/*
* This file is part of the Jikes RVM project (http://jikesrvm.org).
*
* This file is licensed to You under the Eclipse Public License (EPL);
* You may not use this file except in compliance with the License. You
* may obtain a copy of the License at
*
* http://www.opensource.org/licenses/eclipse-1.0.php
*
* See the COPYRIGHT.txt file distributed with this work for information
* regarding copyright ownership.
*/
package org.vmmagic.pragma;
import java.lang.annotation.Retention;
import java.lang.annotation.Target;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.ElementType;
import org.vmmagic.Pragma;
/**
* By default all Java code is interruptible, that is scheduling or garbage
* collection may occur at points within the code. Code can be marked as
* {@link Unpreemptible} or {@link Uninterruptible}, that instructs the JVM to
* avoid garbage collection and thread scheduling. The {@link Uninterruptible}
* annotation disallows any operation that may cause garbage collection or
* thread scheduling, for example memory allocation. The {@link Unpreemptible}
* annotation doesn't disallow operations that can cause garbage collection or
* scheduling, but instructs the JVM to avoid inserting such operations during a
* block of code.
*
* In the internals of a VM most code wants to be {@link Uninterruptible}.
* However, code involved in scheduling and locking will cause context switches,
* and creating exception objects may trigger garbage collection, this code is
* therefore {@link Unpreemptible}.
*
* Any method that is marked as uninterruptible is treated specially by the
* machine code compiler:
*
* (1) the normal thread switch test that would be emitted in the method
* prologue is omitted.
*
* (2) the stack overflow test that would be emitted in the method prologue is
* omitted.
*
* (3) calls to preemptible code causes warnings.
*
* (4) bytecodes that can cause interruption cause warnings.
*
* (5) uninterruptible code will be generated assuming no RuntimeExceptions are
* raised and without any GC maps (since by definition there can be noGC if
* control is not lost).
*
* This is the inverse of {@link Interruptible}.
*/
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.TYPE, ElementType.METHOD})
@Pragma
public @interface Uninterruptible {
/**
* @return Explanation of why code needs to be uninterruptible
*/
String value() default "";
}