1 /*
2 * Copyright (c) 2000, 2006, 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 public native void setMemory(long address, long bytes, byte value);
503
504 /**
505 * Sets all bytes in a given block of memory to a copy of another
506 * block.
507 */
508 public native void copyMemory(long srcAddress, long destAddress,
509 long bytes);
510
511 /**
512 * Disposes of a block of native memory, as obtained from {@link
513 * #allocateMemory} or {@link #reallocateMemory}. The address passed to
514 * this method may be null, in which case no action is taken.
515 *
516 * @see #allocateMemory
517 */
518 public native void freeMemory(long address);
519
520 /// random queries
521
522 /**
523 * This constant differs from all results that will ever be returned from
524 * {@link #staticFieldOffset}, {@link #objectFieldOffset},
525 * or {@link #arrayBaseOffset}.
526 */
527 public static final int INVALID_FIELD_OFFSET = -1;
528
529 /**
530 * Returns the offset of a field, truncated to 32 bits.
531 * This method is implemented as follows:
532 * <blockquote><pre>
533 * public int fieldOffset(Field f) {
534 * if (Modifier.isStatic(f.getModifiers()))
535 * return (int) staticFieldOffset(f);
536 * else
537 * return (int) objectFieldOffset(f);
538 * }
539 * </pre></blockquote>
540 * @deprecated As of 1.4.1, use {@link #staticFieldOffset} for static
541 * fields and {@link #objectFieldOffset} for non-static fields.
542 */
543 @Deprecated
544 public int fieldOffset(Field f) {
545 if (Modifier.isStatic(f.getModifiers()))
546 return (int) staticFieldOffset(f);
547 else
548 return (int) objectFieldOffset(f);
549 }
550
551 /**
552 * Returns the base address for accessing some static field
553 * in the given class. This method is implemented as follows:
554 * <blockquote><pre>
555 * public Object staticFieldBase(Class c) {
556 * Field[] fields = c.getDeclaredFields();
557 * for (int i = 0; i < fields.length; i++) {
558 * if (Modifier.isStatic(fields[i].getModifiers())) {
559 * return staticFieldBase(fields[i]);
560 * }
561 * }
562 * return null;
563 * }
564 * </pre></blockquote>
565 * @deprecated As of 1.4.1, use {@link #staticFieldBase(Field)}
566 * to obtain the base pertaining to a specific {@link Field}.
567 * This method works only for JVMs which store all statics
568 * for a given class in one place.
569 */
570 @Deprecated
571 public Object staticFieldBase(Class c) {
572 Field[] fields = c.getDeclaredFields();
573 for (int i = 0; i < fields.length; i++) {
574 if (Modifier.isStatic(fields[i].getModifiers())) {
575 return staticFieldBase(fields[i]);
576 }
577 }
578 return null;
579 }
580
581 /**
582 * Report the location of a given field in the storage allocation of its
583 * class. Do not expect to perform any sort of arithmetic on this offset;
584 * it is just a cookie which is passed to the unsafe heap memory accessors.
585 *
586 * <p>Any given field will always have the same offset and base, and no
587 * two distinct fields of the same class will ever have the same offset
588 * and base.
589 *
590 * <p>As of 1.4.1, offsets for fields are represented as long values,
591 * although the Sun JVM does not use the most significant 32 bits.
592 * However, JVM implementations which store static fields at absolute
593 * addresses can use long offsets and null base pointers to express
594 * the field locations in a form usable by {@link #getInt(Object,long)}.
595 * Therefore, code which will be ported to such JVMs on 64-bit platforms
596 * must preserve all bits of static field offsets.
597 * @see #getInt(Object, long)
598 */
599 public native long staticFieldOffset(Field f);
600
601 /**
602 * Report the location of a given static field, in conjunction with {@link
603 * #staticFieldBase}.
604 * <p>Do not expect to perform any sort of arithmetic on this offset;
605 * it is just a cookie which is passed to the unsafe heap memory accessors.
606 *
607 * <p>Any given field will always have the same offset, and no two distinct
608 * fields of the same class will ever have the same offset.
609 *
610 * <p>As of 1.4.1, offsets for fields are represented as long values,
611 * although the Sun JVM does not use the most significant 32 bits.
612 * It is hard to imagine a JVM technology which needs more than
613 * a few bits to encode an offset within a non-array object,
614 * However, for consistency with other methods in this class,
615 * this method reports its result as a long value.
616 * @see #getInt(Object, long)
617 */
618 public native long objectFieldOffset(Field f);
619
620 /**
621 * Report the location of a given static field, in conjunction with {@link
622 * #staticFieldOffset}.
623 * <p>Fetch the base "Object", if any, with which static fields of the
624 * given class can be accessed via methods like {@link #getInt(Object,
625 * long)}. This value may be null. This value may refer to an object
626 * which is a "cookie", not guaranteed to be a real Object, and it should
627 * not be used in any way except as argument to the get and put routines in
628 * this class.
629 */
630 public native Object staticFieldBase(Field f);
631
632 /**
633 * Ensure the given class has been initialized. This is often
634 * needed in conjunction with obtaining the static field base of a
635 * class.
636 */
637 public native void ensureClassInitialized(Class c);
638
639 /**
640 * Report the offset of the first element in the storage allocation of a
641 * given array class. If {@link #arrayIndexScale} returns a non-zero value
642 * for the same class, you may use that scale factor, together with this
643 * base offset, to form new offsets to access elements of arrays of the
644 * given class.
645 *
646 * @see #getInt(Object, long)
647 * @see #putInt(Object, long, int)
648 */
649 public native int arrayBaseOffset(Class arrayClass);
650
651 /**
652 * Report the scale factor for addressing elements in the storage
653 * allocation of a given array class. However, arrays of "narrow" types
654 * will generally not work properly with accessors like {@link
655 * #getByte(Object, int)}, so the scale factor for such classes is reported
656 * as zero.
657 *
658 * @see #arrayBaseOffset
659 * @see #getInt(Object, long)
660 * @see #putInt(Object, long, int)
661 */
662 public native int arrayIndexScale(Class arrayClass);
663
664 /**
665 * Report the size in bytes of a native pointer, as stored via {@link
666 * #putAddress}. This value will be either 4 or 8. Note that the sizes of
667 * other primitive types (as stored in native memory blocks) is determined
668 * fully by their information content.
669 */
670 public native int addressSize();
671
672 /**
673 * Report the size in bytes of a native memory page (whatever that is).
674 * This value will always be a power of two.
675 */
676 public native int pageSize();
677
678
679 /// random trusted operations from JNI:
680
681 /**
682 * Tell the VM to define a class, without security checks. By default, the
683 * class loader and protection domain come from the caller's class.
684 */
685 public native Class defineClass(String name, byte[] b, int off, int len,
686 ClassLoader loader,
687 ProtectionDomain protectionDomain);
688
689 public native Class defineClass(String name, byte[] b, int off, int len);
690
691 /** Allocate an instance but do not run any constructor.
692 Initializes the class if it has not yet been. */
693 public native Object allocateInstance(Class cls)
694 throws InstantiationException;
695
696 /** Lock the object. It must get unlocked via {@link #monitorExit}. */
697 public native void monitorEnter(Object o);
698
699 /**
700 * Unlock the object. It must have been locked via {@link
701 * #monitorEnter}.
702 */
703 public native void monitorExit(Object o);
704
705 /**
706 * Tries to lock the object. Returns true or false to indicate
707 * whether the lock succeeded. If it did, the object must be
708 * unlocked via {@link #monitorExit}.
709 */
710 public native boolean tryMonitorEnter(Object o);
711
712 /** Throw the exception without telling the verifier. */
713 public native void throwException(Throwable ee);
714
715
716 /**
717 * Atomically update Java variable to <tt>x</tt> if it is currently
718 * holding <tt>expected</tt>.
719 * @return <tt>true</tt> if successful
720 */
721 public final native boolean compareAndSwapObject(Object o, long offset,
722 Object expected,
723 Object x);
724
725 /**
726 * Atomically update Java variable to <tt>x</tt> if it is currently
727 * holding <tt>expected</tt>.
728 * @return <tt>true</tt> if successful
729 */
730 public final native boolean compareAndSwapInt(Object o, long offset,
731 int expected,
732 int x);
733
734 /**
735 * Atomically update Java variable to <tt>x</tt> if it is currently
736 * holding <tt>expected</tt>.
737 * @return <tt>true</tt> if successful
738 */
739 public final native boolean compareAndSwapLong(Object o, long offset,
740 long expected,
741 long x);
742
743 /**
744 * Fetches a reference value from a given Java variable, with volatile
745 * load semantics. Otherwise identical to {@link #getObject(Object, long)}
746 */
747 public native Object getObjectVolatile(Object o, long offset);
748
749 /**
750 * Stores a reference value into a given Java variable, with
751 * volatile store semantics. Otherwise identical to {@link #putObject(Object, long, Object)}
752 */
753 public native void putObjectVolatile(Object o, long offset, Object x);
754
755 /** Volatile version of {@link #getInt(Object, long)} */
756 public native int getIntVolatile(Object o, long offset);
757
758 /** Volatile version of {@link #putInt(Object, long, int)} */
759 public native void putIntVolatile(Object o, long offset, int x);
760
761 /** Volatile version of {@link #getBoolean(Object, long)} */
762 public native boolean getBooleanVolatile(Object o, long offset);
763
764 /** Volatile version of {@link #putBoolean(Object, long, boolean)} */
765 public native void putBooleanVolatile(Object o, long offset, boolean x);
766
767 /** Volatile version of {@link #getByte(Object, long)} */
768 public native byte getByteVolatile(Object o, long offset);
769
770 /** Volatile version of {@link #putByte(Object, long, byte)} */
771 public native void putByteVolatile(Object o, long offset, byte x);
772
773 /** Volatile version of {@link #getShort(Object, long)} */
774 public native short getShortVolatile(Object o, long offset);
775
776 /** Volatile version of {@link #putShort(Object, long, short)} */
777 public native void putShortVolatile(Object o, long offset, short x);
778
779 /** Volatile version of {@link #getChar(Object, long)} */
780 public native char getCharVolatile(Object o, long offset);
781
782 /** Volatile version of {@link #putChar(Object, long, char)} */
783 public native void putCharVolatile(Object o, long offset, char x);
784
785 /** Volatile version of {@link #getLong(Object, long)} */
786 public native long getLongVolatile(Object o, long offset);
787
788 /** Volatile version of {@link #putLong(Object, long, long)} */
789 public native void putLongVolatile(Object o, long offset, long x);
790
791 /** Volatile version of {@link #getFloat(Object, long)} */
792 public native float getFloatVolatile(Object o, long offset);
793
794 /** Volatile version of {@link #putFloat(Object, long, float)} */
795 public native void putFloatVolatile(Object o, long offset, float x);
796
797 /** Volatile version of {@link #getDouble(Object, long)} */
798 public native double getDoubleVolatile(Object o, long offset);
799
800 /** Volatile version of {@link #putDouble(Object, long, double)} */
801 public native void putDoubleVolatile(Object o, long offset, double x);
802
803 /**
804 * Version of {@link #putObjectVolatile(Object, long, Object)}
805 * that does not guarantee immediate visibility of the store to
806 * other threads. This method is generally only useful if the
807 * underlying field is a Java volatile (or if an array cell, one
808 * that is otherwise only accessed using volatile accesses).
809 */
810 public native void putOrderedObject(Object o, long offset, Object x);
811
812 /** Ordered/Lazy version of {@link #putIntVolatile(Object, long, int)} */
813 public native void putOrderedInt(Object o, long offset, int x);
814
815 /** Ordered/Lazy version of {@link #putLongVolatile(Object, long, long)} */
816 public native void putOrderedLong(Object o, long offset, long x);
817
818 /**
819 * Unblock the given thread blocked on <tt>park</tt>, or, if it is
820 * not blocked, cause the subsequent call to <tt>park</tt> not to
821 * block. Note: this operation is "unsafe" solely because the
822 * caller must somehow ensure that the thread has not been
823 * destroyed. Nothing special is usually required to ensure this
824 * when called from Java (in which there will ordinarily be a live
825 * reference to the thread) but this is not nearly-automatically
826 * so when calling from native code.
827 * @param thread the thread to unpark.
828 *
829 */
830 public native void unpark(Object thread);
831
832 /**
833 * Block current thread, returning when a balancing
834 * <tt>unpark</tt> occurs, or a balancing <tt>unpark</tt> has
835 * already occurred, or the thread is interrupted, or, if not
836 * absolute and time is not zero, the given time nanoseconds have
837 * elapsed, or if absolute, the given deadline in milliseconds
838 * since Epoch has passed, or spuriously (i.e., returning for no
839 * "reason"). Note: This operation is in the Unsafe class only
840 * because <tt>unpark</tt> is, so it would be strange to place it
841 * elsewhere.
842 */
843 public native void park(boolean isAbsolute, long time);
844
845 /**
846 * Gets the load average in the system run queue assigned
847 * to the available processors averaged over various periods of time.
848 * This method retrieves the given <tt>nelem</tt> samples and
849 * assigns to the elements of the given <tt>loadavg</tt> array.
850 * The system imposes a maximum of 3 samples, representing
851 * averages over the last 1, 5, and 15 minutes, respectively.
852 *
853 * @params loadavg an array of double of size nelems
854 * @params nelems the number of samples to be retrieved and
855 * must be 1 to 3.
856 *
857 * @return the number of samples actually retrieved; or -1
858 * if the load average is unobtainable.
859 */
860 public native int getLoadAverage(double[] loadavg, int nelems);
861 }