1 /* 2 * Copyright 2019 Google LLC 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 package io.perfmark.java9; 18 19 import io.perfmark.impl.Generator; 20 import java.lang.invoke.MethodHandles; 21 import java.lang.invoke.VarHandle; 22 23 final class SecretVarHandleGenerator { 24 25 /** 26 * This class let's PerfMark have fairly low overhead detection if it is enabled, with reasonable 27 * time between enabled and other threads noticing. Since this uses Java 9 APIs, it may not be 28 * available. 29 */ 30 public static final class VarHandleGenerator extends Generator { 31 32 private static final VarHandle GEN; 33 34 static { 35 try { 36 GEN = MethodHandles.lookup().findVarHandle(VarHandleGenerator.class, "gen", long.class); 37 } catch (RuntimeException e) { 38 throw e; 39 } catch (Exception e) { 40 throw new RuntimeException(e); 41 } 42 } 43 VarHandleGenerator()44 public VarHandleGenerator() {} 45 46 @SuppressWarnings("unused") 47 private long gen; 48 49 @Override setGeneration(long generation)50 public void setGeneration(long generation) { 51 GEN.setRelease(this, generation); 52 } 53 54 @Override getGeneration()55 public long getGeneration() { 56 return (long) GEN.getAcquire(this); 57 } 58 59 @Override costOfSetNanos()60 public long costOfSetNanos() { 61 return 3; 62 } 63 64 @Override costOfGetNanos()65 public long costOfGetNanos() { 66 return 2; 67 } 68 } 69 SecretVarHandleGenerator()70 private SecretVarHandleGenerator() {} 71 } 72