__malloc_alloc_template分配器:该分配器是对malloc、realloc以及free的封装：

当调用malloc和realloc申请不到内存空间的时候，会改调用oom_malloc()和oom_realloc()，这两个函数会反复调用用户传递过来的out of memory handler处理函数，直到能用malloc或者realloc申请到内存为止。

如果用户没有传递__malloc_alloc_oom_handler，__malloc_alloc_template会抛出__THROW_BAD_ALLOC异常。所以，内存不足的处理任务就交给类客户去完成。

__default_alloc_template分配器

　　这个分配器采用了内存池的思想，有效地避免了内碎片的问题（顺便一句话介绍一下内碎片和外碎片：内碎片是已被分配出去但是用不到的内存空间，外碎片是由于大小太小而无法分配出去的空闲块）。

　如果申请的内存块大于128bytes，就将申请的操作移交__malloc_alloc_template分配器去处理；如果申请的区块大小小于128bytes时，就从本分配器维护的内存池中分配内存。

　　分配器用空闲链表的方式维护内存池中的空闲空间。

#include<iostream>#include<stdarg.h>usingnamespacestd;#define__DEBUG__staticstringGetFileName(conststring&path){charch='/';#ifdef_WIN32ch='\\';#endifsize_tpos=path.rfind(ch);if(pos==string::npos)returnpath;elsereturnpath.substr(pos+1);}//用于调试追溯的traceloginlinestaticvoid__trace_debug(constchar*function,constchar*filename,intline,char*format,...){#ifdef__DEBUG__//输出调用函数的信息fprintf(stdout,"【%s:%d】%s",GetFileName(filename).c_str(),line,function);//输出用户打的trace信息va_listargs;va_start(args,format);vfprintf(stdout,format,args);va_end(args);#endif}#define__TRACE_DEBUG(...)\__trace_debug(__FUNCTION__,__FILE__,__LINE__,__VA_ARGS__);typedefvoid(*MallocAllocHandler)();template<intinst>classMallocAllocTemplate{protected:staticMallocAllocHandler_handler;staticvoid*Oom_Malloc(size_tn){MallocAllocHandlerhandler=NULL;void*ret=NULL;while(1){handler=_handler;if(handler==NULL){cout<<"outofmemory"<<endl;//exit(1);}(*handler)();ret=malloc(n);if(ret)returnret;}}public:staticvoid*Allocate(size_tn){void*result=malloc(n);if(0==result)result=Oom_Malloc(n);__TRACE_DEBUG("调用一级空间配置器开辟内存：ptr:%p,size:%u\n",result,n);returnresult;}staticvoidDeallocate(void*p,size_tn){free(p);__TRACE_DEBUG("调用一级空间配置器释放内存：ptr:%p,size:%u\n",p,n);}staticvoid(*SetMallocHandler(MallocAllocHandlerf))(){void(*old)()=_handler;_handler=f;return(old);}};template<intinst>MallocAllocHandlerMallocAllocTemplate<inst>::_handler=NULL;template<boolthreads,intinst>classDefaultAllocTemplate{enum{ALIGN=8};enum{MAX_BYTES=128};enum{NFREELISTS=MAX_BYTES/ALIGN};unionObj{unionObj*_freeListLink;char_clientData[1];/*Theclientseesthis.*/};staticObj*volatile_freeList[NFREELISTS];//指针数组staticchar*_startFree;staticchar*_endFree;staticsize_t_heapSize;staticsize_tFreeListIndex(size_tbytes){return(((bytes)+ALIGN-1)/ALIGN-1);}staticsize_tRoundUp(size_tbytes){return(((bytes)+ALIGN-1)&~(ALIGN-1));}staticchar*chunkAlloc(size_tn,int&nobjs){char*ret=NULL;size_ttotalBytes=n*nobjs;size_tfreeLeft=_endFree-_startFree;if(freeLeft>=totalBytes){ret=_startFree;_startFree+=totalBytes;__TRACE_DEBUG("内存池足够分配空间：ptr:%p,size:%u\n",ret,totalBytes);return(ret);}elseif(freeLeft>=n){nobjs=freeLeft/n;totalBytes=n*nobjs;ret=_startFree;_startFree+=totalBytes;__TRACE_DEBUG("内存池只有空间：ptr:%p,size:%u\n",ret,totalBytes);return(ret);}else{size_tbytesOfGet=2*totalBytes+RoundUp(_heapSize>>4);//将剩下的小块内存挂载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(inti=n;i<MAX_BYTES;i+=ALIGN){myFreeList=_freeList[FreeListIndex(i)];if(myFreeList!=NULL){p=myFreeList;myFreeList=myFreeList->_freeListLink;_startFree=(char*)p;_endFree=_startFree+i;returnchunkAlloc(n,nobjs);//会进入elseif}}//空闲链表无比n大的内存_endFree=NULL;//防止_startFree返回0，而_endFree为一个很大的值，误认为有内存池内存可分配_startFree=(char*)MallocAllocTemplate<0>::Allocate(bytesOfGet);}_heapSize+=bytesOfGet;_endFree=_startFree+bytesOfGet;returnchunkAlloc(n,nobjs);//会进if}}staticvoid*Refill(size_tn){intnobjs=20;char*chunk=chunkAlloc(n,nobjs);Obj*volatile*myFreeList;Obj*ret;Obj*currentObj=NULL,*nextObj=NULL;inti;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("挂载空间到自由链表\n");currentObj->_freeListLink=NULL;returnret;}public:staticvoidDeallocate(void*p,size_tsize){if(size>MAX_BYTES){MallocAllocTemplate<0>::Deallocate(p,size);__TRACE_DEBUG("调用一级空间配置器释放内存：ptr:%p,size:%u\n",p,size);}else{Obj*myFreeList=_freeList[FreeListIndex(size)];((Obj*)p)->_freeListLink=myFreeList;_freeList[FreeListIndex(size)]=(Obj*)p;__TRACE_DEBUG("挂载到自由链表释放内存：ptr:%p,size:%u\n",p,size);}}staticvoid*Allocate(size_tn){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("分配空间：ptr:%p\n",ret);returnret;}*myFreeList=result->_freeListLink;__TRACE_DEBUG("从自由链表直接取：ptr:%p,size:%u\n",result,n);returnresult;}};template<boolthreads,intinst>typenameDefaultAllocTemplate<threads,inst>::Obj*volatileDefaultAllocTemplate<threads,inst>::_freeList[DefaultAllocTemplate<0,0>::NFREELISTS]={0};//指针数组template<boolthreads,intinst>char*DefaultAllocTemplate<threads,inst>::_startFree=NULL;template<boolthreads,intinst>char*DefaultAllocTemplate<threads,inst>::_endFree=NULL;template<boolthreads,intinst>size_tDefaultAllocTemplate<threads,inst>::_heapSize=0;#ifdef__USE_MALLOCtypedefMallocAllocTemplate<0>Alloc;typedefMallocAllocTemplate<0>Alloc;#elsetypedefDefaultAllocTemplate<0,0>Alloc;typedefDefaultAllocTemplate<0,0>Alloc;#endiftemplate<classT,classAlloc>classSimpleAlloc{public:staticT*Allocate(size_tn){return0==n?0:(T*)Alloc::Allocate(n*sizeof(T));}staticT*Allocate(void){return(T*)Alloc::Allocate(sizeof(T));}staticvoidDeallocate(T*p,size_tn){if(0!=n)Alloc::Deallocate(p,n*sizeof(T));}staticvoidDeallocate(T*p){Alloc::Deallocate(p,sizeof(T));}//将调用传递给配置器的成员函数，可能是第一级也可能是第二级};voidTest1(){//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;//typedefMallocAllocTemplate<0>Alloc;//测试调用一级配置器分配内存cout<<"测试调用一级配置器分配内存"<<endl;char*p1=SimpleAlloc<char,Alloc>::Allocate(129);SimpleAlloc<char,Alloc>::Deallocate(p1,129);//测试调用二级配置器分配内存cout<<"测试调用二级配置器分配内存"<<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(inti=0;i<21;++i){printf("测试第%d次分配\n",i+1);char*p=SimpleAlloc<char,Alloc>::Allocate(128);}}//测试特殊场景voidTest2(){cout<<"测试内存池空间不足分配个"<<endl;//8*20->8*2->320char*p1=SimpleAlloc<char,Alloc>::Allocate(8);char*p2=SimpleAlloc<char,Alloc>::Allocate(8);cout<<"测试内存池空间不足，系统堆进行分配"<<endl;char*p3=SimpleAlloc<char,Alloc>::Allocate(12);}voidTest3(){cout<<"测试系统堆内存耗尽"<<endl;SimpleAlloc<char,Alloc>::Allocate(1024*1024*1024);//SimpleAlloc<char,Alloc>::Allocate(1024*1024*1024);SimpleAlloc<char,Alloc>::Allocate(1024*1024);//不好测试，说明系统管理小块内存的能力还是很强的。for(inti=0;i<100000;++i){char*p1=SimpleAlloc<char,Alloc>::Allocate(128);}}

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