libevent基础文件mm-internal.h(内存分配封装)

libevent并没有实现特别的内存分配，仅仅是给使用者提供了内存分配的接口，当我们没有设置内存分配函数时（也就是这几个全局函数指针为空，

static void *(*_mm_malloc_fn)(size_t sz) = NULL;
static void *(*_mm_realloc_fn)(void *p, size_t sz) = NULL;
static void (*_mm_free_fn)(void *p) = NULL;），会相应的调用库函数malloc、calloc、free、strdup。

如：#define mm_malloc(sz) malloc(sz)
#define mm_calloc(n, sz) calloc((n), (sz))
#define mm_strdup(s) strdup(s)
#define mm_realloc(p, sz) realloc((p), (sz))
#define mm_free(p) free(p)

#ifndef _EVENT_MM_INTERNAL_H
#define _EVENT_MM_INTERNAL_H

#include <sys/types.h>

#ifdef __cplusplus
extern "C" {
#endif

#ifndef _EVENT_DISABLE_MM_REPLACEMENT//没有禁止用户使用自己的内存分配函数，就给用户提供接口
/* Internal use only: Memory allocation functions. We give them nice short
 * mm_names for our own use, but make sure that the symbols have longer names
 * so they don't conflict with other libraries (like, say, libmm). */

void *event_mm_malloc_(size_t sz);
void *event_mm_calloc_(size_t count, size_t size);
char *event_mm_strdup_(const char *s);
void *event_mm_realloc_(void *p, size_t sz);
void event_mm_free_(void *p);
#define mm_malloc(sz) event_mm_malloc_(sz)
#define mm_calloc(count, size) event_mm_calloc_((count), (size))
#define mm_strdup(s) event_mm_strdup_(s)
#define mm_realloc(p, sz) event_mm_realloc_((p), (sz))
#define mm_free(p) event_mm_free_(p)
#else//禁止用户使用自己的内存分配函数
#define mm_malloc(sz) malloc(sz)
#define mm_calloc(n, sz) calloc((n), (sz))
#define mm_strdup(s) strdup(s)
#define mm_realloc(p, sz) realloc((p), (sz))
#define mm_free(p) free(p)
#endif

#ifdef __cplusplus
}
#endif

#endif

实际的实现代码在event.c中

void *
event_mm_malloc_(size_t sz)
{
	if (_mm_malloc_fn)
		return _mm_malloc_fn(sz);
	else
		return malloc(sz);
}


void *
event_mm_calloc_(size_t count, size_t size)
{
	if (_mm_malloc_fn) {
		size_t sz = count * size;
		void *p = _mm_malloc_fn(sz);
		if (p)
			memset(p, 0, sz);
		return p;
	} else
		return calloc(count, size);
}


char *
event_mm_strdup_(const char *str)
{
	if (_mm_malloc_fn) {
		size_t ln = strlen(str);
		void *p = _mm_malloc_fn(ln+1);
		if (p)
			memcpy(p, str, ln+1);
		return p;
	} else
#ifdef WIN32
		return _strdup(str);
#else
		return strdup(str);
#endif
}


void *
event_mm_realloc_(void *ptr, size_t sz)
{
	if (_mm_realloc_fn)
		return _mm_realloc_fn(ptr, sz);
	else
		return realloc(ptr, sz);
}


void
event_mm_free_(void *ptr)
{
	if (_mm_free_fn)
		_mm_free_fn(ptr);
	else
		free(ptr);
}


void
event_set_mem_functions(void *(*malloc_fn)(size_t sz),
			void *(*realloc_fn)(void *ptr, size_t sz),
			void (*free_fn)(void *ptr))
{
	_mm_malloc_fn = malloc_fn;
	_mm_realloc_fn = realloc_fn;
	_mm_free_fn = free_fn;
}
#endif