The returned Unsafe object should be carefully guarded
* by the caller, since it can be used to read and write data at arbitrary
* memory addresses. It must never be passed to untrusted code.
*
*
Most methods in this class are very low-level, and correspond to a * small number of hardware instructions (on typical machines). Compilers * are encouraged to optimize these methods accordingly. * *
Here is a suggested idiom for using unsafe operations: * *
* class MyTrustedClass {
* private static final Unsafe unsafe = Unsafe.getUnsafe();
* ...
* private long myCountAddress = ...;
* public int getCount() { return unsafe.getByte(myCountAddress); }
* }
* final.)
*
* @exception SecurityException if a security manager exists and its
* checkPropertiesAccess method doesn't allow
* access to the system properties.
*/
public static Unsafe getUnsafe() {
Class cc = sun.reflect.Reflection.getCallerClass(2);
if (cc.getClassLoader() != null)
throw new SecurityException("Unsafe");
return theUnsafe;
}
/// peek and poke operations
/// (compilers should optimize these to memory ops)
// These work on object fields in the Java heap.
// They will not work on elements of packed arrays.
/**
* 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: *
o is of a class compatible with that
* field's class.
*
* o (either null or
* non-null) were both obtained via {@link #staticFieldOffset}
* and {@link #staticFieldBase} (respectively) from the
* reflective {@link Field} representation of some Java field.
*
* 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 {@link #arrayBaseOffset} and {@link
* #arrayIndexScale} (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 {@link #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. * * @param o Java heap object in which the variable resides, if any, else * null * @param offset indication of where the variable resides in a Java heap * object, if any, else a memory address locating the variable * statically * @return the value fetched from the indicated Java variable * @throws RuntimeException No defined exceptions are thrown, not even * {@link NullPointerException} */ public native int getInt(Object o, long offset); /** * Stores a value into a given Java variable. *
* The first two parameters are interpreted exactly as with * {@link #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.
*
* @param o Java heap object in which the variable resides, if any, else
* null
* @param offset indication of where the variable resides in a Java heap
* object, if any, else a memory address locating the variable
* statically
* @param x the value to store into the indicated Java variable
* @throws RuntimeException No defined exceptions are thrown, not even
* {@link NullPointerException}
*/
public native void putInt(Object o, long offset, int x);
/**
* Fetches a reference value from a given Java variable.
* @see #getInt(Object, long)
*/
public native Object getObject(Object o, long offset);
/**
* 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, car marks or
* other store barriers for that object (if the VM requires them)
* are updated.
* @see #putInt(Object, int, int)
*/
public native void putObject(Object o, long offset, Object x);
/** @see #getInt(Object, long) */
public native boolean getBoolean(Object o, long offset);
/** @see #putInt(Object, int, int) */
public native void putBoolean(Object o, long offset, boolean x);
/** @see #getInt(Object, long) */
public native byte getByte(Object o, long offset);
/** @see #putInt(Object, int, int) */
public native void putByte(Object o, long offset, byte x);
/** @see #getInt(Object, long) */
public native short getShort(Object o, long offset);
/** @see #putInt(Object, int, int) */
public native void putShort(Object o, long offset, short x);
/** @see #getInt(Object, long) */
public native char getChar(Object o, long offset);
/** @see #putInt(Object, int, int) */
public native void putChar(Object o, long offset, char x);
/** @see #getInt(Object, long) */
public native long getLong(Object o, long offset);
/** @see #putInt(Object, int, int) */
public native void putLong(Object o, long offset, long x);
/** @see #getInt(Object, long) */
public native float getFloat(Object o, long offset);
/** @see #putInt(Object, int, int) */
public native void putFloat(Object o, long offset, float x);
/** @see #getInt(Object, long) */
public native double getDouble(Object o, long offset);
/** @see #putInt(Object, int, int) */
public native void putDouble(Object o, long offset, double x);
/**
* This method, like all others with 32-bit offsets, was native
* in a previous release but is now a wrapper which simply casts
* the offset to a long value. It provides backward compatibility
* with bytecodes compiled against 1.4.
* @deprecated As of 1.4.1, cast the 32-bit offset argument to a long.
* See {@link #staticFieldOffset}.
*/
@Deprecated
public int getInt(Object o, int offset) {
return getInt(o, (long)offset);
}
/**
* @deprecated As of 1.4.1, cast the 32-bit offset argument to a long.
* See {@link #staticFieldOffset}.
*/
@Deprecated
public void putInt(Object o, int offset, int x) {
putInt(o, (long)offset, x);
}
/**
* @deprecated As of 1.4.1, cast the 32-bit offset argument to a long.
* See {@link #staticFieldOffset}.
*/
@Deprecated
public Object getObject(Object o, int offset) {
return getObject(o, (long)offset);
}
/**
* @deprecated As of 1.4.1, cast the 32-bit offset argument to a long.
* See {@link #staticFieldOffset}.
*/
@Deprecated
public void putObject(Object o, int offset, Object x) {
putObject(o, (long)offset, x);
}
/**
* @deprecated As of 1.4.1, cast the 32-bit offset argument to a long.
* See {@link #staticFieldOffset}.
*/
@Deprecated
public boolean getBoolean(Object o, int offset) {
return getBoolean(o, (long)offset);
}
/**
* @deprecated As of 1.4.1, cast the 32-bit offset argument to a long.
* See {@link #staticFieldOffset}.
*/
@Deprecated
public void putBoolean(Object o, int offset, boolean x) {
putBoolean(o, (long)offset, x);
}
/**
* @deprecated As of 1.4.1, cast the 32-bit offset argument to a long.
* See {@link #staticFieldOffset}.
*/
@Deprecated
public byte getByte(Object o, int offset) {
return getByte(o, (long)offset);
}
/**
* @deprecated As of 1.4.1, cast the 32-bit offset argument to a long.
* See {@link #staticFieldOffset}.
*/
@Deprecated
public void putByte(Object o, int offset, byte x) {
putByte(o, (long)offset, x);
}
/**
* @deprecated As of 1.4.1, cast the 32-bit offset argument to a long.
* See {@link #staticFieldOffset}.
*/
@Deprecated
public short getShort(Object o, int offset) {
return getShort(o, (long)offset);
}
/**
* @deprecated As of 1.4.1, cast the 32-bit offset argument to a long.
* See {@link #staticFieldOffset}.
*/
@Deprecated
public void putShort(Object o, int offset, short x) {
putShort(o, (long)offset, x);
}
/**
* @deprecated As of 1.4.1, cast the 32-bit offset argument to a long.
* See {@link #staticFieldOffset}.
*/
@Deprecated
public char getChar(Object o, int offset) {
return getChar(o, (long)offset);
}
/**
* @deprecated As of 1.4.1, cast the 32-bit offset argument to a long.
* See {@link #staticFieldOffset}.
*/
@Deprecated
public void putChar(Object o, int offset, char x) {
putChar(o, (long)offset, x);
}
/**
* @deprecated As of 1.4.1, cast the 32-bit offset argument to a long.
* See {@link #staticFieldOffset}.
*/
@Deprecated
public long getLong(Object o, int offset) {
return getLong(o, (long)offset);
}
/**
* @deprecated As of 1.4.1, cast the 32-bit offset argument to a long.
* See {@link #staticFieldOffset}.
*/
@Deprecated
public void putLong(Object o, int offset, long x) {
putLong(o, (long)offset, x);
}
/**
* @deprecated As of 1.4.1, cast the 32-bit offset argument to a long.
* See {@link #staticFieldOffset}.
*/
@Deprecated
public float getFloat(Object o, int offset) {
return getFloat(o, (long)offset);
}
/**
* @deprecated As of 1.4.1, cast the 32-bit offset argument to a long.
* See {@link #staticFieldOffset}.
*/
@Deprecated
public void putFloat(Object o, int offset, float x) {
putFloat(o, (long)offset, x);
}
/**
* @deprecated As of 1.4.1, cast the 32-bit offset argument to a long.
* See {@link #staticFieldOffset}.
*/
@Deprecated
public double getDouble(Object o, int offset) {
return getDouble(o, (long)offset);
}
/**
* @deprecated As of 1.4.1, cast the 32-bit offset argument to a long.
* See {@link #staticFieldOffset}.
*/
@Deprecated
public void putDouble(Object o, int offset, double x) {
putDouble(o, (long)offset, x);
}
// These work on values in the C heap.
/**
* Fetches a value from a given memory address. If the address is zero, or
* does not point into a block obtained from {@link #allocateMemory}, the
* results are undefined.
*
* @see #allocateMemory
*/
public native byte getByte(long address);
/**
* Stores a value into a given memory address. If the address is zero, or
* does not point into a block obtained from {@link #allocateMemory}, the
* results are undefined.
*
* @see #getByte(long)
*/
public native void putByte(long address, byte x);
/** @see #getByte(long) */
public native short getShort(long address);
/** @see #putByte(long, byte) */
public native void putShort(long address, short x);
/** @see #getByte(long) */
public native char getChar(long address);
/** @see #putByte(long, byte) */
public native void putChar(long address, char x);
/** @see #getByte(long) */
public native int getInt(long address);
/** @see #putByte(long, byte) */
public native void putInt(long address, int x);
/** @see #getByte(long) */
public native long getLong(long address);
/** @see #putByte(long, byte) */
public native void putLong(long address, long x);
/** @see #getByte(long) */
public native float getFloat(long address);
/** @see #putByte(long, byte) */
public native void putFloat(long address, float x);
/** @see #getByte(long) */
public native double getDouble(long address);
/** @see #putByte(long, byte) */
public native void putDouble(long address, double x);
/**
* Fetches a native pointer from a given memory address. If the address is
* zero, or does not point into a block obtained from {@link
* #allocateMemory}, the results are undefined.
*
*
If the native pointer is less than 64 bits wide, it is extended as * an unsigned number to a Java long. The pointer may be indexed by any * given byte offset, simply by adding that offset (as a simple integer) to * the long representing the pointer. The number of bytes actually read * from the target address maybe determined by consulting {@link * #addressSize}. * * @see #allocateMemory */ public native long getAddress(long address); /** * Stores a native pointer into a given memory address. If the address is * zero, or does not point into a block obtained from {@link * #allocateMemory}, the results are undefined. * *
The number of bytes actually written at the target address maybe * determined by consulting {@link #addressSize}. * * @see #getAddress(long) */ public native void putAddress(long address, long x); /// wrappers for malloc, realloc, free: /** * 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 {@link * #freeMemory}, or resize it with {@link #reallocateMemory}. * * @throws IllegalArgumentException if the size is negative or too large * for the native size_t type * * @throws OutOfMemoryError if the allocation is refused by the system * * @see #getByte(long) * @see #putByte(long, byte) */ public native long allocateMemory(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 {@link #freeMemory}, or resize it with {@link * #reallocateMemory}. The address passed to this method may be null, in * which case an allocation will be performed. * * @throws IllegalArgumentException if the size is negative or too large * for the native size_t type * * @throws OutOfMemoryError if the allocation is refused by the system * * @see #allocateMemory */ public native long reallocateMemory(long address, long bytes); /** * Sets all bytes in a given block of memory to a fixed value * (usually zero). * *
This method determines a block's base address by means of two parameters, * and so it provides (in effect) a double-register addressing mode, * as discussed in {@link #getInt(Object,long)}. When the object reference is null, * the offset supplies an absolute base address. * *
The stores are in coherent (atomic) units of a size determined * by the address and length parameters. If the effective address and * length are all even modulo 8, the stores take place in 'long' units. * If the effective address and length are (resp.) even modulo 4 or 2, * the stores take place in units of 'int' or 'short'. * * @since 1.7 */ public native void setMemory(Object o, long offset, long bytes, byte value); /** * Sets all bytes in a given block of memory to a fixed value * (usually zero). This provides a single-register addressing mode, * as discussed in {@link #getInt(Object,long)}. * *
Equivalent to setMemory(null, address, bytes, value).
*/
public void setMemory(long address, long bytes, byte value) {
setMemory(null, address, bytes, value);
}
/**
* Sets all bytes in a given block of memory to a copy of another
* block.
*
*
This method determines each block's base address by means of two parameters, * and so it provides (in effect) a double-register addressing mode, * as discussed in {@link #getInt(Object,long)}. When the object reference is null, * the offset supplies an absolute base address. * *
The transfers are in coherent (atomic) units of a size determined
* by the address and length parameters. If the effective addresses and
* length are all even modulo 8, the transfer takes place in 'long' units.
* If the effective addresses and length are (resp.) even modulo 4 or 2,
* the transfer takes place in units of 'int' or 'short'.
*
* @since 1.7
*/
public native void copyMemory(Object srcBase, long srcOffset,
Object destBase, long destOffset,
long bytes);
/**
* Sets all bytes in a given block of memory to a copy of another
* block. This provides a single-register addressing mode,
* as discussed in {@link #getInt(Object,long)}.
*
* Equivalent to copyMemory(null, srcAddress, null, destAddress, bytes).
*/
public void copyMemory(long srcAddress, long destAddress, long bytes) {
copyMemory(null, srcAddress, null, destAddress, bytes);
}
/**
* Disposes of a block of native memory, as obtained from {@link
* #allocateMemory} or {@link #reallocateMemory}. The address passed to
* this method may be null, in which case no action is taken.
*
* @see #allocateMemory
*/
public native void freeMemory(long address);
/// random queries
/**
* This constant differs from all results that will ever be returned from
* {@link #staticFieldOffset}, {@link #objectFieldOffset},
* or {@link #arrayBaseOffset}.
*/
public static final int INVALID_FIELD_OFFSET = -1;
/**
* Returns the offset of a field, truncated to 32 bits.
* This method is implemented as follows:
*
* public int fieldOffset(Field f) {
* if (Modifier.isStatic(f.getModifiers()))
* return (int) staticFieldOffset(f);
* else
* return (int) objectFieldOffset(f);
* }
*
* public Object staticFieldBase(Class c) {
* Field[] fields = c.getDeclaredFields();
* for (int i = 0; i < fields.length; i++) {
* if (Modifier.isStatic(fields[i].getModifiers())) {
* return staticFieldBase(fields[i]);
* }
* }
* return null;
* }
* 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 {@link #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 #getInt(Object, long) */ public native long staticFieldOffset(Field f); /** * Report the location of a given static field, in conjunction with {@link * #staticFieldBase}. *
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 #getInt(Object, long) */ public native long objectFieldOffset(Field f); /** * Report the location of a given static field, in conjunction with {@link * #staticFieldOffset}. *
Fetch the base "Object", if any, with which static fields of the * given class can be accessed via methods like {@link #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. */ public native Object staticFieldBase(Field f); /** * Ensure the given class has been initialized. This is often * needed in conjunction with obtaining the static field base of a * class. */ public native void ensureClassInitialized(Class c); /** * Report the offset of the first element in the storage allocation of a * given array class. If {@link #arrayIndexScale} 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 #getInt(Object, long) * @see #putInt(Object, long, int) */ public native int arrayBaseOffset(Class arrayClass); /** The value of {@code arrayBaseOffset(boolean[].class)} */ public static final int ARRAY_BOOLEAN_BASE_OFFSET = theUnsafe.arrayBaseOffset(boolean[].class); /** The value of {@code arrayBaseOffset(byte[].class)} */ public static final int ARRAY_BYTE_BASE_OFFSET = theUnsafe.arrayBaseOffset(byte[].class); /** The value of {@code arrayBaseOffset(short[].class)} */ public static final int ARRAY_SHORT_BASE_OFFSET = theUnsafe.arrayBaseOffset(short[].class); /** The value of {@code arrayBaseOffset(char[].class)} */ public static final int ARRAY_CHAR_BASE_OFFSET = theUnsafe.arrayBaseOffset(char[].class); /** The value of {@code arrayBaseOffset(int[].class)} */ public static final int ARRAY_INT_BASE_OFFSET = theUnsafe.arrayBaseOffset(int[].class); /** The value of {@code arrayBaseOffset(long[].class)} */ public static final int ARRAY_LONG_BASE_OFFSET = theUnsafe.arrayBaseOffset(long[].class); /** The value of {@code arrayBaseOffset(float[].class)} */ public static final int ARRAY_FLOAT_BASE_OFFSET = theUnsafe.arrayBaseOffset(float[].class); /** The value of {@code arrayBaseOffset(double[].class)} */ public static final int ARRAY_DOUBLE_BASE_OFFSET = theUnsafe.arrayBaseOffset(double[].class); /** The value of {@code arrayBaseOffset(Object[].class)} */ public static final int ARRAY_OBJECT_BASE_OFFSET = theUnsafe.arrayBaseOffset(Object[].class); /** * Report 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 {@link * #getByte(Object, int)}, so the scale factor for such classes is reported * as zero. * * @see #arrayBaseOffset * @see #getInt(Object, long) * @see #putInt(Object, long, int) */ public native int arrayIndexScale(Class arrayClass); /** The value of {@code arrayIndexScale(boolean[].class)} */ public static final int ARRAY_BOOLEAN_INDEX_SCALE = theUnsafe.arrayIndexScale(boolean[].class); /** The value of {@code arrayIndexScale(byte[].class)} */ public static final int ARRAY_BYTE_INDEX_SCALE = theUnsafe.arrayIndexScale(byte[].class); /** The value of {@code arrayIndexScale(short[].class)} */ public static final int ARRAY_SHORT_INDEX_SCALE = theUnsafe.arrayIndexScale(short[].class); /** The value of {@code arrayIndexScale(char[].class)} */ public static final int ARRAY_CHAR_INDEX_SCALE = theUnsafe.arrayIndexScale(char[].class); /** The value of {@code arrayIndexScale(int[].class)} */ public static final int ARRAY_INT_INDEX_SCALE = theUnsafe.arrayIndexScale(int[].class); /** The value of {@code arrayIndexScale(long[].class)} */ public static final int ARRAY_LONG_INDEX_SCALE = theUnsafe.arrayIndexScale(long[].class); /** The value of {@code arrayIndexScale(float[].class)} */ public static final int ARRAY_FLOAT_INDEX_SCALE = theUnsafe.arrayIndexScale(float[].class); /** The value of {@code arrayIndexScale(double[].class)} */ public static final int ARRAY_DOUBLE_INDEX_SCALE = theUnsafe.arrayIndexScale(double[].class); /** The value of {@code arrayIndexScale(Object[].class)} */ public static final int ARRAY_OBJECT_INDEX_SCALE = theUnsafe.arrayIndexScale(Object[].class); /** * Report the size in bytes of a native pointer, as stored via {@link * #putAddress}. This value will be either 4 or 8. Note that the sizes of * other primitive types (as stored in native memory blocks) is determined * fully by their information content. */ public native int addressSize(); /** The value of {@code addressSize()} */ public static final int ADDRESS_SIZE = theUnsafe.addressSize(); /** * Report the size in bytes of a native memory page (whatever that is). * This value will always be a power of two. */ public native int pageSize(); /// random trusted operations from JNI: /** * Tell the VM to define a class, without security checks. By default, the * class loader and protection domain come from the caller's class. */ public native Class defineClass(String name, byte[] b, int off, int len, ClassLoader loader, ProtectionDomain protectionDomain); public native Class defineClass(String name, byte[] b, int off, int len); /** * Define a class but do not make it known to the class loader or system dictionary. *
* For each CP entry, the corresponding CP patch must either be null or have * the a format that matches its tag: *