SGI 特殊的空间配置器 std::alloc
向 system heap 要求空间。
考虑多绪（multi-threads）状态。
考虑内存不足时的应变措施。
考虑过多「小型区块」可能造成的内存破碎问题
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如果定义了 __USE_MALLOC 则采用 一级配置器 （向系统申请内存）
否则采用 二级配置器（考虑到小型对象，采用内存池）
注意： 当二级配置器向系统申请内存时候，则调用一级配置器
SGI 标准的接口
template<class T, class Alloc>
class simple_alloc {
public:
static T *allocate(size_t n)
{ return 0 == n? 0 : (T*) Alloc::allocate(n * sizeof (T)); }
static T *allocate(void)
{ return (T*) Alloc::allocate(sizeof (T)); }
static void deallocate(T *p, size_t n)
{ if (0 != n) Alloc::deallocate(p, n * sizeof (T)); }
static void deallocate(T *p)
{ Alloc::deallocate(p, sizeof (T)); }
};
一级配置器
template<class T, class Alloc>
class simple_alloc {
public:
static T *allocate(size_t n)
{ return 0 == n? 0 : (T*) Alloc::allocate(n * sizeof (T)); }
static T *allocate(void)
{ return (T*) Alloc::allocate(sizeof (T)); }
static void deallocate(T *p, size_t n)
{ if (0 != n) Alloc::deallocate(p, n * sizeof (T)); }
static void deallocate(T *p)
{ Alloc::deallocate(p, sizeof (T)); }
};
一级配置器
template <int inst>
class __malloc_alloc_template
{
private:
static void *oom_malloc(size_t);
static void *oom_realloc(void *, size_t);
#ifndef __STL_STATIC_TEMPLATE_MEMBER_BUG
static void (* __malloc_alloc_oom_handler)();
#endif
public:
static void * allocate(size_t n)
{
void *result = malloc(n);
if (0 == result)
result = oom_malloc(n);
return result;
}
static void deallocate(void *p, size_t /* n */)
{
free(p);
}
static void * reallocate(void *p, size_t /* old_sz */, size_t new_sz)
{
void * result = realloc(p, new_sz);
if (0 == result)
result = oom_realloc(p, new_sz);
return result;
}
static void (* set_malloc_handler(void (*f)()))()
{
void (* old)() = __malloc_alloc_oom_handler;
__malloc_alloc_oom_handler = f;
return(old);
}
};
// malloc_alloc out-of-memory handling
#ifndef __STL_STATIC_TEMPLATE_MEMBER_BUG
template <int inst>
void (* __malloc_alloc_template<inst>::__malloc_alloc_oom_handler)() = 0;
#endif
template <int inst>
void * __malloc_alloc_template<inst>::oom_malloc(size_t n)
{
void (* my_malloc_handler)();
void *result;
for (;;)
{
my_malloc_handler = __malloc_alloc_oom_handler;
if (0 == my_malloc_handler)
{
__THROW_BAD_ALLOC;
}
(*my_malloc_handler)();
result = malloc(n);
if (result)
return(result);
}
}
template <int inst>
void * __malloc_alloc_template<inst>::oom_realloc(void *p, size_t n)
{
void (* my_malloc_handler)();
void *result;
for (;;)
{
my_malloc_handler = __malloc_alloc_oom_handler;
if (0 == my_malloc_handler)
{
__THROW_BAD_ALLOC;
}
(*my_malloc_handler)();
result = realloc(p, n);
if (result)
return(result);
}
}
typedef __malloc_alloc_template<0> malloc_alloc;
static void (*set_malloc_handler(void (*f)()))() {
void (*old)() = __malloc_alloc_oom_handler;
__malloc_alloc_oom_handler = f;
return (old);
}
解释一下 set_malloc_handler 是函数名称， void (f)() 是函数参数， 这个函数的返回值也是
void ()() 。
模拟 C++ 的 set_new_handler()。
二级配置器
template <bool threads, int inst>
class __default_alloc_template {
private:
// Really we should use static const int x = N
// instead of enum { x = N }, but few compilers accept the former.
#if ! (defined(__SUNPRO_CC) || defined(__GNUC__))
enum {_ALIGN = 8};
enum {_MAX_BYTES = 128};
enum {_NFREELISTS = 16}; // _MAX_BYTES/_ALIGN
# endif
static size_t
_S_round_up(size_t __bytes)
{ return (((__bytes) + (size_t) _ALIGN-1) & ~((size_t) _ALIGN - 1)); }
__PRIVATE:
union _Obj {
union _Obj* _M_free_list_link;
char _M_client_data[1]; /* The client sees this. */
};
private:
# if defined(__SUNPRO_CC) || defined(__GNUC__) || defined(__HP_aCC)
static _Obj* __STL_VOLATILE _S_free_list[];
// Specifying a size results in duplicate def for 4.1
# else
static _Obj* __STL_VOLATILE _S_free_list[_NFREELISTS];
# endif
static size_t _S_freelist_index(size_t __bytes) {
return (((__bytes) + (size_t)_ALIGN-1)/(size_t)_ALIGN - 1);
}
// Returns an object of size __n, and optionally adds to size __n free list.
static void* _S_refill(size_t __n);
// Allocates a chunk for nobjs of size size. nobjs may be reduced
// if it is inconvenient to allocate the requested number.
static char* _S_chunk_alloc(size_t __size, int& __nobjs);
// Chunk allocation state.
static char* _S_start_free;
static char* _S_end_free;
static size_t _S_heap_size;
# ifdef __STL_THREADS
static _STL_mutex_lock _S_node_allocator_lock;
# endif
// It would be nice to use _STL_auto_lock here. But we
// don't need the NULL check. And we do need a test whether
// threads have actually been started.
class _Lock;
friend class _Lock;
class _Lock {
public:
_Lock() { __NODE_ALLOCATOR_LOCK; }
~_Lock() { __NODE_ALLOCATOR_UNLOCK; }
};
public:
/* __n must be > 0 */
static void* allocate(size_t __n)
{
void* __ret = 0;
if (__n > (size_t) _MAX_BYTES) {
__ret = malloc_alloc::allocate(__n);
}
else {
_Obj* __STL_VOLATILE* __my_free_list
= _S_free_list + _S_freelist_index(__n);
// Acquire the lock here with a constructor call.
// This ensures that it is released in exit or during stack
// unwinding.
# ifndef _NOTHREADS
/*REFERENCED*/
_Lock __lock_instance;
# endif
_Obj* __RESTRICT __result = *__my_free_list;
if (__result == 0)
__ret = _S_refill(_S_round_up(__n));
else {
*__my_free_list = __result -> _M_free_list_link;
__ret = __result;
}
}
return __ret;
};
/* __p may not be 0 */
static void deallocate(void* __p, size_t __n)
{
if (__n > (size_t) _MAX_BYTES)
malloc_alloc::deallocate(__p, __n);
else {
_Obj* __STL_VOLATILE* __my_free_list
= _S_free_list + _S_freelist_index(__n);
_Obj* __q = (_Obj*)__p;
// acquire lock
# ifndef _NOTHREADS
/*REFERENCED*/
_Lock __lock_instance;
# endif /* _NOTHREADS */
__q -> _M_free_list_link = *__my_free_list;
*__my_free_list = __q;
// lock is released here
}
}
static void* reallocate(void* __p, size_t __old_sz, size_t __new_sz);
} ;
typedef __default_alloc_template<__NODE_ALLOCATOR_THREADS, 0> alloc;
typedef __default_alloc_template<false, 0> single_client_alloc;
