Nginx memory pool source code analysis

// The dividing point between SGI STL small and large memory blocks: 128B
// nginx (allocates memory to all modules of HTTP server) the dividing point between small and large blocks of memory: 4096B
#define NGX_MAX_ALLOC_FROM_POOL (ngx_pagesize - 1) 

// Memory pool default size #define NGX_DEFAULT_POOL_SIZE (16 * 1024)

// Memory pool byte alignment, SGI STL is 8B
#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

// Adjust the allocated memory to an integer multiple of 16 #define ngx_align(d, a) (((d) + (a - 1)) & ~(a - 1))

typedef struct ngx_pool_s ngx_pool_t;

typedef struct {
    u_char *last; // points to the starting address of available memory u_char *end; // points to the end address of available memory ngx_pool_t *next; // points to the next memory block ngx_uint_t failed; // the number of times the current memory block failed to allocate space} ngx_pool_data_t;

// Memory pool block type struct ngx_pool_s {
    ngx_pool_data_t d; // Memory pool block header information size_t max;	
    ngx_pool_t *current; // Points to the starting address of the memory block that can be used to allocate space (failed < 4) ngx_chain_t *chain; // Connect all memory pool blocks ngx_pool_large_t *large; // Entry pointer for large blocks of memory ngx_pool_cleanup_t *cleanup; // Cleanup operation of memory pool blocks. Users can set callback functions to perform cleanup operations before releasing memory pool blocks ngx_log_t *log; // Log };

// Open up memory according to size ngx_pool_t * ngx_create_pool(size_t size, ngx_log_t *log){
    ngx_pool_t *p;
	// According to the macros defined by the system platform and the size executed by the user, call the API of different platforms to open up a memory pool p = ngx_memalign(NGX_POOL_ALIGNMENT, size, log);
    if (p == NULL) {
        return NULL;
    }

    p->d.last = (u_char *) p + sizeof(ngx_pool_t); // Points to the starting address of available memory p->d.end = (u_char *) p + size; // Points to the end address of available memory p->d.next = NULL; // Points to the next memory block. The memory block has just been requested, so it is left blank p->d.failed = 0; // Whether the memory block is successfully allocated size = size - sizeof(ngx_pool_t); // Available space = total space - header information // If the specified size is larger than one page, use one page, otherwise use the specified size // max = min(size, 4096), max refers to the size of the memory block excluding the beginning information p->max = (size < NGX_MAX_ALLOC_FROM_POOL) ? size : NGX_MAX_ALLOC_FROM_POOL;

    p->current = p; // Points to the starting address of the memory block that can be used to allocate space p->chain = NULL;
    p->large = NULL; // Small blocks of memory are directly allocated in the memory block, and large blocks of memory are allocated in the memory pointed to by large p->cleanup = NULL;
    p->log = log;

    return p;
}

void *
ngx_palloc(ngx_pool_t *pool, size_t size)
{
#if !(NGX_DEBUG_PALLOC)
    if (size <= pool->max) {
    	// The currently allocated space is less than max, small memory allocation return ngx_palloc_small(pool, size, 1); // Consider memory alignment}
#endif

    return ngx_palloc_large(pool, size);
}

void *
ngx_pnalloc(ngx_pool_t *pool, size_t size)
{
#if !(NGX_DEBUG_PALLOC)
    if (size <= pool->max) {
        return ngx_palloc_small(pool, size, 0); // Memory alignment is not considered}
#endif

    return ngx_palloc_large(pool, size);
}

void* ngx_pcalloc(ngx_pool_t *pool, size_t size){
    void *p;
    p = ngx_palloc(pool, size); // Consider memory alignment if (p) {
        ngx_memzero(p, size); // Initialize memory to 0
    }

    return p;
}

static ngx_inline void *
ngx_palloc_small(ngx_pool_t *pool, size_t size, ngx_uint_t align)
{
    u_char *m;
    ngx_pool_t *p;
	// Allocate from the memory pool pointed to by the current pointer of the first memory block p = pool->current;

    do {
        m = p->d.last; // m points to the starting address of allocatable memory if (align) {
        	// Adjust m to an integer multiple of NGX_ALIGNMENT m = ngx_align_ptr(m, NGX_ALIGNMENT);
        }
		//Core code for allocating memory from memory poolif ((size_t) (p->d.end - m) >= size) {
        	// If the allocatable space >= the requested space // offset the d.last pointer and record the first address of the free space p->d.last = m + size;
            return m;
        }
        // The free space of the current memory block is not enough to allocate. If there is a next memory block, turn to the next memory block. // If not, p will be set to NULL and exit while
        p = p->d.next;
    } while (p);
	
    return ngx_palloc_block(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;
	// Open up a memory block with the same size as the previous one psize = (size_t) (pool->d.end - (u_char *) pool);
	
	// After aligning psize to an integer multiple of NGX_POOL_ALIGNMENT, apply for space from OS m = ngx_memalign(NGX_POOL_ALIGNMENT, psize, pool->log);
    if (m == NULL) {
        return NULL;
    }

    new = (ngx_pool_t *) m; // points to the starting address of the newly allocated memory block new->d.end = m + psize; // points to the end address of the newly allocated memory block new->d.next = NULL; // the address of the next memory block is NULL 
    new->d.failed = 0; // The number of times the current memory block fails to allocate space // Points to the end of the header information, while max, current, chain, etc. are only in the first memory block m += sizeof(ngx_pool_data_t);  
    m = ngx_align_ptr(m, NGX_ALIGNMENT);
    new->d.last = m + size; // last points to the starting address of the free space in the current block	
	// Since space is allocated from pool->current each time // If the execution reaches here, except for the new memory block, all other memory blocks fail to be allocated for (p = pool->current; p->d.next != NULL; p = p->d.next) {
    	// For all memory blocks, failed++ is added until the number of allocation failures for the memory block is greater than 4. // This means that the remaining space of the memory block is very small and no more space can be allocated. // Then modify the current pointer and start allocating space from current next time. When allocating again, you don't need to traverse the previous memory blocks if (p->d.failed++ > 4) {
            pool->current = p->d.next;
        }
    }
	
    p->d.next = new; // Connect the first memory block of the allocatable space and the newly opened memory block return m;
}

typedef struct ngx_pool_large_s ngx_pool_large_t;

struct ngx_pool_large_s {
    ngx_pool_large_t *next; // The starting address of the next large block of memory void *alloc; // The starting address of the large block of memory };

static void * ngx_palloc_large(ngx_pool_t *pool, size_t size){
    void *p;
    ngx_uint_t n;
    ngx_pool_large_t *large;
	
	// Calling malloc
    p = ngx_alloc(size, pool->log);
    if (p == NULL) {
        return NULL;
    }

    n = 0;
	// for loop traverses the linked list storing large blocks of memory information for (large = pool->large; large; large = large->next) {
        if (large->alloc == NULL) {
        	// When a large block of memory is ngx_pfree, alloc is NULL
        	// Traverse the linked list, if the first address of the large block of memory is empty, write the current malloc memory address into alloc
            large->alloc = p;
            return p;
        }
		// After traversing 4 times, if the corresponding information of the large block of memory that has been released has not been found // In order to improve efficiency, directly apply for space in the small block of memory to save the information of the large block of memory if (n++ > 3) {
            break;
        }
    }
	// Allocate the space for storing large memory blocks *next and *alloc in the small memory pool through pointer offset large = ngx_palloc_small(pool, sizeof(ngx_pool_large_t), 1);
    if (large == NULL) {
    	// If the allocation of storage *next and *alloc space on the small block of memory fails, the large block of memory cannot be recorded // Release the large block of memory p
        ngx_free(p);
        return NULL;
    }
	
    large->alloc = p; // alloc points to the first address of the large memory block large->next = pool->large; // These two sentences use the head insertion method to store the record information of the new memory block in the linked list with large as the head node pool->large = large;

    return p;
}

// Release the large block of memory pointed to by p ngx_int_t ngx_pfree(ngx_pool_t *pool, void *p){
    ngx_pool_large_t *l;

    for (l = pool->large; l; l = l->next) {
    	// Traverse the linked list storing large memory blocks and find the large memory block corresponding to p if (p == l->alloc) {
            ngx_log_debug1(NGX_LOG_DEBUG_ALLOC, pool->log, 0,
                           "free: %p", l->alloc);
            // Release large blocks of memory, but do not release the memory space where information is stored ngx_free(l->alloc); // free
            l->alloc = NULL; // alloc is set to NULL and return NGX_OK;
        }
    }

    return NGX_DECLINED;
}

void ngx_reset_pool(ngx_pool_t *pool){
    ngx_pool_t *p;
    ngx_pool_large_t *l;
	
	// Since the small memory needs to be reset, and the control information of the large memory is saved in the small memory // So you need to release the large memory first, and then reset the small memory for (l = pool->large; l; l = l->next) {
        if (l->alloc) {
            ngx_free(l->alloc);
        }
    }
	
	// Traverse the linked list of small memory blocks and reset management information such as last, failed, current, chain, large, etc. for (p = pool; p; ​​p = p->d.next) {
    	// Since only the first memory block has management information other than ngx_pool_data_t, other memory blocks only have information of ngx_pool_data_t // No error will occur, but space will be wasted p->d.last = (u_char *) p + sizeof(ngx_pool_t);
        p->d.failed = 0;
    }
	
	// current points to a memory block that can be used to allocate memory pool->current = pool;
    pool->chain = NULL;
    pool->large = NULL;
}

// Assume the memory alignment is 4B
typedef struct{
	char* p;
	char data[508];
}stData;

ngx_pool_t *pool = ngx_create_pool(512, log); // Create an nginx memory block with a total space of 512B stData* data_ptr = ngx_alloc(512); // Because the actual available memory size is: 512-sizeof(ngx_pool_t), it belongs to large memory allocation data_ptr->p = malloc(10); // p points to external heap memory, similar to the use of external resources in C++ objects

typedef void (*ngx_pool_cleanup_pt)(void *data);

typedef struct ngx_pool_cleanup_s ngx_pool_cleanup_t;

// The following structure is pointed to by ngx_pool_s.cleanup, which is also a small block of memory stored in the memory pool. struct ngx_pool_cleanup_s {
    ngx_pool_cleanup_pt handler;
    void *data; // Point to the resource that needs to be released ngx_pool_cleanup_t *next; // Functions that release resources are placed in a linked list, and next is used to point to this linked list};

// p represents the entry address of the memory pool, size represents the size of the p->cleanup->data pointer // p->cleanup points to a structure containing cleanup function information // ngx_pool_cleanup_add returns a pointer to a structure containing cleanup function information ngx_pool_cleanup_t* ngx_pool_cleanup_add(ngx_pool_t *p, size_t size){
    ngx_pool_cleanup_t *c;
	
	// The structure of the cleanup function is actually a small block of memory stored in the memory pool c = ngx_palloc(p, sizeof(ngx_pool_cleanup_t));
    if (c == NULL) {
        return NULL;
    }
	
    if (size) {
    	// Apply for space of size for c->data c->data = ngx_palloc(p, size);
        if (c->data == NULL) {
            return NULL;
        }
    } else {
        c->data = NULL;
    }

    c->handler = NULL;
    //Use the head insertion method to string the current structure after pool->cleanup c->next = p->cleanup;
    p->cleanup = c;

    ngx_log_debug1(NGX_LOG_DEBUG_ALLOC, p->log, 0, "add cleanup: %p", c);

    return c;
}

void release(void* p){
	free(p);
}

ngx_pool_cleanup_t* clean_ptr = ngx_clean_cleanup_add(pool, sizeof(char*));
clean_ptr->handler = &release; // The user sets the function to be called before destroying the memory pool clean_ptr->data = data_ptr->p; // The user sets the address of the memory to be released before destroying the memory pool ngx_destroy_pool(pool); // User destroys the memory pool

void ngx_destroy_pool(ngx_pool_t *pool)
{
    ngx_pool_t *p, *n;
    ngx_pool_large_t *l;
    ngx_pool_cleanup_t *c;
	
	// Traverse the cleanup list (stored as functions that need to be called before release) to release external resources 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);
        }
    }

	// Release large blocks of memory for (l = pool->large; l; l = l->next) {
        if (l->alloc) {
            ngx_free(l->alloc);
        }
    }
	
	// Release small memory pool for (p = pool, n = pool->d.next; /* void */; p = n, n = n->d.next) {
        ngx_free(p);
        
        if (n == NULL) {
            break;
        }
    }
} 

#include <ngx_config.h>
#include <nginx.h>
#include <ngx_core.h>
#include <ngx_palloc.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

void ngx_log_error_core(ngx_uint_t level, ngx_log_t *log, ngx_err_t err,
            const char *fmt, ...){

}

typedef struct Data stData;
struct Data{
    char *ptr;
    FILE *pfile;
};

void func1(char *p){
    printf("free ptr mem!\n");
    free(p);
}

void func2(FILE *pf){
    printf("close file!\n");
    fclose(pf);
}

void main(){
	// max = 512 - sizeof(ngx_pool_t)
	// Create an nginx memory block with a total space of 512 bytes ngx_pool_t *pool = ngx_create_pool(512, NULL);
    if(pool == NULL){
        printf("ngx_create_pool fail...");
        return;
    }
    
	// void *p1 allocated from small memory pool = ngx_palloc(pool, 128); 
    if(p1 == NULL){
        printf("ngx_palloc 128 bytes fail...");
        return;
    }
	
	// stData *p2 allocated from large memory pool = ngx_palloc(pool, 512); 
    if(p2 == NULL){
        printf("ngx_palloc 512 bytes fail...");
        return;
    }
    
    // Occupy external heap memory p2->ptr = malloc(12);
    strcpy(p2->ptr, "hello world");
    // File descriptor p2->pfile = fopen("data.txt", "w");
    
    ngx_pool_cleanup_t *c1 = ngx_pool_cleanup_add(pool, sizeof(char*));
    c1->handler = func1; // Set callback function c1->data = p2->ptr; // Set resource address ngx_pool_cleanup_t *c2 = ngx_pool_cleanup_add(pool, sizeof(FILE*));
    c2->handler = func2;
    c2->data = p2->pfile;
	
	// 1. Call all preset cleanup functions 2. Release large blocks of memory 3. Release all memory in the small memory pool ngx_destroy_pool(pool); 

    return;
}