+-
前提说明
注意对比 G2.9 #207 和 G4.9 #97 行， 新版本中，使用 ::operator new 进行内存申请，意味着我们可以对其进行重载后做一些观察统计
G2.9 chunk_alloc 的实现
注意：start_free = (char *)malloc(bytes_to_get);
template <bool threads, int inst>
char *default_alloc_template<threads, inst>::chunk_alloc(size_t size, int &nobjs)
{
char *result;
size_t total_bytes = size * nobjs;
size_t bytes_left = end_free - start_free;
if (bytes_left > total_bytes)
{
result = start_free;
start_free += total_bytes;
return result;
}
else if (bytes_left >= size)
{
nobjs = bytes_left / size;
total_bytes = size * nobjs;
result = start_free;
start_free += total_bytes;
return result;
}
else
{
size_t bytes_to_get = 2 * total_bytes + ROUND_UP(heap_size >> 4);
if (bytes_left > 0)
{
obj **my_free_list = free_list + FREELIST_INDEX(bytes_left);
((obj*)start_free)->free_list_link = *my_free_list;
*my_free_list = (obj*)start_free;
}
start_free = (char *)malloc(bytes_to_get);
if (0 == start_free)
{
int i;
obj **my_free_list;
obj *p;
for (i=size+__ALIGN; i<=__MAX_BYTES; i+=__ALIGN)
{
my_free_list = free_list + FREELIST_INDEX(i);
p = *my_free_list;
if (0 != p)
{
*my_free_list = p->free_list_link;
start_free = (char*)p;
end_free = start_free + i;
return chunk_alloc(size, nobjs);
}
}
}
heap_size += bytes_to_get;
end_free = start_free + bytes_to_get;
return chunk_alloc(size, nobjs);
}
}G4.9 chunk_alloc 的实现
注意：_S_start_free = static_cast<char*>(::operator new(__bytes_to_get));
char *__pool_alloc_base::_M_allocate_chunk(size_t __n, int& __nobjs)
{
char* __result;
size_t __total_bytes = __n * __nobjs;
size_t __bytes_left = _S_end_free - _S_start_free;
if (__bytes_left >= __total_bytes)
{
__result = _S_start_free;
_S_start_free += __total_bytes;
return __result ;
}
else if (__bytes_left >= __n)
{
__nobjs = (int)(__bytes_left / __n);
__total_bytes = __n * __nobjs;
__result = _S_start_free;
_S_start_free += __total_bytes;
return __result;
}
else
{
// Try to make use of the left-over piece.
if (__bytes_left > 0)
{
_Obj* volatile* __free_list = _M_get_free_list(__bytes_left);
((_Obj*)(void*)_S_start_free)->_M_free_list_link = *__free_list;
*__free_list = (_Obj*)(void*)_S_start_free;
}
size_t __bytes_to_get = (2 * __total_bytes
+ _M_round_up(_S_heap_size >> 4));
__try
{
_S_start_free = static_cast<char*>(::operator new(__bytes_to_get));
}
__catch(const std::bad_alloc&)
{
// Try to make do with what we have. That can't hurt. We
// do not try smaller requests, since that tends to result
// in disaster on multi-process machines.
size_t __i = __n;
for (; __i <= (size_t) _S_max_bytes; __i += (size_t) _S_align)
{
_Obj* volatile* __free_list = _M_get_free_list(__i);
_Obj* __p = *__free_list;
if (__p != 0)
{
*__free_list = __p->_M_free_list_link;
_S_start_free = (char*)__p;
_S_end_free = _S_start_free + __i;
return _M_allocate_chunk(__n, __nobjs);
// Any leftover piece will eventually make it to the
// right free list.
}
}
// What we have wasn't enough. Rethrow.
_S_start_free = _S_end_free = 0; // We have no chunk.
__throw_exception_again;
}
_S_heap_size += __bytes_to_get;
_S_end_free = _S_start_free + __bytes_to_get;
return _M_allocate_chunk(__n, __nobjs);
}
}观察 G2.9 : start_free = (char *)malloc(bytes_to_get); 和 G4.9 : _S_start_free = static_cast<char*>(::operator new(__bytes_to_get));
G4.9 内存分配使用 ::operator new, 意味着我们可以对重载以观察统计内存申请情况
G4.9 pool allocator 进行观察
设计一个可累计统计分配量和释放量的 operator new/delete
除非用户直接使用 malloc/free, 否则都避不开它们，这样就可以累计总量基础代码
#include <iostream>
#include <string>
#include <list>
#include <vector>
#include<cstdlib>
using std::cout;
using std::endl;
using std::string;
using std::list;
using std::vector;
static long long countNew = 0;
static long long countDel = 0;
static long long countArrayNew = 0;
static long long countArrayDel = 0;
static long long timesNew = 0;
void *operator new(size_t size)
{
cout << "operator new, \t" << size << "\n";
countNew += size;
timesNew ++;
return malloc(size);
}
void *operator new[](size_t size)
{
cout << "operator new[], \t" << size << "\n";
countArrayNew += size;
return malloc(size);
}
// 一下 （1）（2）可以并存并由（2）抓住流程（但对这的测试无用）
// 当只存在 （1） 时，任无法扎住流程
// 在 class members 中二者只能选一 （任一均可）
// (1)
void operator delete(void *ptr, size_t size)
{
cout << "operator delete(ptr, size), \t" << ptr << "\n";
countDel += size;
free(ptr);
}
// (2)
void operator delete(void *ptr)
{
cout << "operator delete(ptr), \t" << ptr << "\n";
free(ptr);
}
// (1)
void operator delete[](void *ptr, size_t size)
{
cout << "operator delete[](ptr, size), \t" << ptr << "\n";
countArrayDel += size;
free(ptr);
}
// (2)
void operator delete[](void *ptr)
{
cout << "operator delete[](ptr), \t" << ptr << "\n";
free(ptr);
}func1
void func1()
{
cout << "::countNew= " << ::countNew << endl;
cout << "::countDel= " << ::countDel << endl;
cout << "::timesNew= " << ::timesNew << endl;
string *p = new string("My name is Ace");
delete p;
cout << "::countNew= " << ::countNew << endl;
cout << "::countDel= " << ::countDel << endl;
cout << "::timesNew= " << ::timesNew << endl;
}输出：
::countNew= 0
::countDel= 0
::timesNew= 0
operator new, 4 // string size
operator new, 27 // string(REP) + extra
operator delete(ptr), 0xc92380
operator delete(ptr), 0xc956b0
::countNew= 31 // 4 + 27
::countDel= 0 // 本测试永远观察不到想要的结果，因为进不去 operator delete(pre, size) 版本
::timesNew= 2 func2
void func2()
{
string *p = new string[3];
delete[] p;
cout << "::countNew= " << ::countNew << endl;
cout << "::countArrayNew= " << ::countArrayNew<< endl;
cout << "::timesNew= " << ::timesNew << endl;
}输出：
operator new[], 16 // 其中包含 arraySize filed: 4 bytes. 所以 16 - 4 = 12 ==> 4 * 3， 也就是三个 string 每个占 4 bytes
operator new, 13 // Nil string
operator new, 13 // Nil string
operator new, 13 // Nil string
operator delete(ptr), 0x835bc0
operator delete(ptr), 0x835ba8
operator delete(ptr), 0x832398
operator delete[](ptr), 0x832380
::countNew= 39 // 13 + 13 + 13
::countArrayNew= 16
::timesNew= 3func3
void func3()
{
vector<int> vec(10); // vector object 本身不是 dynamic allocated
vec.push_back(1);
vec.push_back(1);
vec.push_back(1);
cout << "::countNew= " << ::countNew << endl;
cout << "::timesNew= " << ::timesNew << endl;
}输出：
operator new, 40 // 10 ints
operator new, 80
operator delete(ptr), 0x772380
::countNew= 120 // 80 + 40
::timesNew= 2
operator delete(ptr), 0x775ba8func4
void func4()
{
list<int> lst; // list object 本身不是 dynamic allocated
lst.push_back(1);
lst.push_back(1);
lst.push_back(1);
cout << "::countNew= " << ::countNew << endl;
cout << "::timesNew= " << ::timesNew << endl;
} 输出
operator new, 12 // 每个 node 是 12 bytes
operator new, 12
operator new, 12
::countNew= 36
::timesNew= 3
operator delete(ptr), 0x712380
operator delete(ptr), 0x712398
operator delete(ptr), 0x715ba8重点
func5
void func6()
{
list<double> lst;
for (int i=0; i< 1000000; ++i)
lst.push_back(i);
cout << "::countNew= " << ::countNew << endl;
cout << "::timesNew= " << ::timesNew << endl;
}输出：
::countNew= 16000000 // 注意, node 都帶 cookie !!!
::timesNew= 1000000 func6
template <typename T>
using listPoll = list<T, __gnu_cxx::__pool_alloc<T>>;
void func5()
{
//list<double, __gnu_cxx::__pool_alloc<double>> lst;
//上一行改用 C++/11 alias template 來寫 :
listPoll<double> lst;
for (int i=0; i< 1000000; ++i)
lst.push_back(i);
cout << "::countNew= " << ::countNew << endl; //16752832 (注意, node 都不帶 cookie), 由于添加了额外的内存管理，因此申请了多于 func6 的申请量
cout << "::timesNew= " << ::timesNew << endl;
}输出：
::countNew= 16752832 // 注意, node 都不帶 cookie). 由于添加了额外的内存管理，因此产生了多于 func6 的申请量
::timesNew= 122 // 内存的申请次数明显降低 ！！！ G2.9 std::alloc 移植至 C
std::alloc 整个由 static data member 和 static member functions 构成，整体只有一个 class 而无分支，因此移植至 C 很容易。需注意：
chunck_alloc(size_t size, int &nobjs);pass by reference 移至 C 时或需改为 pass by pointer
移植步骤除去 template 将 union obj 移至 _default_alloc_template 外部独立 将所有 static data 移为 global 将 __malloc_alloc 改名为 malloc_alloc， 将 __default_alloc 改名为 alloc 将 malloc_alloc 的所有 static function 移为 global 将 alloc 的所有 static functions 移为 global
将 .cpp 改为 .c, 将上述 pass by reference 改为 pass by pointer, 再将：
union obj {
union obj *free_list_link;
};
==>
typedef union __obj {
union __obj *free_list_link;
}obj;
或
typedef struct __obj {
struct __obj *free_list_link;
}obj;alloc.h
// author : Hou Jie (侯捷)
// date : 2015/11/11
// compiler : DevC++ 5.61 (MinGW with GNU 4.9.2)
//
// 說明：這是侯捷 E-learning video "C++內存管理" 的實例程式.
//
// filename : allocc.h
// 取材自 SGI STL 2.91 <stl_alloc.h>, 移植至 C language.
#include <stdlib.h> //for malloc(),realloc()
#include <stddef.h> //for size_t
#include <memory.h> //for memcpy()
//#define __THROW_BAD_ALLOC cerr << "out of memory" << endl; exit(1)
#define __THROW_BAD_ALLOC exit(1)
//----------------------------------------------
// 第1級配置器。
//----------------------------------------------
void (*oom_handler)() = 0;
void* oom_malloc(size_t n)
{
void (*my_malloc_handler)();
void* result;
for (;;) { //不斷嘗試釋放、配置、再釋放、再配置…
my_malloc_handler = oom_handler;
if (0 == my_malloc_handler) { __THROW_BAD_ALLOC; }
(*my_malloc_handler)(); //呼叫處理常式，企圖釋放記憶體
result = malloc(n); //再次嘗試配置記憶體
if (result) return(result);
}
}
void* oom_realloc(void *p, size_t n)
{
void (*my_malloc_handler)();
void* result;
for (;;) { //不斷嘗試釋放、配置、再釋放、再配置…
my_malloc_handler = oom_handler;
if (0 == my_malloc_handler) { __THROW_BAD_ALLOC; }
(*my_malloc_handler)(); //呼叫處理常式，企圖釋放記憶體。
result = realloc(p, n); //再次嘗試配置記憶體。
if (result) return(result);
}
}
void* malloc_allocate(size_t n)
{
void *result = malloc(n); //直接使用 malloc()
if (0 == result) result = oom_malloc(n);
return result;
}
void malloc_deallocate(void* p, size_t n)
{
free(p); //直接使用 free()
}
void* malloc_reallocate(void *p, size_t old_sz, size_t new_sz)
{
void* result = realloc(p, new_sz); //直接使用 realloc()
if (0 == result) result = oom_realloc(p, new_sz);
return result;
}
void (*set_malloc_handler(void (*f)()))()
{ //類似 C++ 的 set_new_handler().
void (*old)() = oom_handler;
oom_handler = f;
return(old);
}
//----------------------------------------------
//第二級配置器
//----------------------------------------------
enum {__ALIGN = 8}; //小區塊的上調邊界
enum {__MAX_BYTES = 128}; //小區塊的上限
enum {__NFREELISTS = __MAX_BYTES/__ALIGN}; //free-lists 個數
// union obj { //G291[o],CB5[x],VC6[x]
// union obj* free_list_link; //這麼寫在 VC6 和 CB5 中也可以，
// }; //但以後就得使用 "union obj" 而不能只寫 "obj"
typedef struct __obj {
struct __obj* free_list_link;
} obj;
char* start_free = 0;
char* end_free = 0;
size_t heap_size = 0;
obj* free_list[__NFREELISTS]
= {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 };
size_t ROUND_UP(size_t bytes) {
return (((bytes) + __ALIGN-1) & ~(__ALIGN - 1));
}
size_t FREELIST_INDEX(size_t bytes) {
return (((bytes) + __ALIGN-1)/__ALIGN - 1);
}
//----------------------------------------------
// We allocate memory in large chunks in order to
// avoid fragmentingthe malloc heap too much.
// We assume that size is properly aligned.
//
// Allocates a chunk for nobjs of size "size".
// nobjs may be reduced if it is inconvenient to
// allocate the requested number.
//----------------------------------------------
//char* chunk_alloc(size_t size, int& nobjs) //G291[o],VC6[x],CB5[x]
char* chunk_alloc(size_t size, int* nobjs)
{
char* result;
size_t total_bytes = size * (*nobjs); //原 nobjs 改為 (*nobjs)
size_t bytes_left = end_free - start_free;
if (bytes_left >= total_bytes) {
result = start_free;
start_free += total_bytes;
return(result);
} else if (bytes_left >= size) {
*nobjs = bytes_left / size; //原 nobjs 改為 (*nobjs)
total_bytes = size * (*nobjs); //原 nobjs 改為 (*nobjs)
result = start_free;
start_free += total_bytes;
return(result);
} else {
size_t bytes_to_get =
2 * total_bytes + ROUND_UP(heap_size >> 4);
// Try to make use of the left-over piece.
if (bytes_left > 0) {
obj* volatile *my_free_list =
free_list + FREELIST_INDEX(bytes_left);
((obj*)start_free)->free_list_link = *my_free_list;
*my_free_list = (obj*)start_free;
}
start_free = (char*)malloc(bytes_to_get);
if (0 == start_free) {
int i;
obj* volatile *my_free_list, *p;
//Try to make do with what we have. That can't
//hurt. We do not try smaller requests, since that tends
//to result in disaster on multi-process machines.
for (i = size; i <= __MAX_BYTES; i += __ALIGN) {
my_free_list = free_list + FREELIST_INDEX(i);
p = *my_free_list;
if (0 != p) {
*my_free_list = p -> free_list_link;
start_free = (char*)p;
end_free = start_free + i;
return(chunk_alloc(size, nobjs));
//Any leftover piece will eventually make it to the
//right free list.
}
}
end_free = 0; //In case of exception.
start_free = (char*)malloc_allocate(bytes_to_get);
//This should either throw an exception or
//remedy the situation. Thus we assume it
//succeeded.
}
heap_size += bytes_to_get;
end_free = start_free + bytes_to_get;
return(chunk_alloc(size, nobjs));
}
}
//----------------------------------------------
// Returns an object of size n, and optionally adds
// to size n free list. We assume that n is properly aligned.
// We hold the allocation lock.
//----------------------------------------------
void* refill(size_t n)
{
int nobjs = 20;
char* chunk = chunk_alloc(n,&nobjs);
obj* volatile *my_free_list; //obj** my_free_list;
obj* result;
obj* current_obj;
obj* next_obj;
int i;
if (1 == nobjs) return(chunk);
my_free_list = free_list + FREELIST_INDEX(n);
//Build free list in chunk
result = (obj*)chunk;
*my_free_list = next_obj = (obj*)(chunk + n);
for (i=1; ; ++i) {
current_obj = next_obj;
next_obj = (obj*)((char*)next_obj + n);
if (nobjs-1 == i) {
current_obj->free_list_link = 0;
break;
} else {
current_obj->free_list_link = next_obj;
}
}
return(result);
}
//----------------------------------------------
//
//----------------------------------------------
void* allocate(size_t n) //n must be > 0
{
obj* volatile *my_free_list; //obj** my_free_list;
obj* result;
if (n > (size_t)__MAX_BYTES) {
return(malloc_allocate(n));
}
my_free_list = free_list + FREELIST_INDEX(n);
result = *my_free_list;
if (result == 0) {
void* r = refill(ROUND_UP(n));
return r;
}
*my_free_list = result->free_list_link;
return (result);
}
//----------------------------------------------
//
//----------------------------------------------
void deallocate(void *p, size_t n) //p may not be 0
{
obj* q = (obj*)p;
obj* volatile *my_free_list; //obj** my_free_list;
if (n > (size_t) __MAX_BYTES) {
malloc_deallocate(p, n);
return;
}
my_free_list = free_list + FREELIST_INDEX(n);
q->free_list_link = *my_free_list;
*my_free_list = q;
}
//----------------------------------------------
//
//----------------------------------------------
void* reallocate(void *p, size_t old_sz, size_t new_sz)
{
void * result;
size_t copy_sz;
if (old_sz > (size_t) __MAX_BYTES && new_sz > (size_t) __MAX_BYTES) {
return(realloc(p, new_sz));
}
if (ROUND_UP(old_sz) == ROUND_UP(new_sz)) return(p);
result = allocate(new_sz);
copy_sz = new_sz > old_sz? old_sz : new_sz;
memcpy(result, p, copy_sz);
deallocate(p, old_sz);
return(result);
}
//----------------------------------------------