1 /*
   2  * Copyright (c) 2000, 2009, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.  Oracle designates this
   8  * particular file as subject to the "Classpath" exception as provided
   9  * by Oracle in the LICENSE file that accompanied this code.
  10  *
  11  * This code is distributed in the hope that it will be useful, but WITHOUT
  12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14  * version 2 for more details (a copy is included in the LICENSE file that
  15  * accompanied this code).
  16  *
  17  * You should have received a copy of the GNU General Public License version
  18  * 2 along with this work; if not, write to the Free Software Foundation,
  19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  20  *
  21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  22  * or visit www.oracle.com if you need additional information or have any
  23  * questions.
  24  */
  25 
  26 package sun.misc;
  27 
  28 import java.security.*;
  29 import java.lang.reflect.*;
  30 
  31 
  32 /**
  33  * A collection of methods for performing low-level, unsafe operations.
  34  * Although the class and all methods are public, use of this class is
  35  * limited because only trusted code can obtain instances of it.
  36  *
  37  * @author John R. Rose
  38  * @see #getUnsafe
  39  */
  40 
  41 public final class Unsafe {
  42 
  43     private static native void registerNatives();
  44     static {
  45         registerNatives();
  46         sun.reflect.Reflection.registerMethodsToFilter(Unsafe.class, "getUnsafe");
  47     }
  48 
  49     private Unsafe() {}
  50 
  51     private static final Unsafe theUnsafe = new Unsafe();
  52 
  53     /**
  54      * Provides the caller with the capability of performing unsafe
  55      * operations.
  56      *
  57      * <p> The returned <code>Unsafe</code> object should be carefully guarded
  58      * by the caller, since it can be used to read and write data at arbitrary
  59      * memory addresses.  It must never be passed to untrusted code.
  60      *
  61      * <p> Most methods in this class are very low-level, and correspond to a
  62      * small number of hardware instructions (on typical machines).  Compilers
  63      * are encouraged to optimize these methods accordingly.
  64      *
  65      * <p> Here is a suggested idiom for using unsafe operations:
  66      *
  67      * <blockquote><pre>
  68      * class MyTrustedClass {
  69      *   private static final Unsafe unsafe = Unsafe.getUnsafe();
  70      *   ...
  71      *   private long myCountAddress = ...;
  72      *   public int getCount() { return unsafe.getByte(myCountAddress); }
  73      * }
  74      * </pre></blockquote>
  75      *
  76      * (It may assist compilers to make the local variable be
  77      * <code>final</code>.)
  78      *
  79      * @exception  SecurityException  if a security manager exists and its
  80      *             <code>checkPropertiesAccess</code> method doesn't allow
  81      *             access to the system properties.
  82      */
  83     public static Unsafe getUnsafe() {
  84         Class cc = sun.reflect.Reflection.getCallerClass(2);
  85         if (cc.getClassLoader() != null)
  86             throw new SecurityException("Unsafe");
  87         return theUnsafe;
  88     }
  89 
  90     /// peek and poke operations
  91     /// (compilers should optimize these to memory ops)
  92 
  93     // These work on object fields in the Java heap.
  94     // They will not work on elements of packed arrays.
  95 
  96     /**
  97      * Fetches a value from a given Java variable.
  98      * More specifically, fetches a field or array element within the given
  99      * object <code>o</code> at the given offset, or (if <code>o</code> is
 100      * null) from the memory address whose numerical value is the given
 101      * offset.
 102      * <p>
 103      * The results are undefined unless one of the following cases is true:
 104      * <ul>
 105      * <li>The offset was obtained from {@link #objectFieldOffset} on
 106      * the {@link java.lang.reflect.Field} of some Java field and the object
 107      * referred to by <code>o</code> is of a class compatible with that
 108      * field's class.
 109      *
 110      * <li>The offset and object reference <code>o</code> (either null or
 111      * non-null) were both obtained via {@link #staticFieldOffset}
 112      * and {@link #staticFieldBase} (respectively) from the
 113      * reflective {@link Field} representation of some Java field.
 114      *
 115      * <li>The object referred to by <code>o</code> is an array, and the offset
 116      * is an integer of the form <code>B+N*S</code>, where <code>N</code> is
 117      * a valid index into the array, and <code>B</code> and <code>S</code> are
 118      * the values obtained by {@link #arrayBaseOffset} and {@link
 119      * #arrayIndexScale} (respectively) from the array's class.  The value
 120      * referred to is the <code>N</code><em>th</em> element of the array.
 121      *
 122      * </ul>
 123      * <p>
 124      * If one of the above cases is true, the call references a specific Java
 125      * variable (field or array element).  However, the results are undefined
 126      * if that variable is not in fact of the type returned by this method.
 127      * <p>
 128      * This method refers to a variable by means of two parameters, and so
 129      * it provides (in effect) a <em>double-register</em> addressing mode
 130      * for Java variables.  When the object reference is null, this method
 131      * uses its offset as an absolute address.  This is similar in operation
 132      * to methods such as {@link #getInt(long)}, which provide (in effect) a
 133      * <em>single-register</em> addressing mode for non-Java variables.
 134      * However, because Java variables may have a different layout in memory
 135      * from non-Java variables, programmers should not assume that these
 136      * two addressing modes are ever equivalent.  Also, programmers should
 137      * remember that offsets from the double-register addressing mode cannot
 138      * be portably confused with longs used in the single-register addressing
 139      * mode.
 140      *
 141      * @param o Java heap object in which the variable resides, if any, else
 142      *        null
 143      * @param offset indication of where the variable resides in a Java heap
 144      *        object, if any, else a memory address locating the variable
 145      *        statically
 146      * @return the value fetched from the indicated Java variable
 147      * @throws RuntimeException No defined exceptions are thrown, not even
 148      *         {@link NullPointerException}
 149      */
 150     public native int getInt(Object o, long offset);
 151 
 152     /**
 153      * Stores a value into a given Java variable.
 154      * <p>
 155      * The first two parameters are interpreted exactly as with
 156      * {@link #getInt(Object, long)} to refer to a specific
 157      * Java variable (field or array element).  The given value
 158      * is stored into that variable.
 159      * <p>
 160      * The variable must be of the same type as the method
 161      * parameter <code>x</code>.
 162      *
 163      * @param o Java heap object in which the variable resides, if any, else
 164      *        null
 165      * @param offset indication of where the variable resides in a Java heap
 166      *        object, if any, else a memory address locating the variable
 167      *        statically
 168      * @param x the value to store into the indicated Java variable
 169      * @throws RuntimeException No defined exceptions are thrown, not even
 170      *         {@link NullPointerException}
 171      */
 172     public native void putInt(Object o, long offset, int x);
 173 
 174     /**
 175      * Fetches a reference value from a given Java variable.
 176      * @see #getInt(Object, long)
 177      */
 178     public native Object getObject(Object o, long offset);
 179 
 180     /**
 181      * Stores a reference value into a given Java variable.
 182      * <p>
 183      * Unless the reference <code>x</code> being stored is either null
 184      * or matches the field type, the results are undefined.
 185      * If the reference <code>o</code> is non-null, car marks or
 186      * other store barriers for that object (if the VM requires them)
 187      * are updated.
 188      * @see #putInt(Object, int, int)
 189      */
 190     public native void putObject(Object o, long offset, Object x);
 191 
 192     /** @see #getInt(Object, long) */
 193     public native boolean getBoolean(Object o, long offset);
 194     /** @see #putInt(Object, int, int) */
 195     public native void    putBoolean(Object o, long offset, boolean x);
 196     /** @see #getInt(Object, long) */
 197     public native byte    getByte(Object o, long offset);
 198     /** @see #putInt(Object, int, int) */
 199     public native void    putByte(Object o, long offset, byte x);
 200     /** @see #getInt(Object, long) */
 201     public native short   getShort(Object o, long offset);
 202     /** @see #putInt(Object, int, int) */
 203     public native void    putShort(Object o, long offset, short x);
 204     /** @see #getInt(Object, long) */
 205     public native char    getChar(Object o, long offset);
 206     /** @see #putInt(Object, int, int) */
 207     public native void    putChar(Object o, long offset, char x);
 208     /** @see #getInt(Object, long) */
 209     public native long    getLong(Object o, long offset);
 210     /** @see #putInt(Object, int, int) */
 211     public native void    putLong(Object o, long offset, long x);
 212     /** @see #getInt(Object, long) */
 213     public native float   getFloat(Object o, long offset);
 214     /** @see #putInt(Object, int, int) */
 215     public native void    putFloat(Object o, long offset, float x);
 216     /** @see #getInt(Object, long) */
 217     public native double  getDouble(Object o, long offset);
 218     /** @see #putInt(Object, int, int) */
 219     public native void    putDouble(Object o, long offset, double x);
 220 
 221     /**
 222      * This method, like all others with 32-bit offsets, was native
 223      * in a previous release but is now a wrapper which simply casts
 224      * the offset to a long value.  It provides backward compatibility
 225      * with bytecodes compiled against 1.4.
 226      * @deprecated As of 1.4.1, cast the 32-bit offset argument to a long.
 227      * See {@link #staticFieldOffset}.
 228      */
 229     @Deprecated
 230     public int getInt(Object o, int offset) {
 231         return getInt(o, (long)offset);
 232     }
 233 
 234     /**
 235      * @deprecated As of 1.4.1, cast the 32-bit offset argument to a long.
 236      * See {@link #staticFieldOffset}.
 237      */
 238     @Deprecated
 239     public void putInt(Object o, int offset, int x) {
 240         putInt(o, (long)offset, x);
 241     }
 242 
 243     /**
 244      * @deprecated As of 1.4.1, cast the 32-bit offset argument to a long.
 245      * See {@link #staticFieldOffset}.
 246      */
 247     @Deprecated
 248     public Object getObject(Object o, int offset) {
 249         return getObject(o, (long)offset);
 250     }
 251 
 252     /**
 253      * @deprecated As of 1.4.1, cast the 32-bit offset argument to a long.
 254      * See {@link #staticFieldOffset}.
 255      */
 256     @Deprecated
 257     public void putObject(Object o, int offset, Object x) {
 258         putObject(o, (long)offset, x);
 259     }
 260 
 261     /**
 262      * @deprecated As of 1.4.1, cast the 32-bit offset argument to a long.
 263      * See {@link #staticFieldOffset}.
 264      */
 265     @Deprecated
 266     public boolean getBoolean(Object o, int offset) {
 267         return getBoolean(o, (long)offset);
 268     }
 269 
 270     /**
 271      * @deprecated As of 1.4.1, cast the 32-bit offset argument to a long.
 272      * See {@link #staticFieldOffset}.
 273      */
 274     @Deprecated
 275     public void putBoolean(Object o, int offset, boolean x) {
 276         putBoolean(o, (long)offset, x);
 277     }
 278 
 279     /**
 280      * @deprecated As of 1.4.1, cast the 32-bit offset argument to a long.
 281      * See {@link #staticFieldOffset}.
 282      */
 283     @Deprecated
 284     public byte getByte(Object o, int offset) {
 285         return getByte(o, (long)offset);
 286     }
 287 
 288     /**
 289      * @deprecated As of 1.4.1, cast the 32-bit offset argument to a long.
 290      * See {@link #staticFieldOffset}.
 291      */
 292     @Deprecated
 293     public void putByte(Object o, int offset, byte x) {
 294         putByte(o, (long)offset, x);
 295     }
 296 
 297     /**
 298      * @deprecated As of 1.4.1, cast the 32-bit offset argument to a long.
 299      * See {@link #staticFieldOffset}.
 300      */
 301     @Deprecated
 302     public short getShort(Object o, int offset) {
 303         return getShort(o, (long)offset);
 304     }
 305 
 306     /**
 307      * @deprecated As of 1.4.1, cast the 32-bit offset argument to a long.
 308      * See {@link #staticFieldOffset}.
 309      */
 310     @Deprecated
 311     public void putShort(Object o, int offset, short x) {
 312         putShort(o, (long)offset, x);
 313     }
 314 
 315     /**
 316      * @deprecated As of 1.4.1, cast the 32-bit offset argument to a long.
 317      * See {@link #staticFieldOffset}.
 318      */
 319     @Deprecated
 320     public char getChar(Object o, int offset) {
 321         return getChar(o, (long)offset);
 322     }
 323 
 324     /**
 325      * @deprecated As of 1.4.1, cast the 32-bit offset argument to a long.
 326      * See {@link #staticFieldOffset}.
 327      */
 328     @Deprecated
 329     public void putChar(Object o, int offset, char x) {
 330         putChar(o, (long)offset, x);
 331     }
 332 
 333     /**
 334      * @deprecated As of 1.4.1, cast the 32-bit offset argument to a long.
 335      * See {@link #staticFieldOffset}.
 336      */
 337     @Deprecated
 338     public long getLong(Object o, int offset) {
 339         return getLong(o, (long)offset);
 340     }
 341 
 342     /**
 343      * @deprecated As of 1.4.1, cast the 32-bit offset argument to a long.
 344      * See {@link #staticFieldOffset}.
 345      */
 346     @Deprecated
 347     public void putLong(Object o, int offset, long x) {
 348         putLong(o, (long)offset, x);
 349     }
 350 
 351     /**
 352      * @deprecated As of 1.4.1, cast the 32-bit offset argument to a long.
 353      * See {@link #staticFieldOffset}.
 354      */
 355     @Deprecated
 356     public float getFloat(Object o, int offset) {
 357         return getFloat(o, (long)offset);
 358     }
 359 
 360     /**
 361      * @deprecated As of 1.4.1, cast the 32-bit offset argument to a long.
 362      * See {@link #staticFieldOffset}.
 363      */
 364     @Deprecated
 365     public void putFloat(Object o, int offset, float x) {
 366         putFloat(o, (long)offset, x);
 367     }
 368 
 369     /**
 370      * @deprecated As of 1.4.1, cast the 32-bit offset argument to a long.
 371      * See {@link #staticFieldOffset}.
 372      */
 373     @Deprecated
 374     public double getDouble(Object o, int offset) {
 375         return getDouble(o, (long)offset);
 376     }
 377 
 378     /**
 379      * @deprecated As of 1.4.1, cast the 32-bit offset argument to a long.
 380      * See {@link #staticFieldOffset}.
 381      */
 382     @Deprecated
 383     public void putDouble(Object o, int offset, double x) {
 384         putDouble(o, (long)offset, x);
 385     }
 386 
 387     // These work on values in the C heap.
 388 
 389     /**
 390      * Fetches a value from a given memory address.  If the address is zero, or
 391      * does not point into a block obtained from {@link #allocateMemory}, the
 392      * results are undefined.
 393      *
 394      * @see #allocateMemory
 395      */
 396     public native byte    getByte(long address);
 397 
 398     /**
 399      * Stores a value into a given memory address.  If the address is zero, or
 400      * does not point into a block obtained from {@link #allocateMemory}, the
 401      * results are undefined.
 402      *
 403      * @see #getByte(long)
 404      */
 405     public native void    putByte(long address, byte x);
 406 
 407     /** @see #getByte(long) */
 408     public native short   getShort(long address);
 409     /** @see #putByte(long, byte) */
 410     public native void    putShort(long address, short x);
 411     /** @see #getByte(long) */
 412     public native char    getChar(long address);
 413     /** @see #putByte(long, byte) */
 414     public native void    putChar(long address, char x);
 415     /** @see #getByte(long) */
 416     public native int     getInt(long address);
 417     /** @see #putByte(long, byte) */
 418     public native void    putInt(long address, int x);
 419     /** @see #getByte(long) */
 420     public native long    getLong(long address);
 421     /** @see #putByte(long, byte) */
 422     public native void    putLong(long address, long x);
 423     /** @see #getByte(long) */
 424     public native float   getFloat(long address);
 425     /** @see #putByte(long, byte) */
 426     public native void    putFloat(long address, float x);
 427     /** @see #getByte(long) */
 428     public native double  getDouble(long address);
 429     /** @see #putByte(long, byte) */
 430     public native void    putDouble(long address, double x);
 431 
 432     /**
 433      * Fetches a native pointer from a given memory address.  If the address is
 434      * zero, or does not point into a block obtained from {@link
 435      * #allocateMemory}, the results are undefined.
 436      *
 437      * <p> If the native pointer is less than 64 bits wide, it is extended as
 438      * an unsigned number to a Java long.  The pointer may be indexed by any
 439      * given byte offset, simply by adding that offset (as a simple integer) to
 440      * the long representing the pointer.  The number of bytes actually read
 441      * from the target address maybe determined by consulting {@link
 442      * #addressSize}.
 443      *
 444      * @see #allocateMemory
 445      */
 446     public native long getAddress(long address);
 447 
 448     /**
 449      * Stores a native pointer into a given memory address.  If the address is
 450      * zero, or does not point into a block obtained from {@link
 451      * #allocateMemory}, the results are undefined.
 452      *
 453      * <p> The number of bytes actually written at the target address maybe
 454      * determined by consulting {@link #addressSize}.
 455      *
 456      * @see #getAddress(long)
 457      */
 458     public native void putAddress(long address, long x);
 459 
 460     /// wrappers for malloc, realloc, free:
 461 
 462     /**
 463      * Allocates a new block of native memory, of the given size in bytes.  The
 464      * contents of the memory are uninitialized; they will generally be
 465      * garbage.  The resulting native pointer will never be zero, and will be
 466      * aligned for all value types.  Dispose of this memory by calling {@link
 467      * #freeMemory}, or resize it with {@link #reallocateMemory}.
 468      *
 469      * @throws IllegalArgumentException if the size is negative or too large
 470      *         for the native size_t type
 471      *
 472      * @throws OutOfMemoryError if the allocation is refused by the system
 473      *
 474      * @see #getByte(long)
 475      * @see #putByte(long, byte)
 476      */
 477     public native long allocateMemory(long bytes);
 478 
 479     /**
 480      * Resizes a new block of native memory, to the given size in bytes.  The
 481      * contents of the new block past the size of the old block are
 482      * uninitialized; they will generally be garbage.  The resulting native
 483      * pointer will be zero if and only if the requested size is zero.  The
 484      * resulting native pointer will be aligned for all value types.  Dispose
 485      * of this memory by calling {@link #freeMemory}, or resize it with {@link
 486      * #reallocateMemory}.  The address passed to this method may be null, in
 487      * which case an allocation will be performed.
 488      *
 489      * @throws IllegalArgumentException if the size is negative or too large
 490      *         for the native size_t type
 491      *
 492      * @throws OutOfMemoryError if the allocation is refused by the system
 493      *
 494      * @see #allocateMemory
 495      */
 496     public native long reallocateMemory(long address, long bytes);
 497 
 498     /**
 499      * Sets all bytes in a given block of memory to a fixed value
 500      * (usually zero).
 501      *
 502      * <p>This method determines a block's base address by means of two parameters,
 503      * and so it provides (in effect) a <em>double-register</em> addressing mode,
 504      * as discussed in {@link #getInt(Object,long)}.  When the object reference is null,
 505      * the offset supplies an absolute base address.
 506      *
 507      * <p>The stores are in coherent (atomic) units of a size determined
 508      * by the address and length parameters.  If the effective address and
 509      * length are all even modulo 8, the stores take place in 'long' units.
 510      * If the effective address and length are (resp.) even modulo 4 or 2,
 511      * the stores take place in units of 'int' or 'short'.
 512      *
 513      * @since 1.7
 514      */
 515     public native void setMemory(Object o, long offset, long bytes, byte value);
 516 
 517     /**
 518      * Sets all bytes in a given block of memory to a fixed value
 519      * (usually zero).  This provides a <em>single-register</em> addressing mode,
 520      * as discussed in {@link #getInt(Object,long)}.
 521      *
 522      * <p>Equivalent to <code>setMemory(null, address, bytes, value)</code>.
 523      */
 524     public void setMemory(long address, long bytes, byte value) {
 525         setMemory(null, address, bytes, value);
 526     }
 527 
 528     /**
 529      * Sets all bytes in a given block of memory to a copy of another
 530      * block.
 531      *
 532      * <p>This method determines each block's base address by means of two parameters,
 533      * and so it provides (in effect) a <em>double-register</em> addressing mode,
 534      * as discussed in {@link #getInt(Object,long)}.  When the object reference is null,
 535      * the offset supplies an absolute base address.
 536      *
 537      * <p>The transfers are in coherent (atomic) units of a size determined
 538      * by the address and length parameters.  If the effective addresses and
 539      * length are all even modulo 8, the transfer takes place in 'long' units.
 540      * If the effective addresses and length are (resp.) even modulo 4 or 2,
 541      * the transfer takes place in units of 'int' or 'short'.
 542      *
 543      * @since 1.7
 544      */
 545     public native void copyMemory(Object srcBase, long srcOffset,
 546                                   Object destBase, long destOffset,
 547                                   long bytes);
 548     /**
 549      * Sets all bytes in a given block of memory to a copy of another
 550      * block.  This provides a <em>single-register</em> addressing mode,
 551      * as discussed in {@link #getInt(Object,long)}.
 552      *
 553      * Equivalent to <code>copyMemory(null, srcAddress, null, destAddress, bytes)</code>.
 554      */
 555     public void copyMemory(long srcAddress, long destAddress, long bytes) {
 556         copyMemory(null, srcAddress, null, destAddress, bytes);
 557     }
 558 
 559     /**
 560      * Disposes of a block of native memory, as obtained from {@link
 561      * #allocateMemory} or {@link #reallocateMemory}.  The address passed to
 562      * this method may be null, in which case no action is taken.
 563      *
 564      * @see #allocateMemory
 565      */
 566     public native void freeMemory(long address);
 567 
 568     /// random queries
 569 
 570     /**
 571      * This constant differs from all results that will ever be returned from
 572      * {@link #staticFieldOffset}, {@link #objectFieldOffset},
 573      * or {@link #arrayBaseOffset}.
 574      */
 575     public static final int INVALID_FIELD_OFFSET   = -1;
 576 
 577     /**
 578      * Returns the offset of a field, truncated to 32 bits.
 579      * This method is implemented as follows:
 580      * <blockquote><pre>
 581      * public int fieldOffset(Field f) {
 582      *     if (Modifier.isStatic(f.getModifiers()))
 583      *         return (int) staticFieldOffset(f);
 584      *     else
 585      *         return (int) objectFieldOffset(f);
 586      * }
 587      * </pre></blockquote>
 588      * @deprecated As of 1.4.1, use {@link #staticFieldOffset} for static
 589      * fields and {@link #objectFieldOffset} for non-static fields.
 590      */
 591     @Deprecated
 592     public int fieldOffset(Field f) {
 593         if (Modifier.isStatic(f.getModifiers()))
 594             return (int) staticFieldOffset(f);
 595         else
 596             return (int) objectFieldOffset(f);
 597     }
 598 
 599     /**
 600      * Returns the base address for accessing some static field
 601      * in the given class.  This method is implemented as follows:
 602      * <blockquote><pre>
 603      * public Object staticFieldBase(Class c) {
 604      *     Field[] fields = c.getDeclaredFields();
 605      *     for (int i = 0; i < fields.length; i++) {
 606      *         if (Modifier.isStatic(fields[i].getModifiers())) {
 607      *             return staticFieldBase(fields[i]);
 608      *         }
 609      *     }
 610      *     return null;
 611      * }
 612      * </pre></blockquote>
 613      * @deprecated As of 1.4.1, use {@link #staticFieldBase(Field)}
 614      * to obtain the base pertaining to a specific {@link Field}.
 615      * This method works only for JVMs which store all statics
 616      * for a given class in one place.
 617      */
 618     @Deprecated
 619     public Object staticFieldBase(Class c) {
 620         Field[] fields = c.getDeclaredFields();
 621         for (int i = 0; i < fields.length; i++) {
 622             if (Modifier.isStatic(fields[i].getModifiers())) {
 623                 return staticFieldBase(fields[i]);
 624             }
 625         }
 626         return null;
 627     }
 628 
 629     /**
 630      * Report the location of a given field in the storage allocation of its
 631      * class.  Do not expect to perform any sort of arithmetic on this offset;
 632      * it is just a cookie which is passed to the unsafe heap memory accessors.
 633      *
 634      * <p>Any given field will always have the same offset and base, and no
 635      * two distinct fields of the same class will ever have the same offset
 636      * and base.
 637      *
 638      * <p>As of 1.4.1, offsets for fields are represented as long values,
 639      * although the Sun JVM does not use the most significant 32 bits.
 640      * However, JVM implementations which store static fields at absolute
 641      * addresses can use long offsets and null base pointers to express
 642      * the field locations in a form usable by {@link #getInt(Object,long)}.
 643      * Therefore, code which will be ported to such JVMs on 64-bit platforms
 644      * must preserve all bits of static field offsets.
 645      * @see #getInt(Object, long)
 646      */
 647     public native long staticFieldOffset(Field f);
 648 
 649     /**
 650      * Report the location of a given static field, in conjunction with {@link
 651      * #staticFieldBase}.
 652      * <p>Do not expect to perform any sort of arithmetic on this offset;
 653      * it is just a cookie which is passed to the unsafe heap memory accessors.
 654      *
 655      * <p>Any given field will always have the same offset, and no two distinct
 656      * fields of the same class will ever have the same offset.
 657      *
 658      * <p>As of 1.4.1, offsets for fields are represented as long values,
 659      * although the Sun JVM does not use the most significant 32 bits.
 660      * It is hard to imagine a JVM technology which needs more than
 661      * a few bits to encode an offset within a non-array object,
 662      * However, for consistency with other methods in this class,
 663      * this method reports its result as a long value.
 664      * @see #getInt(Object, long)
 665      */
 666     public native long objectFieldOffset(Field f);
 667 
 668     /**
 669      * Report the location of a given static field, in conjunction with {@link
 670      * #staticFieldOffset}.
 671      * <p>Fetch the base "Object", if any, with which static fields of the
 672      * given class can be accessed via methods like {@link #getInt(Object,
 673      * long)}.  This value may be null.  This value may refer to an object
 674      * which is a "cookie", not guaranteed to be a real Object, and it should
 675      * not be used in any way except as argument to the get and put routines in
 676      * this class.
 677      */
 678     public native Object staticFieldBase(Field f);
 679 
 680     /**
 681      * Ensure the given class has been initialized. This is often
 682      * needed in conjunction with obtaining the static field base of a
 683      * class.
 684      */
 685     public native void ensureClassInitialized(Class c);
 686 
 687     /**
 688      * Report the offset of the first element in the storage allocation of a
 689      * given array class.  If {@link #arrayIndexScale} returns a non-zero value
 690      * for the same class, you may use that scale factor, together with this
 691      * base offset, to form new offsets to access elements of arrays of the
 692      * given class.
 693      *
 694      * @see #getInt(Object, long)
 695      * @see #putInt(Object, long, int)
 696      */
 697     public native int arrayBaseOffset(Class arrayClass);
 698 
 699     /** The value of {@code arrayBaseOffset(boolean[].class)} */
 700     public static final int ARRAY_BOOLEAN_BASE_OFFSET
 701             = theUnsafe.arrayBaseOffset(boolean[].class);
 702 
 703     /** The value of {@code arrayBaseOffset(byte[].class)} */
 704     public static final int ARRAY_BYTE_BASE_OFFSET
 705             = theUnsafe.arrayBaseOffset(byte[].class);
 706 
 707     /** The value of {@code arrayBaseOffset(short[].class)} */
 708     public static final int ARRAY_SHORT_BASE_OFFSET
 709             = theUnsafe.arrayBaseOffset(short[].class);
 710 
 711     /** The value of {@code arrayBaseOffset(char[].class)} */
 712     public static final int ARRAY_CHAR_BASE_OFFSET
 713             = theUnsafe.arrayBaseOffset(char[].class);
 714 
 715     /** The value of {@code arrayBaseOffset(int[].class)} */
 716     public static final int ARRAY_INT_BASE_OFFSET
 717             = theUnsafe.arrayBaseOffset(int[].class);
 718 
 719     /** The value of {@code arrayBaseOffset(long[].class)} */
 720     public static final int ARRAY_LONG_BASE_OFFSET
 721             = theUnsafe.arrayBaseOffset(long[].class);
 722 
 723     /** The value of {@code arrayBaseOffset(float[].class)} */
 724     public static final int ARRAY_FLOAT_BASE_OFFSET
 725             = theUnsafe.arrayBaseOffset(float[].class);
 726 
 727     /** The value of {@code arrayBaseOffset(double[].class)} */
 728     public static final int ARRAY_DOUBLE_BASE_OFFSET
 729             = theUnsafe.arrayBaseOffset(double[].class);
 730 
 731     /** The value of {@code arrayBaseOffset(Object[].class)} */
 732     public static final int ARRAY_OBJECT_BASE_OFFSET
 733             = theUnsafe.arrayBaseOffset(Object[].class);
 734 
 735     /**
 736      * Report the scale factor for addressing elements in the storage
 737      * allocation of a given array class.  However, arrays of "narrow" types
 738      * will generally not work properly with accessors like {@link
 739      * #getByte(Object, int)}, so the scale factor for such classes is reported
 740      * as zero.
 741      *
 742      * @see #arrayBaseOffset
 743      * @see #getInt(Object, long)
 744      * @see #putInt(Object, long, int)
 745      */
 746     public native int arrayIndexScale(Class arrayClass);
 747 
 748     /** The value of {@code arrayIndexScale(boolean[].class)} */
 749     public static final int ARRAY_BOOLEAN_INDEX_SCALE
 750             = theUnsafe.arrayIndexScale(boolean[].class);
 751 
 752     /** The value of {@code arrayIndexScale(byte[].class)} */
 753     public static final int ARRAY_BYTE_INDEX_SCALE
 754             = theUnsafe.arrayIndexScale(byte[].class);
 755 
 756     /** The value of {@code arrayIndexScale(short[].class)} */
 757     public static final int ARRAY_SHORT_INDEX_SCALE
 758             = theUnsafe.arrayIndexScale(short[].class);
 759 
 760     /** The value of {@code arrayIndexScale(char[].class)} */
 761     public static final int ARRAY_CHAR_INDEX_SCALE
 762             = theUnsafe.arrayIndexScale(char[].class);
 763 
 764     /** The value of {@code arrayIndexScale(int[].class)} */
 765     public static final int ARRAY_INT_INDEX_SCALE
 766             = theUnsafe.arrayIndexScale(int[].class);
 767 
 768     /** The value of {@code arrayIndexScale(long[].class)} */
 769     public static final int ARRAY_LONG_INDEX_SCALE
 770             = theUnsafe.arrayIndexScale(long[].class);
 771 
 772     /** The value of {@code arrayIndexScale(float[].class)} */
 773     public static final int ARRAY_FLOAT_INDEX_SCALE
 774             = theUnsafe.arrayIndexScale(float[].class);
 775 
 776     /** The value of {@code arrayIndexScale(double[].class)} */
 777     public static final int ARRAY_DOUBLE_INDEX_SCALE
 778             = theUnsafe.arrayIndexScale(double[].class);
 779 
 780     /** The value of {@code arrayIndexScale(Object[].class)} */
 781     public static final int ARRAY_OBJECT_INDEX_SCALE
 782             = theUnsafe.arrayIndexScale(Object[].class);
 783 
 784     /**
 785      * Report the size in bytes of a native pointer, as stored via {@link
 786      * #putAddress}.  This value will be either 4 or 8.  Note that the sizes of
 787      * other primitive types (as stored in native memory blocks) is determined
 788      * fully by their information content.
 789      */
 790     public native int addressSize();
 791 
 792     /** The value of {@code addressSize()} */
 793     public static final int ADDRESS_SIZE = theUnsafe.addressSize();
 794 
 795     /**
 796      * Report the size in bytes of a native memory page (whatever that is).
 797      * This value will always be a power of two.
 798      */
 799     public native int pageSize();
 800 
 801 
 802     /// random trusted operations from JNI:
 803 
 804     /**
 805      * Tell the VM to define a class, without security checks.  By default, the
 806      * class loader and protection domain come from the caller's class.
 807      */
 808     public native Class defineClass(String name, byte[] b, int off, int len,
 809                                     ClassLoader loader,
 810                                     ProtectionDomain protectionDomain);
 811 
 812     public native Class defineClass(String name, byte[] b, int off, int len);
 813 
 814     /**
 815      * Define a class but do not make it known to the class loader or system dictionary.
 816      * <p>
 817      * For each CP entry, the corresponding CP patch must either be null or have
 818      * the a format that matches its tag:
 819      * <ul>
 820      * <li>Integer, Long, Float, Double: the corresponding wrapper object type from java.lang
 821      * <li>Utf8: a string (must have suitable syntax if used as signature or name)
 822      * <li>Class: any java.lang.Class object
 823      * <li>String: any object (not just a java.lang.String)
 824      * <li>InterfaceMethodRef: (NYI) a method handle to invoke on that call site's arguments
 825      * </ul>
 826      * @params hostClass context for linkage, access control, protection domain, and class loader
 827      * @params data      bytes of a class file
 828      * @params cpPatches where non-null entries exist, they replace corresponding CP entries in data
 829      */
 830     public native Class defineAnonymousClass(Class hostClass, byte[] data, Object[] cpPatches);
 831 
 832 
 833     /** Allocate an instance but do not run any constructor.
 834         Initializes the class if it has not yet been. */
 835     public native Object allocateInstance(Class cls)
 836         throws InstantiationException;
 837 
 838     /** Lock the object.  It must get unlocked via {@link #monitorExit}. */
 839     public native void monitorEnter(Object o);
 840 
 841     /**
 842      * Unlock the object.  It must have been locked via {@link
 843      * #monitorEnter}.
 844      */
 845     public native void monitorExit(Object o);
 846 
 847     /**
 848      * Tries to lock the object.  Returns true or false to indicate
 849      * whether the lock succeeded.  If it did, the object must be
 850      * unlocked via {@link #monitorExit}.
 851      */
 852     public native boolean tryMonitorEnter(Object o);
 853 
 854     /** Throw the exception without telling the verifier. */
 855     public native void throwException(Throwable ee);
 856 
 857 
 858     /**
 859      * Atomically update Java variable to <tt>x</tt> if it is currently
 860      * holding <tt>expected</tt>.
 861      * @return <tt>true</tt> if successful
 862      */
 863     public final native boolean compareAndSwapObject(Object o, long offset,
 864                                                      Object expected,
 865                                                      Object x);
 866 
 867     /**
 868      * Atomically update Java variable to <tt>x</tt> if it is currently
 869      * holding <tt>expected</tt>.
 870      * @return <tt>true</tt> if successful
 871      */
 872     public final native boolean compareAndSwapInt(Object o, long offset,
 873                                                   int expected,
 874                                                   int x);
 875 
 876     /**
 877      * Atomically update Java variable to <tt>x</tt> if it is currently
 878      * holding <tt>expected</tt>.
 879      * @return <tt>true</tt> if successful
 880      */
 881     public final native boolean compareAndSwapLong(Object o, long offset,
 882                                                    long expected,
 883                                                    long x);
 884 
 885     /**
 886      * Fetches a reference value from a given Java variable, with volatile
 887      * load semantics. Otherwise identical to {@link #getObject(Object, long)}
 888      */
 889     public native Object getObjectVolatile(Object o, long offset);
 890 
 891     /**
 892      * Stores a reference value into a given Java variable, with
 893      * volatile store semantics. Otherwise identical to {@link #putObject(Object, long, Object)}
 894      */
 895     public native void    putObjectVolatile(Object o, long offset, Object x);
 896 
 897     /** Volatile version of {@link #getInt(Object, long)}  */
 898     public native int     getIntVolatile(Object o, long offset);
 899 
 900     /** Volatile version of {@link #putInt(Object, long, int)}  */
 901     public native void    putIntVolatile(Object o, long offset, int x);
 902 
 903     /** Volatile version of {@link #getBoolean(Object, long)}  */
 904     public native boolean getBooleanVolatile(Object o, long offset);
 905 
 906     /** Volatile version of {@link #putBoolean(Object, long, boolean)}  */
 907     public native void    putBooleanVolatile(Object o, long offset, boolean x);
 908 
 909     /** Volatile version of {@link #getByte(Object, long)}  */
 910     public native byte    getByteVolatile(Object o, long offset);
 911 
 912     /** Volatile version of {@link #putByte(Object, long, byte)}  */
 913     public native void    putByteVolatile(Object o, long offset, byte x);
 914 
 915     /** Volatile version of {@link #getShort(Object, long)}  */
 916     public native short   getShortVolatile(Object o, long offset);
 917 
 918     /** Volatile version of {@link #putShort(Object, long, short)}  */
 919     public native void    putShortVolatile(Object o, long offset, short x);
 920 
 921     /** Volatile version of {@link #getChar(Object, long)}  */
 922     public native char    getCharVolatile(Object o, long offset);
 923 
 924     /** Volatile version of {@link #putChar(Object, long, char)}  */
 925     public native void    putCharVolatile(Object o, long offset, char x);
 926 
 927     /** Volatile version of {@link #getLong(Object, long)}  */
 928     public native long    getLongVolatile(Object o, long offset);
 929 
 930     /** Volatile version of {@link #putLong(Object, long, long)}  */
 931     public native void    putLongVolatile(Object o, long offset, long x);
 932 
 933     /** Volatile version of {@link #getFloat(Object, long)}  */
 934     public native float   getFloatVolatile(Object o, long offset);
 935 
 936     /** Volatile version of {@link #putFloat(Object, long, float)}  */
 937     public native void    putFloatVolatile(Object o, long offset, float x);
 938 
 939     /** Volatile version of {@link #getDouble(Object, long)}  */
 940     public native double  getDoubleVolatile(Object o, long offset);
 941 
 942     /** Volatile version of {@link #putDouble(Object, long, double)}  */
 943     public native void    putDoubleVolatile(Object o, long offset, double x);
 944 
 945     /**
 946      * Version of {@link #putObjectVolatile(Object, long, Object)}
 947      * that does not guarantee immediate visibility of the store to
 948      * other threads. This method is generally only useful if the
 949      * underlying field is a Java volatile (or if an array cell, one
 950      * that is otherwise only accessed using volatile accesses).
 951      */
 952     public native void    putOrderedObject(Object o, long offset, Object x);
 953 
 954     /** Ordered/Lazy version of {@link #putIntVolatile(Object, long, int)}  */
 955     public native void    putOrderedInt(Object o, long offset, int x);
 956 
 957     /** Ordered/Lazy version of {@link #putLongVolatile(Object, long, long)} */
 958     public native void    putOrderedLong(Object o, long offset, long x);
 959 
 960     /**
 961      * Unblock the given thread blocked on <tt>park</tt>, or, if it is
 962      * not blocked, cause the subsequent call to <tt>park</tt> not to
 963      * block.  Note: this operation is "unsafe" solely because the
 964      * caller must somehow ensure that the thread has not been
 965      * destroyed. Nothing special is usually required to ensure this
 966      * when called from Java (in which there will ordinarily be a live
 967      * reference to the thread) but this is not nearly-automatically
 968      * so when calling from native code.
 969      * @param thread the thread to unpark.
 970      *
 971      */
 972     public native void unpark(Object thread);
 973 
 974     /**
 975      * Block current thread, returning when a balancing
 976      * <tt>unpark</tt> occurs, or a balancing <tt>unpark</tt> has
 977      * already occurred, or the thread is interrupted, or, if not
 978      * absolute and time is not zero, the given time nanoseconds have
 979      * elapsed, or if absolute, the given deadline in milliseconds
 980      * since Epoch has passed, or spuriously (i.e., returning for no
 981      * "reason"). Note: This operation is in the Unsafe class only
 982      * because <tt>unpark</tt> is, so it would be strange to place it
 983      * elsewhere.
 984      */
 985     public native void park(boolean isAbsolute, long time);
 986 
 987     /**
 988      * Gets the load average in the system run queue assigned
 989      * to the available processors averaged over various periods of time.
 990      * This method retrieves the given <tt>nelem</tt> samples and
 991      * assigns to the elements of the given <tt>loadavg</tt> array.
 992      * The system imposes a maximum of 3 samples, representing
 993      * averages over the last 1,  5,  and  15 minutes, respectively.
 994      *
 995      * @params loadavg an array of double of size nelems
 996      * @params nelems the number of samples to be retrieved and
 997      *         must be 1 to 3.
 998      *
 999      * @return the number of samples actually retrieved; or -1
1000      *         if the load average is unobtainable.
1001      */
1002     public native int getLoadAverage(double[] loadavg, int nelems);
1003 }