OCCI线程安全

线程是任务调度的基本单位，一个进程中可以有多个线程，每个线程有自己的堆栈空间，

进程中的代码段、数据段和堆栈对进程中的线程是可见的。在使用线程时通常都要考虑数据的安全访问。

常用的线程同步方法有:

互斥变量

读写锁

条件变量

屏障

自旋锁(用于CPU，锁住后CPU将不执行其他事情，即一直等待)

在OCCI程序中使能线程安全，则应指定THREADED_MUTEXED选项创建运行环境

例如：

	Environment *env =

		 Environment::createEnvironment(Environment::THREADED_MUTEXED)

注意：

如果应用程序是单线程，则使用默认值创建环境即可；

如果指定THREADED_MUTEXED选项创建将会影响应用程序性能。

OCCI中的线程安全仅仅指的是Environment、Map、ConnectionPool、

StatelessConnectionPool和Connection对象。对于Statement、ResultSet、

SQLException、Stream等不是线程安全的，因此不应该在多个线程中共享。

以下例子创建一个只有一个连接的无状态连接池，创建两个线程去竞争从池中得到连接

当以线程安全创建环境时程序运行正常，当使用默认选项创建环境时，程序将抛出异常：

what():  ORA-03117: two-task save area overflow

#include <iostream>

#include <cstdlib>

#include <pthread.h>

#include <unistd.h>

#include <occi.h>

#define USERNAME	"scott"

#define PASSWORD	"scott"

#define DBNAME		"//192.168.42.135:1521/orcl"

#define MAXCON	1

#define MINCON	0

#define INCCON	1	

using namespace oracle::occi;

using namespace std;

void *displayAllRows(void *arg);

void *updateRow(void *arg);

int main(void)

{

	Environment *env = Environment::createEnvironment(Environment::THREADED_MUTEXED);

	//创建无状态连接池

	StatelessConnectionPool *scp =

		env->createStatelessConnectionPool(

			USERNAME, PASSWORD, DBNAME, MAXCON, MINCON, INCCON,

			StatelessConnectionPool::HOMOGENEOUS);

	//设置池中的连接空闲超时时间，超时后OCCI会自动释放此连接，需要时在创建

	scp->setTimeOut(10);

	cout << "*****************Information**************************" << endl;

	cout << "Open Connection : " << scp->getOpenConnections() << endl;

	cout << "Busy Connection : " << scp->getBusyConnections() << endl;

	cout << "Time Out Connection : " << scp->getTimeOut() << endl;

	cout << "******************************************************" << endl;

	pthread_t tid_1, tid_2;

	int err = 0;

	err = pthread_create(&tid_1, NULL, displayAllRows, (void *)scp);

	if (err != 0) {

		cout << "create thread failure for tid_1." << endl;

	} else {

		cout << ">> create thread successful for tid_1." << endl;

	}

	err = pthread_create(&tid_2, NULL, updateRow, (void *)scp);

	if (err != 0) {

		cout << "create thread failure for tid_2." << endl;

	} else {

		cout << ">> create thread successful for tid_2." << endl;

	}

	pthread_join(tid_1, (void **)NULL);

	pthread_join(tid_2, (void **)NULL);

	env->terminateStatelessConnectionPool(scp);

	Environment::terminateEnvironment(env);

	return 0;

}

void *displayAllRows(void *arg)

{

	StatelessConnectionPool *scp = (StatelessConnectionPool *)arg;

	for ( ; ; )

	{

		std::cout << ">>>> displayAllRows thread runing [" << long(pthread_self()) << "]" << std::endl;

		Connection *conn = scp->getConnection("");

		string sqlStmt = "SELECT * FROM DEPT WHERE DEPTNO=60";

		Statement *stmt = conn->createStatement(sqlStmt);

		ResultSet *rset = stmt->executeQuery();

		try {

			while (rset->next()) {

				cout << int(rset->getNumber(1)) << "	";

				cout << rset->getString(2) << "	";

				cout << rset->getString(3) << "	";

				cout << endl;

			}

		}catch(SQLException &ex) {

			cout << "display all rows failure." << endl;

			cout << ex.getMessage();

			cout << endl;

		}

		sleep(5);

		stmt->closeResultSet(rset);

		conn->terminateStatement(stmt);

		scp->releaseConnection(conn, "");

	}

	pthread_exit((void *)0);

}

void *updateRow(void *arg)

{

	StatelessConnectionPool *scp = (StatelessConnectionPool*)arg;

	for ( ; ; )

	{

		std::cout << ">>> updateRow thread running [" << long(pthread_self()) << "]" << std::endl;

		Connection *conn = scp->getConnection("");

		string sqlStmt = "UPDATE DEPT SET LOC=:deptLocal WHERE DEPTNO=51";

		Statement *stmt = conn->createStatement(sqlStmt);

		try {

			stmt->setString(1, "ShangHai");

			stmt->executeUpdate();

			conn->commit();

		} catch(SQLException &ex) {

			cout << "update row failure." << endl;

			cout << ex.getMessage();

			cout << endl;

		}

		conn->terminateStatement(stmt);

		scp->releaseConnection(conn, "");

		sleep(1);

	}

	pthread_exit((void *)0);

}

巴特西

OCCI线程安全

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