329 lines
14 KiB
Java
329 lines
14 KiB
Java
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/* Unsafe.java - Unsafe operations needed for concurrency
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Copyright (C) 2006 Free Software Foundation
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This file is part of GNU Classpath.
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GNU Classpath is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2, or (at your option)
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any later version.
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GNU Classpath is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with GNU Classpath; see the file COPYING. If not, write to the
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Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
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02110-1301 USA.
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Linking this library statically or dynamically with other modules is
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making a combined work based on this library. Thus, the terms and
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conditions of the GNU General Public License cover the whole
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combination.
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As a special exception, the copyright holders of this library give you
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permission to link this library with independent modules to produce an
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executable, regardless of the license terms of these independent
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modules, and to copy and distribute the resulting executable under
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terms of your choice, provided that you also meet, for each linked
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independent module, the terms and conditions of the license of that
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module. An independent module is a module which is not derived from
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or based on this library. If you modify this library, you may extend
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this exception to your version of the library, but you are not
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obligated to do so. If you do not wish to do so, delete this
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exception statement from your version. */
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package sun.misc;
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import java.lang.reflect.Field;
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/**
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* This class should provide access to low-level operations and its
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* use should be limited to trusted code. Fields can be accessed using
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* memory addresses, with undefined behaviour occurring if invalid memory
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* addresses are given.
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*
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* @author Tom Tromey (tromey@redhat.com)
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* @author Andrew John Hughes (gnu_andrew@member.fsf.org)
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*/
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public class Unsafe
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{
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// Singleton class.
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private static Unsafe unsafe = new Unsafe();
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/**
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* Private default constructor to prevent creation of an arbitrary
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* number of instances.
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*/
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private Unsafe()
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{
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}
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/**
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* Retrieve the singleton instance of <code>Unsafe</code>. The calling
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* method should guard this instance from untrusted code, as it provides
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* access to low-level operations such as direct memory access.
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*
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* @throws SecurityException if a security manager exists and prevents
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* access to the system properties.
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*/
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public static Unsafe getUnsafe()
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{
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SecurityManager sm = System.getSecurityManager();
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if (sm != null)
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sm.checkPropertiesAccess();
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return unsafe;
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}
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/**
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* Returns the memory address offset of the given static field.
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* The offset is merely used as a means to access a particular field
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* in the other methods of this class. The value is unique to the given
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* field and the same value should be returned on each subsequent call.
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*
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* @param field the field whose offset should be returned.
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* @return the offset of the given field.
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*/
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public native long objectFieldOffset(Field field);
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/**
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* Compares the value of the integer field at the specified offset
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* in the supplied object with the given expected value, and updates
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* it if they match. The operation of this method should be atomic,
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* thus providing an uninterruptible way of updating an integer field.
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*
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* @param obj the object containing the field to modify.
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* @param offset the offset of the integer field within <code>obj</code>.
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* @param expect the expected value of the field.
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* @param update the new value of the field if it equals <code>expect</code>.
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* @return true if the field was changed.
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*/
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public native boolean compareAndSwapInt(Object obj, long offset,
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int expect, int update);
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/**
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* Compares the value of the long field at the specified offset
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* in the supplied object with the given expected value, and updates
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* it if they match. The operation of this method should be atomic,
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* thus providing an uninterruptible way of updating a long field.
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*
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* @param obj the object containing the field to modify.
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* @param offset the offset of the long field within <code>obj</code>.
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* @param expect the expected value of the field.
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* @param update the new value of the field if it equals <code>expect</code>.
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* @return true if the field was changed.
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*/
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public native boolean compareAndSwapLong(Object obj, long offset,
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long expect, long update);
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/**
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* Compares the value of the object field at the specified offset
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* in the supplied object with the given expected value, and updates
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* it if they match. The operation of this method should be atomic,
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* thus providing an uninterruptible way of updating an object field.
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*
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* @param obj the object containing the field to modify.
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* @param offset the offset of the object field within <code>obj</code>.
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* @param expect the expected value of the field.
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* @param update the new value of the field if it equals <code>expect</code>.
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* @return true if the field was changed.
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*/
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public native boolean compareAndSwapObject(Object obj, long offset,
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Object expect, Object update);
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/**
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* Sets the value of the integer field at the specified offset in the
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* supplied object to the given value. This is an ordered or lazy
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* version of <code>putIntVolatile(Object,long,int)</code>, which
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* doesn't guarantee the immediate visibility of the change to other
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* threads. It is only really useful where the integer field is
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* <code>volatile</code>, and is thus expected to change unexpectedly.
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*
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* @param obj the object containing the field to modify.
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* @param offset the offset of the integer field within <code>obj</code>.
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* @param value the new value of the field.
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* @see #putIntVolatile(Object,long,int)
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*/
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public native void putOrderedInt(Object obj, long offset, int value);
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/**
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* Sets the value of the long field at the specified offset in the
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* supplied object to the given value. This is an ordered or lazy
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* version of <code>putLongVolatile(Object,long,long)</code>, which
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* doesn't guarantee the immediate visibility of the change to other
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* threads. It is only really useful where the long field is
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* <code>volatile</code>, and is thus expected to change unexpectedly.
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*
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* @param obj the object containing the field to modify.
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* @param offset the offset of the long field within <code>obj</code>.
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* @param value the new value of the field.
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* @see #putLongVolatile(Object,long,long)
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*/
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public native void putOrderedLong(Object obj, long offset, long value);
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/**
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* Sets the value of the object field at the specified offset in the
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* supplied object to the given value. This is an ordered or lazy
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* version of <code>putObjectVolatile(Object,long,Object)</code>, which
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* doesn't guarantee the immediate visibility of the change to other
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* threads. It is only really useful where the object field is
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* <code>volatile</code>, and is thus expected to change unexpectedly.
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*
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* @param obj the object containing the field to modify.
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* @param offset the offset of the object field within <code>obj</code>.
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* @param value the new value of the field.
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*/
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public native void putOrderedObject(Object obj, long offset, Object value);
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/**
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* Sets the value of the integer field at the specified offset in the
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* supplied object to the given value, with volatile store semantics.
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*
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* @param obj the object containing the field to modify.
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* @param offset the offset of the integer field within <code>obj</code>.
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* @param value the new value of the field.
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*/
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public native void putIntVolatile(Object obj, long offset, int value);
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/**
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* Retrieves the value of the integer field at the specified offset in the
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* supplied object with volatile load semantics.
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*
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* @param obj the object containing the field to read.
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* @param offset the offset of the integer field within <code>obj</code>.
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*/
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public native int getIntVolatile(Object obj, long offset);
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/**
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* Sets the value of the long field at the specified offset in the
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* supplied object to the given value, with volatile store semantics.
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*
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* @param obj the object containing the field to modify.
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* @param offset the offset of the long field within <code>obj</code>.
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* @param value the new value of the field.
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* @see #putLong(Object,long,long)
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*/
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public native void putLongVolatile(Object obj, long offset, long value);
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/**
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* Sets the value of the long field at the specified offset in the
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* supplied object to the given value.
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*
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* @param obj the object containing the field to modify.
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* @param offset the offset of the long field within <code>obj</code>.
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* @param value the new value of the field.
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* @see #putLongVolatile(Object,long,long)
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*/
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public native void putLong(Object obj, long offset, long value);
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/**
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* Retrieves the value of the long field at the specified offset in the
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* supplied object with volatile load semantics.
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*
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* @param obj the object containing the field to read.
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* @param offset the offset of the long field within <code>obj</code>.
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* @see #getLong(Object,long)
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*/
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public native long getLongVolatile(Object obj, long offset);
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/**
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* Retrieves the value of the long field at the specified offset in the
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* supplied object.
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*
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* @param obj the object containing the field to read.
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* @param offset the offset of the long field within <code>obj</code>.
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* @see #getLongVolatile(Object,long)
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*/
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public native long getLong(Object obj, long offset);
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/**
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* Sets the value of the object field at the specified offset in the
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* supplied object to the given value, with volatile store semantics.
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*
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* @param obj the object containing the field to modify.
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* @param offset the offset of the object field within <code>obj</code>.
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* @param value the new value of the field.
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* @see #putObject(Object,long,Object)
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*/
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public native void putObjectVolatile(Object obj, long offset, Object value);
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/**
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* Sets the value of the object field at the specified offset in the
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* supplied object to the given value.
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*
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* @param obj the object containing the field to modify.
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* @param offset the offset of the object field within <code>obj</code>.
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* @param value the new value of the field.
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* @see #putObjectVolatile(Object,long,Object)
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*/
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public native void putObject(Object obj, long offset, Object value);
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/**
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* Retrieves the value of the object field at the specified offset in the
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* supplied object with volatile load semantics.
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*
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* @param obj the object containing the field to read.
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* @param offset the offset of the object field within <code>obj</code>.
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*/
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public native Object getObjectVolatile(Object obj, long offset);
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/**
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* Returns the offset of the first element for a given array class.
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* To access elements of the array class, this value may be used along
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* with that returned by
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* <a href="#arrayIndexScale"><code>arrayIndexScale</code></a>,
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* if non-zero.
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*
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* @param arrayClass the class for which the first element's address should
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* be obtained.
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* @return the offset of the first element of the array class.
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* @see arrayIndexScale(Class)
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*/
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public native int arrayBaseOffset(Class arrayClass);
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/**
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* Returns the scale factor used for addressing elements of the supplied
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* array class. Where a suitable scale factor can not be returned (e.g.
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* for primitive types), zero should be returned. The returned value
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* can be used with
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* <a href="#arrayBaseOffset"><code>arrayBaseOffset</code></a>
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* to access elements of the class.
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*
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* @param arrayClass the class whose scale factor should be returned.
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* @return the scale factor, or zero if not supported for this array class.
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*/
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public native int arrayIndexScale(Class arrayClass);
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/**
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* Releases the block on a thread created by
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* <a href="#park"><code>park</code></a>. This method can also be used
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* to terminate a blockage caused by a prior call to <code>park</code>.
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* This operation is unsafe, as the thread must be guaranteed to be
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* live. This is true of Java, but not native code.
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*
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* @param thread the thread to unblock.
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*/
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public native void unpark(Thread thread);
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/**
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* Blocks the thread until a matching
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* <a href="#unpark"><code>unpark</code></a> occurs, the thread is
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* interrupted or the optional timeout expires. If an <code>unpark</code>
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* call has already occurred, this also counts. A timeout value of zero
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* is defined as no timeout. When <code>isAbsolute</code> is
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* <code>true</code>, the timeout is in milliseconds relative to the
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* epoch. Otherwise, the value is the number of nanoseconds which must
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* occur before timeout. This call may also return spuriously (i.e.
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* for no apparent reason).
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*
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* @param isAbsolute true if the timeout is specified in milliseconds from
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* the epoch.
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* @param time either the number of nanoseconds to wait, or a time in
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* milliseconds from the epoch to wait for.
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*/
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public native void park(boolean isAbsolute, long time);
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}
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