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本节将研究Nginx关于内存申请与释放的核心代码；
//大内存管理结构
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
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;
}
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原文地址：http://blog.csdn.net/skyuppour/article/details/45895603
