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VoltDB client interface libraries
/*
* 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 org.jctools_voltpatches.util;
import sun.misc.Unsafe;
import java.lang.reflect.Field;
import java.util.concurrent.atomic.AtomicReferenceArray;
import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;
/**
* Why should we resort to using Unsafe?
*
* - To construct class fields which allow volatile/ordered/plain access: This requirement is covered by
* {@link AtomicReferenceFieldUpdater} and similar but their performance is arguably worse than the DIY approach
* (depending on JVM version) while Unsafe intrinsification is a far lesser challenge for JIT compilers.
*
- To construct flavors of {@link AtomicReferenceArray}.
*
- Other use cases exist but are not present in this library yet.
*
*
* @author nitsanw
*
*/
public class UnsafeAccess {
public static final boolean SUPPORTS_GET_AND_SET;
public static final Unsafe UNSAFE;
static {
try {
final Field field = Unsafe.class.getDeclaredField("theUnsafe");
field.setAccessible(true);
UNSAFE = (Unsafe) field.get(null);
} catch (Exception e) {
SUPPORTS_GET_AND_SET = false;
throw new RuntimeException(e);
}
boolean getAndSetSupport = false;
try {
Unsafe.class.getMethod("getAndSetObject", Object.class, Long.TYPE,Object.class);
getAndSetSupport = true;
} catch (Exception e) {
}
SUPPORTS_GET_AND_SET = getAndSetSupport;
}
}