lib/isc/stats.c

/*
 * Copyright (C) 2009, 2012-2017  Internet Systems Consortium, Inc. ("ISC")
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
 */

/* $Id$ */

/*! \file */

#include <config.h>

#include <string.h>

#include <isc/atomic.h>
#include <isc/buffer.h>
#include <isc/magic.h>
#include <isc/mem.h>
#include <isc/platform.h>
#include <isc/print.h>
#include <isc/rwlock.h>
#include <isc/stats.h>
#include <isc/util.h>

#if defined(ISC_PLATFORM_HAVESTDATOMIC)
#include <stdatomic.h>
#endif

#define ISC_STATS_MAGIC         ISC_MAGIC('S', 't', 'a', 't')
#define ISC_STATS_VALID(x)      ISC_MAGIC_VALID(x, ISC_STATS_MAGIC)

/*%
 * Local macro confirming prescence of 64-bit
 * increment and store operations, just to make
 * the later macros simpler
 */
#if (defined(ISC_PLATFORM_HAVESTDATOMIC) && defined(ATOMIC_LONG_LOCK_FREE)) || \
    (defined(ISC_PLATFORM_HAVEXADDQ) && defined(ISC_PLATFORM_HAVEATOMICSTOREQ))
#define ISC_STATS_HAVEATOMICQ 1
#if (defined(ISC_PLATFORM_HAVESTDATOMIC) && defined(ATOMIC_LONG_LOCK_FREE))
#define ISC_STATS_HAVESTDATOMICQ 1
#endif
#else
#define ISC_STATS_HAVEATOMICQ 0
#endif

/*%
 * Only lock the counters if 64-bit atomic operations are
 * not available but cheap atomic lock operations are.
 * On a modern 64-bit system this should never be the case.
 *
 * Normal locks are too expensive to be used whenever a counter
 * is updated.
 */
#if !ISC_STATS_HAVEATOMICQ && defined(ISC_RWLOCK_HAVEATOMIC)
#define ISC_STATS_LOCKCOUNTERS 1
#else
#define ISC_STATS_LOCKCOUNTERS 0
#endif

/*%
 * If 64-bit atomic operations are not available but
 * 32-bit operations are then split the counter into two,
 * using the atomic operations to try to ensure that any carry
 * from the low word is correctly carried into the high word.
 *
 * Otherwise, just rely on standard 64-bit data types
 * and operations
 */
#if !ISC_STATS_HAVEATOMICQ && ((defined(ISC_PLATFORM_HAVESTDATOMIC) && defined(ATOMIC_INT_LOCK_FREE)) || defined(ISC_PLATFORM_HAVEXADD))
#define ISC_STATS_USEMULTIFIELDS 1
#if (defined(ISC_PLATFORM_HAVESTDATOMIC) && defined(ATOMIC_INT_LOCK_FREE))
#define ISC_STATS_HAVESTDATOMIC 1
#endif
#else
#define ISC_STATS_USEMULTIFIELDS 0
#endif

#if ISC_STATS_USEMULTIFIELDS
typedef struct {
#if defined(ISC_STATS_HAVESTDATOMIC)
    atomic_int_fast32_t hi;
    atomic_int_fast32_t lo;
#else
    isc_uint32_t hi;
    isc_uint32_t lo;
#endif
} isc_stat_t;
#else
#if defined(ISC_STATS_HAVESTDATOMICQ)
typedef atomic_int_fast64_t isc_stat_t;
#else
typedef isc_uint64_t isc_stat_t;
#endif
#endif

struct isc_stats {
    /*% Unlocked */
    unsigned int    magic;
    isc_mem_t   *mctx;
    int     ncounters;

    isc_mutex_t lock;
    unsigned int    references; /* locked by lock */

    /*%
     * Locked by counterlock or unlocked if efficient rwlock is not
     * available.
     */
#if ISC_STATS_LOCKCOUNTERS
    isc_rwlock_t    counterlock;
#endif
    isc_stat_t  *counters;

    /*%
     * We don't want to lock the counters while we are dumping, so we first
     * copy the current counter values into a local array.  This buffer
     * will be used as the copy destination.  It's allocated on creation
     * of the stats structure so that the dump operation won't fail due
     * to memory allocation failure.
     * XXX: this approach is weird for non-threaded build because the
     * additional memory and the copy overhead could be avoided.  We prefer
     * simplicity here, however, under the assumption that this function
     * should be only rarely called.
     */
    isc_uint64_t    *copiedcounters;
};

static isc_result_t
create_stats(isc_mem_t *mctx, int ncounters, isc_stats_t **statsp) {
    isc_stats_t *stats;
    isc_result_t result = ISC_R_SUCCESS;

    REQUIRE(statsp != NULL && *statsp == NULL);

    stats = isc_mem_get(mctx, sizeof(*stats));
    if (stats == NULL)
        return (ISC_R_NOMEMORY);

    result = isc_mutex_init(&stats->lock);
    if (result != ISC_R_SUCCESS)
        goto clean_stats;

    stats->counters = isc_mem_get(mctx, sizeof(isc_stat_t) * ncounters);
    if (stats->counters == NULL) {
        result = ISC_R_NOMEMORY;
        goto clean_mutex;
    }
    stats->copiedcounters = isc_mem_get(mctx,
                        sizeof(isc_uint64_t) * ncounters);
    if (stats->copiedcounters == NULL) {
        result = ISC_R_NOMEMORY;
        goto clean_counters;
    }

#if ISC_STATS_LOCKCOUNTERS
    result = isc_rwlock_init(&stats->counterlock, 0, 0);
    if (result != ISC_R_SUCCESS)
        goto clean_copiedcounters;
#endif

    stats->references = 1;
    memset(stats->counters, 0, sizeof(isc_stat_t) * ncounters);
    stats->mctx = NULL;
    isc_mem_attach(mctx, &stats->mctx);
    stats->ncounters = ncounters;
    stats->magic = ISC_STATS_MAGIC;

    *statsp = stats;

    return (result);

clean_counters:
    isc_mem_put(mctx, stats->counters, sizeof(isc_stat_t) * ncounters);

#if ISC_STATS_LOCKCOUNTERS
clean_copiedcounters:
    isc_mem_put(mctx, stats->copiedcounters,
            sizeof(isc_stat_t) * ncounters);
#endif

clean_mutex:
    DESTROYLOCK(&stats->lock);

clean_stats:
    isc_mem_put(mctx, stats, sizeof(*stats));

    return (result);
}

void
isc_stats_attach(isc_stats_t *stats, isc_stats_t **statsp) {
    REQUIRE(ISC_STATS_VALID(stats));
    REQUIRE(statsp != NULL && *statsp == NULL);

    LOCK(&stats->lock);
    stats->references++;
    UNLOCK(&stats->lock);

    *statsp = stats;
}

void
isc_stats_detach(isc_stats_t **statsp) {
    isc_stats_t *stats;

    REQUIRE(statsp != NULL && ISC_STATS_VALID(*statsp));

    stats = *statsp;
    *statsp = NULL;

    LOCK(&stats->lock);
    stats->references--;

    if (stats->references == 0) {
        isc_mem_put(stats->mctx, stats->copiedcounters,
                sizeof(isc_stat_t) * stats->ncounters);
        isc_mem_put(stats->mctx, stats->counters,
                sizeof(isc_stat_t) * stats->ncounters);
        UNLOCK(&stats->lock);
        DESTROYLOCK(&stats->lock);
#if ISC_STATS_LOCKCOUNTERS
        isc_rwlock_destroy(&stats->counterlock);
#endif
        isc_mem_putanddetach(&stats->mctx, stats, sizeof(*stats));
        return;
    }

    UNLOCK(&stats->lock);
}

int
isc_stats_ncounters(isc_stats_t *stats) {
    REQUIRE(ISC_STATS_VALID(stats));

    return (stats->ncounters);
}

static inline void
incrementcounter(isc_stats_t *stats, int counter) {
    isc_int32_t prev;

#if ISC_STATS_LOCKCOUNTERS
    /*
     * We use a "read" lock to prevent other threads from reading the
     * counter while we "writing" a counter field.  The write access itself
     * is protected by the atomic operation.
     */
    isc_rwlock_lock(&stats->counterlock, isc_rwlocktype_read);
#endif

#if ISC_STATS_USEMULTIFIELDS
#if defined(ISC_STATS_HAVESTDATOMIC)
    prev = atomic_fetch_add_explicit(&stats->counters[counter].lo, 1,
                     memory_order_relaxed);
#else
    prev = isc_atomic_xadd((isc_int32_t *)&stats->counters[counter].lo, 1);
#endif
    /*
     * If the lower 32-bit field overflows, increment the higher field.
     * Note that it's *theoretically* possible that the lower field
     * overlaps again before the higher field is incremented.  It doesn't
     * matter, however, because we don't read the value until
     * isc_stats_copy() is called where the whole process is protected
     * by the write (exclusive) lock.
     */
    if (prev == (isc_int32_t)0xffffffff) {
#if defined(ISC_STATS_HAVESTDATOMIC)
        atomic_fetch_add_explicit(&stats->counters[counter].hi, 1,
                      memory_order_relaxed);
#else
        isc_atomic_xadd((isc_int32_t *)&stats->counters[counter].hi, 1);
#endif
    }
#elif ISC_STATS_HAVEATOMICQ
    UNUSED(prev);
#if defined(ISC_STATS_HAVESTDATOMICQ)
    atomic_fetch_add_explicit(&stats->counters[counter], 1,
                  memory_order_relaxed);
#else
    isc_atomic_xaddq((isc_int64_t *)&stats->counters[counter], 1);
#endif
#else
    UNUSED(prev);
    stats->counters[counter]++;
#endif

#if ISC_STATS_LOCKCOUNTERS
    isc_rwlock_unlock(&stats->counterlock, isc_rwlocktype_read);
#endif
}

static inline void
decrementcounter(isc_stats_t *stats, int counter) {
    isc_int32_t prev;

#if ISC_STATS_LOCKCOUNTERS
    isc_rwlock_lock(&stats->counterlock, isc_rwlocktype_read);
#endif

#if ISC_STATS_USEMULTIFIELDS
#if defined(ISC_STATS_HAVESTDATOMIC)
    prev = atomic_fetch_sub_explicit(&stats->counters[counter].lo, 1,
                     memory_order_relaxed);
#else
    prev = isc_atomic_xadd((isc_int32_t *)&stats->counters[counter].lo, -1);
#endif
    if (prev == 0) {
#if defined(ISC_STATS_HAVESTDATOMIC)
        atomic_fetch_sub_explicit(&stats->counters[counter].hi, 1,
                      memory_order_relaxed);
#else
        isc_atomic_xadd((isc_int32_t *)&stats->counters[counter].hi,
                -1);
#endif
    }
#elif ISC_STATS_HAVEATOMICQ
    UNUSED(prev);
#if defined(ISC_STATS_HAVESTDATOMICQ)
    atomic_fetch_sub_explicit(&stats->counters[counter], 1,
                  memory_order_relaxed);
#else
    isc_atomic_xaddq((isc_int64_t *)&stats->counters[counter], -1);
#endif
#else
    UNUSED(prev);
    stats->counters[counter]--;
#endif

#if ISC_STATS_LOCKCOUNTERS
    isc_rwlock_unlock(&stats->counterlock, isc_rwlocktype_read);
#endif
}

static void
copy_counters(isc_stats_t *stats) {
    int i;

#if ISC_STATS_LOCKCOUNTERS
    /*
     * We use a "write" lock before "reading" the statistics counters as
     * an exclusive lock.
     */
    isc_rwlock_lock(&stats->counterlock, isc_rwlocktype_write);
#endif

    for (i = 0; i < stats->ncounters; i++) {
#if ISC_STATS_USEMULTIFIELDS
        stats->copiedcounters[i] =
            (isc_uint64_t)(stats->counters[i].hi) << 32 |
            stats->counters[i].lo;
#elif ISC_STATS_HAVEATOMICQ
#if defined(ISC_STATS_HAVESTDATOMICQ)
        stats->copiedcounters[i] =
            atomic_load_explicit(&stats->counters[i],
                         memory_order_relaxed);
#else
        /* use xaddq(..., 0) as an atomic load */
        stats->copiedcounters[i] =
            (isc_uint64_t)isc_atomic_xaddq((isc_int64_t *)&stats->counters[i], 0);
#endif
#else
        stats->copiedcounters[i] = stats->counters[i];
#endif
    }

#if ISC_STATS_LOCKCOUNTERS
    isc_rwlock_unlock(&stats->counterlock, isc_rwlocktype_write);
#endif
}

isc_result_t
isc_stats_create(isc_mem_t *mctx, isc_stats_t **statsp, int ncounters) {
    REQUIRE(statsp != NULL && *statsp == NULL);

    return (create_stats(mctx, ncounters, statsp));
}

void
isc_stats_increment(isc_stats_t *stats, isc_statscounter_t counter) {
    REQUIRE(ISC_STATS_VALID(stats));
    REQUIRE(counter < stats->ncounters);

    incrementcounter(stats, (int)counter);
}

void
isc_stats_decrement(isc_stats_t *stats, isc_statscounter_t counter) {
    REQUIRE(ISC_STATS_VALID(stats));
    REQUIRE(counter < stats->ncounters);

    decrementcounter(stats, (int)counter);
}

void
isc_stats_dump(isc_stats_t *stats, isc_stats_dumper_t dump_fn,
           void *arg, unsigned int options)
{
    int i;

    REQUIRE(ISC_STATS_VALID(stats));

    copy_counters(stats);

    for (i = 0; i < stats->ncounters; i++) {
        if ((options & ISC_STATSDUMP_VERBOSE) == 0 &&
            stats->copiedcounters[i] == 0)
                continue;
        dump_fn((isc_statscounter_t)i, stats->copiedcounters[i], arg);
    }
}

void
isc_stats_set(isc_stats_t *stats, isc_uint64_t val,
          isc_statscounter_t counter)
{
    REQUIRE(ISC_STATS_VALID(stats));
    REQUIRE(counter < stats->ncounters);

#if ISC_STATS_LOCKCOUNTERS
    /*
     * We use a "write" lock before "reading" the statistics counters as
     * an exclusive lock.
     */
    isc_rwlock_lock(&stats->counterlock, isc_rwlocktype_write);
#endif

#if ISC_STATS_USEMULTIFIELDS
    stats->counters[counter].hi = (isc_uint32_t)((val >> 32) & 0xffffffff);
    stats->counters[counter].lo = (isc_uint32_t)(val & 0xffffffff);
#elif ISC_STATS_HAVEATOMICQ
#if defined(ISC_STATS_HAVESTDATOMICQ)
    atomic_store_explicit(&stats->counters[counter], val,
                  memory_order_relaxed);
#else
    isc_atomic_storeq((isc_int64_t *)&stats->counters[counter], val);
#endif
#else
    stats->counters[counter] = val;
#endif

#if ISC_STATS_LOCKCOUNTERS
    isc_rwlock_unlock(&stats->counterlock, isc_rwlocktype_write);
#endif
}