nginx共享内存的机制详解

#include <sys/ipc.h>
#include <sys/shm.h>


ngx_int_t
ngx_shm_alloc(ngx_shm_t *shm)
{
    int  id;

    id = shmget(IPC_PRIVATE, shm->size, (SHM_R|SHM_W|IPC_CREAT));

    if (id == -1) {
        ngx_log_error(NGX_LOG_ALERT, shm->log, ngx_errno,
                      "shmget(%uz) failed", shm->size);
        return NGX_ERROR;
    }

    ngx_log_debug1(NGX_LOG_DEBUG_CORE, shm->log, 0, "shmget id: %d", id);

    shm->addr = shmat(id, NULL, 0);

    if (shm->addr == (void *) -1) {
        ngx_log_error(NGX_LOG_ALERT, shm->log, ngx_errno, "shmat() failed");
    }

    if (shmctl(id, IPC_RMID, NULL) == -1) {
        ngx_log_error(NGX_LOG_ALERT, shm->log, ngx_errno,
                      "shmctl(IPC_RMID) failed");
    }

    return (shm->addr == (void *) -1) ? NGX_ERROR : NGX_OK;
}


void
ngx_shm_free(ngx_shm_t *shm)
{
    if (shmdt(shm->addr) == -1) {
        ngx_log_error(NGX_LOG_ALERT, shm->log, ngx_errno,
                      "shmdt(%p) failed", shm->addr);
    }
}

typedef struct {
    u_char      *addr;//共享内存地址
    size_t       size;//大小
    ngx_str_t    name;//名称
    ngx_log_t   *log;
    ngx_uint_t   exists;   
} ngx_shm_t;
typedef ngx_int_t (*ngx_shm_zone_init_pt) (ngx_shm_zone_t *zone, void *data);
struct ngx_shm_zone_s {
    void                     *data;//用户数据
    ngx_shm_t                 shm; //共享内存结构体
    ngx_shm_zone_init_pt      init;//用户数据的初始化函数
    void                     *tag;//创建的模块
    ngx_uint_t                noreuse;  
};

ngx_slab_pool_t  *sp;
sp = (ngx_slab_pool_t *) zn->shm.addr;
sp->addr = zn->shm.addr;
ngx_slab_init(sp);

ngx_shm_zone_t  *shm_zone;//共享内存单元
ngx_conf_t *cf;//ngx配置
ngx_str_t   name；//共享内存名称
ngx_int_t    n;//分配共享内存的大小
ngx_module_t  ngx_stream_ssl_module;//使用共享内存的模块，防止模块间重名
scf->shm_zone = ngx_shared_memory_add(cf, &name, n,&ngx_stream_ssl_module);//从
if (scf->shm_zone == NULL) {
     return NGX_CONF_ERROR;
 }
//初始化函数设置
 scf->shm_zone->init = ngx_ssl_session_cache_init;

ngx_int_t
ngx_ssl_session_cache_init(ngx_shm_zone_t *shm_zone, void *data)
{
    size_t                    len;
    ngx_slab_pool_t          *shpool;
    ngx_ssl_session_cache_t  *cache;

    if (data) {
        shm_zone->data = data;
        return NGX_OK;
    }
	//获取slab_pool
    shpool = (ngx_slab_pool_t *) shm_zone->shm.addr;

    if (shm_zone->shm.exists) {
        shm_zone->data = shpool->data;
        return NGX_OK;
    }
	//为数据分配slab内存块
    cache = ngx_slab_alloc(shpool, sizeof(ngx_ssl_session_cache_t));
    if (cache == NULL) {
        return NGX_ERROR;
    }
	//赋值到slab_pool管理
    shpool->data = cache;
    shm_zone->data = cache;
	//红黑树数据初始化
    ngx_rbtree_init(&cache->session_rbtree, &cache->sentinel,
                    ngx_ssl_session_rbtree_insert_value);
	//队列初始化
    ngx_queue_init(&cache->expire_queue);
	//设置log
    len = sizeof(" in SSL session shared cache \"\"") + shm_zone->shm.name.len;
	//为log分配共享内存
    shpool->log_ctx = ngx_slab_alloc(shpool, len);
    if (shpool->log_ctx == NULL) {
        return NGX_ERROR;
    }
	//写log
    ngx_sprintf(shpool->log_ctx, " in SSL session shared cache \"%V\"%Z",
                &shm_zone->shm.name);

    shpool->log_nomem = 0;

    return NGX_OK;
}