Nginx advanced data structure source code analysis (4)-----memory pool

//大块内存管理结构  
struct ngx_pool_large_s {  
    ngx_pool_large_t     *next;   //连接下一个大内存管理  
    void                 *alloc;  //申请的大内存地址  
};  
  
//内存池中数据管理  
typedef struct {  
    u_char               *last;   //可用内存的起始地址  
    u_char               *end;    //可用内存的末尾地址  
    ngx_pool_t           *next;   //指向下一个内存池节点 
    ngx_uint_t            failed; //申请时，失败的次数  
} ngx_pool_data_t;  
  
//内存池  
struct ngx_pool_s {  
    ngx_pool_data_t       d;       //存放数据  
    size_t                max;      //存放数据的可用内存大小，最大为1页  
    ngx_pool_t           *current; //指向分配内存的内存池  
    ngx_chain_t          *chain;  
    ngx_pool_large_t     *large;   //连接大内存管理结构  
    ngx_pool_cleanup_t   *cleanup;  //清理对象头  
    ngx_log_t            *log;  
};  

//创建一个size的内存池  
ngx_pool_t *  
ngx_create_pool(size_t size, ngx_log_t *log)  
{  
    ngx_pool_t  *p;  
  
    p = ngx_memalign(NGX_POOL_ALIGNMENT, size, log);  //以对齐的方式来申请size字节内存  
    if (p == NULL) {  
        return NULL;  
    }  
  
    p->d.last = (u_char *) p + sizeof(ngx_pool_t);   //指向可用的内存起始地址  
    p->d.end = (u_char *) p + size;                  //指向可用内存的末尾地址  
    p->d.next = NULL;                                //初始时，下一个可用内存为NULL  
    p->d.failed = 0;                             //该内存申请失败零次  
  
    size = size - sizeof(ngx_pool_t);       //实际可用的大小，减去控制结构的大小  
    p->max = (size < NGX_MAX_ALLOC_FROM_POOL) ? size : NGX_MAX_ALLOC_FROM_POOL;       //最大只能是一页大小  
  
    p->current = p;                          //指向正在分配内存的内存池  
    p->chain = NULL;  
    p->large = NULL;  
    p->cleanup = NULL;  
    p->log = log;  
  
    return p;  
}  

//销毁内存池  
void  
ngx_destroy_pool(ngx_pool_t *pool)  
{  
    ngx_pool_t          *p, *n;  
    ngx_pool_large_t    *l;  
    ngx_pool_cleanup_t  *c;  
  
    //运行清理对象的handler  
    for (c = pool->cleanup; c; c = c->next) {  
        if (c->handler) {  
            ngx_log_debug1(NGX_LOG_DEBUG_ALLOC, pool->log, 0,  
                           "run cleanup: %p", c);  
            c->handler(c->data);  
        }  
    }  
  
    //释放大内存  
    for (l = pool->large; l; l = l->next) {  
  
        ngx_log_debug1(NGX_LOG_DEBUG_ALLOC, pool->log, 0, "free: %p", l->alloc);  
  
        if (l->alloc) {  
            ngx_free(l->alloc);      //使用free释放malloc申请的内存  
        }  
    }  
  
#if (NGX_DEBUG)  
  
    /* 
     * we could allocate the pool->log from this pool 
     * so we cannot use this log while free()ing the pool 
     */  
  
    for (p = pool, n = pool->d.next; /* void */; p = n, n = n->d.next) {  
        ngx_log_debug2(NGX_LOG_DEBUG_ALLOC, pool->log, 0,  
                       "free: %p, unused: %uz", p, p->d.end - p->d.last);  
  
        if (n == NULL) {  
            break;  
        }  
    }  
  
#endif  
  
    //释放每一个申请的内存池对象ngx_pool_t  
    for (p = pool, n = pool->d.next; /* void */; p = n, n = n->d.next) {  
        ngx_free(p);  
  
        if (n == NULL) {  
            break;  
        }  
    }  
}  
  
//重设内存池  
void  
ngx_reset_pool(ngx_pool_t *pool)  
{  
    ngx_pool_t        *p;  
    ngx_pool_large_t  *l;  
  
    //释放大内存  
    for (l = pool->large; l; l = l->next) {  
        if (l->alloc) {  
            ngx_free(l->alloc);  
        }  
    }  
  
    //内存池对象，仅仅改变last的指针位置  
    for (p = pool; p; p = p->d.next) {  
        p->d.last = (u_char *) p + sizeof(ngx_pool_t);   //导致所有的内存池对象的可用内存的起始地址偏移都一样  
        p->d.failed = 0;  
    }  
  
    pool->current = pool;  
    pool->chain = NULL;  
    pool->large = NULL;  
}  

//分配内存（地址对齐）  
void *  
ngx_palloc(ngx_pool_t *pool, size_t size)  
{  
    u_char      *m;  
    ngx_pool_t  *p;  
  
    if (size <= pool->max) {  //小内存申请时，以size为标准  
  
        p = pool->current;  
  
        do {  
            m = ngx_align_ptr(p->d.last, NGX_ALIGNMENT); //首先将d.last地址对齐  
  
            if ((size_t) (p->d.end - m) >= size) {        //可用的内存大于要申请的内存  
                p->d.last = m + size;        //直接更新d.last  
  
                return m;       //直接返回  
            }  
  
            p = p->d.next;       //否则找下一个可用的内存池对象  
  
        } while (p);  
  
        //没有找到，则要申请新的内存池对象  
        return ngx_palloc_block(pool, size);  
    }  
  
    return ngx_palloc_large(pool, size);    //大内存申请处理  
}  
  
//分配内存（地址可以不对齐）  
void *  
ngx_pnalloc(ngx_pool_t *pool, size_t size)  
{  
    u_char      *m;  
    ngx_pool_t  *p;  
  
    if (size <= pool->max) {  //小内存  
  
        p = pool->current;  
  
        do {  
            m = p->d.last;  
  
            if ((size_t) (p->d.end - m) >= size) {  
                p->d.last = m + size;  
  
                return m;  
            }  
  
            p = p->d.next;  
  
        } while (p);  
  
        return ngx_palloc_block(pool, size);    //申请新内存池对象  
    }  
  
    return ngx_palloc_large(pool, size);    //大内存  
}  

//申请新的内存池对象  
static void *  
ngx_palloc_block(ngx_pool_t *pool, size_t size)  
{  
    u_char      *m;  
    size_t       psize;  
    ngx_pool_t  *p, *new;  
  
    psize = (size_t) (pool->d.end - (u_char *) pool);    //申请内存的总大小  
  
    m = ngx_memalign(NGX_POOL_ALIGNMENT, psize, pool->log);  //对齐方式申请内存  
    if (m == NULL) {  
        return NULL;  
    }  
  
    new = (ngx_pool_t *) m; //新的内存  
  
    new->d.end = m + psize;      //可用的内存的最后地址  
    new->d.next = NULL;  
    new->d.failed = 0;  
  
    m += sizeof(ngx_pool_data_t);   //只有一个ngx_pool_data_t，节省了ngx_pool_t的其余开销  
    m = ngx_align_ptr(m, NGX_ALIGNMENT);  
    new->d.last = m + size;      //可用的内存的起始地址  
      
    //如果当前申请内存的失败的次数已经有5次了，第6次，current将会指向新的内存池对象  
    for (p = pool->current; p->d.next; p = p->d.next) {  
        if (p->d.failed++ > 4) {  
            pool->current = p->d.next;  
        }  
    }  
  
    p->d.next = new; //连接刚刚申请的内存池对象  
  
    return m;  
}  

//大内存申请处理  
static void *  
ngx_palloc_large(ngx_pool_t *pool, size_t size)  
{  
    void              *p;  
    ngx_uint_t         n;  
    ngx_pool_large_t  *large;  
  
    p = ngx_alloc(size, pool->log);      //直接malloc申请内存  
    if (p == NULL) {  
        return NULL;  
    }  
  
    n = 0;  
  
    for (large = pool->large; large; large = large->next) {  
        if (large->alloc == NULL) {      //如果有内存被释放了，可重用  
            large->alloc = p;      
            return p;  
        }  
  
        if (n++ > 3) {       //但是只找4次，第5次直接break，创建大内存的管理结构  
            break;  
        }  
    }  
  
    large = ngx_palloc(pool, sizeof(ngx_pool_large_t)); //从内存池对象申请内存  
    if (large == NULL) {  
        ngx_free(p);  
        return NULL;  
    }  
  
    large->alloc = p;    //指向申请的大内存  
  
    //插入large的头  
    large->next = pool->large;      
    pool->large = large;  
  
    return p;  
}  

//不管内存大小多大，向操作系统申请内存  
void *  
ngx_pmemalign(ngx_pool_t *pool, size_t size, size_t alignment)  
{  
    void              *p;  
    ngx_pool_large_t  *large;  
  
    p = ngx_memalign(alignment, size, pool->log);    //申请的内存  
    if (p == NULL) {  
        return NULL;  
    }  
  
    large = ngx_palloc(pool, sizeof(ngx_pool_large_t)); //申请一个大内存管理结构  
    if (large == NULL) {  
        ngx_free(p);  
        return NULL;  
    }  
  
    //放入到内存池ngx_pool_t中管理  
    large->alloc = p;    //指向申请的内存  
  
    //插入到头部  
    large->next = pool->large;  
    pool->large = large;  
  
    return p;  
}  

//释放内存  
ngx_int_t  
ngx_pfree(ngx_pool_t *pool, void *p)  
{  
    ngx_pool_large_t  *l;  
  
    //只释放大内存  
    for (l = pool->large; l; l = l->next) {  
        if (p == l->alloc) {  
            ngx_log_debug1(NGX_LOG_DEBUG_ALLOC, pool->log, 0,  
                           "free: %p", l->alloc);  
            ngx_free(l->alloc);  
            l->alloc = NULL; //置为空  
  
            return NGX_OK;  
        }  
    }  
  
    return NGX_DECLINED;  
}