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/integerTypes.hpp"
31 #include "metaprogramming/isDerived.hpp"
32 #include "metaprogramming/isIntegral.hpp"
33 #include "metaprogramming/isPointer.hpp"
34 #include "utilities/align.hpp"
35 #include "utilities/debug.hpp"
36 #include "utilities/macros.hpp"
37
38 enum cmpxchg_memory_order {
39 memory_order_relaxed,
40 // Use value which doesn't interfere with C++2011. We need to be more conservative.
41 memory_order_conservative = 8
42 };
43
44 class GeneralizedAtomic : AllStatic {
45 template<typename T> class Never: public FalseType {};
46
47 template <typename T>
48 inline static void specialized_store(T store_value, volatile T* dest) {
49 STATIC_ASSERT(sizeof(T) <= size_t(BytesPerWord)); // Does the machine support atomic wide accesses?
50 (void)const_cast<T&>(*dest = store_value);
51 }
52
53 template <typename T>
54 inline static T specialized_load(const volatile T* dest) {
55 STATIC_ASSERT(sizeof(T) <= size_t(BytesPerWord)); // Does the machine support atomic wide accesses?
56 return *dest;
57 }
58
59 template <typename T>
60 inline static T specialized_add(T add_value, volatile T* dest) {
61 STATIC_ASSERT(Never<T>::value);
62 return add_value;
63 }
64
65 template <typename T>
66 inline static void specialized_inc(volatile T* dest) {
67 add(1, dest);
68 }
69
70 template <typename T>
71 inline static void specialized_dec(volatile T* dest) {
72 add(-1, dest);
73 }
74
75 template <typename T>
76 inline static T specialized_xchg(T exchange_value, volatile T* dest) {
77 STATIC_ASSERT(Never<T>::value);
78 return exchange_value;
79 }
80
81 template <typename T>
82 inline static T specialized_cmpxchg(T exchange_value, volatile T* dest, T compare_value, cmpxchg_memory_order order) {
83 STATIC_ASSERT(Never<T>::value);
84 return exchange_value;
85 }
86
87 public:
88 template <typename T, typename U>
89 inline static void store(T store_value, volatile U* dest);
90
91 template <typename T>
92 inline static T load(volatile T* src);
93
94 template <typename T, typename U>
95 inline static U add(T add_value, volatile U* dst);
96
97 template <typename T, typename U>
98 inline static U* add(T add_value, U* volatile* dst);
99
100 template <typename T>
101 inline static void inc(volatile T* dest);
102
103 template <typename T>
104 inline static void inc(T* volatile* dest);
105
106 template <typename T>
107 inline static void dec(volatile T* dest);
108
109 template <typename T>
110 inline static void dec(T* volatile* dest);
111
112 template <typename T, typename U>
113 inline static U xchg(T exchange_value, volatile U* dest);
114
115 template <typename T, typename U, typename V>
116 inline static U cmpxchg(T exchange_value, volatile U* dest, V compare_value, cmpxchg_memory_order order);
117 };
118
119
120 // platform specific in-line definitions - must come before shared definitions
121
122 class PlatformAtomic;
123
124 #include OS_CPU_HEADER(atomic)
125
126 typedef Conditional<IsDerived<PlatformAtomic, AllStatic>::value, PlatformAtomic, GeneralizedAtomic>::type AtomicImpl;
127
128 class Atomic : AllStatic {
129 public:
130 // Atomic operations on 64-bit types are not available on all 32-bit
131 // platforms. If atomic ops on 64-bit types are defined here they must only
132 // be used from code that verifies they are available at runtime and
133 // can provide an alternative action if not - see supports_cx8() for
134 // a means to test availability.
135
136 // The memory operations that are mentioned with each of the atomic
137 // function families come from src/share/vm/runtime/orderAccess.hpp,
138 // e.g., <fence> is described in that file and is implemented by the
139 // OrderAccess::fence() function. See that file for the gory details
140 // on the Memory Access Ordering Model.
141
142 // All of the atomic operations that imply a read-modify-write action
143 // guarantee a two-way memory barrier across that operation. Historically
144 // these semantics reflect the strength of atomic operations that are
145 // provided on SPARC/X86. We assume that strength is necessary unless
146 // we can prove that a weaker form is sufficiently safe.
147
148 // Atomically store to a location
149 // See comment above about using 64-bit atomics on 32-bit platforms
150 template <typename T, typename U>
151 inline static void store(T store_value, volatile U* dest);
152
153 // The store_ptr() member functions are deprecated. Use store() instead.
154 static void store_ptr(intptr_t store_value, volatile intptr_t* dest) {
155 store(store_value, dest);
156 }
157
158 static void store_ptr(void* store_value, volatile void* dest) {
159 store((intptr_t)store_value, (volatile intptr_t*)dest);
160 }
161
162 // Atomically load from a location
163 // See comment above about using 64-bit atomics on 32-bit platforms
164 template <typename T>
165 inline static T load(volatile T* src);
166
167 // Atomically add to a location. Returns updated value. add*() provide:
168 // <fence> add-value-to-dest <membar StoreLoad|StoreStore>
169 // add(I1 v, I* d)
170 // add(I1 v, P* d)
171 // where I, I1 are integral types, P is a pointer type.
172 // Functional behavior is modelled on *dest += add_value.
173 template <typename T, typename U>
174 inline static U add(T add_value, volatile U* dst);
175
176 // The add_ptr() member functions are deprecated. Use add() instead.
177 static intptr_t add_ptr(intptr_t add_value, volatile intptr_t* dest) {
178 return add(add_value, dest);
179 }
180
181 static void* add_ptr(intptr_t add_value, volatile void* dest) {
182 return (void*)add(add_value, (volatile intptr_t*)dest);
183 }
184
185 // Atomically increment location. inc*() provide:
186 // <fence> increment-dest <membar StoreLoad|StoreStore>
187 // Functional behavior is modelled on *dest++
188 template <typename T>
189 inline static void inc(volatile T* dest);
190
191 // The inc_ptr member functions are deprecated. Use inc() instead.
192 static void inc_ptr(volatile intptr_t* dest) {
193 inc(dest);
194 }
195
196 static void inc_ptr(volatile void* dest) {
197 inc((volatile intptr_t*)dest);
198 }
199
200 // Atomically decrement a location. dec*() provide:
201 // <fence> decrement-dest <membar StoreLoad|StoreStore>
202 // Functional behavior is modelled on *dest--
203 template <typename T>
204 inline static void dec(volatile T* dest);
205
206 // The dec_ptr member functions are deprecated. Use dec() instead.
207 static void dec_ptr(volatile intptr_t* dest) {
208 dec(dest);
209 }
210
211 static void dec_ptr(volatile void* dest) {
212 dec((volatile intptr_t*)dest);
213 }
214
215 // Performs atomic exchange of *dest with exchange_value. Returns old
216 // prior value of *dest. xchg*() provide:
217 // <fence> exchange-value-with-dest <membar StoreLoad|StoreStore>
218 template <typename T, typename U>
219 inline static U xchg(T exchange_value, volatile U* dest);
220
221 // The xchg_ptr() member functions are deprecated. Use xchg() instead.
222 static intptr_t xchg_ptr(intptr_t exchange_value, volatile intptr_t* dest) {
223 return xchg(exchange_value, dest);
224 }
225
226 static void* xchg_ptr(void* exchange_value, volatile void* dest) {
227 return (void*)xchg((intptr_t)exchange_value, (volatile intptr_t*)dest);
228 }
229
230 // Performs atomic compare of *dest and compare_value, and exchanges
231 // *dest with exchange_value if the comparison succeeded. Returns prior
232 // value of *dest. cmpxchg*() provide:
233 // <fence> compare-and-exchange <membar StoreLoad|StoreStore>
234 // See comment above about using 64-bit atomics on 32-bit platforms
235 template <typename T, typename U, typename V>
236 inline static U cmpxchg(T exchange_value, volatile U* dest, V compare_value, cmpxchg_memory_order order = memory_order_conservative);
237
238 // The cmpxchg_ptr member functions are deprecated. Use cmpxchg() instead.
239 inline static intptr_t cmpxchg_ptr(intptr_t exchange_value, volatile intptr_t* dest,
240 intptr_t compare_value, cmpxchg_memory_order order = memory_order_conservative) {
241 return cmpxchg(exchange_value, dest, compare_value, order);
242 }
243
244 inline static void* cmpxchg_ptr(void* exchange_value, volatile void* dest,
245 void* compare_value, cmpxchg_memory_order order = memory_order_conservative) {
246 return (void*)cmpxchg((intptr_t)exchange_value, (volatile intptr_t*)dest, (intptr_t)compare_value, order);
247 }
248 };
249
250 // internal implementation
251
252 template <typename T, typename U>
253 inline void GeneralizedAtomic::store(T store_value, volatile U* dest) {
254 typedef typename IntegerTypes::Signed<U>::type Raw;
255 U store_value_cast = store_value;
256 specialized_store(IntegerTypes::cast_to_signed(store_value_cast), reinterpret_cast<volatile Raw*>(dest));
257 }
258
259 template <typename T>
260 inline T GeneralizedAtomic::load(volatile T* src) {
261 typedef typename IntegerTypes::Signed<T>::type Raw;
262 return IntegerTypes::cast<T>(specialized_load(reinterpret_cast<const volatile Raw*>(src)));
263 }
264
265 template <typename T, typename U>
266 inline U GeneralizedAtomic::add(T add_value, volatile U* dst) {
267 STATIC_ASSERT(IsIntegral<T>::value);
268 STATIC_ASSERT(IsIntegral<U>::value);
269 typedef typename IntegerTypes::Signed<U>::type Raw;
270 // Allow -Wconversion or the like to complain about unsafe conversions.
271 U value = add_value;
272 Raw raw_value = IntegerTypes::cast_to_signed(value);
273 Raw result = specialized_add(raw_value, reinterpret_cast<volatile Raw*>(dst));
274 return IntegerTypes::cast<U>(result);
275 }
276
277 template <typename T, typename U>
278 inline U* GeneralizedAtomic::add(T add_value, U* volatile* dst) {
279 STATIC_ASSERT(IsIntegral<T>::value);
280 typedef typename IntegerTypes::Signed<U*>::type Raw;
281 ptrdiff_t value = add_value;
282 Raw raw_value = IntegerTypes::cast_to_signed(value * sizeof(U));
283 Raw result = specialized_add(raw_value, reinterpret_cast<volatile Raw*>(dst));
284 return IntegerTypes::cast<U*>(result);
285 }
286
287 template <typename T>
288 inline void GeneralizedAtomic::inc(volatile T* src) {
289 STATIC_ASSERT(IsIntegral<T>::value);
290 typedef typename IntegerTypes::Signed<T>::type Raw;
291 specialized_inc(reinterpret_cast<volatile Raw*>(src));
292 }
293
294 template <typename T>
295 inline void GeneralizedAtomic::inc(T* volatile* src) {
296 if (sizeof(T) != 1) {
297 add(1, src);
298 } else {
299 typedef typename IntegerTypes::Signed<T*>::type Raw;
300 specialized_inc(reinterpret_cast<volatile Raw*>(src));
301 }
302 }
303
304 template <typename T>
305 inline void GeneralizedAtomic::dec(volatile T* src) {
306 STATIC_ASSERT(IsIntegral<T>::value);
307 typedef typename IntegerTypes::Signed<T>::type Raw;
308 specialized_dec(reinterpret_cast<volatile Raw*>(src));
309 }
310
311 template <typename T>
312 inline void GeneralizedAtomic::dec(T* volatile* src) {
313 if (sizeof(T) != 1) {
314 add(-1, src);
315 } else {
316 typedef typename IntegerTypes::Signed<T*>::type Raw;
317 specialized_dec(reinterpret_cast<volatile Raw*>(src));
318 }
319 }
320
321 template <typename T, typename U>
322 inline U GeneralizedAtomic::xchg(T exchange_value, volatile U* dest) {
323 typedef typename IntegerTypes::Signed<U>::type Raw;
324 U exchange_value_cast = exchange_value;
325 Raw result = specialized_xchg(IntegerTypes::cast_to_signed(exchange_value_cast),
326 reinterpret_cast<volatile Raw*>(dest));
327 return IntegerTypes::cast<U>(result);
328 }
329
330 template <typename T, typename U, typename V>
331 inline U GeneralizedAtomic::cmpxchg(T exchange_value, volatile U* dest, V compare_value, cmpxchg_memory_order order) {
332 typedef typename IntegerTypes::Signed<U>::type Raw;
333 U exchange_value_cast = exchange_value;
334 U compare_value_cast = compare_value;
335 Raw result = specialized_cmpxchg(IntegerTypes::cast_to_signed(exchange_value_cast),
336 reinterpret_cast<volatile Raw*>(dest),
337 IntegerTypes::cast_to_signed(compare_value_cast), order);
338 return IntegerTypes::cast<U>(result);
339 }
340
341 template <typename T, typename U>
342 inline void Atomic::store(T store_value, volatile U* dest) {
343 AtomicImpl::store(store_value, dest);
344 }
345
346 template <typename T>
347 inline T Atomic::load(volatile T* src) {
348 return AtomicImpl::load(src);
349 }
350
351 template <typename T, typename U>
352 inline U Atomic::add(T add_value, volatile U* dst) {
353 return AtomicImpl::add(add_value, dst);
354 }
355
356 template <typename T>
357 inline void Atomic::inc(volatile T* src) {
358 AtomicImpl::inc(src);
359 }
360
361 template <typename T>
362 inline void Atomic::dec(volatile T* src) {
363 AtomicImpl::dec(src);
364 }
365
366 template <typename T, typename U>
367 inline U Atomic::xchg(T exchange_value, volatile U* dest) {
368 return AtomicImpl::xchg(exchange_value, dest);
369 }
370
371 template <typename T, typename U, typename V>
372 inline U Atomic::cmpxchg(T exchange_value, volatile U* dest, V compare_value, cmpxchg_memory_order order) {
373 return AtomicImpl::cmpxchg(exchange_value, dest, compare_value, order);
374 }
375
376 // shared in-line definitions
377
378 #ifndef VM_HAS_SPECIALIZED_CMPXCHG_BYTE
379 /*
380 * This is the default implementation of byte-sized cmpxchg. It emulates 8-bit-sized cmpxchg
381 * in terms of 32-bit-sized cmpxchg. Platforms may override this by defining their own inline definition
382 * as well as defining VM_HAS_SPECIALIZED_CMPXCHG_BYTE. This will cause the platform specific
383 * implementation to be used instead.
384 */
385 template <>
386 inline int8_t GeneralizedAtomic::specialized_cmpxchg<int8_t>(int8_t exchange_value, volatile int8_t* dest,
387 int8_t compare_value, cmpxchg_memory_order order) {
388 volatile int32_t* dest_int =
389 reinterpret_cast<volatile int32_t*>(align_down(dest, sizeof(int32_t)));
390 size_t offset = pointer_delta(dest, dest_int, 1);
391 int32_t cur = *dest_int;
392 int8_t* cur_as_bytes = reinterpret_cast<int8_t*>(&cur);
393
394 // current value may not be what we are looking for, so force it
395 // to that value so the initial cmpxchg will fail if it is different
396 cur_as_bytes[offset] = compare_value;
397
398 // always execute a real cmpxchg so that we get the required memory
399 // barriers even on initial failure
400 do {
401 // value to swap in matches current value ...
402 int32_t new_value = cur;
403 // ... except for the one byte we want to update
404 reinterpret_cast<int8_t*>(&new_value)[offset] = exchange_value;
405
406 int32_t res = cmpxchg(new_value, dest_int, cur, order);
407 if (res == cur) break; // success
408
409 // at least one byte in the int changed value, so update
410 // our view of the current int
411 cur = res;
412 // if our byte is still as cur we loop and try again
413 } while (cur_as_bytes[offset] == compare_value);
414
415 return cur_as_bytes[offset];
416 }
417
418 #endif // VM_HAS_SPECIALIZED_CMPXCHG_BYTE
419
420 template <>
421 inline int16_t GeneralizedAtomic::specialized_add<int16_t>(int16_t add_value, volatile int16_t* dest) {
422 // Most platforms do not support atomic add on a 2-byte value. However,
423 // if the value occupies the most significant 16 bits of an aligned 32-bit
424 // word, then we can do this with an atomic add of (add_value << 16)
425 // to the 32-bit word.
426 //
427 // The least significant parts of this 32-bit word will never be affected, even
428 // in case of overflow/underflow.
429 //
430 // Use the ATOMIC_SHORT_PAIR macro (see macros.hpp) to get the desired alignment.
431 #ifdef VM_LITTLE_ENDIAN
432 assert((intx(dest) & 0x03) == 0x02, "wrong alignment");
433 int32_t new_value = Atomic::add(int32_t(add_value) << 16, (volatile int32_t*)(dest-1));
434 #else
435 assert((intx(dest) & 0x03) == 0x00, "wrong alignment");
436 int32_t new_value = Atomic::add(int32_t(add_value) << 16, (volatile int32_t*)(dest));
437 #endif
438 return (int16_t)(new_value >> 16); // preserves sign
439 }
440
441 template <>
442 inline void GeneralizedAtomic::specialized_inc<int16_t>(volatile int16_t* dest) {
443 (void)add(int16_t(1), dest);
444 }
445
446 template <>
447 inline void GeneralizedAtomic::specialized_dec<int16_t>(volatile int16_t* dest) {
448 (void)add(int16_t(-1), dest);
449 }
450
451 #endif // SHARE_VM_RUNTIME_ATOMIC_HPP