view src/core/ngx_rwlock.c @ 6133:af7eba90645d

Win32: shared memory base addresses and remapping. Two mechanisms are implemented to make it possible to store pointers in shared memory on Windows, in particular on Windows Vista and later versions with ASLR: - The ngx_shm_remap() function added to allow remapping of a shared memory zone to the address originally used for it in the master process. While important, it doesn't solve the problem by itself as in many cases it's not possible to use the address because of conflicts with other allocations. - We now create mappings at the same address in all processes by starting mappings at predefined addresses normally unused by newborn processes. These two mechanisms combined allow to use shared memory on Windows almost without problems, including reloads. Based on the patch by Sergey Brester: http://mailman.nginx.org/pipermail/nginx-devel/2015-April/006836.html
author Maxim Dounin <mdounin@mdounin.ru>
date Mon, 27 Apr 2015 18:25:42 +0300
parents 79ddb0bdb273
children e769cc88f996
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)
{
    ngx_atomic_uint_t  readers;

    readers = *lock;

    if (readers == NGX_RWLOCK_WLOCK) {
        *lock = 0;
        return;
    }

    for ( ;; ) {

        if (ngx_atomic_cmp_set(lock, readers, readers - 1)) {
            return;
        }

        readers = *lock;
    }
}


#else

#if (NGX_HTTP_UPSTREAM_ZONE)

#error ngx_atomic_cmp_set() is not defined!

#endif

#endif