sun.misc

Class Unsafe

java.lang.Object

sun.misc.Unsafe

public final class Unsafe
extends Object

The package name notwithstanding, this class is the quasi-standard way for Java code to gain access to and use functionality which, when unsupervised, would allow one to break the pointer/type safety of Java.

Method Summary

Modifier and Type	Method and Description
Object	allocateInstance(Class<?> c) Allocates an instance of the given class without running the constructor.
int	arrayBaseOffset(Class clazz) Gets the offset from the start of an array object's memory to the memory used to store its initial (zeroeth) element.
int	arrayIndexScale(Class clazz) Gets the size of each element of the given array class.
boolean	compareAndSwapInt(Object obj, long offset, int expectedValue, int newValue) Performs a compare-and-set operation on an int field within the given object.
boolean	compareAndSwapLong(Object obj, long offset, long expectedValue, long newValue) Performs a compare-and-set operation on a long field within the given object.
boolean	compareAndSwapObject(Object obj, long offset, Object expectedValue, Object newValue) Performs a compare-and-set operation on an Object field (that is, a reference field) within the given object.
int	getAndAddInt(Object o, long offset, int delta) Atomically adds the given value to the current value of a field or array element within the given object o at the given offset.
long	getAndAddLong(Object o, long offset, long delta) Atomically adds the given value to the current value of a field or array element within the given object o at the given offset.
int	getAndSetInt(Object o, long offset, int newValue) Atomically exchanges the given value with the current value of a field or array element within the given object o at the given offset.
long	getAndSetLong(Object o, long offset, long newValue) Atomically exchanges the given value with the current value of a field or array element within the given object o at the given offset.
Object	getAndSetObject(Object o, long offset, Object newValue) Atomically exchanges the given reference value with the current reference value of a field or array element within the given object o at the given offset.
int	getInt(Object obj, long offset) Gets an int field from the given object.
int	getIntVolatile(Object obj, long offset) Gets an int field from the given object, using volatile semantics.
long	getLong(Object obj, long offset) Gets a long field from the given object.
long	getLongVolatile(Object obj, long offset) Gets a long field from the given object, using volatile semantics.
Object	getObject(Object obj, long offset) Gets an Object field from the given object.
Object	getObjectVolatile(Object obj, long offset) Gets an Object field from the given object, using volatile semantics.
static Unsafe	getUnsafe() Gets the unique instance of this class.
long	objectFieldOffset(Field field) Gets the raw byte offset from the start of an object's memory to the memory used to store the indicated instance field.
void	park(boolean absolute, long time) Parks the calling thread for the specified amount of time, unless the "permit" for the thread is already available (due to a previous call to unpark(java.lang.Object).
void	putInt(Object obj, long offset, int newValue) Stores an int field into the given object.
void	putIntVolatile(Object obj, long offset, int newValue) Stores an int field into the given object, using volatile semantics.
void	putLong(Object obj, long offset, long newValue) Stores a long field into the given object.
void	putLongVolatile(Object obj, long offset, long newValue) Stores a long field into the given object, using volatile semantics.
void	putObject(Object obj, long offset, Object newValue) Stores an Object field into the given object.
void	putObjectVolatile(Object obj, long offset, Object newValue) Stores an Object field into the given object, using volatile semantics.
void	putOrderedInt(Object obj, long offset, int newValue) Lazy set an int field.
void	putOrderedLong(Object obj, long offset, long newValue) Lazy set a long field.
void	putOrderedObject(Object obj, long offset, Object newValue) Lazy set an object field.
void	unpark(Object obj) Unparks the given object, which must be a Thread.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Detail

getUnsafe

public static Unsafe getUnsafe()

Gets the unique instance of this class. This is only allowed in very limited situations.

objectFieldOffset

public long objectFieldOffset(Field field)

Gets the raw byte offset from the start of an object's memory to the memory used to store the indicated instance field.

Parameters:

field - non-null; the field in question, which must be an instance field

Returns:

the offset to the field

arrayBaseOffset

public int arrayBaseOffset(Class clazz)

Gets the offset from the start of an array object's memory to the memory used to store its initial (zeroeth) element.

Parameters:

clazz - non-null; class in question; must be an array class

Returns:

the offset to the initial element

arrayIndexScale

public int arrayIndexScale(Class clazz)

Gets the size of each element of the given array class.

Parameters:

clazz - non-null; class in question; must be an array class

Returns:

> 0; the size of each element of the array

compareAndSwapInt

public boolean compareAndSwapInt(Object obj,
                                 long offset,
                                 int expectedValue,
                                 int newValue)

Performs a compare-and-set operation on an int field within the given object.

Parameters:

obj - non-null; object containing the field

offset - offset to the field within obj

expectedValue - expected value of the field

newValue - new value to store in the field if the contents are as expected

Returns:

true if the new value was in fact stored, and false if not

compareAndSwapLong

public boolean compareAndSwapLong(Object obj,
                                  long offset,
                                  long expectedValue,
                                  long newValue)

Performs a compare-and-set operation on a long field within the given object.

Parameters:

obj - non-null; object containing the field

offset - offset to the field within obj

expectedValue - expected value of the field

newValue - new value to store in the field if the contents are as expected

Returns:

true if the new value was in fact stored, and false if not

compareAndSwapObject

public boolean compareAndSwapObject(Object obj,
                                    long offset,
                                    Object expectedValue,
                                    Object newValue)

Performs a compare-and-set operation on an Object field (that is, a reference field) within the given object.

Parameters:

obj - non-null; object containing the field

offset - offset to the field within obj

expectedValue - expected value of the field

newValue - new value to store in the field if the contents are as expected

Returns:

true if the new value was in fact stored, and false if not

getIntVolatile

public int getIntVolatile(Object obj,
                          long offset)

Gets an int field from the given object, using volatile semantics.

Parameters:

obj - non-null; object containing the field

offset - offset to the field within obj

Returns:

the retrieved value

putIntVolatile

public void putIntVolatile(Object obj,
                           long offset,
                           int newValue)

Stores an int field into the given object, using volatile semantics.

Parameters:

obj - non-null; object containing the field

offset - offset to the field within obj

newValue - the value to store

getLongVolatile

public long getLongVolatile(Object obj,
                            long offset)

Gets a long field from the given object, using volatile semantics.

Parameters:

obj - non-null; object containing the field

offset - offset to the field within obj

Returns:

the retrieved value

putLongVolatile

public void putLongVolatile(Object obj,
                            long offset,
                            long newValue)

Stores a long field into the given object, using volatile semantics.

Parameters:

obj - non-null; object containing the field

offset - offset to the field within obj

newValue - the value to store

getObjectVolatile

public Object getObjectVolatile(Object obj,
                                long offset)

Gets an Object field from the given object, using volatile semantics.

Parameters:

obj - non-null; object containing the field

offset - offset to the field within obj

Returns:

the retrieved value

putObjectVolatile

public void putObjectVolatile(Object obj,
                              long offset,
                              Object newValue)

Stores an Object field into the given object, using volatile semantics.

Parameters:

obj - non-null; object containing the field

offset - offset to the field within obj

newValue - the value to store

getInt

public int getInt(Object obj,
                  long offset)

Gets an int field from the given object.

Parameters:

obj - non-null; object containing the field

offset - offset to the field within obj

Returns:

the retrieved value

putInt

public void putInt(Object obj,
                   long offset,
                   int newValue)

Stores an int field into the given object.

Parameters:

obj - non-null; object containing the field

offset - offset to the field within obj

newValue - the value to store

putOrderedInt

public void putOrderedInt(Object obj,
                          long offset,
                          int newValue)

Lazy set an int field.

getLong

public long getLong(Object obj,
                    long offset)

Gets a long field from the given object.

Parameters:

obj - non-null; object containing the field

offset - offset to the field within obj

Returns:

the retrieved value

putLong

public void putLong(Object obj,
                    long offset,
                    long newValue)

Stores a long field into the given object.

Parameters:

obj - non-null; object containing the field

offset - offset to the field within obj

newValue - the value to store

putOrderedLong

public void putOrderedLong(Object obj,
                           long offset,
                           long newValue)

Lazy set a long field.

getObject

public Object getObject(Object obj,
                        long offset)

Gets an Object field from the given object.

Parameters:

obj - non-null; object containing the field

offset - offset to the field within obj

Returns:

the retrieved value

putObject

public void putObject(Object obj,
                      long offset,
                      Object newValue)

Stores an Object field into the given object.

Parameters:

obj - non-null; object containing the field

offset - offset to the field within obj

newValue - the value to store

putOrderedObject

public void putOrderedObject(Object obj,
                             long offset,
                             Object newValue)

Lazy set an object field.

park

public void park(boolean absolute,
                 long time)

Parks the calling thread for the specified amount of time, unless the "permit" for the thread is already available (due to a previous call to unpark(java.lang.Object). This method may also return spuriously (that is, without the thread being told to unpark and without the indicated amount of time elapsing).

See LockSupport for more in-depth information of the behavior of this method.

Parameters:

absolute - whether the given time value is absolute milliseconds-since-the-epoch (true) or relative nanoseconds-from-now (false)

time - the (absolute millis or relative nanos) time value

unpark

public void unpark(Object obj)

Unparks the given object, which must be a Thread.

See LockSupport for more in-depth information of the behavior of this method.

Parameters:

obj - non-null; the object to unpark

allocateInstance

public Object allocateInstance(Class<?> c)

Allocates an instance of the given class without running the constructor. The class' will be run, if necessary.

getAndAddInt

public final int getAndAddInt(Object o,
                              long offset,
                              int delta)

Atomically adds the given value to the current value of a field or array element within the given object o at the given offset.

Parameters:

o - object/array to update the field/element in

offset - field/element offset

delta - the value to add

Returns:

the previous value

Since:

1.8

getAndAddLong

public final long getAndAddLong(Object o,
                                long offset,
                                long delta)

Atomically adds the given value to the current value of a field or array element within the given object o at the given offset.

Parameters:

o - object/array to update the field/element in

offset - field/element offset

delta - the value to add

Returns:

the previous value

Since:

1.8

getAndSetInt

public final int getAndSetInt(Object o,
                              long offset,
                              int newValue)

Atomically exchanges the given value with the current value of a field or array element within the given object o at the given offset.

Parameters:

o - object/array to update the field/element in

offset - field/element offset

newValue - new value

Returns:

the previous value

Since:

1.8

getAndSetLong

public final long getAndSetLong(Object o,
                                long offset,
                                long newValue)

Atomically exchanges the given value with the current value of a field or array element within the given object o at the given offset.

Parameters:

o - object/array to update the field/element in

offset - field/element offset

newValue - new value

Returns:

the previous value

Since:

1.8

getAndSetObject

public final Object getAndSetObject(Object o,
                                    long offset,
                                    Object newValue)

Atomically exchanges the given reference value with the current reference value of a field or array element within the given object o at the given offset.

Parameters:

o - object/array to update the field/element in

offset - field/element offset

newValue - new value

Returns:

the previous value

Since:

1.8