC
*
* 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.google.cloud.spanner;
/**
* Generic {@link AbstractLazyInitializer} for any heavy-weight object that might throw an exception
* during initialization. The underlying object is initialized at most once.
*/
public abstract class AbstractLazyInitializer<T> {
private final Object lock = new Object();
private volatile boolean initialized;
private volatile T object;
private volatile Exception error;
/** Returns an initialized instance of T. */
public T get() throws Exception {
// First check without a lock to improve performance.
if (!initialized) {
synchronized (lock) {
if (!initialized) {
try {
object = initialize();
} catch (Exception e) {
error = e;
}
initialized = true;
}
}
}
if (error != null) {
throw error;
}
return object;
}
/**
* Initializes the actual object that should be returned. Is called once the first time an
* instance of T is required.
*/
protected abstract T initialize() throws Exception;
}