Line data Source code
1 : /*-------------------------------------------------------------------------
2 : *
3 : * atomics.h
4 : * Atomic operations.
5 : *
6 : * Hardware and compiler dependent functions for manipulating memory
7 : * atomically and dealing with cache coherency. Used to implement locking
8 : * facilities and lockless algorithms/data structures.
9 : *
10 : * To bring up postgres on a platform/compiler at the very least
11 : * implementations for the following operations should be provided:
12 : * * pg_compiler_barrier(), pg_write_barrier(), pg_read_barrier()
13 : * * pg_atomic_compare_exchange_u32(), pg_atomic_fetch_add_u32()
14 : * * pg_atomic_test_set_flag(), pg_atomic_init_flag(), pg_atomic_clear_flag()
15 : * * PG_HAVE_8BYTE_SINGLE_COPY_ATOMICITY should be defined if appropriate.
16 : *
17 : * There exist generic, hardware independent, implementations for several
18 : * compilers which might be sufficient, although possibly not optimal, for a
19 : * new platform. If no such generic implementation is available spinlocks will
20 : * be used to implement the 64-bit parts of the API.
21 : *
22 : * Implement _u64 atomics if and only if your platform can use them
23 : * efficiently (and obviously correctly).
24 : *
25 : * Use higher level functionality (lwlocks, spinlocks, heavyweight locks)
26 : * whenever possible. Writing correct code using these facilities is hard.
27 : *
28 : * For an introduction to using memory barriers within the PostgreSQL backend,
29 : * see src/backend/storage/lmgr/README.barrier
30 : *
31 : * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
32 : * Portions Copyright (c) 1994, Regents of the University of California
33 : *
34 : * src/include/port/atomics.h
35 : *
36 : *-------------------------------------------------------------------------
37 : */
38 : #ifndef ATOMICS_H
39 : #define ATOMICS_H
40 :
41 : #ifdef FRONTEND
42 : #error "atomics.h may not be included from frontend code"
43 : #endif
44 :
45 : #define INSIDE_ATOMICS_H
46 :
47 : #include <limits.h>
48 :
49 : /*
50 : * First a set of architecture specific files is included.
51 : *
52 : * These files can provide the full set of atomics or can do pretty much
53 : * nothing if all the compilers commonly used on these platforms provide
54 : * usable generics.
55 : *
56 : * Don't add an inline assembly of the actual atomic operations if all the
57 : * common implementations of your platform provide intrinsics. Intrinsics are
58 : * much easier to understand and potentially support more architectures.
59 : *
60 : * It will often make sense to define memory barrier semantics here, since
61 : * e.g. generic compiler intrinsics for x86 memory barriers can't know that
62 : * postgres doesn't need x86 read/write barriers do anything more than a
63 : * compiler barrier.
64 : *
65 : */
66 : #if defined(__arm__) || defined(__arm) || defined(__aarch64__)
67 : #include "port/atomics/arch-arm.h"
68 : #elif defined(__i386__) || defined(__i386) || defined(__x86_64__)
69 : #include "port/atomics/arch-x86.h"
70 : #elif defined(__ppc__) || defined(__powerpc__) || defined(__ppc64__) || defined(__powerpc64__)
71 : #include "port/atomics/arch-ppc.h"
72 : #endif
73 :
74 : /*
75 : * Compiler specific, but architecture independent implementations.
76 : *
77 : * Provide architecture independent implementations of the atomic
78 : * facilities. At the very least compiler barriers should be provided, but a
79 : * full implementation of
80 : * * pg_compiler_barrier(), pg_write_barrier(), pg_read_barrier()
81 : * * pg_atomic_compare_exchange_u32(), pg_atomic_fetch_add_u32()
82 : * using compiler intrinsics are a good idea.
83 : */
84 : /*
85 : * gcc or compatible, including clang and icc.
86 : */
87 : #if defined(__GNUC__) || defined(__INTEL_COMPILER)
88 : #include "port/atomics/generic-gcc.h"
89 : #elif defined(_MSC_VER)
90 : #include "port/atomics/generic-msvc.h"
91 : #else
92 : /* Unknown compiler. */
93 : #endif
94 :
95 : /* Fail if we couldn't find implementations of required facilities. */
96 : #if !defined(PG_HAVE_ATOMIC_U32_SUPPORT)
97 : #error "could not find an implementation of pg_atomic_uint32"
98 : #endif
99 : #if !defined(pg_compiler_barrier_impl)
100 : #error "could not find an implementation of pg_compiler_barrier"
101 : #endif
102 : #if !defined(pg_memory_barrier_impl)
103 : #error "could not find an implementation of pg_memory_barrier_impl"
104 : #endif
105 :
106 :
107 : /*
108 : * Provide a spinlock-based implementation of the 64 bit variants, if
109 : * necessary.
110 : */
111 : #include "port/atomics/fallback.h"
112 :
113 : /*
114 : * Provide additional operations using supported infrastructure. These are
115 : * expected to be efficient if the underlying atomic operations are efficient.
116 : */
117 : #include "port/atomics/generic.h"
118 :
119 :
120 : /*
121 : * pg_compiler_barrier - prevent the compiler from moving code across
122 : *
123 : * A compiler barrier need not (and preferably should not) emit any actual
124 : * machine code, but must act as an optimization fence: the compiler must not
125 : * reorder loads or stores to main memory around the barrier. However, the
126 : * CPU may still reorder loads or stores at runtime, if the architecture's
127 : * memory model permits this.
128 : */
129 : #define pg_compiler_barrier() pg_compiler_barrier_impl()
130 :
131 : /*
132 : * pg_memory_barrier - prevent the CPU from reordering memory access
133 : *
134 : * A memory barrier must act as a compiler barrier, and in addition must
135 : * guarantee that all loads and stores issued prior to the barrier are
136 : * completed before any loads or stores issued after the barrier. Unless
137 : * loads and stores are totally ordered (which is not the case on most
138 : * architectures) this requires issuing some sort of memory fencing
139 : * instruction.
140 : */
141 : #define pg_memory_barrier() pg_memory_barrier_impl()
142 :
143 : /*
144 : * pg_(read|write)_barrier - prevent the CPU from reordering memory access
145 : *
146 : * A read barrier must act as a compiler barrier, and in addition must
147 : * guarantee that any loads issued prior to the barrier are completed before
148 : * any loads issued after the barrier. Similarly, a write barrier acts
149 : * as a compiler barrier, and also orders stores. Read and write barriers
150 : * are thus weaker than a full memory barrier, but stronger than a compiler
151 : * barrier. In practice, on machines with strong memory ordering, read and
152 : * write barriers may require nothing more than a compiler barrier.
153 : */
154 : #define pg_read_barrier() pg_read_barrier_impl()
155 : #define pg_write_barrier() pg_write_barrier_impl()
156 :
157 : /*
158 : * Spinloop delay - Allow CPU to relax in busy loops
159 : */
160 : #define pg_spin_delay() pg_spin_delay_impl()
161 :
162 : /*
163 : * pg_atomic_init_flag - initialize atomic flag.
164 : *
165 : * No barrier semantics.
166 : */
167 : static inline void
168 24796 : pg_atomic_init_flag(volatile pg_atomic_flag *ptr)
169 : {
170 24796 : pg_atomic_init_flag_impl(ptr);
171 24796 : }
172 :
173 : /*
174 : * pg_atomic_test_set_flag - TAS()
175 : *
176 : * Returns true if the flag has successfully been set, false otherwise.
177 : *
178 : * Acquire (including read barrier) semantics.
179 : */
180 : static inline bool
181 294168 : pg_atomic_test_set_flag(volatile pg_atomic_flag *ptr)
182 : {
183 294168 : return pg_atomic_test_set_flag_impl(ptr);
184 : }
185 :
186 : /*
187 : * pg_atomic_unlocked_test_flag - Check if the lock is free
188 : *
189 : * Returns true if the flag currently is not set, false otherwise.
190 : *
191 : * No barrier semantics.
192 : */
193 : static inline bool
194 597188 : pg_atomic_unlocked_test_flag(volatile pg_atomic_flag *ptr)
195 : {
196 597188 : return pg_atomic_unlocked_test_flag_impl(ptr);
197 : }
198 :
199 : /*
200 : * pg_atomic_clear_flag - release lock set by TAS()
201 : *
202 : * Release (including write barrier) semantics.
203 : */
204 : static inline void
205 2850 : pg_atomic_clear_flag(volatile pg_atomic_flag *ptr)
206 : {
207 2850 : pg_atomic_clear_flag_impl(ptr);
208 2850 : }
209 :
210 :
211 : /*
212 : * pg_atomic_init_u32 - initialize atomic variable
213 : *
214 : * Has to be done before any concurrent usage..
215 : *
216 : * No barrier semantics.
217 : */
218 : static inline void
219 49394646 : pg_atomic_init_u32(volatile pg_atomic_uint32 *ptr, uint32 val)
220 : {
221 : AssertPointerAlignment(ptr, 4);
222 :
223 49394646 : pg_atomic_init_u32_impl(ptr, val);
224 49394646 : }
225 :
226 : /*
227 : * pg_atomic_read_u32 - unlocked read from atomic variable.
228 : *
229 : * The read is guaranteed to return a value as it has been written by this or
230 : * another process at some point in the past. There's however no cache
231 : * coherency interaction guaranteeing the value hasn't since been written to
232 : * again.
233 : *
234 : * No barrier semantics.
235 : */
236 : static inline uint32
237 1017182250 : pg_atomic_read_u32(volatile pg_atomic_uint32 *ptr)
238 : {
239 : AssertPointerAlignment(ptr, 4);
240 1017182250 : return pg_atomic_read_u32_impl(ptr);
241 : }
242 :
243 : /*
244 : * pg_atomic_read_membarrier_u32 - read with barrier semantics.
245 : *
246 : * This read is guaranteed to return the current value, provided that the value
247 : * is only ever updated via operations with barrier semantics, such as
248 : * pg_atomic_compare_exchange_u32() and pg_atomic_write_membarrier_u32().
249 : * While this may be less performant than pg_atomic_read_u32(), it may be
250 : * easier to reason about correctness with this function in less performance-
251 : * sensitive code.
252 : *
253 : * Full barrier semantics.
254 : */
255 : static inline uint32
256 : pg_atomic_read_membarrier_u32(volatile pg_atomic_uint32 *ptr)
257 : {
258 : AssertPointerAlignment(ptr, 4);
259 :
260 : return pg_atomic_read_membarrier_u32_impl(ptr);
261 : }
262 :
263 : /*
264 : * pg_atomic_write_u32 - write to atomic variable.
265 : *
266 : * The write is guaranteed to succeed as a whole, i.e. it's not possible to
267 : * observe a partial write for any reader. Note that this correctly interacts
268 : * with pg_atomic_compare_exchange_u32, in contrast to
269 : * pg_atomic_unlocked_write_u32().
270 : *
271 : * No barrier semantics.
272 : */
273 : static inline void
274 138588 : pg_atomic_write_u32(volatile pg_atomic_uint32 *ptr, uint32 val)
275 : {
276 : AssertPointerAlignment(ptr, 4);
277 :
278 138588 : pg_atomic_write_u32_impl(ptr, val);
279 138588 : }
280 :
281 : /*
282 : * pg_atomic_unlocked_write_u32 - unlocked write to atomic variable.
283 : *
284 : * Write to an atomic variable, without atomicity guarantees. I.e. it is not
285 : * guaranteed that a concurrent reader will not see a torn value, nor is this
286 : * guaranteed to correctly interact with concurrent read-modify-write
287 : * operations like pg_atomic_compare_exchange_u32. This should only be used
288 : * in cases where minor performance regressions due to atomic operations are
289 : * unacceptable and where exclusive access is guaranteed via some external
290 : * means.
291 : *
292 : * No barrier semantics.
293 : */
294 : static inline void
295 8733106 : pg_atomic_unlocked_write_u32(volatile pg_atomic_uint32 *ptr, uint32 val)
296 : {
297 : AssertPointerAlignment(ptr, 4);
298 :
299 8733106 : pg_atomic_unlocked_write_u32_impl(ptr, val);
300 8733106 : }
301 :
302 : /*
303 : * pg_atomic_write_membarrier_u32 - write with barrier semantics.
304 : *
305 : * The write is guaranteed to succeed as a whole, i.e., it's not possible to
306 : * observe a partial write for any reader. Note that this correctly interacts
307 : * with both pg_atomic_compare_exchange_u32() and
308 : * pg_atomic_read_membarrier_u32(). While this may be less performant than
309 : * pg_atomic_write_u32(), it may be easier to reason about correctness with
310 : * this function in less performance-sensitive code.
311 : *
312 : * Full barrier semantics.
313 : */
314 : static inline void
315 28 : pg_atomic_write_membarrier_u32(volatile pg_atomic_uint32 *ptr, uint32 val)
316 : {
317 : AssertPointerAlignment(ptr, 4);
318 :
319 28 : pg_atomic_write_membarrier_u32_impl(ptr, val);
320 28 : }
321 :
322 : /*
323 : * pg_atomic_exchange_u32 - exchange newval with current value
324 : *
325 : * Returns the old value of 'ptr' before the swap.
326 : *
327 : * Full barrier semantics.
328 : */
329 : static inline uint32
330 30010 : pg_atomic_exchange_u32(volatile pg_atomic_uint32 *ptr, uint32 newval)
331 : {
332 : AssertPointerAlignment(ptr, 4);
333 :
334 30010 : return pg_atomic_exchange_u32_impl(ptr, newval);
335 : }
336 :
337 : /*
338 : * pg_atomic_compare_exchange_u32 - CAS operation
339 : *
340 : * Atomically compare the current value of ptr with *expected and store newval
341 : * iff ptr and *expected have the same value. The current value of *ptr will
342 : * always be stored in *expected.
343 : *
344 : * Return true if values have been exchanged, false otherwise.
345 : *
346 : * Full barrier semantics.
347 : */
348 : static inline bool
349 980261850 : pg_atomic_compare_exchange_u32(volatile pg_atomic_uint32 *ptr,
350 : uint32 *expected, uint32 newval)
351 : {
352 : AssertPointerAlignment(ptr, 4);
353 : AssertPointerAlignment(expected, 4);
354 :
355 980261850 : return pg_atomic_compare_exchange_u32_impl(ptr, expected, newval);
356 : }
357 :
358 : /*
359 : * pg_atomic_fetch_add_u32 - atomically add to variable
360 : *
361 : * Returns the value of ptr before the arithmetic operation.
362 : *
363 : * Full barrier semantics.
364 : */
365 : static inline uint32
366 15128924 : pg_atomic_fetch_add_u32(volatile pg_atomic_uint32 *ptr, int32 add_)
367 : {
368 : AssertPointerAlignment(ptr, 4);
369 15128924 : return pg_atomic_fetch_add_u32_impl(ptr, add_);
370 : }
371 :
372 : /*
373 : * pg_atomic_fetch_sub_u32 - atomically subtract from variable
374 : *
375 : * Returns the value of ptr before the arithmetic operation. Note that sub_
376 : * may not be INT_MIN due to platform limitations.
377 : *
378 : * Full barrier semantics.
379 : */
380 : static inline uint32
381 138221330 : pg_atomic_fetch_sub_u32(volatile pg_atomic_uint32 *ptr, int32 sub_)
382 : {
383 : AssertPointerAlignment(ptr, 4);
384 : Assert(sub_ != INT_MIN);
385 138221330 : return pg_atomic_fetch_sub_u32_impl(ptr, sub_);
386 : }
387 :
388 : /*
389 : * pg_atomic_fetch_and_u32 - atomically bit-and and_ with variable
390 : *
391 : * Returns the value of ptr before the arithmetic operation.
392 : *
393 : * Full barrier semantics.
394 : */
395 : static inline uint32
396 13733274 : pg_atomic_fetch_and_u32(volatile pg_atomic_uint32 *ptr, uint32 and_)
397 : {
398 : AssertPointerAlignment(ptr, 4);
399 13733274 : return pg_atomic_fetch_and_u32_impl(ptr, and_);
400 : }
401 :
402 : /*
403 : * pg_atomic_fetch_or_u32 - atomically bit-or or_ with variable
404 : *
405 : * Returns the value of ptr before the arithmetic operation.
406 : *
407 : * Full barrier semantics.
408 : */
409 : static inline uint32
410 101072632 : pg_atomic_fetch_or_u32(volatile pg_atomic_uint32 *ptr, uint32 or_)
411 : {
412 : AssertPointerAlignment(ptr, 4);
413 101072632 : return pg_atomic_fetch_or_u32_impl(ptr, or_);
414 : }
415 :
416 : /*
417 : * pg_atomic_add_fetch_u32 - atomically add to variable
418 : *
419 : * Returns the value of ptr after the arithmetic operation.
420 : *
421 : * Full barrier semantics.
422 : */
423 : static inline uint32
424 784 : pg_atomic_add_fetch_u32(volatile pg_atomic_uint32 *ptr, int32 add_)
425 : {
426 : AssertPointerAlignment(ptr, 4);
427 784 : return pg_atomic_add_fetch_u32_impl(ptr, add_);
428 : }
429 :
430 : /*
431 : * pg_atomic_sub_fetch_u32 - atomically subtract from variable
432 : *
433 : * Returns the value of ptr after the arithmetic operation. Note that sub_ may
434 : * not be INT_MIN due to platform limitations.
435 : *
436 : * Full barrier semantics.
437 : */
438 : static inline uint32
439 746421996 : pg_atomic_sub_fetch_u32(volatile pg_atomic_uint32 *ptr, int32 sub_)
440 : {
441 : AssertPointerAlignment(ptr, 4);
442 : Assert(sub_ != INT_MIN);
443 746421996 : return pg_atomic_sub_fetch_u32_impl(ptr, sub_);
444 : }
445 :
446 : /* ----
447 : * The 64 bit operations have the same semantics as their 32bit counterparts
448 : * if they are available. Check the corresponding 32bit function for
449 : * documentation.
450 : * ----
451 : */
452 : static inline void
453 6038598 : pg_atomic_init_u64(volatile pg_atomic_uint64 *ptr, uint64 val)
454 : {
455 : /*
456 : * Can't necessarily enforce alignment - and don't need it - when using
457 : * the spinlock based fallback implementation. Therefore only assert when
458 : * not using it.
459 : */
460 : #ifndef PG_HAVE_ATOMIC_U64_SIMULATION
461 : AssertPointerAlignment(ptr, 8);
462 : #endif
463 6038598 : pg_atomic_init_u64_impl(ptr, val);
464 6038598 : }
465 :
466 : static inline uint64
467 577290934 : pg_atomic_read_u64(volatile pg_atomic_uint64 *ptr)
468 : {
469 : #ifndef PG_HAVE_ATOMIC_U64_SIMULATION
470 : AssertPointerAlignment(ptr, 8);
471 : #endif
472 577290934 : return pg_atomic_read_u64_impl(ptr);
473 : }
474 :
475 : static inline uint64
476 4999500 : pg_atomic_read_membarrier_u64(volatile pg_atomic_uint64 *ptr)
477 : {
478 : #ifndef PG_HAVE_ATOMIC_U64_SIMULATION
479 : AssertPointerAlignment(ptr, 8);
480 : #endif
481 4999500 : return pg_atomic_read_membarrier_u64_impl(ptr);
482 : }
483 :
484 : static inline void
485 40551448 : pg_atomic_write_u64(volatile pg_atomic_uint64 *ptr, uint64 val)
486 : {
487 : #ifndef PG_HAVE_ATOMIC_U64_SIMULATION
488 : AssertPointerAlignment(ptr, 8);
489 : #endif
490 40551448 : pg_atomic_write_u64_impl(ptr, val);
491 40551448 : }
492 :
493 : static inline void
494 : pg_atomic_unlocked_write_u64(volatile pg_atomic_uint64 *ptr, uint64 val)
495 : {
496 : #ifndef PG_HAVE_ATOMIC_U64_SIMULATION
497 : AssertPointerAlignment(ptr, 8);
498 : #endif
499 :
500 : pg_atomic_unlocked_write_u64_impl(ptr, val);
501 : }
502 :
503 : static inline void
504 1972 : pg_atomic_write_membarrier_u64(volatile pg_atomic_uint64 *ptr, uint64 val)
505 : {
506 : #ifndef PG_HAVE_ATOMIC_U64_SIMULATION
507 : AssertPointerAlignment(ptr, 8);
508 : #endif
509 1972 : pg_atomic_write_membarrier_u64_impl(ptr, val);
510 1972 : }
511 :
512 : static inline uint64
513 36344756 : pg_atomic_exchange_u64(volatile pg_atomic_uint64 *ptr, uint64 newval)
514 : {
515 : #ifndef PG_HAVE_ATOMIC_U64_SIMULATION
516 : AssertPointerAlignment(ptr, 8);
517 : #endif
518 36344756 : return pg_atomic_exchange_u64_impl(ptr, newval);
519 : }
520 :
521 : static inline bool
522 3367996 : pg_atomic_compare_exchange_u64(volatile pg_atomic_uint64 *ptr,
523 : uint64 *expected, uint64 newval)
524 : {
525 : #ifndef PG_HAVE_ATOMIC_U64_SIMULATION
526 : AssertPointerAlignment(ptr, 8);
527 : #endif
528 3367996 : return pg_atomic_compare_exchange_u64_impl(ptr, expected, newval);
529 : }
530 :
531 : static inline uint64
532 193488 : pg_atomic_fetch_add_u64(volatile pg_atomic_uint64 *ptr, int64 add_)
533 : {
534 : #ifndef PG_HAVE_ATOMIC_U64_SIMULATION
535 : AssertPointerAlignment(ptr, 8);
536 : #endif
537 193488 : return pg_atomic_fetch_add_u64_impl(ptr, add_);
538 : }
539 :
540 : static inline uint64
541 6 : pg_atomic_fetch_sub_u64(volatile pg_atomic_uint64 *ptr, int64 sub_)
542 : {
543 : #ifndef PG_HAVE_ATOMIC_U64_SIMULATION
544 : AssertPointerAlignment(ptr, 8);
545 : #endif
546 : Assert(sub_ != PG_INT64_MIN);
547 6 : return pg_atomic_fetch_sub_u64_impl(ptr, sub_);
548 : }
549 :
550 : static inline uint64
551 18 : pg_atomic_fetch_and_u64(volatile pg_atomic_uint64 *ptr, uint64 and_)
552 : {
553 : #ifndef PG_HAVE_ATOMIC_U64_SIMULATION
554 : AssertPointerAlignment(ptr, 8);
555 : #endif
556 18 : return pg_atomic_fetch_and_u64_impl(ptr, and_);
557 : }
558 :
559 : static inline uint64
560 12 : pg_atomic_fetch_or_u64(volatile pg_atomic_uint64 *ptr, uint64 or_)
561 : {
562 : #ifndef PG_HAVE_ATOMIC_U64_SIMULATION
563 : AssertPointerAlignment(ptr, 8);
564 : #endif
565 12 : return pg_atomic_fetch_or_u64_impl(ptr, or_);
566 : }
567 :
568 : static inline uint64
569 1182 : pg_atomic_add_fetch_u64(volatile pg_atomic_uint64 *ptr, int64 add_)
570 : {
571 : #ifndef PG_HAVE_ATOMIC_U64_SIMULATION
572 : AssertPointerAlignment(ptr, 8);
573 : #endif
574 1182 : return pg_atomic_add_fetch_u64_impl(ptr, add_);
575 : }
576 :
577 : static inline uint64
578 10 : pg_atomic_sub_fetch_u64(volatile pg_atomic_uint64 *ptr, int64 sub_)
579 : {
580 : #ifndef PG_HAVE_ATOMIC_U64_SIMULATION
581 : AssertPointerAlignment(ptr, 8);
582 : #endif
583 : Assert(sub_ != PG_INT64_MIN);
584 10 : return pg_atomic_sub_fetch_u64_impl(ptr, sub_);
585 : }
586 :
587 : /*
588 : * Monotonically advance the given variable using only atomic operations until
589 : * it's at least the target value. Returns the latest value observed, which
590 : * may or may not be the target value.
591 : *
592 : * Full barrier semantics (even when value is unchanged).
593 : */
594 : static inline uint64
595 891998 : pg_atomic_monotonic_advance_u64(volatile pg_atomic_uint64 *ptr, uint64 target)
596 : {
597 : uint64 currval;
598 :
599 : #ifndef PG_HAVE_ATOMIC_U64_SIMULATION
600 : AssertPointerAlignment(ptr, 8);
601 : #endif
602 :
603 891998 : currval = pg_atomic_read_u64_impl(ptr);
604 891998 : if (currval >= target)
605 : {
606 117642 : pg_memory_barrier();
607 117642 : return currval;
608 : }
609 :
610 776036 : while (currval < target)
611 : {
612 774370 : if (pg_atomic_compare_exchange_u64(ptr, &currval, target))
613 772690 : return target;
614 : }
615 :
616 1666 : return currval;
617 : }
618 :
619 : #undef INSIDE_ATOMICS_H
620 :
621 : #endif /* ATOMICS_H */
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