Nginx源码完全注释（7）ngx_palloc.h/ngx_palloc.c
ngx_palloc.h
/*
* NGX_MAX_ALLOC_FROM_POOL should be (ngx_pagesize - 1), i.e. 4095 on x86.
* On Windows NT it decreases a number of locked pages in a kernel.
*/
#define NGX_MAX_ALLOC_FROM_POOL (ngx_pagesize - 1)
#define NGX_DEFAULT_POOL_SIZE (16 * 1024)
#define NGX_POOL_ALIGNMENT 16
#define NGX_MIN_POOL_SIZE \
ngx_align((sizeof(ngx_pool_t) + 2 * sizeof(ngx_pool_large_t)), \
NGX_POOL_ALIGNMENT)
typedef void (*ngx_pool_cleanup_pt)(void *data);
typedef struct ngx_pool_cleanup_s ngx_pool_cleanup_t;
struct ngx_pool_cleanup_s {
ngx_pool_cleanup_pt handler;
void *data;
ngx_pool_cleanup_t *next;
};
typedef struct ngx_pool_large_s ngx_pool_large_t;
struct ngx_pool_large_s {
ngx_pool_large_t *next;
void *alloc;
};
typedef struct {
u_char *last; // 数据存储的已用区尾地址
u_char *end; // 数据存储区的尾地址
ngx_pool_t *next; // 下一个内存池地址
ngx_uint_t failed; // 失败次数
} ngx_pool_data_t;
struct ngx_pool_s {
ngx_pool_data_t d; // 数据区
size_t max; // 内存池的最大存储空间
ngx_pool_t *current; // 内存池
ngx_chain_t *chain;
ngx_pool_large_t *large; // 用于存储大数据，链表结构
ngx_pool_cleanup_t *cleanup; // 用于清理，链表结构
ngx_log_t *log;
};
typedef struct {
ngx_fd_t fd; // 文件描述符，用于 ngx_pool_cleanup_file
u_char *name; // 文件名，用于 ngx_pool_delete_file
ngx_log_t *log;
} ngx_pool_cleanup_file_t;
void *ngx_alloc(size_t size, ngx_log_t *log);
void *ngx_calloc(size_t size, ngx_log_t *log);
ngx_pool_t *ngx_create_pool(size_t size, ngx_log_t *log);
void ngx_destroy_pool(ngx_pool_t *pool);
void ngx_reset_pool(ngx_pool_t *pool);
void *ngx_palloc(ngx_pool_t *pool, size_t size);
void *ngx_pnalloc(ngx_pool_t *pool, size_t size);
void *ngx_pcalloc(ngx_pool_t *pool, size_t size);
void *ngx_pmemalign(ngx_pool_t *pool, size_t size, size_t alignment);
ngx_int_t ngx_pfree(ngx_pool_t *pool, void *p);
ngx_pool_cleanup_t *ngx_pool_cleanup_add(ngx_pool_t *p, size_t size);
void ngx_pool_run_cleanup_file(ngx_pool_t *p, ngx_fd_t fd);
void ngx_pool_cleanup_file(void *data);
void ngx_pool_delete_file(void *data);
ngx_palloc.c
static void *ngx_palloc_block(ngx_pool_t *pool, size_t size);
static void *ngx_palloc_large(ngx_pool_t *pool, size_t size);
// 创建 size 大小的内存池
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);
if (p == NULL) {
return NULL;
}
p->d.last = (u_char *) p + sizeof(ngx_pool_t);
p->d.end = (u_char *) p + size;
p->d.next = NULL;
p->d.failed = 0;
size = size - sizeof(ngx_pool_t);
p->max = (size < NGX_MAX_ALLOC_FROM_POOL) ? size : NGX_MAX_ALLOC_FROM_POOL;
p->current = p;
p->chain = NULL;
p->large = NULL;
p->cleanup = NULL;
p->log = log;
return p;
}
// 销毁内存池 pool
void
ngx_destroy_pool(ngx_pool_t *pool)
{
ngx_pool_t *p, *n;
ngx_pool_large_t *l;
ngx_pool_cleanup_t *c;
// 处理 pool->cleanup 链表，处理函数由此前赋值到 pool->cleanup->handler 的函数指针确定
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 pool->large 链表
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);
}
}
#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 pool->d 链表
for (p = pool, n = pool->d.next; /* void */; p = n, n = n->d.next) {
ngx_free(p);
if (n == NULL) {
break;
}
}
}
// 重置内存池
void
ngx_reset_pool(ngx_pool_t *pool)
{
ngx_pool_t *p;
ngx_pool_large_t *l;
// 释放 large 链的每个节点的内存
for (l = pool->large; l; l = l->next) {
if (l->alloc) {
ngx_free(l->alloc);
}
}
pool->large = NULL;
// 重置数据 d 链的每个节点，即重置每个节点的可用区首地址 d.last
for (p = pool; p; p = p->d.next) {
p->d.last = (u_char *) p + sizeof(ngx_pool_t);
}
}
// 从内存池 pool 分配大小为 size 的内存块，并返回其地址
// 是被外部使用最多的内存池相关 API，并且考虑对齐问题
void *
ngx_palloc(ngx_pool_t *pool, size_t size)
{
u_char *m;
ngx_pool_t *p;
// 如果还未超出内存池的 max 值，超过了则用 large
if (size <= pool->max) {
p = pool->current;
do {
// 对齐内存
m = ngx_align_ptr(p->d.last, NGX_ALIGNMENT);
// 该节点剩余可用空间够用
if ((size_t) (p->d.end - m) >= size) {
p->d.last = m + size;
return m;
}
// 该节点剩余空间不够用，看下一个节点
p = p->d.next;
} while (p);
// 现有节点都不给力，重新分配一个 d 节点
return ngx_palloc_block(pool, size);
}
// size 超过 pool->max，从 large 取
return ngx_palloc_large(pool, size);
}
// 类似 ngx_palloc，不考虑对齐问题
void *
ngx_pnalloc(ngx_pool_t *pool, size_t size)
{
u_char *m;
ngx_pool_t *p;
if (size <= pool->max) {
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);
}
return ngx_palloc_large(pool, size);
}
static void *
ngx_palloc_block(ngx_pool_t *pool, size_t size)
{
u_char *m;
size_t psize;
ngx_pool_t *p, *new, *current;
// pool 结构定义区和 pool->d 数据区的总大小
psize = (size_t) (pool->d.end - (u_char *) pool);
// 分配 psize 大小的内存
m = ngx_memalign(NGX_POOL_ALIGNMENT, psize, pool->log);
if (m == NULL) {
return NULL;
}
// 用 new 来表示上面分配的新内存块
new = (ngx_pool_t *) m;
// 初始化这个 new，设定 new 的 d.end、d.next、d.failed
new->d.end = m + psize;
new->d.next = NULL;
new->d.failed = 0;
// m 加上内存池数据定义结构体的大小
m += sizeof(ngx_pool_data_t);
// 内存对齐 m
m = ngx_align_ptr(m, NGX_ALIGNMENT);
// 设定 new 的 d.last
new->d.last = m + size;
current = pool->current;
// TODO
for (p = current; p->d.next; p = p->d.next) {
if (p->d.failed++ > 4) {
current = p->d.next;
}
}
// new 节点放入内存池数据链
p->d.next = new;
pool->current = current ? current : new;
return m;
}
static void *
ngx_palloc_large(ngx_pool_t *pool, size_t size)
{
void *p;
ngx_uint_t n;
ngx_pool_large_t *large;
// 分配 size 大小的内存
p = ngx_alloc(size, pool->log);
if (p == NULL) {
return NULL;
}
n = 0;
// 在 pool 的 large 链中寻找存储区为空的节点，把新分配的内存区首地址赋给它
for (large = pool->large; large; large = large->next) {
// 找到 large 链末尾，在其后插入之，并返回给外部使用
if (large->alloc == NULL) {
large->alloc = p;
return p;
}
// 查看的 large 节点超过 3 个，不再尝试和寻找，由下面代码实现创建新 large 节点的逻辑
if (n++ > 3) {
break;
}
}
// 创建 large 链的一个新节点，如果失败则释放刚才创建的 size 大小的内存，并返回 NULL
large = ngx_palloc(pool, sizeof(ngx_pool_large_t));
if (large == NULL) {
ngx_free(p);
return NULL;
}
// 一切顺利，善后工作
large->alloc = p;
large->next = pool->large;
pool->large = large;
return p;
}
void *
ngx_pmemalign(ngx_pool_t *pool, size_t size, size_t alignment)
{
void *p;
ngx_pool_large_t *large;
// 创建一块 size 大小的内存，内存以 alignment 字节对齐
p = ngx_memalign(alignment, size, pool->log);
if (p == NULL) {
return NULL;
}
// 创建一个 large 节点
large = ngx_palloc(pool, sizeof(ngx_pool_large_t));
if (large == NULL) {
ngx_free(p);
return NULL;
}
// 将这个新的 large 节点交付给 pool 的 large 字段
large->alloc = p;
large->next = pool->large;
pool->large = large;
return p;
}
ngx_int_t
ngx_pfree(ngx_pool_t *pool, void *p)
{
ngx_pool_large_t *l;
// 逐一释放 large 链表的每一个节点
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;
return NGX_OK;
}
}
return NGX_DECLINED;
}
// 封装 palloc 为 pcalloc，实现分配内存并初始化为 0
void *
ngx_pcalloc(ngx_pool_t *pool, size_t size)
{
void *p;
p = ngx_palloc(pool, size);
if (p) {
ngx_memzero(p, size);
}
return p;
}
// 向 cleanup 链添加 p->cleanup 这个节点
ngx_pool_cleanup_t *
ngx_pool_cleanup_add(ngx_pool_t *p, size_t size)
{
ngx_pool_cleanup_t *c;
// 创建一个 cleanup 节点
c = ngx_palloc(p, sizeof(ngx_pool_cleanup_t));
if (c == NULL) {
return NULL;
}
if (size) {
// cleanup 节点数据区
c->data = ngx_palloc(p, size);
if (c->data == NULL) {
return NULL;
}
} else {
c->data = NULL;
}
// 善后
c->handler = NULL;
c->next = p->cleanup;
p->cleanup = c;
ngx_log_debug1(NGX_LOG_DEBUG_ALLOC, p->log, 0, "add cleanup: %p", c);
return c;
}
// 查找指定的 fd，且其 handler 为 ngx_pool_cleanup_file，执行相应动作
// 这里面有一个遍历的操作
void
ngx_pool_run_cleanup_file(ngx_pool_t *p, ngx_fd_t fd)
{
ngx_pool_cleanup_t *c;
ngx_pool_cleanup_file_t *cf;
for (c = p->cleanup; c; c = c->next) {
if (c->handler == ngx_pool_cleanup_file) {
cf = c->data;
if (cf->fd == fd) {
c->handler(cf);
c->handler = NULL;
return;
}
}
}
}
// 释放文件描述符
void
ngx_pool_cleanup_file(void *data)
{
ngx_pool_cleanup_file_t *c = data;
ngx_log_debug1(NGX_LOG_DEBUG_ALLOC, c->log, 0, "file cleanup: fd:%d",
c->fd);
if (ngx_close_file(c->fd) == NGX_FILE_ERROR) {
ngx_log_error(NGX_LOG_ALERT, c->log, ngx_errno,
ngx_close_file_n " \"%s\" failed", c->name);
}
}
// 从文件系统删除文件，data 指针指向一个 ngx_pool_cleanup_file_t 类型的数据
void
ngx_pool_delete_file(void *data)
{
ngx_pool_cleanup_file_t *c = data;
ngx_err_t err;
ngx_log_debug2(NGX_LOG_DEBUG_ALLOC, c->log, 0, "file cleanup: fd:%d %s",
c->fd, c->name);
// 删除文件
if (ngx_delete_file(c->name) == NGX_FILE_ERROR) {
err = ngx_errno;
if (err != NGX_ENOENT) {
ngx_log_error(NGX_LOG_CRIT, c->log, err,
ngx_delete_file_n " \"%s\" failed", c->name);
}
}
// 关闭对应的文件描述符
if (ngx_close_file(c->fd) == NGX_FILE_ERROR) {
ngx_log_error(NGX_LOG_ALERT, c->log, ngx_errno,
ngx_close_file_n " \"%s\" failed", c->name);
}
}
#if 0
static void *
ngx_get_cached_block(size_t size)
{
void *p;
ngx_cached_block_slot_t *slot;
if (ngx_cycle->cache == NULL) {
return NULL;
}
slot = &ngx_cycle->cache[(size + ngx_pagesize - 1) / ngx_pagesize];
slot->tries++;
if (slot->number) {
p = slot->block;
slot->block = slot->block->next;
slot->number--;
return p;
}
return NULL;
}
