c++ - 无法解释的行为 boost::scoped_lock

Question

我写的是C++多线程TCP服务器，使用boost:scoped_lock进行同步

连接到服务器后客户端卡住。

在 gdb 中，我在调用 boost::mutex::lock 后在 pthread_kill 中看到了更多线程

(gdb) info thread

277 Thread 808779c00 (LWP 245289330/xgps)  0x0000000802579d5c in poll () at poll.S:3
  276 Thread 808779800 (LWP 245289329/xgps)  0x00000008019799bc in pthread_kill () from /lib/libthr.so.3
  275 Thread 808779400 (LWP 245289328/xgps)  0x00000008019799bc in pthread_kill () from /lib/libthr.so.3
 .....
  246 Thread 808c92800 (LWP 245289296/xgps)  0x00000008019799bc in pthread_kill () from /lib/libthr.so.3
  245 Thread 808643800 (LWP 245289295/xgps)  0x00000008019799bc in pthread_kill () from /lib/libthr.so.3
  244 Thread 808643400 (LWP 245289294/xgps)  0x00000008019799bc in pthread_kill () from /lib/libthr.so.3
  243 Thread 806c8f400 (LWP 245289292/xgps)  0x00000008019799bc in pthread_kill () from /lib/libthr.so.3
  242 Thread 808643000 (LWP 245286262/xgps)  0x00000008019799bc in pthread_kill () from /lib/libthr.so.3
  241 Thread 808c92400 (LWP 245289288/xgps)  0x00000008019799bc in pthread_kill () from /lib/libthr.so.3



[Switching to thread 205 (Thread 80863a000 (LWP 245289251/xgps))]#0  0x00000008019799bc in pthread_kill () from /lib/libthr.so.3
(gdb) where
#0  0x00000008019799bc in pthread_kill () from /lib/libthr.so.3
#1  0x0000000801973cfc in pthread_getschedparam () from /lib/libthr.so.3
#2  0x00000008019782fc in pthread_mutex_getprioceiling () from /lib/libthr.so.3
#3  0x000000080197838b in pthread_mutex_lock () from /lib/libthr.so.3
#4  0x0000000000442b2e in boost::mutex::lock (this=0x803835f10) at mutex.hpp:62
#5  0x0000000000442c36 in boost::unique_lock<boost::mutex>::lock (this=0x7fffe7334270) at lock_types.hpp:346
#6  0x0000000000442c7c in unique_lock (this=0x7fffe7334270, m_=@0x803835f10) at lock_types.hpp:124
#7  0x0000000000466e31 in XDevice::getDeviceIMEI (this=0x803835e20) at /home/xgps_app/device.cpp:639
#8  0x000000000049071f in XDevicePool::get_device (this=0x7fffffffd9c0, device_imei=868683024674230) at /home/xgps_app/pool_devices.cpp:351

device.cpp:639 行的代码

IMEI 
XDevice::getDeviceIMEI()
{
    try {
        boost::mutex::scoped_lock lock(cn_mutex);
        return  device_imei;
    }
    catch (std::exception &e )
    {
        cout << " ERROR in getDeviceIMEI " << e.what() << "\n";
    }
    return 0;
}

pool_device 中的代码

XDevicePtr  
XDevicePool::get_device(IMEI device_imei)
{
    XDevicePtr device;
    unsigned int i = 0;

    while(i < this->devices.size())
    {
        device = devices[i]; 
        if (device->getDeviceIMEI() == device_imei) {
            LOG4CPLUS_DEBUG(logger,  "XDevicePool::get_device found!");
            return device;
        }
        i++;
    }   
    device.reset();
    return device;
}

XDevicePtr 
XDevicePool::get_device_mt(IMEI device_imei)
{
    try 
    {
        boost::mutex::scoped_lock lock(pool_mutex);

    }
    catch (std::exception & e)
    {
        LOG4CPLUS_ERROR(logger,  "XDevicePool::get_device error! " << e.what());
    } 
//  boost::mutex::scoped_lock lock(pool_mutex);
    return get_device(device_imei); 
}

为什么在调用互斥锁线程终止后？我认为死锁不是这种行为的原因请帮忙!

Answer 1

你有多个锁。

当您有多个可能同时需要的锁时，您需要以固定顺序获取它们，以避免死锁。

您似乎遇到了这样的死锁。查看 Boost Thread 的免费函数 boost::lock http://www.boost.org/doc/libs/1_63_0/doc/html/thread/synchronization.html#thread.synchronization.lock_functions.lock_multiple帮助以可靠的顺序获取多个锁。

您还想了解 std::defer_lock。

---

除此之外，在多线程程序中可能会受到 fork 的干扰。我认为这超出了现在解释的范围，除非你确实在你的过程中使用了 fork