githubmirror/rsyslog

runtime/atomic.h
319 строк13 KB
Rainer Gerhards
runtime: clarify atomic helper usage
29 янв 2026, 19:17
29 янв 2026, 19:179250101
/* This header supplies atomic operations. So far, we rely on GCC's
 * atomic builtins. During configure, we check if atomic operatons are
 * available. If they are not, I am making the necessary provisioning to live without them if
 * they are not available. Please note that you should only use the macros
 * here if you think you can actually live WITHOUT an explicit atomic operation,
 * because in the non-presence of them, we simply do it without atomicitiy.
 * Which, for word-aligned data types, usually (but only usually!) should work.
 *
 * We are using the functions described in
 * http:/gcc.gnu.org/onlinedocs/gcc/Atomic-Builtins.html
 *
 * THESE MACROS MUST ONLY BE USED WITH WORD-SIZED DATA TYPES!
 *
 * Usage guidance (important for portability and static analysis tools):
 * - Operations are provided as macros or inline functions. Prefer simple lvalues
 *   for the "data" argument to avoid double-evaluation surprises.
 * - The "phlpmut" argument is a helper mutex used when atomics are unavailable.
 *   If atomics are supported, these helper mutex macros become no-ops.
 *   Callers must still pass a valid pointer where required to keep signatures
 *   uniform across platforms.
 * - Some macros are "best effort" (PREFER_*). They may degrade to non-atomic
 *   operations when no atomic support is available. Use them only for
 *   statistics or counters where occasional lost updates are acceptable.
 * - The remaining ATOMIC_* helpers provide true atomicity when available and
 *   fall back to mutex-based critical sections when not.
 * - Mixing atomic loads/stores with plain reads/writes to the same variable is
 *   undefined on modern compilers. If you use ATOMIC_* on a variable, access it
 *   exclusively via these helpers (or other synchronized paths).
 *
 * Copyright 2008-2012 Rainer Gerhards and Adiscon GmbH.
 *
 * This file is part of the rsyslog runtime library.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *       http://www.apache.org/licenses/LICENSE-2.0
 *       -or-
 *       see COPYING.ASL20 in the source distribution
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
#ifndef INCLUDED_ATOMIC_H
#define INCLUDED_ATOMIC_H
#include <time.h>
#include "typedefs.h"

/* for this release, we disable atomic calls because there seem to be some
 * portability problems and we can not fix that without destabilizing the build.
 * They simply came in too late. -- rgerhards, 2008-04-02
 */
#ifdef HAVE_ATOMIC_BUILTINS
    #define ATOMIC_SUB(data, val, phlpmut) __sync_fetch_and_sub(data, val)
    #define ATOMIC_SUB_unsigned(data, val, phlpmut) __sync_fetch_and_sub(data, val)
    #define ATOMIC_ADD(data, val) __sync_fetch_and_add(&(data), val)
    #define ATOMIC_INC(data, phlpmut) ((void)__sync_fetch_and_add(data, 1))
    #define ATOMIC_INC_AND_FETCH_int(data, phlpmut) __sync_fetch_and_add(data, 1)
    #define ATOMIC_INC_AND_FETCH_unsigned(data, phlpmut) __sync_fetch_and_add(data, 1)
    #define ATOMIC_DEC(data, phlpmut) ((void)__sync_sub_and_fetch(data, 1))
    #define ATOMIC_DEC_AND_FETCH(data, phlpmut) __sync_sub_and_fetch(data, 1)
    #define ATOMIC_FETCH_32BIT(data, phlpmut) ((int)__sync_fetch_and_and(data, 0xffffffff))
    #define ATOMIC_FETCH_32BIT_unsigned(data, phlpmut) ((unsigned)__sync_fetch_and_and(data, 0xffffffff))
    #define ATOMIC_STORE_1_TO_32BIT(data) __sync_lock_test_and_set(&(data), 1)
    #define ATOMIC_STORE_0_TO_INT(data, phlpmut) __sync_fetch_and_and(data, 0)
    #define ATOMIC_STORE_1_TO_INT(data, phlpmut) __sync_fetch_and_or(data, 1)
    #define ATOMIC_STORE_INT(data, phlpmut, val) ((void)__sync_lock_test_and_set((data), (val)))
    #define ATOMIC_OR_INT_TO_INT(data, phlpmut, val) __sync_fetch_and_or((data), (val))
    #define ATOMIC_CAS(data, oldVal, newVal, phlpmut) __sync_bool_compare_and_swap(data, (oldVal), (newVal))
    #define ATOMIC_CAS_time_t(data, oldVal, newVal, phlpmut) __sync_bool_compare_and_swap(data, (oldVal), (newVal))
    #define ATOMIC_CAS_VAL(data, oldVal, newVal, phlpmut) __sync_val_compare_and_swap(data, (oldVal), (newVal));
    /* Atomic operations for pointers (word-sized on all supported platforms) */
    #define ATOMIC_FETCH_PTR(data, phlpmut) ((void *)__sync_fetch_and_add(data, 0))
    #define ATOMIC_STORE_PTR(data, phlpmut, val) ((void)__sync_lock_test_and_set((data), (val)))
    #define ATOMIC_CAS_PTR(data, oldVal, newVal, phlpmut) __sync_bool_compare_and_swap(data, (oldVal), (newVal))

    /* functions below are not needed if we have atomics */
    #define DEF_ATOMIC_HELPER_MUT(x)
    #define INIT_ATOMIC_HELPER_MUT(x)
    #define DESTROY_ATOMIC_HELPER_MUT(x)

    /* the following operations should preferrably be done atomic, but it is
     * not fatal if not -- that means we can live with some missed updates. So be
     * sure to use these macros only if that really does not matter!
     */
    #define PREFER_ATOMIC_INC(data) ((void)__sync_fetch_and_add(&(data), 1))
    #define PREFER_FETCH_32BIT(data) ((unsigned)__sync_fetch_and_and(&(data), 0xffffffff))
    #define PREFER_STORE_0_TO_INT(data) __sync_fetch_and_and(data, 0)
    #define PREFER_STORE_1_TO_INT(data) __sync_fetch_and_or(data, 1)
#else
    /* note that we gained parctical proof that theoretical problems DO occur
     * if we do not properly address them. See this blog post for details:
     * http://blog.gerhards.net/2009/01/rsyslog-data-race-analysis.html
     * The bottom line is that if there are no atomics available, we should NOT
     * simply go ahead and do without them - use mutexes or other things. The
     * code needs to be checked against all those cases. -- rgerhards, 2009-01-30
     */
    #include <pthread.h>
    #define ATOMIC_INC(data, phlpmut)      \
        {                                  \
            pthread_mutex_lock(phlpmut);   \
            ++(*(data));                   \
            pthread_mutex_unlock(phlpmut); \
        }

    #define ATOMIC_STORE_0_TO_INT(data, hlpmut) \
        {                                       \
            pthread_mutex_lock(hlpmut);         \
            *(data) = 0;                        \
            pthread_mutex_unlock(hlpmut);       \
        }

    #define ATOMIC_STORE_1_TO_INT(data, hlpmut) \
        {                                       \
            pthread_mutex_lock(hlpmut);         \
            *(data) = 1;                        \
            pthread_mutex_unlock(hlpmut);       \
        }

    #define ATOMIC_STORE_INT(data, hlpmut, val) \
        do {                                    \
            pthread_mutex_lock(hlpmut);         \
            *(data) = (val);                    \
            pthread_mutex_unlock(hlpmut);       \
        } while (0)

    #define ATOMIC_OR_INT_TO_INT(data, hlpmut, val) \
        {                                           \
            pthread_mutex_lock(hlpmut);             \
            *(data) = val;                          \
            pthread_mutex_unlock(hlpmut);           \
        }

static inline int ATOMIC_CAS(int *data, int oldVal, int newVal, pthread_mutex_t *phlpmut) {
    int bSuccess;
    pthread_mutex_lock(phlpmut);
    if (*data == oldVal) {
        *data = newVal;
        bSuccess = 1;
    } else {
        bSuccess = 0;
    }
    pthread_mutex_unlock(phlpmut);
    return (bSuccess);
}

static inline int ATOMIC_CAS_time_t(time_t *data, time_t oldVal, time_t newVal, pthread_mutex_t *phlpmut) {
    int bSuccess;
    pthread_mutex_lock(phlpmut);
    if (*data == oldVal) {
        *data = newVal;
        bSuccess = 1;
    } else {
        bSuccess = 0;
    }
    pthread_mutex_unlock(phlpmut);
    return (bSuccess);
}


static inline int ATOMIC_CAS_VAL(int *data, int oldVal, int newVal, pthread_mutex_t *phlpmut) {
    int val;
    pthread_mutex_lock(phlpmut);
    if (*data == oldVal) {
        *data = newVal;
    }
    val = *data;
    pthread_mutex_unlock(phlpmut);
    return (val);
}

    #define ATOMIC_DEC(data, phlpmut)      \
        {                                  \
            pthread_mutex_lock(phlpmut);   \
            --(*(data));                   \
            pthread_mutex_unlock(phlpmut); \
        }

static inline int ATOMIC_INC_AND_FETCH_int(int *data, pthread_mutex_t *phlpmut) {
    int val;
    pthread_mutex_lock(phlpmut);
    val = ++(*data);
    pthread_mutex_unlock(phlpmut);
    return (val);
}

static inline unsigned ATOMIC_INC_AND_FETCH_unsigned(unsigned *data, pthread_mutex_t *phlpmut) {
    unsigned val;
    pthread_mutex_lock(phlpmut);
    val = ++(*data);
    pthread_mutex_unlock(phlpmut);
    return (val);
}

static inline int ATOMIC_DEC_AND_FETCH(int *data, pthread_mutex_t *phlpmut) {
    int val;
    pthread_mutex_lock(phlpmut);
    val = --(*data);
    pthread_mutex_unlock(phlpmut);
    return (val);
}

static inline int ATOMIC_FETCH_32BIT(int *data, pthread_mutex_t *phlpmut) {
    int val;
    pthread_mutex_lock(phlpmut);
    val = (*data);
    pthread_mutex_unlock(phlpmut);
    return (val);
}

static inline int ATOMIC_FETCH_32BIT_unsigned(unsigned *data, pthread_mutex_t *phlpmut) {
    int val;
    pthread_mutex_lock(phlpmut);
    val = (*data);
    pthread_mutex_unlock(phlpmut);
    return (val);
}

static inline void ATOMIC_SUB(int *data, int val, pthread_mutex_t *phlpmut) {
    pthread_mutex_lock(phlpmut);
    (*data) -= val;
    pthread_mutex_unlock(phlpmut);
}

static inline void ATOMIC_SUB_unsigned(unsigned *data, int val, pthread_mutex_t *phlpmut) {
    pthread_mutex_lock(phlpmut);
    (*data) -= val;
    pthread_mutex_unlock(phlpmut);
}

/* Atomic operations for pointers - fallback to mutex-protected operations */
static inline void *ATOMIC_FETCH_PTR(void **data, pthread_mutex_t *phlpmut) {
    void *val;
    pthread_mutex_lock(phlpmut);
    val = *data;
    pthread_mutex_unlock(phlpmut);
    return val;
}

static inline void ATOMIC_STORE_PTR(void **data, pthread_mutex_t *phlpmut, void *val) {
    pthread_mutex_lock(phlpmut);
    *data = val;
    pthread_mutex_unlock(phlpmut);
}

static inline int ATOMIC_CAS_PTR(void **data, void *oldVal, void *newVal, pthread_mutex_t *phlpmut) {
    int bSuccess;
    pthread_mutex_lock(phlpmut);
    if (*data == oldVal) {
        *data = newVal;
        bSuccess = 1;
    } else {
        bSuccess = 0;
    }
    pthread_mutex_unlock(phlpmut);
    return bSuccess;
}

    #define DEF_ATOMIC_HELPER_MUT(x) pthread_mutex_t x
    #define INIT_ATOMIC_HELPER_MUT(x) pthread_mutex_init(&(x), NULL)
    #define DESTROY_ATOMIC_HELPER_MUT(x) pthread_mutex_destroy(&(x))

    #define PREFER_ATOMIC_INC(data) ((void)++data)
    #define PREFER_FETCH_32BIT(data) ((unsigned)(data))
    #define PREFER_STORE_0_TO_INT(data) (*(data) = 0)
    #define PREFER_STORE_1_TO_INT(data) (*(data) = 1)

#endif

/* we need to handle 64bit atomics seperately as some platforms have
 * 32 bit atomics, but not 64 bit ones... -- rgerhards, 2010-12-01
 */
#ifdef HAVE_ATOMIC_BUILTINS64
    #define ATOMIC_INC_uint64(data, phlpmut) ((void)__sync_fetch_and_add(data, 1))
    #define ATOMIC_ADD_uint64(data, phlpmut, value) ((void)__sync_fetch_and_add(data, value))
    #define ATOMIC_DEC_uint64(data, phlpmut) ((void)__sync_sub_and_fetch(data, 1))
    #define ATOMIC_INC_AND_FETCH_uint64(data, phlpmut) __sync_fetch_and_add(data, 1)

    #define DEF_ATOMIC_HELPER_MUT64(x)
    #define INIT_ATOMIC_HELPER_MUT64(x)
    #define DESTROY_ATOMIC_HELPER_MUT64(x)
#else
    #define ATOMIC_INC_uint64(data, phlpmut) \
        {                                    \
            pthread_mutex_lock(phlpmut);     \
            ++(*(data));                     \
            pthread_mutex_unlock(phlpmut);   \
        }
    #define ATOMIC_ADD_uint64(data, phlpmut, value) \
        {                                           \
            pthread_mutex_lock(phlpmut);            \
            *data += value;                         \
            pthread_mutex_unlock(phlpmut);          \
        }
    #define ATOMIC_DEC_uint64(data, phlpmut) \
        {                                    \
            pthread_mutex_lock(phlpmut);     \
            --(*(data));                     \
            pthread_mutex_unlock(phlpmut);   \
        }

static inline unsigned ATOMIC_INC_AND_FETCH_uint64(uint64 *data, pthread_mutex_t *phlpmut) {
    uint64 val;
    pthread_mutex_lock(phlpmut);
    val = ++(*data);
    pthread_mutex_unlock(phlpmut);
    return (val);
}

    #define DEF_ATOMIC_HELPER_MUT64(x) pthread_mutex_t x
    #define INIT_ATOMIC_HELPER_MUT64(x) pthread_mutex_init(&(x), NULL)
    #define DESTROY_ATOMIC_HELPER_MUT64(x) pthread_mutex_destroy(&(x))
#endif /* #ifdef HAVE_ATOMIC_BUILTINS64 */

#endif /* #ifndef INCLUDED_ATOMIC_H */