001/* 002 * This file is part of the Jikes RVM project (http://jikesrvm.org). 003 * 004 * This file is licensed to You under the Eclipse Public License (EPL); 005 * You may not use this file except in compliance with the License. You 006 * may obtain a copy of the License at 007 * 008 * http://www.opensource.org/licenses/eclipse-1.0.php 009 * 010 * See the COPYRIGHT.txt file distributed with this work for information 011 * regarding copyright ownership. 012 */ 013package org.vmmagic.pragma; 014 015import java.lang.annotation.Retention; 016import java.lang.annotation.Target; 017import java.lang.annotation.RetentionPolicy; 018import java.lang.annotation.ElementType; 019import org.vmmagic.Pragma; 020 021/** 022 * By default all Java code is interruptible, that is scheduling or garbage 023 * collection may occur at points within the code. Code can be marked as 024 * {@link Unpreemptible} or {@link Uninterruptible}, that instructs the JVM to 025 * avoid garbage collection and thread scheduling. The {@link Uninterruptible} 026 * annotation disallows any operation that may cause garbage collection or 027 * thread scheduling, for example memory allocation. The {@link Unpreemptible} 028 * annotation doesn't disallow operations that can cause garbage collection or 029 * scheduling, but instructs the JVM to avoid inserting such operations during a 030 * block of code.<p> 031 * 032 * In the internals of a VM most code wants to be {@link Uninterruptible}. 033 * However, code involved in scheduling and locking will cause context switches, 034 * and creating exception objects may trigger garbage collection, this code is 035 * therefore {@link Unpreemptible}.<p> 036 * 037 * This pragma is used to declare that a particular method is preemptible. It 038 * is used to override the class-wide pragma {@link Unpreemptible}. 039 */ 040@Retention(RetentionPolicy.RUNTIME) 041@Target({ElementType.TYPE, ElementType.METHOD}) 042@Pragma 043public @interface Preemptible { 044 /** 045 * @return Explanation of why code needs to be preemptible 046 */ 047 String value() default ""; 048}