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一种利用ADO连接池操作MySQL的解决方案(VC++)
VC++连接MySQL数据库 常用的方式有三种:ADO、mysql++,mysql API ; 本文只讲述ADO的连接方式。
为什么要使用连接池? 对于简单的数据库应用,完全可以先创建一个常连接(此连接永远不关闭,直接数进程退出),但是这样做至少会引起两个问题:(1)资源竞争,多个数据库请求操作不能同时进行,后一请求必须要等到前一请求完成后才能进行;(2)多线程情况下容易出现混乱,甚至出现资源异常释放。还有一种方法,就是使用数据库时创建连接,使用完后关闭连接回收资源。这种方式在数据库操作频繁的情况下会出现严重的效率问题。
数据库连接池
百度百科给出的解释说明如下:
数据库连接池负责分配、管理和释放数据库连接,它允许应用程序重复使用一个现有的数据库连接,而不是再重新建立一个;释放空闲时间超过最大空闲时间的数据库连接来避免因为没有释放数据库连接而引起的数据库连接遗漏。这项技术能明显提高对数据库操作的性能。
使用数据库连接池至少带来以下几个好处:
1、资源复用
数据库连接得到复用,避免了频繁创建、释放引起的系统性能开销。减少了内存碎片以及数据库线程(甚至是进程)的数量。
2、提高系统响应速度
由于数据库连接资源得到复用,这毫无疑问会提高系统的整体响应速度。
3、避免资源泄漏
所有的连接都集中在连接池中统一管理,这可以避免使用单一连接带来的两个问题。
实现原理
一个较为完备的数据库连接池应具备以下几个条件:
(1)实始化时创建一定数据量的连接对象放于连接池中。
(2)连接池对象要有上限。
(3)连接使用完毕后要放回连接池而不是直接释放掉。
(4)长期处于空闲态的连接要释放。
最为完整的实现原理请参考百度百科:数据库连接池。
下面给出一个简单的ADO数据库连接池实现代码:
(说明:以下代码没有考虑到上述原理的第(4)点,读者请根据自身需要自行实现之。)
1 //==================头文件 =====================// 2 //定义数据库连结基本信息结构 3 typedef struct 4 { 5 char db_ip[20]; //ip地址 6 uint32 db_port; //端口 7 char db_user[20];//用户 8 char db_pwd[32];//密码 9 char db_dbname[32];//数据库名 10 }vos_dbxmlinfo_stru; 11 12 13 14 class CXCADOPOOL 15 { 16 protected: 17 CXCADOPOOL(); 18 19 public: 20 virtual ~CXCADOPOOL(void); 21 22 //接口 23 public: 24 void InitConnection(const int iMin, const int iMax); 25 bool ExcuteSql(_bstr_t bSql, bool bCheck = true); 26 bool GetRecordSet(_bstr_t bSql, _RecordsetPtr& pRecord, long lOption = adCmdText, bool bCheck = true); 27 28 29 bool GetItemValue(_RecordsetPtr pRecord, long nIndex, int& nValue); 30 bool GetItemValue(_RecordsetPtr pRecord, long nIndex, UINT64& unValue); 31 bool GetItemValue(_RecordsetPtr pRecord, long nIndex, string& strValue); 32 bool GetItemValue(_RecordsetPtr pRecord, long nIndex, double& fValue); 33 bool GetItemValue(_RecordsetPtr pRecord, long nIndex, float& fValue); 34 bool GetItemValue(_RecordsetPtr pRecord, long nIndex, ULONG & nValue); 35 36 bool GetItemValue(_RecordsetPtr pRecord, long nIndex, short& nValue); 37 bool GetItemValue(_RecordsetPtr pRecord, long nIndex, unsigned char& nValue); 38 bool GetItemValue(_RecordsetPtr pRecord, string fieldname, string& strValue); 39 40 template<class T> 41 bool GetItemValue(_RecordsetPtr pRecord, string fieldname, T& tValue); 42 43 static CXCADOPOOL *Instance(); 44 _ConnectionPtr *GetTransConnection(); 45 void SendTransCompMsg(_ConnectionPtr *pConptr); 46 bool ExecuteTransSql(_ConnectionPtr *pConptr, _bstr_t bSql); 47 private: 48 bool CreateDBConnection(_ConnectionPtr & conptr); //返回一个连接 49 void GetConnectionString(string &strConnect); 50 _ConnectionPtr * GetConnectionPtr(); 51 void ReleaseConnectionPtr(_ConnectionPtr &conptr); 52 void InitDBConfig(); 53 bool ExcuteWithoutCheck(_ConnectionPtr &conptr, _bstr_t bSql); 54 bool GetRecordSetWithoutCheck(_ConnectionPtr &conptr, _bstr_t bSql, _RecordsetPtr& pRecord, long lOption = adCmdText); 55 static DWORD WINAPI IdleConnThreadFunc(LPVOID lParam); 56 private: 57 58 queue<_ConnectionPtr *> m_qConn; 59 int m_MinConNum; //最小连接数 60 int m_MaxConNum; //最大连接数 61 int m_CurrentNum; //当前连接数 62 63 HANDLE m_Mutex; 64 HANDLE m_hEvent; 65 HANDLE m_hThread; 66 DWORD m_dwThreadId; 67 HANDLE m_hThreadEvent; 68 string m_strConnect; 69 static CXCADOPOOL* _instance; 70 public: 71 vos_dbxmlinfo_stru m_stDBInfo; 72 73 }; 74 75 template<class T> 76 bool CXCADOPOOL::GetItemValue(_RecordsetPtr pRecord, string fieldname, T& tValue) 77 { 78 try 79 { 80 ASSERT_RECORDSET(pRecord); 81 _variant_t vart = pRecord->GetCollect(_variant_t(fieldname.c_str())); 82 (tValue =http://www.mamicode.com/ (T)(vart)); 83 } 84 catch (_com_error &) 85 { 86 return false; 87 } 88 return true; 89 } 90 extern CXCADOPOOL *pAdoPool; 91 //===================.CPP文件=====================// 92 93 bool CXCADOPOOL::GetItemValue( _RecordsetPtr pRecord, long nIndex, int& nValue ) 94 { 95 try 96 { 97 ASSERT_RECORDSET(pRecord); 98 99 nValue = http://www.mamicode.com/(int)(pRecord->GetFields()->GetItem(nIndex)->Value);100 }101 catch (_com_error &)102 {103 return false;104 }105 return true;106 }107 108 bool CXCADOPOOL::GetItemValue(_RecordsetPtr pRecord, long nIndex, UINT64& unValue)109 {110 try111 {112 ASSERT_RECORDSET(pRecord);113 114 unValue = http://www.mamicode.com/(UINT64)pRecord->GetFields()->GetItem(nIndex)->Value;115 }116 catch (_com_error &)117 {118 return false;119 }120 return true;121 }122 123 124 bool CXCADOPOOL::GetItemValue(_RecordsetPtr pRecord, long nIndex, ULONG& nValue)125 {126 127 try128 {129 ASSERT_RECORDSET(pRecord);130 131 nValue = http://www.mamicode.com/(ULONG)pRecord->GetFields()->GetItem(nIndex)->Value;132 }133 catch (_com_error &)134 {135 return false;136 }137 return true;138 139 }140 bool CXCADOPOOL::GetItemValue(_RecordsetPtr pRecord, long nIndex, string& strValue)141 {142 try143 {144 ASSERT_RECORDSET(pRecord);145 146 _variant_t vart = pRecord->GetFields()->GetItem(nIndex)->Value;147 if (vart.vt == VT_NULL)148 return true;149 150 strValue = http://www.mamicode.com/(std::string)(bstr_t)vart;151 }152 catch (_com_error &)153 {154 return false;155 }156 157 return true;158 }159 160 bool CXCADOPOOL::GetItemValue(_RecordsetPtr pRecord, long nIndex, double& fValue)161 {162 try163 {164 ASSERT_RECORDSET(pRecord);165 166 fValue = http://www.mamicode.com/(double)pRecord->GetFields()->GetItem(nIndex)->Value;167 }168 catch (_com_error &)169 {170 return false;171 }172 173 return true;174 175 }176 177 178 bool CXCADOPOOL::GetItemValue(_RecordsetPtr pRecord, long nIndex, float& fValue)179 {180 try181 {182 ASSERT_RECORDSET(pRecord);183 184 fValue = http://www.mamicode.com/(float)pRecord->GetFields()->GetItem(nIndex)->Value;185 }186 catch (_com_error &)187 {188 return false;189 }190 return true;191 }192 193 bool CXCADOPOOL::GetItemValue(_RecordsetPtr pRecord, long nIndex, short &sValue)194 {195 try196 {197 ASSERT_RECORDSET(pRecord);198 sValue = http://www.mamicode.com/(short)pRecord->GetFields()->GetItem(nIndex)->Value;199 }200 catch (_com_error &)201 {202 return false;203 }204 return true;205 }206 207 bool CXCADOPOOL::GetItemValue(_RecordsetPtr pRecord, long nIndex, unsigned char& cValue)208 {209 try210 {211 ASSERT_RECORDSET(pRecord);212 cValue = http://www.mamicode.com/(unsigned char)pRecord->GetFields()->GetItem(nIndex)->Value;213 }214 catch (_com_error &)215 {216 return false;217 }218 return true;219 }220 221 222 CXCADOPOOL *pAdoPool = NULL;223 224 CXCADOPOOL *CXCADOPOOL::_instance = NULL;225 226 227 CXCADOPOOL::CXCADOPOOL()228 {229 230 ::CoInitialize(NULL);231 232 InitDBConfig();233 GetConnectionString(m_strConnect);234 m_Mutex = ::CreateMutex(NULL, FALSE, NULL);235 m_hEvent = ::CreateEvent(NULL, TRUE, FALSE, NULL);236 m_CurrentNum = 0;237 238 m_hThreadEvent = ::CreateEvent(NULL, FALSE, FALSE, NULL);239 m_hThread = ::CreateThread(NULL, 0,(LPTHREAD_START_ROUTINE)IdleConnThreadFunc, this, 0, &m_dwThreadId);240 WaitForSingleObject(m_hThreadEvent, INFINITE);241 CloseHandle(m_hThreadEvent);242 245 }246 247 CXCADOPOOL::~CXCADOPOOL(void)248 {249 ::CoUninitialize();250 }251 252 void CXCADOPOOL::InitConnection(const int iMin, const int iMax)253 {254 static bool bInitial = true;255 if (bInitial)256 {257 m_MinConNum = iMin;258 m_MaxConNum = iMax;259 for (int i = 0; i < iMin; i++)260 {261 _ConnectionPtr *conptr = new _ConnectionPtr;262 if (CreateDBConnection(*conptr))263 {264 WaitForSingleObject(m_Mutex,INFINITE);265 m_qConn.push(conptr);266 m_CurrentNum++;267 ReleaseMutex(m_Mutex);268 }269 }270 bInitial = false;271 }272 }273 274 bool CXCADOPOOL::CreateDBConnection(_ConnectionPtr & conptr)275 {276 try277 {278 //conptr.CreateInstance("ADODB.Connection");279 conptr.CreateInstance(__uuidof(Connection));280 281 HRESULT hr = conptr->Open(m_strConnect.c_str(), "", "", adModeUnknown);282 if (FAILED(hr))283 {284 return false;285 } 286 }287 catch (_com_error &e)288 {289 return false;290 }291 return true;292 }293 294 void CXCADOPOOL::GetConnectionString(string &strConnect)295 {296 USES_CONVERSION;297 CString str;298 str.Format(_T("Driver=MySQL ODBC 5.3 Unicode Driver;SERVER=%s;UID=%s;PWD=%s;DATABASE=%s;PORT=%d"),299 A2T((char*)m_stDBInfo.db_ip), A2T((char*)m_stDBInfo.db_user), A2T((char*)m_stDBInfo.db_pwd), A2T((char*)m_stDBInfo.db_dbname), m_stDBInfo.db_port);300 strConnect = T2A(str);301 302 }303 304 void CXCADOPOOL::InitDBConfig()305 {306 GetPrivateProfileStringA("DBInfo", "host", "localhost", m_stDBInfo.db_ip, 20, ".\\DB.ini");307 m_stDBInfo.db_port = GetPrivateProfileIntA("DBInfo", "port", 3306, ".\\DB.ini");308 GetPrivateProfileStringA("DBInfo", "dbname", "", m_stDBInfo.db_dbname, 32, ".\\DB.ini");309 GetPrivateProfileStringA("DBInfo", "user", "", m_stDBInfo.db_user, 20, ".\\DB.ini");310 311 char pbuf_text[255] = { 0 };312 GetPrivateProfileStringA("DBInfo", "password", "", pbuf_text, 255, ".\\DB.ini"); 313 }314 315 bool CXCADOPOOL::ExcuteSql(_bstr_t bSql, bool bCheck)316 {317 326 _ConnectionPtr *conptr = GetConnectionPtr();327 bool bExec = ExcuteWithoutCheck(*conptr, bSql);330 PostThreadMessage(m_dwThreadId, WM_USER_DB_THREAD_MSG, (WPARAM)conptr,NULL);331 return bExec;332 }333 334 _ConnectionPtr * CXCADOPOOL::GetConnectionPtr()335 {336 //找出空闲连接337 while (1)338 {339 WaitForSingleObject(m_Mutex, INFINITE);340 _ConnectionPtr *conptr;341 if (m_qConn.empty())342 {343 if (m_CurrentNum < m_MaxConNum)344 {345 conptr = new _ConnectionPtr;346 if (CreateDBConnection(*conptr))347 {348 m_CurrentNum++;349 }350 }351 else352 {353 //等待连接释放354 ResetEvent(m_hEvent);355 ReleaseMutex(m_Mutex);356 WaitForSingleObject(m_hEvent, INFINITE);357 continue;358 }359 }360 else361 {362 conptr = m_qConn.front();363 m_qConn.pop();364 }365 366 ReleaseMutex(m_Mutex);367 return conptr;368 }369 370 371 }372 373 DWORD WINAPI CXCADOPOOL::IdleConnThreadFunc(LPVOID lParam)374 {375 MSG msg;376 PeekMessage(&msg, NULL, WM_USER, WM_USER, PM_NOREMOVE);377 CXCADOPOOL *pCXCADOPOOL = static_cast<CXCADOPOOL *>(lParam);378 SetEvent(pCXCADOPOOL->m_hThreadEvent);379 380 while (1)381 {382 if (GetMessage(&msg, 0, 0, 0))383 {384 switch (msg.message)385 {386 case WM_USER_DB_THREAD_MSG:387 {388 _ConnectionPtr *conptr = (_ConnectionPtr *) (msg.wParam);389 390 WaitForSingleObject(pCXCADOPOOL->m_Mutex,INFINITE);391 pCXCADOPOOL->m_qConn.push(conptr);392 ReleaseMutex(pCXCADOPOOL->m_Mutex);393 SetEvent(pCXCADOPOOL->m_hEvent);394 395 }396 default:397 break;398 }399 }400 }401 return 0;402 }403 404 void CXCADOPOOL::ReleaseConnectionPtr(_ConnectionPtr &conptr)405 {406 if (conptr != NULL)407 {408 conptr->Close(); //关闭连接409 conptr.Release(); //释放内存410 conptr = NULL;411 412 }413 414 }415 416 bool CXCADOPOOL::ExcuteWithoutCheck(_ConnectionPtr &conptr, _bstr_t bSql)417 {418 int i = 0;419 while (i < 3)420 {421 try422 {423 if (0 != i)424 {425 ReleaseConnectionPtr(conptr);426 CreateDBConnection(conptr);427 }428 ++i;429 VARIANT nRecordAffected = { 0 };430 conptr->Execute(bSql, &nRecordAffected, adCmdText);431 //ReleaseMutex(m_Mutex);432 433 if (nRecordAffected.date < 0)434 {435 return false;436 }437 break;438 }439 catch (_com_error&e)440 {441 }442 catch (...)443 {444 445 }446 }447 if (i == 3)448 {449 return false;450 }451 452 return true;453 }454 455 bool CXCADOPOOL::GetRecordSet(_bstr_t bSql, _RecordsetPtr& pRecord, long lOption /*= adCmdText*/, bool bCheck)456 { 465 _ConnectionPtr *conptr = GetConnectionPtr();466 bool bExec = GetRecordSetWithoutCheck(*conptr, bSql, pRecord,lOption);467 PostThreadMessage(m_dwThreadId, WM_USER_DB_THREAD_MSG, (WPARAM)conptr, NULL);468 return bExec;469 }470 471 bool CXCADOPOOL::GetRecordSetWithoutCheck(_ConnectionPtr &conptr, _bstr_t bSql, _RecordsetPtr& pRecord, long lOption /*= adCmdText*/)472 {473 for (int i = 0; i < 3; ++i)474 {475 try476 {477 if (0 != i)478 {479 ReleaseConnectionPtr(conptr);480 CreateDBConnection(conptr);481 }482 HRESULT hr = pRecord.CreateInstance(__uuidof(Recordset));483 if (SUCCEEDED(hr))484 {485 pRecord->CursorLocation = adUseClient;486 HRESULT ht = pRecord->Open(bSql, _variant_t((IDispatch *)conptr), adOpenDynamic, adLockOptimistic, lOption);487 return SUCCEEDED(ht);488 }489 return false;490 }491 catch (_com_error&e)492 { }493 catch (...)494 {495 }496 }497 return false;498 }499 500 bool CXCADOPOOL::GetItemValue(_RecordsetPtr pRecord, string fieldname, string& strValue)501 {502 try503 {504 ASSERT_RECORDSET(pRecord);505 _variant_t vart = pRecord->GetCollect(_variant_t(fieldname.c_str()));506 strValue = http://www.mamicode.com/(std::string)(bstr_t)vart;507 }508 catch (_com_error &)509 {510 return false;511 }512 return true;513 }514 515 CXCADOPOOL * CXCADOPOOL::Instance()516 {517 if (NULL == _instance)518 {519 _instance = new CXCADOPOOL;520 }521 return _instance;522 }523 524 _ConnectionPtr * CXCADOPOOL::GetTransConnection()525 {526 _ConnectionPtr *pConptr = this->GetConnectionPtr();527 //执行一个查询语句验证下确保当前连接可用528 if ((*pConptr)->State != adStateOpen)529 {530 ReleaseConnectionPtr(*pConptr);531 CreateDBConnection(*pConptr);532 }533 return pConptr;534 }535 536 void CXCADOPOOL::SendTransCompMsg(_ConnectionPtr *pConptr)537 {538 PostThreadMessage(m_dwThreadId, WM_USER_DB_THREAD_MSG, (WPARAM)pConptr, NULL);539 }540 541 bool CXCADOPOOL::ExecuteTransSql(_ConnectionPtr *pConptr, _bstr_t bSql)542 {543 return ExcuteWithoutCheck(*pConptr, bSql);544 }545 546 547 548 549
一种利用ADO连接池操作MySQL的解决方案(VC++)