1. Redis内存管理通过在zmalloc.h和zmalloc.c中重写c语言对内存的管理来完成的。

封装就是为了屏蔽底层平台的差异，同时方便自己实现相关的统计函数。

定义平台之间的差异，主要是tcmalloc（google）、jemalloc（facebook）、苹果平台。

具体来说就是：

若系统中存在Google的TC_MALLOC库，则使用tc_malloc一族函数代替原本的malloc一族函数。
若系统中存在facebook的JE_MALLOC库，则使用je_malloc一族函数替换原来的malloc一族函数。
若当前系统是Mac系统或者其它系统，则使用中的内存分配函数。

__xstr(s) __str(s) __str(s) #s

#if defined(USE_TCMALLOC)
#define ZMALLOC_LIB ("tcmalloc-" xstr(TC_VERSION_MAJOR) "." xstr(TC_VERSION_MINOR))

include <google/tcmalloc.h>

#if (TC_VERSION_MAJOR == 1 && TC_VERSION_MINOR >= 6) || (TC_VERSION_MAJOR > 1)
#define HAVE_MALLOC_SIZE 1
#define zmalloc_size(p) tc_malloc_size(p)
#else
#error "Newer version of tcmalloc required"
#endif

#elif defined(USE_JEMALLOC)
#define ZMALLOC_LIB ("jemalloc-" xstr(JEMALLOC_VERSION_MAJOR) "." xstr(JEMALLOC_VERSION_MINOR) "." __xstr(JEMALLOC_VERSION_BUGFIX))

include <jemalloc/jemalloc.h>

#if (JEMALLOC_VERSION_MAJOR == 2 && JEMALLOC_VERSION_MINOR >= 1) || (JEMALLOC_VERSION_MAJOR > 2)
#define HAVE_MALLOC_SIZE 1
#define zmalloc_size(p) je_malloc_usable_size(p)
#else
#error "Newer version of jemalloc required"
#endif

#elif defined(APPLE)

include <malloc/malloc.h>

#define HAVE_MALLOC_SIZE 1
#define zmalloc_size(p) malloc_size(p)
#endif

具体如下：

defined(USE_TCMALLOC) malloc(size) tc_malloc(size) calloc(count,size) tc_calloc(count,size) realloc(ptr,size) tc_realloc(ptr,size) free(ptr) tc_free(ptr) defined(USE_JEMALLOC) malloc(size) je_malloc(size) calloc(count,size) je_calloc(count,size) je_realloc(ptr,size) free(ptr) je_free(ptr) ifdef HAVE_ATOMIC

#define update_zmalloc_stat_add(n) sync_add_and_fetch(&used_memory,(n))
#define update_zmalloc_stat_sub(n) sync_sub_and_fetch(&used_memory,(__n))
#else
#define update_zmalloc_stat_add(n) do { \
pthread_mutex_lock(&used_memory_mutex); \
used_memory += (__n); \
pthread_mutex_unlock(&used_memory_mutex); \
} while(0)

#define update_zmalloc_stat_sub(__n) do { \
pthread_mutex_lock(&used_memory_mutex); \
used_memory -= (__n); \
pthread_mutex_unlock(&used_memory_mutex); \
} while(0)

#endif

说明：

Both libraries try to de-contention memory acquire by having threads pick the memory from different caches,but they have different strategies:

jemalloc (used by Facebook) maintains a cache per thread
tcmalloc (from Google) maintains a pool of caches,and threads develop a "natural" affinity for a cache,but may change

This led,once again if I remember correctly,to an important difference in term of thread management.

jemalloc is faster if threads are static,for example using pools
tcmalloc is faster when threads are created/destructed

1.1 zmalloc实现

* *ptr = malloc(size+

</span><span style="color: #0000ff;"&gt;if</span> (!<span style="color: #000000;"&gt;ptr) zmalloc_oom_handler(size); //如果没有发生内存溢出，则使用的分配方式static void (*zmalloc_oom_handler)(size_t) = zmalloc_default_oom;

ifdef HAVE_MALLOC_SIZE //HAVE_MALLOC_SIZE用来确定系统是否有函数malloc_size,定义如上所示。

update_zmalloc_stat_alloc(zmalloc_size(ptr)); //更新分配内存的状态。处理线程安全和线程不安全
</span><span style="color: #0000ff;"&gt;return</span><span style="color: #000000;"&gt; ptr;

#else
((size_t)ptr) = size;
update_zmalloc_stat_alloc(size+PREFIX_SIZE);
return (char*)ptr+PREFIX_SIZE;
#endif
}

 update_zmalloc_stat_alloc(__n) do { \= (_n&(()-)) _n += ()-(_n&(()-+=(ifdef HAVE_ATOMIC
<span style="color: #0000ff;">#define update_zmalloc_stat_add(n) sync_add_and_fetch(&used_memory,(n))

<span style="color: #0000ff;">#else

<span style="color: #0000ff;">#define update_zmalloc_stat_add(__n) do { \<span style="color: #000000;">

pthread_mutex_lock(&<span style="color: #000000;">used_memory_mutex); \

used_memory +=<span style="color: #000000;"> (n); \

pthread_mutex_unlock(&<span style="color: #000000;">used_memory_mutex); \

} <span style="color: #0000ff;">while(<span style="color: #800080;">0<span style="color: #000000;">)
<span style="color: #0000ff;">#define update_zmalloc_stat_sub(__n) do { \<span style="color: #000000;">

pthread_mutex_lock(&<span style="color: #000000;">used_memory_mutex); \

used_memory -=<span style="color: #000000;"> (__n); \

pthread_mutex_unlock(&<span style="color: #000000;">used_memory_mutex); \

} <span style="color: #0000ff;">while(<span style="color: #800080;">0<span style="color: #000000;">)
<span style="color: #0000ff;">#endif