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這篇文章主要講解了“C++中內(nèi)存池的原理及實(shí)現(xiàn)方法是什么”,文中的講解內(nèi)容簡(jiǎn)單清晰,易于學(xué)習(xí)與理解,下面請(qǐng)大家跟著小編的思路慢慢深入,一起來研究和學(xué)習(xí)“C++中內(nèi)存池的原理及實(shí)現(xiàn)方法是什么”吧!
C++程序默認(rèn)的內(nèi)存管理(new,delete,malloc,free)會(huì)頻繁地在堆上分配和釋放內(nèi)存,導(dǎo)致性能的損失,產(chǎn)生大量的內(nèi)存碎片,降低內(nèi)存的利用率。默認(rèn)的內(nèi)存管理因?yàn)楸辉O(shè)計(jì)的比較通用,所以在性能上并不能做到極致。
因此,很多時(shí)候需要根據(jù)業(yè)務(wù)需求設(shè)計(jì)專用內(nèi)存管理器,便于針對(duì)特定數(shù)據(jù)結(jié)構(gòu)和使用場(chǎng)合的內(nèi)存管理,比如:內(nèi)存池。
內(nèi)存池的思想是,在真正使用內(nèi)存之前,預(yù)先申請(qǐng)分配一定數(shù)量、大小預(yù)設(shè)的內(nèi)存塊留作備用。當(dāng)有新的內(nèi)存需求時(shí),就從內(nèi)存池中分出一部分內(nèi)存塊,若內(nèi)存塊不夠再繼續(xù)申請(qǐng)新的內(nèi)存,當(dāng)內(nèi)存釋放后就回歸到內(nèi)存塊留作后續(xù)的復(fù)用,使得內(nèi)存使用效率得到提升,一般也不會(huì)產(chǎn)生不可控制的內(nèi)存碎片。
算法原理:
1.預(yù)申請(qǐng)一個(gè)內(nèi)存區(qū)chunk,將內(nèi)存中按照對(duì)象大小劃分成多個(gè)內(nèi)存塊block
2.維持一個(gè)空閑內(nèi)存塊鏈表,通過指針相連,標(biāo)記頭指針為第一個(gè)空閑塊
3.每次新申請(qǐng)一個(gè)對(duì)象的空間,則將該內(nèi)存塊從空閑鏈表中去除,更新空閑鏈表頭指針
4.每次釋放一個(gè)對(duì)象的空間,則重新將該內(nèi)存塊加到空閑鏈表頭
5.如果一個(gè)內(nèi)存區(qū)占滿了,則新開辟一個(gè)內(nèi)存區(qū),維持一個(gè)內(nèi)存區(qū)的鏈表,同指針相連,頭指針指向最新的內(nèi)存區(qū),新的內(nèi)存塊從該區(qū)內(nèi)重新劃分和申請(qǐng)
如圖所示:
memory_pool.hpp
#ifndef _MEMORY_POOL_H_ #define _MEMORY_POOL_H_ #include <stdint.h> #include <mutex> template<size_t BlockSize, size_t BlockNum = 10> class MemoryPool { public: MemoryPool() { std::lock_guard<std::mutex> lk(mtx); // avoid race condition // init empty memory pointer free_block_head = NULL; mem_chunk_head = NULL; } ~MemoryPool() { std::lock_guard<std::mutex> lk(mtx); // avoid race condition // destruct automatically MemChunk* p; while (mem_chunk_head) { p = mem_chunk_head->next; delete mem_chunk_head; mem_chunk_head = p; } } void* allocate() { std::lock_guard<std::mutex> lk(mtx); // avoid race condition // allocate one object memory // if no free block in current chunk, should create new chunk if (!free_block_head) { // malloc mem chunk MemChunk* new_chunk = new MemChunk; new_chunk->next = NULL; // set this chunk's first block as free block head free_block_head = &(new_chunk->blocks[0]); // link the new chunk's all blocks for (int i = 1; i < BlockNum; i++) new_chunk->blocks[i - 1].next = &(new_chunk->blocks[i]); new_chunk->blocks[BlockNum - 1].next = NULL; // final block next is NULL if (!mem_chunk_head) mem_chunk_head = new_chunk; else { // add new chunk to chunk list mem_chunk_head->next = new_chunk; mem_chunk_head = new_chunk; } } // allocate the current free block to the object void* object_block = free_block_head; free_block_head = free_block_head->next; return object_block; } void* allocate(size_t size) { std::lock_guard<std::mutex> lk(array_mtx); // avoid race condition for continuous memory // calculate objects num int n = size / BlockSize; // allocate n objects in continuous memory // FIXME: make sure n > 0 void* p = allocate(); for (int i = 1; i < n; i++) allocate(); return p; } void deallocate(void* p) { std::lock_guard<std::mutex> lk(mtx); // avoid race condition // free object memory FreeBlock* block = static_cast<FreeBlock*>(p); block->next = free_block_head; // insert the free block to head free_block_head = block; } private: // free node block, every block size exactly can contain one object struct FreeBlock { unsigned char data[BlockSize]; FreeBlock* next; }; FreeBlock* free_block_head; // memory chunk, every chunk contains blocks number with fixed BlockNum struct MemChunk { FreeBlock blocks[BlockNum]; MemChunk* next; }; MemChunk* mem_chunk_head; // thread safe related std::mutex mtx; std::mutex array_mtx; }; #endif // !_MEMORY_POOL_H_
main.cpp
#include <iostream> #include "memory_pool.hpp" class MyObject { public: MyObject(int x): data(x) { //std::cout << "contruct object" << std::endl; } ~MyObject() { //std::cout << "destruct object" << std::endl; } int data; // override new and delete to use memory pool void* operator new(size_t size); void operator delete(void* p); void* operator new[](size_t size); void operator delete[](void* p); }; // define memory pool with block size as class size MemoryPool<sizeof(MyObject), 3> gMemPool; void* MyObject::operator new(size_t size) { //std::cout << "new object space" << std::endl; return gMemPool.allocate(); } void MyObject::operator delete(void* p) { //std::cout << "free object space" << std::endl; gMemPool.deallocate(p); } void* MyObject::operator new[](size_t size) { // TODO: not supported continuous memoery pool for now //return gMemPool.allocate(size); return NULL; } void MyObject::operator delete[](void* p) { // TODO: not supported continuous memoery pool for now //gMemPool.deallocate(p); } int main(int argc, char* argv[]) { MyObject* p1 = new MyObject(1); std::cout << "p1 " << p1 << " " << p1->data<< std::endl; MyObject* p2 = new MyObject(2); std::cout << "p2 " << p2 << " " << p2->data << std::endl; delete p2; MyObject* p3 = new MyObject(3); std::cout << "p3 " << p3 << " " << p3->data << std::endl; MyObject* p4 = new MyObject(4); std::cout << "p4 " << p4 << " " << p4->data << std::endl; MyObject* p5 = new MyObject(5); std::cout << "p5 " << p5 << " " << p5->data << std::endl; MyObject* p6 = new MyObject(6); std::cout << "p6 " << p6 << " " << p6->data << std::endl; delete p1; delete p2; //delete p3; delete p4; delete p5; delete p6; getchar(); return 0; }
運(yùn)行結(jié)果
p1 00000174BEDE0440 1
p2 00000174BEDE0450 2
p3 00000174BEDE0450 3
p4 00000174BEDE0460 4
p5 00000174BEDD5310 5
p6 00000174BEDD5320 6
可以看到內(nèi)存地址是連續(xù),并且回收一個(gè)節(jié)點(diǎn)后,依然有序地開辟內(nèi)存
對(duì)象先開辟內(nèi)存再構(gòu)造,先析構(gòu)再釋放內(nèi)存
注意
在內(nèi)存分配和釋放的環(huán)節(jié)需要加鎖來保證線程安全
還沒有實(shí)現(xiàn)對(duì)象數(shù)組的分配和釋放
感謝各位的閱讀,以上就是“C++中內(nèi)存池的原理及實(shí)現(xiàn)方法是什么”的內(nèi)容了,經(jīng)過本文的學(xué)習(xí)后,相信大家對(duì)C++中內(nèi)存池的原理及實(shí)現(xiàn)方法是什么這一問題有了更深刻的體會(huì),具體使用情況還需要大家實(shí)踐驗(yàn)證。這里是億速云,小編將為大家推送更多相關(guān)知識(shí)點(diǎn)的文章,歡迎關(guān)注!
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