io.perfmark.java9.SecretVarHandleGenerator Maven / Gradle / Ivy
/*
* Copyright 2019 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 io.perfmark.java9;
import io.perfmark.impl.Generator;
import java.lang.invoke.MethodHandles;
import java.lang.invoke.VarHandle;
final class SecretVarHandleGenerator {
/**
* This class let's PerfMark have fairly low overhead detection if it is enabled, with reasonable
* time between enabled and other threads noticing. Since this uses Java 9 APIs, it may not be
* available.
*/
public static final class VarHandleGenerator extends Generator {
private static final VarHandle GEN;
static {
try {
GEN = MethodHandles.lookup().findVarHandle(VarHandleGenerator.class, "gen", long.class);
} catch (RuntimeException e) {
throw e;
} catch (Exception e) {
throw new RuntimeException(e);
}
}
public VarHandleGenerator() {}
@SuppressWarnings("unused")
private long gen;
@Override
public void setGeneration(long generation) {
GEN.setOpaque(this, generation);
}
@Override
public long getGeneration() {
return (long) GEN.getOpaque(this);
}
@Override
public long costOfSetNanos() {
return 3;
}
@Override
public long costOfGetNanos() {
return 2;
}
}
private SecretVarHandleGenerator() {
throw new AssertionError("nope");
}
}