MySQL C ++连接器中的内存泄漏

时间：2012-10-26 07:10:35

标签： c++ mysql mysql-connector

我正在使用MySQL C ++连接器。 Valgrind显示每个连接泄漏192个字节。 它只是在线程环境中泄漏内存而没有线程，它没有泄漏任何内存。我做错了什么？我是否需要调用其他一些功能进行清理？ 示例代码：

#include <pthread.h>
#include <iostream>
#include <cppconn/driver.h>
#include <cppconn/exception.h>
#include <cppconn/resultset.h>
#include <cppconn/statement.h>
#include <cppconn/prepared_statement.h>

using namespace std;

void* test(void* arg) {

  try {
    sql::Driver *driver;
    sql::Connection *con;
    /* Create a connection */
    driver = get_driver_instance();
    con = driver->connect("tcp://127.0.0.1:3306", "root", "root");
    /* Connect to the MySQL test database */
    con->setSchema("test");
    delete con;
  } catch (sql::SQLException &e) {
    cout << "# ERR: SQLException in " << __FILE__;
    cout << "(" << __FUNCTION__ << ") on line " << __LINE__ << endl;
    cout << "# ERR: " << e.what();
    cout << " (MySQL error code: " << e.getErrorCode();
    cout << ", SQLState: " << e.getSQLState() << " )" << endl;
  }
  return NULL;
}

int main() {
  pthread_t thread1, thread2, thread3, thread4;
  pthread_create(&thread1, NULL, test, NULL);
  pthread_create(&thread2, NULL, test, NULL);
  pthread_join(thread1, NULL);
  pthread_join(thread2, NULL);
  return 0;
}

Valgrind输出：

==10252== Memcheck, a memory error detector
==10252== Copyright (C) 2002-2011, and GNU GPL'd, by Julian Seward et al.
==10252== Using Valgrind-3.7.0 and LibVEX; rerun with -h for copyright info
==10252== Command: ./app/bin/app-test
==10252== Parent PID: 6312
==10252== 
==10252== 
==10252== HEAP SUMMARY:
==10252==     in use at exit: 384 bytes in 2 blocks
==10252==   total heap usage: 212 allocs, 210 frees, 208,400 bytes allocated
==10252== 
==10252== 192 bytes in 1 blocks are definitely lost in loss record 1 of 2
==10252==    at 0x4C29DB4: calloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==10252==    by 0x5E1CB3E: my_thread_init (in /usr/lib/x86_64-linux-gnu/libmysqlclient.so.18.0.0)
==10252==    by 0x5E1CE3C: my_thread_global_init (in /usr/lib/x86_64-linux-gnu/libmysqlclient.so.18.0.0)
==10252==    by 0x5E1AA54: my_init (in /usr/lib/x86_64-linux-gnu/libmysqlclient.so.18.0.0)
==10252==    by 0x5DF86CA: mysql_server_init (in /usr/lib/x86_64-linux-gnu/libmysqlclient.so.18.0.0)
==10252==    by 0x4EA3C08: sql::mysql::NativeAPI::getCApiHandle(sql::SQLString const&) (in /usr/lib/libmysqlcppconn.so.5.1.1.0)
==10252==    by 0x4EA40EA: sql::mysql::NativeAPI::MySQL_NativeDriverWrapper::MySQL_NativeDriverWrapper(sql::SQLString const&) (in /usr/lib/libmysqlcppconn.so.5.1.1.0)
==10252==    by 0x4EA4138: sql::mysql::NativeAPI::createNativeDriverWrapper(sql::SQLString const&) (in /usr/lib/libmysqlcppconn.so.5.1.1.0)
==10252==    by 0x4E6F2F3: sql::mysql::MySQL_Driver::MySQL_Driver(sql::SQLString const&) (in /usr/lib/libmysqlcppconn.so.5.1.1.0)
==10252==    by 0x4E6F50B: sql::mysql::get_driver_instance_by_name(char const*) (in /usr/lib/libmysqlcppconn.so.5.1.1.0)
==10252==    by 0x40AB8C: test(void*) (main.cc:17)
==10252==    by 0x50D9E99: start_thread (pthread_create.c:308)
==10252== 
==10252== 192 bytes in 1 blocks are definitely lost in loss record 2 of 2
==10252==    at 0x4C29DB4: calloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==10252==    by 0x5E1CB3E: my_thread_init (in /usr/lib/x86_64-linux-gnu/libmysqlclient.so.18.0.0)
==10252==    by 0x5DF86DC: mysql_server_init (in /usr/lib/x86_64-linux-gnu/libmysqlclient.so.18.0.0)
==10252==    by 0x5DFE85E: mysql_init (in /usr/lib/x86_64-linux-gnu/libmysqlclient.so.18.0.0)
==10252==    by 0x4EA4A82: sql::mysql::NativeAPI::MySQL_NativeConnectionWrapper::MySQL_NativeConnectionWrapper(boost::shared_ptr<sql::mysql::NativeAPI::IMySQLCAPI>) (in /usr/lib/libmysqlcppconn.so.5.1.1.0)
==10252==    by 0x4EA4014: sql::mysql::NativeAPI::MySQL_NativeDriverWrapper::conn_init() (in /usr/lib/libmysqlcppconn.so.5.1.1.0)
==10252==    by 0x4E6F0DC: sql::mysql::MySQL_Driver::connect(sql::SQLString const&, sql::SQLString const&, sql::SQLString const&) (in /usr/lib/libmysqlcppconn.so.5.1.1.0)
==10252==    by 0x40ABE8: test(void*) (main.cc:18)
==10252==    by 0x50D9E99: start_thread (pthread_create.c:308)
==10252==    by 0x5AFCCBC: clone (clone.S:112)
==10252== 
==10252== LEAK SUMMARY:
==10252==    definitely lost: 384 bytes in 2 blocks
==10252==    indirectly lost: 0 bytes in 0 blocks
==10252==      possibly lost: 0 bytes in 0 blocks
==10252==    still reachable: 0 bytes in 0 blocks
==10252==         suppressed: 0 bytes in 0 blocks
==10252== 
==10252== For counts of detected and suppressed errors, rerun with: -v
==10252== ERROR SUMMARY: 2 errors from 2 contexts (suppressed: 2 from 2)

2 个答案:

答案 0 :(得分：4)

正如WhozCraig建议您可以将delete Driver;添加到测试函数中，但我建议使用auto_ptr或C ++ 11 unique_ptr或shared_ptr来处理所有MYSQL和你永远不必担心内存泄漏

以此为例

使用C ++ 11 

std::unique_ptr< sql::Connection > con( driver->connect("tcp://127.0.0.1:3306", "root", "root"));

或C ++ 

std::auto_ptr< sql::Connection > con( driver->connect("tcp://127.0.0.1:3306", "root", "root"));

修改

你不能只是delete Driver，我会在有空的时候更多地研究它

<强>更新

我查看了driver.h源代码，确实是protected: virtual ~Driver() {}所以你不能只使用删除，在public:中有两个

virtual void threadInit() = 0;

    virtual void threadEnd() = 0;

这可能是你需要的

还有这个example可能非常有用，并且与你

有点不同

答案 1 :(得分：1)

第一个问题是你的代码错了。如果offset()块中存在任何异常，程序将永远不会到达try语句，您将保持与MySQL服务器的开放连接和内存泄漏。您必须在delete con;块之外声明并删除con或使用C ++ 11智能指针：

错误： 

try

正确，在C ++ 11之前： 

  try {
    sql::Connection *con = driver->connect("URL", "user", "password");

    // code

    delete con;
  }
  catch (const sql::SQLException &e) {
    // code
  }

正确，C ++ 11，推荐方式： 

  sql::Connection *con = NULL;     
  try {
    con = driver->connect("URL", "user", "password");

    // code

  }
  catch (const sql::SQLException &e) {
    // code
  }
  delete con; // delete on NULL is harmless.
  con = NULL;

此外， try { // unique_ptr will automatically call delete when it goes out of scope. // That will also happen in case of exception. std::unique_ptr<sql::Connection> con (driver->connect("URL", "user", "password")); // code } catch (const sql::SQLException &e) { // code } 只应在程序中调用一次，而不是在每个线程中调用。因此，您应该将driver = get_driver_instance();设为全局变量，并在创建任何线程之前在sql::Driver *driver;中调用driver = get_driver_instance();。

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