1 /* 2 * Copyright (c) 2019, 2024, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. Oracle designates this 8 * particular file as subject to the "Classpath" exception as provided 9 * by Oracle in the LICENSE file that accompanied this code. 10 * 11 * This code is distributed in the hope that it will be useful, but WITHOUT 12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 14 * version 2 for more details (a copy is included in the LICENSE file that 15 * accompanied this code). 16 * 17 * You should have received a copy of the GNU General Public License version 18 * 2 along with this work; if not, write to the Free Software Foundation, 19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 20 * 21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 22 * or visit www.oracle.com if you need additional information or have any 23 * questions. 24 */ 25 26 package jdk.internal.misc; 27 28 import jdk.internal.access.JavaLangAccess; 29 import jdk.internal.access.SharedSecrets; 30 31 /** 32 * Defines static methods to mark the beginning and end of a possibly blocking 33 * operation. The methods are intended to be used with try-finally as follows: 34 * {@snippet lang=java : 35 * boolean attempted = Blocker.begin(); 36 * try { 37 * // blocking operation 38 * } finally { 39 * Blocker.end(attempted); 40 * } 41 * } 42 * If invoked from a virtual thread and the underlying carrier thread is a 43 * CarrierThread then the code in the block runs as if it were in run in 44 * ForkJoinPool.ManagedBlocker. This means the pool can be expanded to support 45 * additional parallelism during the blocking operation. 46 */ 47 public class Blocker { 48 private static final JavaLangAccess JLA; 49 static { 50 JLA = SharedSecrets.getJavaLangAccess(); 51 if (JLA == null) { 52 throw new InternalError("JavaLangAccess not setup"); 53 } 54 } 55 56 private Blocker() { } 57 58 private static Thread currentCarrierThread() { 59 return JLA.currentCarrierThread(); 60 } 61 62 /** 63 * Marks the beginning of a blocking operation. 64 * @return true if tryCompensate attempted 65 */ 66 public static boolean begin() { 67 if (VM.isBooted() 68 && Thread.currentThread().isVirtual() 69 && currentCarrierThread() instanceof CarrierThread ct) { 70 ct.beginBlocking(); 71 return true; 72 } 73 return false; 74 } 75 76 /** 77 * Marks the beginning of a possibly blocking operation. 78 * @param blocking true if the operation may block, otherwise false 79 * @return true if tryCompensate attempted 80 */ 81 public static boolean begin(boolean blocking) { 82 return (blocking) ? begin() : false; 83 } 84 85 /** 86 * Marks the end of an operation that may have blocked. 87 * @param attempted if tryCompensate attempted 88 */ 89 public static void end(boolean attempted) { 90 if (attempted) { 91 CarrierThread ct = (CarrierThread) currentCarrierThread(); 92 ct.endBlocking(); 93 } 94 } 95 }