__malloc_alloc_template分配器:該分配器是對malloc、realloc以及free的封裝:
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當調(diào)用malloc和realloc申請不到內(nèi)存空間的時候,會改調(diào)用oom_malloc()和oom_realloc(),這兩個函數(shù)會反復(fù)調(diào)用用戶傳遞過來的out of memory handler處理函數(shù),直到能用malloc或者realloc申請到內(nèi)存為止。
如果用戶沒有傳遞__malloc_alloc_oom_handler,__malloc_alloc_template會拋出__THROW_BAD_ALLOC異常。所以,內(nèi)存不足的處理任務(wù)就交給類客戶去完成。
__default_alloc_template分配器
這個分配器采用了內(nèi)存池的思想,有效地避免了內(nèi)碎片的問題(順便一句話介紹一下內(nèi)碎片和外碎片:內(nèi)碎片是已被分配出去但是用不到的內(nèi)存空間,外碎片是由于大小太小而無法分配出去的空閑塊)。
如果申請的內(nèi)存塊大于128bytes,就將申請的操作移交__malloc_alloc_template分配器去處理;如果申請的區(qū)塊大小小于128bytes時,就從本分配器維護的內(nèi)存池中分配內(nèi)存。
分配器用空閑鏈表的方式維護內(nèi)存池中的空閑空間。
#include<iostream> #include<stdarg.h> using namespace std; #define __DEBUG__ static string GetFileName(const string& path) { char ch = '/'; #ifdef _WIN32 ch = '\\'; #endif size_t pos = path.rfind(ch); if (pos == string::npos) return path; else return path.substr(pos + 1); } // 用于調(diào)試追溯的trace log inline static void __trace_debug(const char* function, const char * filename, int line, char* format, ...) { #ifdef __DEBUG__ // 輸出調(diào)用函數(shù)的信息 fprintf(stdout, "【%s:%d】 %s", GetFileName(filename).c_str(), line, function); // 輸出用戶打的trace信息 va_list args; va_start(args, format); vfprintf(stdout, format, args); va_end(args); #endif } #define __TRACE_DEBUG(...) \ __trace_debug(__FUNCTION__, __FILE__, __LINE__, __VA_ARGS__); typedef void(*MallocAllocHandler)(); template <int inst> class MallocAllocTemplate { protected: static MallocAllocHandler _handler; static void* Oom_Malloc(size_t n) { MallocAllocHandler handler = NULL; void* ret = NULL; while (1) { handler = _handler; if (handler == NULL) { cout << "out of memory" << endl; //exit(1); } (*handler)(); ret = malloc(n); if (ret) return ret; } } public: static void * Allocate(size_t n) { void *result = malloc(n); if (0 == result) result = Oom_Malloc(n); __TRACE_DEBUG("調(diào)用一級空間配置器開辟內(nèi)存:ptr:%p,size:%u\n", result,n); return result; } static void Deallocate(void *p, size_t n) { free(p); __TRACE_DEBUG("調(diào)用一級空間配置器釋放內(nèi)存:ptr:%p,size:%u\n", p, n); } static void(*SetMallocHandler(MallocAllocHandler f))() { void(*old)() = _handler; _handler = f; return(old); } }; template<int inst> MallocAllocHandler MallocAllocTemplate<inst>::_handler = NULL; template <bool threads, int inst> class DefaultAllocTemplate { enum { ALIGN = 8 }; enum { MAX_BYTES = 128 }; enum { NFREELISTS = MAX_BYTES / ALIGN }; union Obj { union Obj * _freeListLink; char _clientData[1]; /* The client sees this. */ }; static Obj * volatile _freeList[NFREELISTS];//指針數(shù)組 static char *_startFree; static char *_endFree; static size_t _heapSize; static size_t FreeListIndex(size_t bytes) { return (((bytes)+ALIGN - 1) / ALIGN - 1); } static size_t RoundUp(size_t bytes) { return (((bytes)+ALIGN - 1) & ~(ALIGN - 1)); } static char* chunkAlloc(size_t n, int& nobjs) { char* ret = NULL; size_t totalBytes = n*nobjs; size_t freeLeft = _endFree - _startFree; if (freeLeft >= totalBytes) { ret = _startFree; _startFree += totalBytes; __TRACE_DEBUG("內(nèi)存池足夠分配空間:ptr:%p,size:%u\n", ret, totalBytes); return(ret); } else if (freeLeft >= n) { nobjs = freeLeft / n; totalBytes = n*nobjs; ret = _startFree; _startFree += totalBytes; __TRACE_DEBUG("內(nèi)存池只有空間:ptr:%p,size:%u\n", ret, totalBytes); return(ret); } else { size_t bytesOfGet = 2 * totalBytes + RoundUp(_heapSize >> 4); //將剩下的小塊內(nèi)存掛載 if (freeLeft > 0) { Obj* myFreeList = _freeList[FreeListIndex(freeLeft)]; ((Obj*)_startFree)->_freeListLink = myFreeList; _freeList[FreeListIndex(freeLeft)] = (Obj*)_startFree; } _startFree =(char*) malloc(bytesOfGet); if (_startFree == NULL) { Obj* myFreeList, *p; for (int i = n; i < MAX_BYTES; i += ALIGN) { myFreeList = _freeList[FreeListIndex(i)]; if (myFreeList != NULL) { p = myFreeList; myFreeList = myFreeList->_freeListLink; _startFree = (char*)p; _endFree = _startFree + i; return chunkAlloc(n, nobjs);//會進入else if } } //空閑鏈表無比n大的內(nèi)存 _endFree = NULL;//防止_startFree返回0,而_endFree為一個很大的值,誤認為有內(nèi)存池內(nèi)存可分配 _startFree = (char*)MallocAllocTemplate<0>::Allocate(bytesOfGet); } _heapSize += bytesOfGet; _endFree = _startFree + bytesOfGet; return chunkAlloc(n, nobjs);//會進if } } static void* Refill(size_t n) { int nobjs = 20; char * chunk = chunkAlloc(n, nobjs); Obj* volatile * myFreeList; Obj* ret; Obj * currentObj=NULL, *nextObj=NULL; int i; if (1 == nobjs) return(chunk); myFreeList = _freeList + FreeListIndex(n); ret = (Obj *)chunk; *myFreeList = nextObj = (Obj *)(chunk + n); /*for (i = 1;; i++) { currentObj = nextObj; nextObj = (Obj *)((char *)nextObj + n); if (nobjs - 1 == i) { currentObj->freeListLink = 0; break; } else { currentObj->freeListLink = nextObj; } }*/ // for (i = 0; i < nobjs - 1; ++i) { currentObj = nextObj; nextObj = nextObj + 1; currentObj->_freeListLink = nextObj; } __TRACE_DEBUG("掛載空間到自由鏈表\n"); currentObj->_freeListLink = NULL; return ret; } public: static void Deallocate(void* p, size_t size) { if (size > MAX_BYTES) { MallocAllocTemplate<0>::Deallocate(p, size); __TRACE_DEBUG("調(diào)用一級空間配置器釋放內(nèi)存:ptr:%p,size:%u\n",p,size); } else { Obj * myFreeList = _freeList[FreeListIndex(size)]; ((Obj*)p)->_freeListLink = myFreeList; _freeList[FreeListIndex(size)] = (Obj*)p; __TRACE_DEBUG("掛載到自由鏈表釋放內(nèi)存:ptr:%p,size:%u\n", p, size); } } static void * Allocate(size_t n) { Obj * volatile * myFreeList; Obj * result; if (n > MAX_BYTES) { return(MallocAllocTemplate<1>::Allocate(n)); } myFreeList = _freeList + FreeListIndex(n); result = *myFreeList; if (result == NULL) { void* ret = Refill(RoundUp(n)); __TRACE_DEBUG("分配空間:ptr:%p\n", ret); return ret; } *myFreeList = result->_freeListLink; __TRACE_DEBUG("從自由鏈表直接?。簆tr:%p,size:%u\n", result,n); return result; } }; template<bool threads,int inst> typename DefaultAllocTemplate<threads, inst>::Obj* volatile DefaultAllocTemplate<threads, inst>::_freeList[DefaultAllocTemplate<0, 0>::NFREELISTS] = { 0 };//指針數(shù)組 template<bool threads,int inst> char* DefaultAllocTemplate<threads, inst>::_startFree = NULL; template<bool threads, int inst> char* DefaultAllocTemplate<threads, inst>::_endFree = NULL; template<bool threads, int inst> size_t DefaultAllocTemplate<threads, inst>::_heapSize = 0; # ifdef __USE_MALLOC typedef MallocAllocTemplate<0> Alloc; typedef MallocAllocTemplate<0> Alloc; # else typedef DefaultAllocTemplate<0, 0> Alloc; typedef DefaultAllocTemplate<0, 0> Alloc; #endif template<class T, class Alloc> class SimpleAlloc { 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)); } //將調(diào)用傳遞給配置器的成員函數(shù),可能是第一級也可能是第二級 }; void Test1() { //MallocAllocTemplate<1> d; ////int *p=(int*)MallocAllocTemplate<1>::Allocate(sizeof(int)); //int *p=(int*)d.Allocate(sizeof(int)); //*p = 2; //cout << *p << endl; //d.Deallocate(p, sizeof(int)); //DefaultAllocTemplate<0, 0> a; //int* p1 = (int*)a.Allocate(sizeof(int)); //*p1 = 3; //cout << *p1 << endl; //typedef MallocAllocTemplate<0> Alloc; // 測試調(diào)用一級配置器分配內(nèi)存 cout << " 測試調(diào)用一級配置器分配內(nèi)存 " << endl; char*p1 = SimpleAlloc< char, Alloc>::Allocate(129); SimpleAlloc<char, Alloc>::Deallocate(p1, 129); // 測試調(diào)用二級配置器分配內(nèi)存 cout << " 測試調(diào)用二級配置器分配內(nèi)存 " << endl; char*p2 = SimpleAlloc< char, Alloc>::Allocate(128); char*p3 = SimpleAlloc< char, Alloc>::Allocate(128); char*p4 = SimpleAlloc< char, Alloc>::Allocate(128); char*p5 = SimpleAlloc< char, Alloc>::Allocate(128); SimpleAlloc<char, Alloc>::Deallocate(p2, 128); SimpleAlloc<char, Alloc>::Deallocate(p3, 128); SimpleAlloc<char, Alloc>::Deallocate(p4, 128); SimpleAlloc<char, Alloc>::Deallocate(p5, 128); for (int i = 0; i < 21; ++i) { printf(" 測試第%d次分配 \n", i + 1); char*p = SimpleAlloc< char, Alloc>::Allocate(128); } } // 測試特殊場景 void Test2() { cout << " 測試內(nèi)存池空間不足分配個 " << endl; // 8*20->8*2->320 char*p1 = SimpleAlloc< char, Alloc>::Allocate(8); char*p2 = SimpleAlloc< char, Alloc>::Allocate(8); cout << " 測試內(nèi)存池空間不足, 系統(tǒng)堆進行分配 " << endl; char*p3 = SimpleAlloc< char, Alloc>::Allocate(12); } void Test3() { cout << " 測試系統(tǒng)堆內(nèi)存耗盡 " << endl; SimpleAlloc<char, Alloc>::Allocate(1024 * 1024 * 1024); //SimpleAlloc<char, Alloc>::Allocate(1024*1024*1024); SimpleAlloc<char, Alloc>::Allocate(1024 * 1024); // 不好測試, 說明系統(tǒng)管理小塊內(nèi)存的能力還是很強的。 for (int i = 0; i < 100000; ++i) { char*p1 = SimpleAlloc< char, Alloc>::Allocate(128); } }
運行截圖:
標題名稱:STL——空間配置器
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