java.util.concurrent.atomic.AtomicIntegerFieldUpdater Maven / Gradle / Ivy
/*
* Written by Doug Lea with assistance from members of JCP JSR-166
* Expert Group and released to the public domain, as explained at
* http://creativecommons.org/publicdomain/zero/1.0/
*/
package java.util.concurrent.atomic;
import dalvik.system.VMStack; // android-added
import sun.misc.Unsafe;
import java.lang.reflect.Field;
import java.lang.reflect.Modifier;
/**
* A reflection-based utility that enables atomic updates to
* designated {@code volatile int} fields of designated classes.
* This class is designed for use in atomic data structures in which
* several fields of the same node are independently subject to atomic
* updates.
*
* Note that the guarantees of the {@code compareAndSet}
* method in this class are weaker than in other atomic classes.
* Because this class cannot ensure that all uses of the field
* are appropriate for purposes of atomic access, it can
* guarantee atomicity only with respect to other invocations of
* {@code compareAndSet} and {@code set} on the same updater.
*
* @since 1.5
* @author Doug Lea
* @param The type of the object holding the updatable field
*/
public abstract class AtomicIntegerFieldUpdater {
/**
* Creates and returns an updater for objects with the given field.
* The Class argument is needed to check that reflective types and
* generic types match.
*
* @param tclass the class of the objects holding the field
* @param fieldName the name of the field to be updated
* @return the updater
* @throws IllegalArgumentException if the field is not a
* volatile integer type
* @throws RuntimeException with a nested reflection-based
* exception if the class does not hold field or is the wrong type,
* or the field is inaccessible to the caller according to Java language
* access control
*/
public static AtomicIntegerFieldUpdater newUpdater(Class tclass, String fieldName) {
return new AtomicIntegerFieldUpdaterImpl(tclass, fieldName);
}
/**
* Protected do-nothing constructor for use by subclasses.
*/
protected AtomicIntegerFieldUpdater() {
}
/**
* Atomically sets the field of the given object managed by this updater
* to the given updated value if the current value {@code ==} the
* expected value. This method is guaranteed to be atomic with respect to
* other calls to {@code compareAndSet} and {@code set}, but not
* necessarily with respect to other changes in the field.
*
* @param obj An object whose field to conditionally set
* @param expect the expected value
* @param update the new value
* @return true if successful
* @throws ClassCastException if {@code obj} is not an instance
* of the class possessing the field established in the constructor
*/
public abstract boolean compareAndSet(T obj, int expect, int update);
/**
* Atomically sets the field of the given object managed by this updater
* to the given updated value if the current value {@code ==} the
* expected value. This method is guaranteed to be atomic with respect to
* other calls to {@code compareAndSet} and {@code set}, but not
* necessarily with respect to other changes in the field.
*
* May fail
* spuriously and does not provide ordering guarantees, so is
* only rarely an appropriate alternative to {@code compareAndSet}.
*
* @param obj An object whose field to conditionally set
* @param expect the expected value
* @param update the new value
* @return true if successful
* @throws ClassCastException if {@code obj} is not an instance
* of the class possessing the field established in the constructor
*/
public abstract boolean weakCompareAndSet(T obj, int expect, int update);
/**
* Sets the field of the given object managed by this updater to the
* given updated value. This operation is guaranteed to act as a volatile
* store with respect to subsequent invocations of {@code compareAndSet}.
*
* @param obj An object whose field to set
* @param newValue the new value
*/
public abstract void set(T obj, int newValue);
/**
* Eventually sets the field of the given object managed by this
* updater to the given updated value.
*
* @param obj An object whose field to set
* @param newValue the new value
* @since 1.6
*/
public abstract void lazySet(T obj, int newValue);
/**
* Gets the current value held in the field of the given object managed
* by this updater.
*
* @param obj An object whose field to get
* @return the current value
*/
public abstract int get(T obj);
/**
* Atomically sets the field of the given object managed by this updater
* to the given value and returns the old value.
*
* @param obj An object whose field to get and set
* @param newValue the new value
* @return the previous value
*/
public int getAndSet(T obj, int newValue) {
for (;;) {
int current = get(obj);
if (compareAndSet(obj, current, newValue))
return current;
}
}
/**
* Atomically increments by one the current value of the field of the
* given object managed by this updater.
*
* @param obj An object whose field to get and set
* @return the previous value
*/
public int getAndIncrement(T obj) {
for (;;) {
int current = get(obj);
int next = current + 1;
if (compareAndSet(obj, current, next))
return current;
}
}
/**
* Atomically decrements by one the current value of the field of the
* given object managed by this updater.
*
* @param obj An object whose field to get and set
* @return the previous value
*/
public int getAndDecrement(T obj) {
for (;;) {
int current = get(obj);
int next = current - 1;
if (compareAndSet(obj, current, next))
return current;
}
}
/**
* Atomically adds the given value to the current value of the field of
* the given object managed by this updater.
*
* @param obj An object whose field to get and set
* @param delta the value to add
* @return the previous value
*/
public int getAndAdd(T obj, int delta) {
for (;;) {
int current = get(obj);
int next = current + delta;
if (compareAndSet(obj, current, next))
return current;
}
}
/**
* Atomically increments by one the current value of the field of the
* given object managed by this updater.
*
* @param obj An object whose field to get and set
* @return the updated value
*/
public int incrementAndGet(T obj) {
for (;;) {
int current = get(obj);
int next = current + 1;
if (compareAndSet(obj, current, next))
return next;
}
}
/**
* Atomically decrements by one the current value of the field of the
* given object managed by this updater.
*
* @param obj An object whose field to get and set
* @return the updated value
*/
public int decrementAndGet(T obj) {
for (;;) {
int current = get(obj);
int next = current - 1;
if (compareAndSet(obj, current, next))
return next;
}
}
/**
* Atomically adds the given value to the current value of the field of
* the given object managed by this updater.
*
* @param obj An object whose field to get and set
* @param delta the value to add
* @return the updated value
*/
public int addAndGet(T obj, int delta) {
for (;;) {
int current = get(obj);
int next = current + delta;
if (compareAndSet(obj, current, next))
return next;
}
}
/**
* Standard hotspot implementation using intrinsics
*/
private static class AtomicIntegerFieldUpdaterImpl extends AtomicIntegerFieldUpdater {
private static final Unsafe unsafe = Unsafe.getUnsafe();
private final long offset;
private final Class tclass;
private final Class cclass;
AtomicIntegerFieldUpdaterImpl(Class tclass, String fieldName) {
final Field field;
final Class caller;
final int modifiers;
try {
field = tclass.getDeclaredField(fieldName); // android-changed
caller = VMStack.getStackClass2(); // android-changed
modifiers = field.getModifiers();
// BEGIN android-removed
// sun.reflect.misc.ReflectUtil.ensureMemberAccess(
// caller, tclass, null, modifiers);
// ClassLoader cl = tclass.getClassLoader();
// ClassLoader ccl = caller.getClassLoader();
// if ((ccl != null) && (ccl != cl) &&
// ((cl == null) || !isAncestor(cl, ccl))) {
// sun.reflect.misc.ReflectUtil.checkPackageAccess(tclass);
// }
// END android-removed
// BEGIN android-removed
// } catch (PrivilegedActionException pae) {
// throw new RuntimeException(pae.getException());
// END android-removed
} catch (Exception ex) {
throw new RuntimeException(ex);
}
Class fieldt = field.getType();
if (fieldt != int.class)
throw new IllegalArgumentException("Must be integer type");
if (!Modifier.isVolatile(modifiers))
throw new IllegalArgumentException("Must be volatile type");
this.cclass = (Modifier.isProtected(modifiers) &&
caller != tclass) ? caller : null;
this.tclass = tclass;
offset = unsafe.objectFieldOffset(field);
}
// BEGIN android-removed
// /**
// * Returns true if the second classloader can be found in the first
// * classloader's delegation chain.
// * Equivalent to the inaccessible: first.isAncestor(second).
// */
// private static boolean isAncestor(ClassLoader first, ClassLoader second) {
// ClassLoader acl = first;
// do {
// acl = acl.getParent();
// if (second == acl) {
// return true;
// }
// } while (acl != null);
// return false;
// }
// END android-removed
private void fullCheck(T obj) {
if (!tclass.isInstance(obj))
throw new ClassCastException();
if (cclass != null)
ensureProtectedAccess(obj);
}
public boolean compareAndSet(T obj, int expect, int update) {
if (obj == null || obj.getClass() != tclass || cclass != null) fullCheck(obj);
return unsafe.compareAndSwapInt(obj, offset, expect, update);
}
public boolean weakCompareAndSet(T obj, int expect, int update) {
if (obj == null || obj.getClass() != tclass || cclass != null) fullCheck(obj);
return unsafe.compareAndSwapInt(obj, offset, expect, update);
}
public void set(T obj, int newValue) {
if (obj == null || obj.getClass() != tclass || cclass != null) fullCheck(obj);
unsafe.putIntVolatile(obj, offset, newValue);
}
public void lazySet(T obj, int newValue) {
if (obj == null || obj.getClass() != tclass || cclass != null) fullCheck(obj);
unsafe.putOrderedInt(obj, offset, newValue);
}
public final int get(T obj) {
if (obj == null || obj.getClass() != tclass || cclass != null) fullCheck(obj);
return unsafe.getIntVolatile(obj, offset);
}
private void ensureProtectedAccess(T obj) {
if (cclass.isInstance(obj)) {
return;
}
throw new RuntimeException(
new IllegalAccessException("Class " +
cclass.getName() +
" can not access a protected member of class " +
tclass.getName() +
" using an instance of " +
obj.getClass().getName()
)
);
}
}
}