sf.tools.reflect

Class UnsafeWrapper

java.lang.Object

sf.tools.reflect.UnsafeWrapper

public final class UnsafeWrapper
extends Object

https://www.jianshu.com/p/ce616620e720 使用反射实现对unsafe的调用.

Method Summary

Modifier and Type	Method and Description
static <T> T	allocateInstance(Class<T> klass) Allocates an instance but does not run any constructor.
static long	allocateMemory(long bytes) Allocates a new block of native memory, of the given size in bytes.
static int	arrayBaseOffset(Class<?> arrayClass) Reports the offset of the first element in the storage allocation of a given array class.
static int	arrayIndexScale(Class<?> arrayClass) Reports the scale factor for addressing elements in the storage allocation of a given array class.
static boolean	compareAndSwapInt(Object o, long offset, int expected, int x) Atomically updates Java variable to x if it is currently holding expected.
static boolean	compareAndSwapLong(Object o, long offset, long expected, long x) Atomically updates Java variable to x if it is currently holding expected.
static boolean	compareAndSwapObject(Object o, long offset, Object expected, Object x) Atomically updates Java variable to x if it is currently holding expected.
static void	freeMemory(long address) Disposes of a block of native memory, as obtained from allocateMemory(long) or reallocateMemory(long, long).
static boolean	getBoolean(Object o, long offset)
static byte	getByte(long address) Fetches a value from a given memory address.
static byte	getByte(Object o, long offset)
static char	getChar(long address)
static char	getChar(Object o, long offset)
static double	getDouble(long address)
static double	getDouble(Object o, long offset)
static float	getFloat(long address)
static float	getFloat(Object o, long offset)
static UnsafeWrapper	getInstance()
static int	getInt(long address)
static int	getInt(Object o, long offset) Fetches a value from a given Java variable.
static long	getLong(long address)
static long	getLong(Object o, long offset)
static Object	getObject(Object o, long offset) Fetches a reference value from a given Java variable.
static short	getShort(long address)
static short	getShort(Object o, long offset)
static long	objectFieldOffset(Field field) Reports the location of a given field in the storage allocation of its class.
void	park(boolean isAbsolute, long time) Blocks current thread, returning when a balancing unpark occurs, or a balancing unpark has already occurred, or the thread is interrupted, or, if not absolute and time is not zero, the given time nanoseconds have elapsed, or if absolute, the given deadline in milliseconds since Epoch has passed, or spuriously (i.e., returning for no "reason").
static void	putBoolean(Object o, long offset, boolean x)
static void	putByte(long address, byte x) Stores a value into a given memory address.
static void	putByte(Object o, long offset, byte x)
static void	putByteArray(long startAddress, byte[] bytes) 把一个byte[]放到指定的内存块中
static void	putChar(long address, char x)
static void	putChar(Object o, long offset, char x)
static void	putDouble(long address, double x)
static void	putDouble(Object o, long offset, double x)
static void	putFloat(long address, float x)
static void	putFloat(Object o, long offset, float x)
static void	putInt(long address, int x)
static void	putInt(Object o, long offset, int x) Stores a value into a given Java variable.
static void	putLong(long address, long x)
static void	putLong(Object o, long offset, long x)
static void	putObject(Object o, long offset, Object x) Stores a reference value into a given Java variable.
static void	putShort(long address, short x)
static void	putShort(Object o, long offset, short x)
static byte[]	readByteArray(long startAddress, int len) 从内存中读取一个数组
static long	reallocateMemory(long address, long bytes) Resizes a new block of native memory, to the given size in bytes.
static Object	staticFieldBase(Field field) Reports the location of a given static field, in conjunction with staticFieldOffset(java.lang.reflect.Field).
static long	staticFieldOffset(Field field) Reports the location of a given static field, in conjunction with staticFieldBase(java.lang.reflect.Field).
void	unpark(Object thread) Unblocks the given thread blocked on park, or, if it is not blocked, causes the subsequent call to park not to block.

Methods inherited from class java.lang.Object

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

Method Detail

getInstance

public static UnsafeWrapper getInstance()

allocateMemory

public static long allocateMemory(long bytes)

Allocates a new block of native memory, of the given size in bytes. The contents of the memory are uninitialized; they will generally be garbage. The resulting native pointer will never be zero, and will be aligned for all value types. Dispose of this memory by calling freeMemory(long), or resize it with reallocateMemory(long, long). Note: It is the resposibility of the caller to make sure arguments are checked before the methods are called. While some rudimentary checks are performed on the input, the checks are best effort and when performance is an overriding priority, as when methods of this class are optimized by the runtime compiler, some or all checks (if any) may be elided. Hence, the caller must not rely on the checks and corresponding exceptions!

Throws:

RuntimeException - if the size is negative or too large for the native size_t type

OutOfMemoryError - if the allocation is refused by the system

See Also:

getByte(long), putByte(long, byte)

reallocateMemory

public static long reallocateMemory(long address,
                                    long bytes)

Resizes a new block of native memory, to the given size in bytes. The contents of the new block past the size of the old block are uninitialized; they will generally be garbage. The resulting native pointer will be zero if and only if the requested size is zero. The resulting native pointer will be aligned for all value types. Dispose of this memory by calling freeMemory(long), or resize it with reallocateMemory(long, long). The address passed to this method may be null, in which case an allocation will be performed. Note: It is the resposibility of the caller to make sure arguments are checked before the methods are called. While some rudimentary checks are performed on the input, the checks are best effort and when performance is an overriding priority, as when methods of this class are optimized by the runtime compiler, some or all checks (if any) may be elided. Hence, the caller must not rely on the checks and corresponding exceptions!

Throws:

RuntimeException - if the size is negative or too large for the native size_t type

OutOfMemoryError - if the allocation is refused by the system

See Also:

allocateMemory(long)

freeMemory

public static void freeMemory(long address)

Disposes of a block of native memory, as obtained from allocateMemory(long) or reallocateMemory(long, long). The address passed to this method may be null, in which case no action is taken. Note: It is the resposibility of the caller to make sure arguments are checked before the methods are called. While some rudimentary checks are performed on the input, the checks are best effort and when performance is an overriding priority, as when methods of this class are optimized by the runtime compiler, some or all checks (if any) may be elided. Hence, the caller must not rely on the checks and corresponding exceptions!

Throws:

RuntimeException - if any of the arguments is invalid

See Also:

allocateMemory(long)

getByte

public static byte getByte(long address)

Fetches a value from a given memory address. If the address is zero, or does not point into a block obtained from allocateMemory(long), the results are undefined.

See Also:

allocateMemory(long)

putByte

public static void putByte(long address,
                           byte x)

Stores a value into a given memory address. If the address is zero, or does not point into a block obtained from allocateMemory(long), the results are undefined.

See Also:

getByte(long)

readByteArray

public static byte[] readByteArray(long startAddress,
                                   int len)

从内存中读取一个数组

Parameters:

startAddress - 内存起始地址

len - 要读取的数组的长度

Returns:

返回从内存中读取到的数组

putByteArray

public static void putByteArray(long startAddress,
                                byte[] bytes)

把一个byte[]放到指定的内存块中

Parameters:

startAddress - 内存块的起始位置

bytes - 要被存放的内存

getShort

public static short getShort(long address)

See Also:

getByte(long)

putShort

public static void putShort(long address,
                            short x)

See Also:

putByte(long, byte)

getChar

public static char getChar(long address)

See Also:

getByte(long)

putChar

public static void putChar(long address,
                           char x)

See Also:

putByte(long, byte)

getInt

public static int getInt(long address)

See Also:

getByte(long)

putInt

public static void putInt(long address,
                          int x)

See Also:

putByte(long, byte)

getLong

public static long getLong(long address)

See Also:

getByte(long)

putLong

public static void putLong(long address,
                           long x)

See Also:

putByte(long, byte)

getFloat

public static float getFloat(long address)

See Also:

getByte(long)

putFloat

public static void putFloat(long address,
                            float x)

See Also:

putByte(long, byte)

getDouble

public static double getDouble(long address)

See Also:

getByte(long)

putDouble

public static void putDouble(long address,
                             double x)

See Also:

putByte(long, byte)

allocateInstance

public static <T> T allocateInstance(Class<T> klass)

Allocates an instance but does not run any constructor. Initializes the class if it has not yet been.

getByte

public static byte getByte(Object o,
                           long offset)

See Also:

getInt(Object, long)

putByte

public static void putByte(Object o,
                           long offset,
                           byte x)

See Also:

putInt(Object, long, int)

getInt

public static int getInt(Object o,
                         long offset)

Fetches a value from a given Java variable. More specifically, fetches a field or array element within the given object o at the given offset, or (if o is null) from the memory address whose numerical value is the given offset.

The results are undefined unless one of the following cases is true:

• The offset was obtained from objectFieldOffset(java.lang.reflect.Field) on the Field of some Java field and the object referred to by o is of a class compatible with that field's class.
• The offset and object reference o (either null or non-null) were both obtained via staticFieldOffset(java.lang.reflect.Field) and staticFieldBase(java.lang.reflect.Field) (respectively) from the reflective Field representation of some Java field.
• The object referred to by o is an array, and the offset is an integer of the form B+N*S, where N is a valid index into the array, and B and S are the values obtained by arrayBaseOffset(java.lang.Class<?>) and arrayIndexScale(java.lang.Class<?>) (respectively) from the array's class. The value referred to is the Nth element of the array.

If one of the above cases is true, the call references a specific Java variable (field or array element). However, the results are undefined if that variable is not in fact of the type returned by this method.

This method refers to a variable by means of two parameters, and so it provides (in effect) a double-register addressing mode for Java variables. When the object reference is null, this method uses its offset as an absolute address. This is similar in operation to methods such as getInt(long), which provide (in effect) a single-register addressing mode for non-Java variables. However, because Java variables may have a different layout in memory from non-Java variables, programmers should not assume that these two addressing modes are ever equivalent. Also, programmers should remember that offsets from the double-register addressing mode cannot be portably confused with longs used in the single-register addressing mode.

Parameters:

o - Java heap object in which the variable resides, if any, else null

offset - indication of where the variable resides in a Java heap object, if any, else a memory address locating the variable statically

Returns:

the value fetched from the indicated Java variable

Throws:

RuntimeException - No defined exceptions are thrown, not even NullPointerException

putInt

public static void putInt(Object o,
                          long offset,
                          int x)

Stores a value into a given Java variable.

The first two parameters are interpreted exactly as with getInt(Object, long) to refer to a specific Java variable (field or array element). The given value is stored into that variable.

The variable must be of the same type as the method parameter x.

Parameters:

o - Java heap object in which the variable resides, if any, else null

offset - indication of where the variable resides in a Java heap object, if any, else a memory address locating the variable statically

x - the value to store into the indicated Java variable

Throws:

RuntimeException - No defined exceptions are thrown, not even NullPointerException

getObject

public static Object getObject(Object o,
                               long offset)

Fetches a reference value from a given Java variable.

See Also:

getInt(Object, long)

putObject

public static void putObject(Object o,
                             long offset,
                             Object x)

Stores a reference value into a given Java variable.

Unless the reference x being stored is either null or matches the field type, the results are undefined. If the reference o is non-null, card marks or other store barriers for that object (if the VM requires them) are updated.

See Also:

putInt(Object, long, int)

getBoolean

public static boolean getBoolean(Object o,
                                 long offset)

See Also:

getInt(Object, long)

putBoolean

public static void putBoolean(Object o,
                              long offset,
                              boolean x)

See Also:

putInt(Object, long, int)

getShort

public static short getShort(Object o,
                             long offset)

See Also:

getInt(Object, long)

putShort

public static void putShort(Object o,
                            long offset,
                            short x)

See Also:

putInt(Object, long, int)

getChar

public static char getChar(Object o,
                           long offset)

See Also:

getInt(Object, long)

putChar

public static void putChar(Object o,
                           long offset,
                           char x)

See Also:

putInt(Object, long, int)

getLong

public static long getLong(Object o,
                           long offset)

See Also:

getInt(Object, long)

putLong

public static void putLong(Object o,
                           long offset,
                           long x)

See Also:

putInt(Object, long, int)

getFloat

public static float getFloat(Object o,
                             long offset)

See Also:

getInt(Object, long)

putFloat

public static void putFloat(Object o,
                            long offset,
                            float x)

See Also:

putInt(Object, long, int)

getDouble

public static double getDouble(Object o,
                               long offset)

See Also:

getInt(Object, long)

putDouble

public static void putDouble(Object o,
                             long offset,
                             double x)

See Also:

putInt(Object, long, int)

objectFieldOffset

public static long objectFieldOffset(Field field)

Reports the location of a given field in the storage allocation of its class. Do not expect to perform any sort of arithmetic on this offset; it is just a cookie which is passed to the unsafe heap memory accessors.

Any given field will always have the same offset and base, and no two distinct fields of the same class will ever have the same offset and base.

As of 1.4.1, offsets for fields are represented as long values, although the Sun JVM does not use the most significant 32 bits. However, JVM implementations which store static fields at absolute addresses can use long offsets and null base pointers to express the field locations in a form usable by getInt(Object, long). Therefore, code which will be ported to such JVMs on 64-bit platforms must preserve all bits of static field offsets.

See Also:

getInt(Object, long)

staticFieldOffset

public static long staticFieldOffset(Field field)

Reports the location of a given static field, in conjunction with staticFieldBase(java.lang.reflect.Field).

Do not expect to perform any sort of arithmetic on this offset; it is just a cookie which is passed to the unsafe heap memory accessors.

Any given field will always have the same offset, and no two distinct fields of the same class will ever have the same offset.

As of 1.4.1, offsets for fields are represented as long values, although the Sun JVM does not use the most significant 32 bits. It is hard to imagine a JVM technology which needs more than a few bits to encode an offset within a non-array object, However, for consistency with other methods in this class, this method reports its result as a long value.

See Also:

getInt(Object, long)

staticFieldBase

public static Object staticFieldBase(Field field)

Reports the location of a given static field, in conjunction with staticFieldOffset(java.lang.reflect.Field).

Fetch the base "Object", if any, with which static fields of the given class can be accessed via methods like getInt(Object, long). This value may be null. This value may refer to an object which is a "cookie", not guaranteed to be a real Object, and it should not be used in any way except as argument to the get and put routines in this class.

arrayBaseOffset

public static int arrayBaseOffset(Class<?> arrayClass)

Reports the offset of the first element in the storage allocation of a given array class. If arrayIndexScale(java.lang.Class<?>) returns a non-zero value for the same class, you may use that scale factor, together with this base offset, to form new offsets to access elements of arrays of the given class.

See Also:

getInt(Object, long), putInt(Object, long, int)

arrayIndexScale

public static int arrayIndexScale(Class<?> arrayClass)

Reports the scale factor for addressing elements in the storage allocation of a given array class. However, arrays of "narrow" types will generally not work properly with accessors like getByte(Object, long), so the scale factor for such classes is reported as zero.

See Also:

arrayBaseOffset(java.lang.Class<?>), getInt(Object, long), putInt(Object, long, int)

compareAndSwapObject

public static boolean compareAndSwapObject(Object o,
                                           long offset,
                                           Object expected,
                                           Object x)

Atomically updates Java variable to x if it is currently holding expected.

This operation has memory semantics of a volatile read and write. Corresponds to C11 atomic_compare_exchange_strong.

Returns:

true if successful

compareAndSwapInt

public static boolean compareAndSwapInt(Object o,
                                        long offset,
                                        int expected,
                                        int x)

Atomically updates Java variable to x if it is currently holding expected.

This operation has memory semantics of a volatile read and write. Corresponds to C11 atomic_compare_exchange_strong.

Returns:

true if successful

compareAndSwapLong

public static boolean compareAndSwapLong(Object o,
                                         long offset,
                                         long expected,
                                         long x)

Atomically updates Java variable to x if it is currently holding expected.

This operation has memory semantics of a volatile read and write. Corresponds to C11 atomic_compare_exchange_strong.

Returns:

true if successful

unpark

public void unpark(Object thread)

Unblocks the given thread blocked on park, or, if it is not blocked, causes the subsequent call to park not to block. Note: this operation is "unsafe" solely because the caller must somehow ensure that the thread has not been destroyed. Nothing special is usually required to ensure this when called from Java (in which there will ordinarily be a live reference to the thread) but this is not nearly-automatically so when calling from native code.

Parameters:

thread - the thread to unpark.

park

public void park(boolean isAbsolute,
                 long time)

Blocks current thread, returning when a balancing unpark occurs, or a balancing unpark has already occurred, or the thread is interrupted, or, if not absolute and time is not zero, the given time nanoseconds have elapsed, or if absolute, the given deadline in milliseconds since Epoch has passed, or spuriously (i.e., returning for no "reason"). Note: This operation is in the Unsafe class only because unpark is, so it would be strange to place it elsewhere.