并发访问sqlite数据库出现databse is locked的错误的一个解决办法

作者：朱金灿

来源：http://blog.****.net/clever101

在并发访问sqlite数据库会出现这样一个错误：databseis locked，这是sqlite数据库对并发支持不太好的缘故造成的。采用网上的一种的思路是通过互斥信号量来达到并发访问的目的。下面是一个跨平台的互斥信号量类：

//ProcessMutex.h文件：
#ifndef __PROCESS_MUTEX_H__
#define __PROCESS_MUTEX_H__

#if defined _WIN32 || defined _WIN64

     #include <Windows.h>

#endif

#ifdef linux
#include <unistd.h>
#include <semaphore.h>
#include <stdio.h>
#include <fcntl.h>
#include <signal.h>
#include <string.h>
#include <memory.h>
#endif

class CProcessMutex
{
public:
    /* 默认创建匿名的互斥 */
    CProcessMutex(const char* name = NULL);
    ~CProcessMutex();

    bool Lock();
    bool UnLock();
private:

#if defined _WIN32 || defined _WIN64

    void* m_pMutex;

#endif

#ifdef linux
    set_t* m_pSem;
#ednif
    char m_cMutexName[30];
};
#endif

 //ProcessMutex.cpp文件：
#include "ProcessMutex.h"

#if defined _WIN32 || defined _WIN64

CProcessMutex::CProcessMutex(const char* name)
{
    memset(m_cMutexName, 0 ,sizeof(m_cMutexName));
    int min = strlen(name)>(sizeof(m_cMutexName)-1)?(sizeof(m_cMutexName)-1):strlen(name);
    strncpy(m_cMutexName, name, min);
    m_pMutex = CreateMutex(NULL, false, m_cMutexName);
}

CProcessMutex::~CProcessMutex()
{
    CloseHandle(m_pMutex);
}

bool CProcessMutex::Lock()
{
    //互斥锁创建失败
    if (NULL == m_pMutex)
    {
        return false;
    }

    DWORD nRet = WaitForSingleObject(m_pMutex, INFINITE);
    if (nRet != WAIT_OBJECT_0)
    {
        return false;
    }

    return true;
}

bool CProcessMutex::UnLock()
{
    return ReleaseMutex(m_pMutex);
}

#endif

#ifdef linux

CProcessMutex::CProcessMutex(const char* name)
{
    memset(m_cMutexName, 0 ,sizeof(m_cMutexName));
    int min = strlen(name)>(sizeof(m_cMutexName)-1)?(sizeof(m_cMutexName)-1):strlen(name);
    strncpy(m_cMutexName, name, min);
    m_pSem = sem_open(name, O_CREAT, 0644, 1);
}

CProcessMutex::~CProcessMutex()
{
    int ret = sem_close(m_pSem);
    if (0 != ret)
    {
        printf("sem_close error %d\n", ret);
    }
    sem_unlink(m_cMutexName);
}

bool CProcessMutex::Lock()
{
    int ret = sem_wait(m_pSem);
    if (ret != 0)
    {
        return false;
    }
    return true;
}

bool CProcessMutex::UnLock()
{
    int ret = sem_post(m_pSem);
    if (ret != 0)
    {
        return false;
    }
    return true;
}

#endif

使用示例代码如下：

CProcessMutex pMutex("MutexName");

pMutex.Lock();

sqlite3_exec( myconn, sql, 0, 0, &m_sqlerr_msg); // 执行sqlite的相关操作

pMutex.UnLock();

参考文献：

1. 多进程之间的互斥信号量的实现（Linux和windows跨平台）

2.sqlite遇到database is locked问题的完美解决