view src/core/ngx_rwlock.c @ 9225:1c9264603adc

Syslog: introduced ngx_syslog_send() error logging moderation. Errors when logging to syslog are now logged at most once per second. This ensures that persistent errors won't flood other logs, and spontaneous errors, such as ENOBUFS as observed on BSD systems when syslogd cannot cope with load, or EAGAIN as seen in similar situation on Linux, won't further overload logging subsystem, leading to more errors. Further, errors now can only trigger reconnects at most once per second. This ensures that persistent errors, which cannot be fixed with reconnects, don't trigger too much unneeded work. Additionally, in case of connection errors, such as when syslogd is not running, connection attempts are only made once per second.
author Maxim Dounin <mdounin@mdounin.ru>
date Fri, 01 Mar 2024 05:42:12 +0300
parents 7752d8523066
children
line wrap: on
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/*
 * Copyright (C) Ruslan Ermilov
 * Copyright (C) Nginx, Inc.
 */


#include <ngx_config.h>
#include <ngx_core.h>


#if (NGX_HAVE_ATOMIC_OPS)


#define NGX_RWLOCK_SPIN   2048
#define NGX_RWLOCK_WLOCK  ((ngx_atomic_uint_t) -1)


void
ngx_rwlock_wlock(ngx_atomic_t *lock)
{
    ngx_uint_t  i, n;

    for ( ;; ) {

        if (*lock == 0 && ngx_atomic_cmp_set(lock, 0, NGX_RWLOCK_WLOCK)) {
            return;
        }

        if (ngx_ncpu > 1) {

            for (n = 1; n < NGX_RWLOCK_SPIN; n <<= 1) {

                for (i = 0; i < n; i++) {
                    ngx_cpu_pause();
                }

                if (*lock == 0
                    && ngx_atomic_cmp_set(lock, 0, NGX_RWLOCK_WLOCK))
                {
                    return;
                }
            }
        }

        ngx_sched_yield();
    }
}


void
ngx_rwlock_rlock(ngx_atomic_t *lock)
{
    ngx_uint_t         i, n;
    ngx_atomic_uint_t  readers;

    for ( ;; ) {
        readers = *lock;

        if (readers != NGX_RWLOCK_WLOCK
            && ngx_atomic_cmp_set(lock, readers, readers + 1))
        {
            return;
        }

        if (ngx_ncpu > 1) {

            for (n = 1; n < NGX_RWLOCK_SPIN; n <<= 1) {

                for (i = 0; i < n; i++) {
                    ngx_cpu_pause();
                }

                readers = *lock;

                if (readers != NGX_RWLOCK_WLOCK
                    && ngx_atomic_cmp_set(lock, readers, readers + 1))
                {
                    return;
                }
            }
        }

        ngx_sched_yield();
    }
}


void
ngx_rwlock_unlock(ngx_atomic_t *lock)
{
    if (*lock == NGX_RWLOCK_WLOCK) {
        (void) ngx_atomic_cmp_set(lock, NGX_RWLOCK_WLOCK, 0);
    } else {
        (void) ngx_atomic_fetch_add(lock, -1);
    }
}


void
ngx_rwlock_downgrade(ngx_atomic_t *lock)
{
    if (*lock == NGX_RWLOCK_WLOCK) {
        *lock = 1;
    }
}


#else

#if (NGX_HTTP_UPSTREAM_ZONE || NGX_STREAM_UPSTREAM_ZONE)

#error ngx_atomic_cmp_set() is not defined!

#endif

#endif