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/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You 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.landawn.abacus.util;
import java.util.concurrent.atomic.AtomicReference;
import com.landawn.abacus.util.function.Supplier;
// TODO: Auto-generated Javadoc
/**
* Copied from Apache Commons Lang.
*
*
*
* A specialized {@code ConcurrentInitializer} implementation which is similar
* to AtomicInitializer, but ensures that the {@link #initialize()}
* method is called only once.
*
*
* As AtomicInitializer this class is based on atomic variables, so it
* can create an object under concurrent access without synchronization.
* However, it implements an additional check to guarantee that the
* {@link #initialize()} method which actually creates the object cannot be
* called multiple times.
*
*
* Because of this additional check this implementation is slightly less
* efficient than AtomicInitializer, but if the object creation in the
* {@code initialize()} method is expensive or if multiple invocations of
* {@code initialize()} are problematic, it is the better alternative.
*
*
* From its semantics this class has the same properties as
* LazyInitializer. It is a "save" implementation of the lazy
* initializer pattern. Comparing both classes in terms of efficiency is
* difficult because which one is faster depends on multiple factors. Because
* {@code AtomicSafeInitializer} does not use synchronization at all it probably
* outruns LazyInitializer, at least under low or moderate concurrent
* access. Developers should run their own benchmarks on the expected target
* platform to decide which implementation is suitable for their specific use
* case.
*
*
* @param the type of the object managed by this initializer class
* @since 3.0
*/
public final class SafeInitializer {
/** A guard which ensures that initialize() is called only once. */
private final AtomicReference> factory = new AtomicReference<>();
/** Holds the reference to the managed object. */
private final AtomicReference reference = new AtomicReference<>();
/** The supplier. */
private final Supplier supplier;
/**
* Instantiates a new safe initializer.
*
* @param supplier
*/
SafeInitializer(final Supplier supplier) {
this.supplier = supplier;
}
/**
* Get (and initialize, if not initialized yet) the required object.
*
* @return lazily initialized object
* exception
*/
public final T get() {
T result = reference.get();
if (result == null) {
while ((result = reference.get()) == null) {
if (factory.compareAndSet(null, this)) {
reference.set(supplier.get());
}
}
}
return result;
}
/**
*
* @param
* @param supplier
* @return
*/
public static SafeInitializer of(final Supplier supplier) {
N.checkArgNotNull(supplier);
return new SafeInitializer<>(supplier);
}
}