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8.8.1
src/atomicvar.h
205 строк
9 KB
Ozan Tezcan
Reduce memory allocation overhead (#15096)
09 май 2026, 11:48
Не верифицирован
09 май 2026, 11:48
7bdab45
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/* This file implements atomic counters using c11 _Atomic, __atomic or __sync * macros if available, otherwise we will throw an error when compile. * * The exported interface is composed of the following macros: * * atomicIncr(var,count) -- Increment the atomic counter * atomicGetIncr(var,oldvalue_var,count) -- Get and increment the atomic counter * atomicIncrGet(var,newvalue_var,count) -- Increment and get the atomic counter new value * atomicDecr(var,count) -- Decrement the atomic counter * atomicGet(var,dstvar) -- Fetch the atomic counter value * atomicSet(var,value) -- Set the atomic counter value * atomicGetWithSync(var,value) -- 'atomicGet' with inter-thread synchronization * atomicSetWithSync(var,value) -- 'atomicSet' with inter-thread synchronization * atomicCompareExchange(type,var,expected_var,desired) -- Compare and exchange (CAS) operation * * Atomic operations on flags. * Flag type can be int, long, long long or their unsigned counterparts. * The value of the flag can be 1 or 0. * * atomicFlagGetSet(var,oldvalue_var) -- Get and set the atomic counter value * * NOTE1: __atomic* and _Atomic implementations can be actually elaborated to support any value by changing the * hardcoded new value passed to __atomic_exchange* from 1 to @param count * i.e oldvalue_var = atomic_exchange_explicit(&var, count). * However, in order to be compatible with the __sync functions family, we can use only 0 and 1. * The only exchange alternative suggested by __sync is __sync_lock_test_and_set, * But as described by the gnu manual for __sync_lock_test_and_set(): * https://gcc.gnu.org/onlinedocs/gcc/_005f_005fsync-Builtins.html * "A target may support reduced functionality here by which the only valid value to store is the immediate constant 1. The exact value * actually stored in *ptr is implementation defined." * Hence, we can't rely on it for a any value other than 1. * We eventually chose to implement this method with __sync_val_compare_and_swap since it satisfies functionality needed for atomicFlagGetSet * (if the flag was 0 -> set to 1, if it's already 1 -> do nothing, but the final result is that the flag is set), * and also it has a full barrier (__sync_lock_test_and_set has acquire barrier). * * NOTE2: Unlike other atomic type, which aren't guaranteed to be lock free, c11 atomic_flag does. * To check whether a type is lock free, atomic_is_lock_free() can be used. * It can be considered to limit the flag type to atomic_flag to improve performance. * * Never use return value from the macros, instead use the AtomicGetIncr() * if you need to get the current value and increment it atomically, like * in the following example: * * long oldvalue; * atomicGetIncr(myvar,oldvalue,1); * doSomethingWith(oldvalue); * * ---------------------------------------------------------------------------- * * Copyright (c) 2015-Present, Redis Ltd. * All rights reserved. * * Licensed under your choice of (a) the Redis Source Available License 2.0 * (RSALv2); or (b) the Server Side Public License v1 (SSPLv1); or (c) the * GNU Affero General Public License v3 (AGPLv3). */ #include <pthread.h> #include "config.h" #ifndef __ATOMIC_VAR_H #define __ATOMIC_VAR_H /* Define redisAtomic for atomic variable. */ #define redisAtomic /* To test Redis with Helgrind (a Valgrind tool) it is useful to define * the following macro, so that __sync macros are used: those can be detected * by Helgrind (even if they are less efficient) so that no false positive * is reported. */ // #define __ATOMIC_VAR_FORCE_SYNC_MACROS /* There will be many false positives if we test Redis with Helgrind, since * Helgrind can't understand we have imposed ordering on the program, so * we use macros in helgrind.h to tell Helgrind inter-thread happens-before * relationship explicitly for avoiding false positives. * * For more details, please see: valgrind/helgrind.h and * https://www.valgrind.org/docs/manual/hg-manual.html#hg-manual.effective-use * * These macros take effect only when 'make helgrind', and you must first * install Valgrind in the default path configuration. */ #ifdef __ATOMIC_VAR_FORCE_SYNC_MACROS #include <valgrind/helgrind.h> #else #define ANNOTATE_HAPPENS_BEFORE(v) ((void) v) #define ANNOTATE_HAPPENS_AFTER(v) ((void) v) #endif #if !defined(__ATOMIC_VAR_FORCE_SYNC_MACROS) && defined(__STDC_VERSION__) && \ (__STDC_VERSION__ >= 201112L) && !defined(__STDC_NO_ATOMICS__) /* Use '_Atomic' keyword if the compiler supports. */ #undef redisAtomic #define redisAtomic _Atomic /* Implementation using _Atomic in C11. */ #include <stdatomic.h> #define atomicIncr(var,count) atomic_fetch_add_explicit(&var,(count),memory_order_relaxed) #define atomicGetIncr(var,oldvalue_var,count) do { \ oldvalue_var = atomic_fetch_add_explicit(&var,(count),memory_order_relaxed); \ } while(0) #define atomicIncrGet(var, newvalue_var, count) \ newvalue_var = atomicIncr(var,count) + count #define atomicDecr(var,count) atomic_fetch_sub_explicit(&var,(count),memory_order_relaxed) #define atomicGet(var,dstvar) do { \ dstvar = atomic_load_explicit(&var,memory_order_relaxed); \ } while(0) #define atomicSet(var,value) atomic_store_explicit(&var,value,memory_order_relaxed) #define atomicGetWithSync(var,dstvar) do { \ dstvar = atomic_load_explicit(&var,memory_order_seq_cst); \ } while(0) #define atomicSetWithSync(var,value) \ atomic_store_explicit(&var,value,memory_order_seq_cst) #define atomicCompareExchange(type,var,expected_var,desired) \ atomic_compare_exchange_weak_explicit(&var,&expected_var,desired,memory_order_relaxed,memory_order_relaxed) #define atomicFlagGetSet(var,oldvalue_var) \ oldvalue_var = atomic_exchange_explicit(&var,1,memory_order_relaxed) #define REDIS_ATOMIC_API "c11-builtin" #elif !defined(__ATOMIC_VAR_FORCE_SYNC_MACROS) && \ (!defined(__clang__) || !defined(__APPLE__) || __apple_build_version__ > 4210057) && \ defined(__ATOMIC_RELAXED) && defined(__ATOMIC_SEQ_CST) /* Implementation using __atomic macros. */ #define atomicIncr(var,count) __atomic_add_fetch(&var,(count),__ATOMIC_RELAXED) #define atomicIncrGet(var, newvalue_var, count) \ newvalue_var = __atomic_add_fetch(&var,(count),__ATOMIC_RELAXED) #define atomicGetIncr(var,oldvalue_var,count) do { \ oldvalue_var = __atomic_fetch_add(&var,(count),__ATOMIC_RELAXED); \ } while(0) #define atomicDecr(var,count) __atomic_sub_fetch(&var,(count),__ATOMIC_RELAXED) #define atomicGet(var,dstvar) do { \ dstvar = __atomic_load_n(&var,__ATOMIC_RELAXED); \ } while(0) #define atomicSet(var,value) __atomic_store_n(&var,value,__ATOMIC_RELAXED) #define atomicGetWithSync(var,dstvar) do { \ dstvar = __atomic_load_n(&var,__ATOMIC_SEQ_CST); \ } while(0) #define atomicSetWithSync(var,value) \ __atomic_store_n(&var,value,__ATOMIC_SEQ_CST) #define atomicCompareExchange(type,var,expected_var,desired) \ __atomic_compare_exchange_n(&var,&expected_var,desired,1,__ATOMIC_RELAXED,__ATOMIC_RELAXED) #define atomicFlagGetSet(var,oldvalue_var) \ oldvalue_var = __atomic_exchange_n(&var,1,__ATOMIC_RELAXED) #define REDIS_ATOMIC_API "atomic-builtin" #elif defined(HAVE_ATOMIC) /* Implementation using __sync macros. */ #define atomicIncr(var,count) __sync_add_and_fetch(&var,(count)) #define atomicIncrGet(var, newvalue_var, count) \ newvalue_var = __sync_add_and_fetch(&var,(count)) #define atomicGetIncr(var,oldvalue_var,count) do { \ oldvalue_var = __sync_fetch_and_add(&var,(count)); \ } while(0) #define atomicDecr(var,count) __sync_sub_and_fetch(&var,(count)) #define atomicGet(var,dstvar) do { \ dstvar = __sync_sub_and_fetch(&var,0); \ } while(0) #define atomicSet(var,value) do { \ while(!__sync_bool_compare_and_swap(&var,var,value)); \ } while(0) /* Actually the builtin issues a full memory barrier by default. */ #define atomicGetWithSync(var,dstvar) do { \ dstvar = __sync_sub_and_fetch(&var,0,__sync_synchronize); \ ANNOTATE_HAPPENS_AFTER(&var); \ } while(0) #define atomicSetWithSync(var,value) do { \ ANNOTATE_HAPPENS_BEFORE(&var); \ while(!__sync_bool_compare_and_swap(&var,var,value,__sync_synchronize)); \ } while(0) #define atomicCompareExchange(type,var,expected_var,desired) ({ \ type _old = __sync_val_compare_and_swap(&var,expected_var,desired); \ int _success = (_old == expected_var); \ if (!_success) expected_var = _old; \ _success; \ }) #define atomicFlagGetSet(var,oldvalue_var) \ oldvalue_var = __sync_val_compare_and_swap(&var,0,1) #define REDIS_ATOMIC_API "sync-builtin" #else #error "Unable to determine atomic operations for your platform" #endif /* atomicIncrGetSingleWriter(var, delta, newvalue_var) * * Adds `delta` to `var` and writes the resulting value to `newvalue_var`. * Same end result as atomicIncrGet() but implemented as load+add+store instead * of an atomic read-modify-write. This avoids the `lock` prefix on x86 * (~20-40 cycles vs ~2-3 for plain load+store). * * SAFETY: the caller MUST guarantee that no other thread ever writes to `var` * (no atomicIncr, no atomicSet, no other call to this macro from a different * thread). Concurrent writers cause silent lost updates. Readers on other * threads using atomicGet are fine: they will observe either the pre or * post update value. */ #define atomicIncrGetSingleWriter(var, delta, newvalue_var) do { \ atomicGet((var), (newvalue_var)); \ (newvalue_var) += (delta); \ atomicSet((var), (newvalue_var)); \ } while(0) #endif /* __ATOMIC_VAR_H */