stats.c

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/*
 * Copyright (C) 2009, 2012-2015  Internet Systems Consortium, Inc. ("ISC")
 *
 * Permission to use, copy, modify, and/or distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES WITH
 * REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
 * AND FITNESS.  IN NO EVENT SHALL ISC BE LIABLE FOR ANY SPECIAL, DIRECT,
 * INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
 * LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE
 * OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
 * PERFORMANCE OF THIS SOFTWARE.
 */

/* $Id$ */

/*! \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>

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

#ifndef ISC_STATS_USEMULTIFIELDS
#if defined(ISC_RWLOCK_USEATOMIC) && defined(ISC_PLATFORM_HAVEXADD) && !defined(ISC_PLATFORM_HAVEXADDQ)
#define ISC_STATS_USEMULTIFIELDS 1
#else
#define ISC_STATS_USEMULTIFIELDS 0
#endif
#endif  /* ISC_STATS_USEMULTIFIELDS */

#if ISC_STATS_USEMULTIFIELDS
typedef struct {
        isc_uint32_t hi;
        isc_uint32_t lo;
} isc_stat_t;
#else
typedef isc_uint64_t isc_stat_t;
#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.
         */
#ifdef ISC_RWLOCK_USEATOMIC
        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;
        }

#ifdef ISC_RWLOCK_USEATOMIC
        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);

#ifdef ISC_RWLOCK_USEATOMIC
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);
#ifdef ISC_RWLOCK_USEATOMIC
                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;

#ifdef ISC_RWLOCK_USEATOMIC
        /*
         * 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
        prev = isc_atomic_xadd((isc_int32_t *)&stats->counters[counter].lo, 1);
        /*
         * 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)
                isc_atomic_xadd((isc_int32_t *)&stats->counters[counter].hi, 1);
#elif defined(ISC_PLATFORM_HAVEXADDQ)
        UNUSED(prev);
        isc_atomic_xaddq((isc_int64_t *)&stats->counters[counter], 1);
#else
        UNUSED(prev);
        stats->counters[counter]++;
#endif

#ifdef ISC_RWLOCK_USEATOMIC
        isc_rwlock_unlock(&stats->counterlock, isc_rwlocktype_read);
#endif
}

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

#ifdef ISC_RWLOCK_USEATOMIC
        isc_rwlock_lock(&stats->counterlock, isc_rwlocktype_read);
#endif

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

#ifdef ISC_RWLOCK_USEATOMIC
        isc_rwlock_unlock(&stats->counterlock, isc_rwlocktype_read);
#endif
}

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

#ifdef ISC_RWLOCK_USEATOMIC
        /*
         * 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
        for (i = 0; i < stats->ncounters; i++) {
                stats->copiedcounters[i] =
                                (isc_uint64_t)(stats->counters[i].hi) << 32 |
                                stats->counters[i].lo;
        }
#else
        UNUSED(i);
        memmove(stats->copiedcounters, stats->counters,
                stats->ncounters * sizeof(isc_stat_t));
#endif

#ifdef ISC_RWLOCK_USEATOMIC
        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);

#ifdef ISC_RWLOCK_USEATOMIC
        /*
         * 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);
#else
        stats->counters[counter] = val;
#endif

#ifdef ISC_RWLOCK_USEATOMIC
        isc_rwlock_unlock(&stats->counterlock, isc_rwlocktype_write);
#endif
}

---