rx.internal.util.unsafe.UnsafeAccess Maven / Gradle / Ivy
/**
* Copyright 2014 Netflix, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package rx.internal.util.unsafe;
import java.lang.reflect.Field;
import rx.internal.util.SuppressAnimalSniffer;
import sun.misc.Unsafe;
/**
* All use of this class MUST first check that UnsafeAccess.isUnsafeAvailable() == true
* otherwise NPEs will happen in environments without "suc.misc.Unsafe" such as Android.
*
* Note that you can force RxJava to not use Unsafe API by setting any value to System Property
* {@code rx.unsafe-disable}.
*/
@SuppressAnimalSniffer
public final class UnsafeAccess {
public static final Unsafe UNSAFE;
private static final boolean DISABLED_BY_USER = System.getProperty("rx.unsafe-disable") != null;
private UnsafeAccess() {
throw new IllegalStateException("No instances!");
}
static {
Unsafe u = null;
try {
/*
* This mechanism for getting UNSAFE originally from:
*
* Original License: https://github.com/JCTools/JCTools/blob/master/LICENSE
* Original location: https://github.com/JCTools/JCTools/blob/master/jctools-core/src/main/java/org/jctools/util/UnsafeAccess.java
*/
Field field = Unsafe.class.getDeclaredField("theUnsafe");
field.setAccessible(true);
u = (Unsafe) field.get(null);
} catch (Throwable e) { // NOPMD
// do nothing, hasUnsafe() will return false
}
UNSAFE = u;
}
public static boolean isUnsafeAvailable() {
return UNSAFE != null && !DISABLED_BY_USER;
}
/*
* Methods below are utilities to offer functionality on top of Unsafe. Several of these already exist in Java7/8 but we must support Java 6.
*/
public static int getAndIncrementInt(Object obj, long offset) {
for (;;) {
int current = UNSAFE.getIntVolatile(obj, offset);
int next = current + 1;
if (UNSAFE.compareAndSwapInt(obj, offset, current, next)) {
return current;
}
}
}
public static int getAndAddInt(Object obj, long offset, int n) {
for (;;) {
int current = UNSAFE.getIntVolatile(obj, offset);
int next = current + n;
if (UNSAFE.compareAndSwapInt(obj, offset, current, next)) {
return current;
}
}
}
public static int getAndSetInt(Object obj, long offset, int newValue) {
for (;;) {
int current = UNSAFE.getIntVolatile(obj, offset);
if (UNSAFE.compareAndSwapInt(obj, offset, current, newValue)) {
return current;
}
}
}
public static boolean compareAndSwapInt(Object obj, long offset, int expected, int newValue) {
return UNSAFE.compareAndSwapInt(obj, offset, expected, newValue);
}
/**
* Returns the address of the specific field on the class and
* wraps a NoSuchFieldException into an internal error.
*
* One can avoid using static initializers this way and just assign
* the address directly to the target static field.
* @param clazz the target class
* @param fieldName the target field name
* @return the address (offset) of the field
*/
public static long addressOf(Class clazz, String fieldName) {
try {
Field f = clazz.getDeclaredField(fieldName);
return UNSAFE.objectFieldOffset(f);
} catch (NoSuchFieldException ex) {
InternalError ie = new InternalError();
ie.initCause(ex);
throw ie;
}
}
}