1 /*
2 * Copyright (c) 1999, 2017, 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.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #ifndef SHARE_VM_RUNTIME_ATOMIC_HPP
26 #define SHARE_VM_RUNTIME_ATOMIC_HPP
27
28 #include "memory/allocation.hpp"
29 #include "metaprogramming/conditional.hpp"
30 #include "metaprogramming/enableIf.hpp"
31 #include "metaprogramming/isIntegral.hpp"
32 #include "metaprogramming/isPointer.hpp"
33 #include "metaprogramming/isSame.hpp"
34 #include "metaprogramming/primitiveConversions.hpp"
35 #include "metaprogramming/removeCV.hpp"
36 #include "metaprogramming/removePointer.hpp"
37 #include "utilities/align.hpp"
38 #include "utilities/macros.hpp"
39
40 enum cmpxchg_memory_order {
41 memory_order_relaxed,
42 // Use value which doesn't interfere with C++2011. We need to be more conservative.
43 memory_order_conservative = 8
44 };
45
46 class Atomic : AllStatic {
47 public:
48 // Atomic operations on jlong types are not available on all 32-bit
49 // platforms. If atomic ops on jlongs are defined here they must only
50 // be used from code that verifies they are available at runtime and
51 // can provide an alternative action if not - see supports_cx8() for
52 // a means to test availability.
53
54 // The memory operations that are mentioned with each of the atomic
55 // function families come from src/share/vm/runtime/orderAccess.hpp,
56 // e.g., <fence> is described in that file and is implemented by the
57 // OrderAccess::fence() function. See that file for the gory details
58 // on the Memory Access Ordering Model.
59
60 // All of the atomic operations that imply a read-modify-write action
61 // guarantee a two-way memory barrier across that operation. Historically
62 // these semantics reflect the strength of atomic operations that are
63 // provided on SPARC/X86. We assume that strength is necessary unless
64 // we can prove that a weaker form is sufficiently safe.
65
66 // Atomically store to a location
67 inline static void store (jbyte store_value, jbyte* dest);
68 inline static void store (jshort store_value, jshort* dest);
69 inline static void store (jint store_value, jint* dest);
70 // See comment above about using jlong atomics on 32-bit platforms
71 inline static void store (jlong store_value, jlong* dest);
72 inline static void store_ptr(intptr_t store_value, intptr_t* dest);
73 inline static void store_ptr(void* store_value, void* dest);
74
75 inline static void store (jbyte store_value, volatile jbyte* dest);
76 inline static void store (jshort store_value, volatile jshort* dest);
77 inline static void store (jint store_value, volatile jint* dest);
78 // See comment above about using jlong atomics on 32-bit platforms
79 inline static void store (jlong store_value, volatile jlong* dest);
80 inline static void store_ptr(intptr_t store_value, volatile intptr_t* dest);
81 inline static void store_ptr(void* store_value, volatile void* dest);
82
83 // See comment above about using jlong atomics on 32-bit platforms
84 inline static jlong load(const volatile jlong* src);
85
86 // Atomically add to a location. Returns updated value. add*() provide:
87 // <fence> add-value-to-dest <membar StoreLoad|StoreStore>
88
89 template<typename I, typename D>
90 inline static D add(I add_value, D volatile* dest);
91
92 inline static intptr_t add_ptr(intptr_t add_value, volatile intptr_t* dest) {
93 return add(add_value, dest);
94 }
95
96 inline static void* add_ptr(intptr_t add_value, volatile void* dest) {
97 return add(add_value, reinterpret_cast<char* volatile*>(dest));
98 }
99
100 // Atomically increment location. inc*() provide:
101 // <fence> increment-dest <membar StoreLoad|StoreStore>
102 inline static void inc (volatile jint* dest);
103 inline static void inc (volatile jshort* dest);
104 inline static void inc (volatile size_t* dest);
105 inline static void inc_ptr(volatile intptr_t* dest);
106 inline static void inc_ptr(volatile void* dest);
107
108 // Atomically decrement a location. dec*() provide:
109 // <fence> decrement-dest <membar StoreLoad|StoreStore>
110 inline static void dec (volatile jint* dest);
111 inline static void dec (volatile jshort* dest);
112 inline static void dec (volatile size_t* dest);
113 inline static void dec_ptr(volatile intptr_t* dest);
114 inline static void dec_ptr(volatile void* dest);
115
116 // Performs atomic exchange of *dest with exchange_value. Returns old
117 // prior value of *dest. xchg*() provide:
118 // <fence> exchange-value-with-dest <membar StoreLoad|StoreStore>
119 inline static jint xchg (jint exchange_value, volatile jint* dest);
120 inline static unsigned int xchg (unsigned int exchange_value, volatile unsigned int* dest);
121 inline static intptr_t xchg_ptr(intptr_t exchange_value, volatile intptr_t* dest);
122 inline static void* xchg_ptr(void* exchange_value, volatile void* dest);
123
124 // Performs atomic compare of *dest and compare_value, and exchanges
125 // *dest with exchange_value if the comparison succeeded. Returns prior
126 // value of *dest. cmpxchg*() provide:
127 // <fence> compare-and-exchange <membar StoreLoad|StoreStore>
128
129 template<typename T, typename D, typename U>
130 inline static D cmpxchg(T exchange_value,
131 D volatile* dest,
132 U compare_value,
133 cmpxchg_memory_order order = memory_order_conservative);
134
135 // Performs atomic compare of *dest and NULL, and replaces *dest
136 // with exchange_value if the comparison succeeded. Returns true if
137 // the comparison succeeded and the exchange occurred. This is
138 // often used as part of lazy initialization, as a lock-free
139 // alternative to the Double-Checked Locking Pattern.
140 template<typename T, typename D>
141 inline static bool replace_if_null(T* value, D* volatile* dest,
142 cmpxchg_memory_order order = memory_order_conservative);
143
144 inline static intptr_t cmpxchg_ptr(intptr_t exchange_value,
145 volatile intptr_t* dest,
146 intptr_t compare_value,
147 cmpxchg_memory_order order = memory_order_conservative) {
148 return cmpxchg(exchange_value, dest, compare_value, order);
149 }
150
151 inline static void* cmpxchg_ptr(void* exchange_value,
152 volatile void* dest,
153 void* compare_value,
154 cmpxchg_memory_order order = memory_order_conservative) {
155 return cmpxchg(exchange_value,
156 reinterpret_cast<void* volatile*>(dest),
157 compare_value,
158 order);
159 }
160
161 private:
162 // Test whether From is implicitly convertible to To.
163 // From and To must be pointer types.
164 // Note: Provides the limited subset of C++11 std::is_convertible
165 // that is needed here.
166 template<typename From, typename To> struct IsPointerConvertible;
167
168 // Dispatch handler for add. Provides type-based validity checking
169 // and limited conversions around calls to the platform-specific
170 // implementation layer provided by PlatformAdd.
171 template<typename I, typename D, typename Enable = void>
172 struct AddImpl;
173
174 // Platform-specific implementation of add. Support for sizes of 4
175 // bytes and (if different) pointer size bytes are required. The
176 // class is a function object that must be default constructable,
177 // with these requirements:
178 //
179 // - dest is of type D*, an integral or pointer type.
180 // - add_value is of type I, an integral type.
181 // - sizeof(I) == sizeof(D).
182 // - if D is an integral type, I == D.
183 // - platform_add is an object of type PlatformAdd<sizeof(D)>.
184 //
185 // Then
186 // platform_add(add_value, dest)
187 // must be a valid expression, returning a result convertible to D.
188 //
189 // No definition is provided; all platforms must explicitly define
190 // this class and any needed specializations.
191 template<size_t byte_size> struct PlatformAdd;
192
193 // Helper base classes for defining PlatformAdd. To use, define
194 // PlatformAdd or a specialization that derives from one of these,
195 // and include in the PlatformAdd definition the support function
196 // (described below) required by the base class.
197 //
198 // These classes implement the required function object protocol for
199 // PlatformAdd, using a support function template provided by the
200 // derived class. Let add_value (of type I) and dest (of type D) be
201 // the arguments the object is called with. If D is a pointer type
202 // P*, then let addend (of type I) be add_value * sizeof(P);
203 // otherwise, addend is add_value.
204 //
205 // FetchAndAdd requires the derived class to provide
206 // fetch_and_add(addend, dest)
207 // atomically adding addend to the value of dest, and returning the
208 // old value.
209 //
210 // AddAndFetch requires the derived class to provide
211 // add_and_fetch(addend, dest)
212 // atomically adding addend to the value of dest, and returning the
213 // new value.
214 //
215 // When D is a pointer type P*, both fetch_and_add and add_and_fetch
216 // treat it as if it were a uintptr_t; they do not perform any
217 // scaling of the addend, as that has already been done by the
218 // caller.
219 public: // Temporary, can't be private: C++03 11.4/2. Fixed by C++11.
220 template<typename Derived> struct FetchAndAdd;
221 template<typename Derived> struct AddAndFetch;
222 private:
223
224 // Support for platforms that implement some variants of add using a
225 // (typically out of line) non-template helper function. The
226 // generic arguments passed to PlatformAdd need to be translated to
227 // the appropriate type for the helper function, the helper function
228 // invoked on the translated arguments, and the result translated
229 // back. Type is the parameter / return type of the helper
230 // function. No scaling of add_value is performed when D is a pointer
231 // type, so this function can be used to implement the support function
232 // required by AddAndFetch.
233 template<typename Type, typename Fn, typename I, typename D>
234 static D add_using_helper(Fn fn, I add_value, D volatile* dest);
235
236 // Dispatch handler for cmpxchg. Provides type-based validity
237 // checking and limited conversions around calls to the
238 // platform-specific implementation layer provided by
239 // PlatformCmpxchg.
240 template<typename T, typename D, typename U, typename Enable = void>
241 struct CmpxchgImpl;
242
243 // Platform-specific implementation of cmpxchg. Support for sizes
244 // of 1, 4, and 8 are required. The class is a function object that
245 // must be default constructable, with these requirements:
246 //
247 // - dest is of type T*.
248 // - exchange_value and compare_value are of type T.
249 // - order is of type cmpxchg_memory_order.
250 // - platform_cmpxchg is an object of type PlatformCmpxchg<sizeof(T)>.
251 //
252 // Then
253 // platform_cmpxchg(exchange_value, dest, compare_value, order)
254 // must be a valid expression, returning a result convertible to T.
255 //
256 // A default definition is provided, which declares a function template
257 // T operator()(T, T volatile*, T, cmpxchg_memory_order) const
258 //
259 // For each required size, a platform must either provide an
260 // appropriate definition of that function, or must entirely
261 // specialize the class template for that size.
262 template<size_t byte_size> struct PlatformCmpxchg;
263
264 // Support for platforms that implement some variants of cmpxchg
265 // using a (typically out of line) non-template helper function.
266 // The generic arguments passed to PlatformCmpxchg need to be
267 // translated to the appropriate type for the helper function, the
268 // helper invoked on the translated arguments, and the result
269 // translated back. Type is the parameter / return type of the
270 // helper function.
271 template<typename Type, typename Fn, typename T>
272 static T cmpxchg_using_helper(Fn fn,
273 T exchange_value,
274 T volatile* dest,
275 T compare_value);
276
277 // Support platforms that do not provide Read-Modify-Write
278 // byte-level atomic access. To use, derive PlatformCmpxchg<1> from
279 // this class.
280 public: // Temporary, can't be private: C++03 11.4/2. Fixed by C++11.
281 struct CmpxchgByteUsingInt;
282 private:
283 };
284
285 template<typename From, typename To>
286 struct Atomic::IsPointerConvertible<From*, To*> : AllStatic {
287 // Determine whether From* is implicitly convertible to To*, using
288 // the "sizeof trick".
289 typedef char yes;
290 typedef char (&no)[2];
291
292 static yes test(To*);
293 static no test(...);
294 static From* test_value;
295
296 static const bool value = (sizeof(yes) == sizeof(test(test_value)));
297 };
298
299 // Define FetchAndAdd and AddAndFetch helper classes before including
300 // platform file, which may use these as base classes, requiring they
301 // be complete.
302
303 template<typename Derived>
304 struct Atomic::FetchAndAdd VALUE_OBJ_CLASS_SPEC {
305 template<typename I, typename D>
306 D operator()(I add_value, D volatile* dest) const;
307 };
308
309 template<typename Derived>
310 struct Atomic::AddAndFetch VALUE_OBJ_CLASS_SPEC {
311 template<typename I, typename D>
312 D operator()(I add_value, D volatile* dest) const;
313 };
314
315 // Define the class before including platform file, which may specialize
316 // the operator definition. No generic definition of specializations
317 // of the operator template are provided, nor are there any generic
318 // specializations of the class. The platform file is responsible for
319 // providing those.
320 template<size_t byte_size>
321 struct Atomic::PlatformCmpxchg VALUE_OBJ_CLASS_SPEC {
322 template<typename T>
323 T operator()(T exchange_value,
324 T volatile* dest,
325 T compare_value,
326 cmpxchg_memory_order order) const;
327 };
328
329 // Define the class before including platform file, which may use this
330 // as a base class, requiring it be complete. The definition is later
331 // in this file, near the other definitions related to cmpxchg.
332 struct Atomic::CmpxchgByteUsingInt VALUE_OBJ_CLASS_SPEC {
333 template<typename T>
334 T operator()(T exchange_value,
335 T volatile* dest,
336 T compare_value,
337 cmpxchg_memory_order order) const;
338 };
339
340 // platform specific in-line definitions - must come before shared definitions
341
342 #include OS_CPU_HEADER(atomic)
343
344 // shared in-line definitions
345
346 // size_t casts...
347 #if (SIZE_MAX != UINTPTR_MAX)
348 #error size_t is not WORD_SIZE, interesting platform, but missing implementation here
349 #endif
350
351 template<typename I, typename D>
352 inline D Atomic::add(I add_value, D volatile* dest) {
353 return AddImpl<I, D>()(add_value, dest);
354 }
355
356 template<typename I, typename D>
357 struct Atomic::AddImpl<
358 I, D,
359 typename EnableIf<IsIntegral<I>::value &&
360 IsIntegral<D>::value &&
361 (sizeof(I) <= sizeof(D)) &&
362 (IsSigned<I>::value == IsSigned<D>::value)>::type>
363 VALUE_OBJ_CLASS_SPEC
364 {
365 D operator()(I add_value, D volatile* dest) const {
366 D addend = add_value;
367 return PlatformAdd<sizeof(D)>()(addend, dest);
368 }
369 };
370
371 template<typename I, typename P>
372 struct Atomic::AddImpl<
373 I, P*,
374 typename EnableIf<IsIntegral<I>::value && (sizeof(I) <= sizeof(P*))>::type>
375 VALUE_OBJ_CLASS_SPEC
376 {
377 P* operator()(I add_value, P* volatile* dest) const {
378 STATIC_ASSERT(sizeof(intptr_t) == sizeof(P*));
379 STATIC_ASSERT(sizeof(uintptr_t) == sizeof(P*));
380 typedef typename Conditional<IsSigned<I>::value,
381 intptr_t,
382 uintptr_t>::type CI;
383 CI addend = add_value;
384 return PlatformAdd<sizeof(P*)>()(addend, dest);
385 }
386 };
387
388 // Most platforms do not support atomic add on a 2-byte value. However,
389 // if the value occupies the most significant 16 bits of an aligned 32-bit
390 // word, then we can do this with an atomic add of (add_value << 16)
391 // to the 32-bit word.
392 //
393 // The least significant parts of this 32-bit word will never be affected, even
394 // in case of overflow/underflow.
395 //
396 // Use the ATOMIC_SHORT_PAIR macro (see macros.hpp) to get the desired alignment.
397 template<>
398 struct Atomic::AddImpl<jshort, jshort> VALUE_OBJ_CLASS_SPEC {
399 jshort operator()(jshort add_value, jshort volatile* dest) const {
400 #ifdef VM_LITTLE_ENDIAN
401 assert((intx(dest) & 0x03) == 0x02, "wrong alignment");
402 jint new_value = Atomic::add(add_value << 16, (volatile jint*)(dest-1));
403 #else
404 assert((intx(dest) & 0x03) == 0x00, "wrong alignment");
405 jint new_value = Atomic::add(add_value << 16, (volatile jint*)(dest));
406 #endif
407 return (jshort)(new_value >> 16); // preserves sign
408 }
409 };
410
411 template<typename Derived>
412 template<typename I, typename D>
413 inline D Atomic::FetchAndAdd<Derived>::operator()(I add_value, D volatile* dest) const {
414 I addend = add_value;
415 // If D is a pointer type P*, scale by sizeof(P).
416 if (IsPointer<D>::value) {
417 addend *= sizeof(typename RemovePointer<D>::type);
418 }
419 D old = static_cast<const Derived*>(this)->fetch_and_add(addend, dest);
420 return old + add_value;
421 }
422
423 template<typename Derived>
424 template<typename I, typename D>
425 inline D Atomic::AddAndFetch<Derived>::operator()(I add_value, D volatile* dest) const {
426 // If D is a pointer type P*, scale by sizeof(P).
427 if (IsPointer<D>::value) {
428 add_value *= sizeof(typename RemovePointer<D>::type);
429 }
430 return static_cast<const Derived*>(this)->add_and_fetch(add_value, dest);
431 }
432
433 template<typename Type, typename Fn, typename I, typename D>
434 inline D Atomic::add_using_helper(Fn fn, I add_value, D volatile* dest) {
435 return PrimitiveConversions::cast<D>(
436 fn(PrimitiveConversions::cast<Type>(add_value),
437 reinterpret_cast<Type volatile*>(dest)));
438 }
439
440 inline void Atomic::inc(volatile size_t* dest) {
441 inc_ptr((volatile intptr_t*) dest);
442 }
443
444 inline void Atomic::dec(volatile size_t* dest) {
445 dec_ptr((volatile intptr_t*) dest);
446 }
447
448 template<typename T, typename D, typename U>
449 inline D Atomic::cmpxchg(T exchange_value,
450 D volatile* dest,
451 U compare_value,
452 cmpxchg_memory_order order) {
453 return CmpxchgImpl<T, D, U>()(exchange_value, dest, compare_value, order);
454 }
455
456 template<typename T, typename D>
457 inline bool Atomic::replace_if_null(T* value, D* volatile* dest,
458 cmpxchg_memory_order order) {
459 // Presently using a trivial implementation in terms of cmpxchg.
460 // Consider adding platform support, to permit the use of compiler
461 // intrinsics like gcc's __sync_bool_compare_and_swap.
462 D* expected_null = NULL;
463 return expected_null == cmpxchg(value, dest, expected_null, order);
464 }
465
466 // Handle cmpxchg for integral and enum types.
467 //
468 // All the involved types must be identical.
469 template<typename T>
470 struct Atomic::CmpxchgImpl<
471 T, T, T,
472 typename EnableIf<IsIntegral<T>::value || IsRegisteredEnum<T>::value>::type>
473 VALUE_OBJ_CLASS_SPEC
474 {
475 T operator()(T exchange_value, T volatile* dest, T compare_value,
476 cmpxchg_memory_order order) const {
477 // Forward to the platform handler for the size of T.
478 return PlatformCmpxchg<sizeof(T)>()(exchange_value,
479 dest,
480 compare_value,
481 order);
482 }
483 };
484
485 // Handle cmpxchg for pointer types.
486 //
487 // The destination's type and the compare_value type must be the same,
488 // ignoring cv-qualifiers; we don't care about the cv-qualifiers of
489 // the compare_value.
490 //
491 // The exchange_value must be implicitly convertible to the
492 // destination's type; it must be type-correct to store the
493 // exchange_value in the destination.
494 template<typename T, typename D, typename U>
495 struct Atomic::CmpxchgImpl<
496 T*, D*, U*,
497 typename EnableIf<Atomic::IsPointerConvertible<T*, D*>::value &&
498 IsSame<typename RemoveCV<D>::type,
499 typename RemoveCV<U>::type>::value>::type>
500 VALUE_OBJ_CLASS_SPEC
501 {
502 D* operator()(T* exchange_value, D* volatile* dest, U* compare_value,
503 cmpxchg_memory_order order) const {
504 // Allow derived to base conversion, and adding cv-qualifiers.
505 D* new_value = exchange_value;
506 // Don't care what the CV qualifiers for compare_value are,
507 // but we need to match D* when calling platform support.
508 D* old_value = const_cast<D*>(compare_value);
509 return PlatformCmpxchg<sizeof(D*)>()(new_value, dest, old_value, order);
510 }
511 };
512
513 // Handle cmpxchg for types that have a translator.
514 //
515 // All the involved types must be identical.
516 //
517 // This translates the original call into a call on the decayed
518 // arguments, and returns the recovered result of that translated
519 // call.
520 template<typename T>
521 struct Atomic::CmpxchgImpl<
522 T, T, T,
523 typename EnableIf<PrimitiveConversions::Translate<T>::value>::type>
524 VALUE_OBJ_CLASS_SPEC
525 {
526 T operator()(T exchange_value, T volatile* dest, T compare_value,
527 cmpxchg_memory_order order) const {
528 typedef PrimitiveConversions::Translate<T> Translator;
529 typedef typename Translator::Decayed Decayed;
530 STATIC_ASSERT(sizeof(T) == sizeof(Decayed));
531 return Translator::recover(
532 cmpxchg(Translator::decay(exchange_value),
533 reinterpret_cast<Decayed volatile*>(dest),
534 Translator::decay(compare_value),
535 order));
536 }
537 };
538
539 template<typename Type, typename Fn, typename T>
540 inline T Atomic::cmpxchg_using_helper(Fn fn,
541 T exchange_value,
542 T volatile* dest,
543 T compare_value) {
544 STATIC_ASSERT(sizeof(Type) == sizeof(T));
545 return PrimitiveConversions::cast<T>(
546 fn(PrimitiveConversions::cast<Type>(exchange_value),
547 reinterpret_cast<Type volatile*>(dest),
548 PrimitiveConversions::cast<Type>(compare_value)));
549 }
550
551 template<typename T>
552 inline T Atomic::CmpxchgByteUsingInt::operator()(T exchange_value,
553 T volatile* dest,
554 T compare_value,
555 cmpxchg_memory_order order) const {
556 STATIC_ASSERT(sizeof(T) == sizeof(uint8_t));
557 uint8_t canon_exchange_value = exchange_value;
558 uint8_t canon_compare_value = compare_value;
559 volatile uint32_t* aligned_dest
560 = reinterpret_cast<volatile uint32_t*>(align_down(dest, sizeof(uint32_t)));
561 size_t offset = pointer_delta(dest, aligned_dest, 1);
562 uint32_t cur = *aligned_dest;
563 uint8_t* cur_as_bytes = reinterpret_cast<uint8_t*>(&cur);
564
565 // current value may not be what we are looking for, so force it
566 // to that value so the initial cmpxchg will fail if it is different
567 cur_as_bytes[offset] = canon_compare_value;
568
569 // always execute a real cmpxchg so that we get the required memory
570 // barriers even on initial failure
571 do {
572 // value to swap in matches current value ...
573 uint32_t new_value = cur;
574 // ... except for the one jbyte we want to update
575 reinterpret_cast<uint8_t*>(&new_value)[offset] = canon_exchange_value;
576
577 uint32_t res = cmpxchg(new_value, aligned_dest, cur, order);
578 if (res == cur) break; // success
579
580 // at least one byte in the int changed value, so update
581 // our view of the current int
582 cur = res;
583 // if our byte is still as cur we loop and try again
584 } while (cur_as_bytes[offset] == canon_compare_value);
585
586 return PrimitiveConversions::cast<T>(cur_as_bytes[offset]);
587 }
588
589 inline unsigned Atomic::xchg(unsigned int exchange_value, volatile unsigned int* dest) {
590 assert(sizeof(unsigned int) == sizeof(jint), "more work to do");
591 return (unsigned int)Atomic::xchg((jint)exchange_value, (volatile jint*)dest);
592 }
593
594 inline void Atomic::inc(volatile jshort* dest) {
595 (void)add(jshort(1), dest);
596 }
597
598 inline void Atomic::dec(volatile jshort* dest) {
599 (void)add(jshort(-1), dest);
600 }
601
602 #endif // SHARE_VM_RUNTIME_ATOMIC_HPP