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Qt线程同步问题 [复制链接]

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离线songhuirong1
侠客
 
只看楼主 倒序阅读 楼主  发表于: 2019-07-26
直接上代码：
复制代码
  1. #include <QCoreApplication>
  2. #include <QtConcurrent>
  3. #include <QWaitCondition>
  4. #include <QDebug>
  6. QMutex mutex;
  7. QWaitCondition wc;
  9. void testFunc()
  10. {
  11.     qDebug() << "exec testFunc...";
  12.     wc.wakeAll();
  13. }
  15. int main(int argc, char *argv[])
  16. {
  17.     QCoreApplication a(argc, argv);
  18.     QtConcurrent::run(testFunc);
  19.     QThread::sleep(3);
  21.     {
  22.         QMutexLocker locker(&mutex);
  24.         if (!wc.wait(&mutex))
  25.         {
  26.             return -1;
  27.         }
  29.         qDebug() << "wait for testFunc end...";
  30.     }
  32.     return a.exec();
  33. }

这段代码的意图是让主线程等待testFunc函数执行线程结束，然后testFunc函数执行线程唤醒主线程。但是由于主线程sleep了3s，那么testFunc函数执行线程瞬间就执行结束了，它调用了wc.wakeAll()函数，但是此时主线程还没有执行到wc.wait(&mutex)处，所以此时wakeAll无效，子线程执行结束。过了3
s后，主线程执行到wc.wait()处，由于testFunc函数执行线程已经结束，所以再也没有其它线程可以唤醒它，然后主程序就将永远wait。然后我修改了代码解决此问题，请各位看看我写的有没有问题，或者说有没有隐藏的bug。新的代码如下：
复制代码
  1. #include <QCoreApplication>
  2. #include <QtConcurrent>
  3. #include <QWaitCondition>
  4. #include <QDebug>
  6. QMutex mutex;
  7. QWaitCondition wc;
  9. void testFunc()
  10. {
  11.     {
  12.         qDebug() << "testFunc wait start...";
  13.         QMutexLocker locker(&mutex);
  14.         wc.wait(&mutex);
  15.         qDebug() << "testFunc wait end...";
  16.     }
  18.     QMutexLocker locker(&mutex);
  19.     qDebug() << "exec testFunc...";
  20.     wc.wakeAll();
  21.     qDebug() << "testFunc wakeAll...";
  22. }
  24. int main(int argc, char *argv[])
  25. {
  26.     QCoreApplication a(argc, argv);
  27.     qDebug() << "start call testFunc...";
  28.     QtConcurrent::run(testFunc);
  29.     QThread::sleep(3);
  31.     {
  32.         qDebug() << "wait for testFunc start...";
  33.         QMutexLocker locker(&mutex);
  34.         wc.wakeAll();
  35.         qDebug() << "main wakeAll...";
  37.         if (!wc.wait(&mutex))
  38.         {
  39.             return -1;
  40.         }
  42.         qDebug() << "wait for testFunc end...";
  43.     }
  45.     return a.exec();
  46. }
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离线fsu0413
圣骑士
只看该作者 1楼 发表于: 2019-07-26
难道你的代码就没有一个用mutex保护的量来标志testFunc是否执行完吗？


复制代码
  1. #include <QCoreApplication>
  2. #include <QtConcurrent>
  3. #include <QWaitCondition>
  4. #include <QDebug>
  6. QMutex mutex;
  7. QWaitCondition wc;
  8. bool flag=false;
  10. void testFunc()
  11. {
  12.     qDebug() << "exec testFunc...";
  13.     QMutexLocker locker(&mutex);
  14.     flag = true;
  15.     wc.wakeAll();
  16. }
  18. int main(int argc, char *argv[])
  19. {
  20.     QCoreApplication a(argc, argv);
  21.     QtConcurrent::run(testFunc);
  22.     QThread::sleep(3);
  24.     {
  25.         QMutexLocker locker(&mutex);
  27.         if (!flag)
  28.             if (!wc.wait(&mutex))
  29.             {
  30.                 return -1;
  31.             }
  33.         qDebug() << "wait for testFunc end...";
  34.     }
  36.     return a.exec();
  37. }
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离线songhuirong1
侠客
只看该作者 2楼 发表于: 2019-07-27
回 fsu0413 的帖子
fsu0413:难道你的代码就没有一个用mutex保护的量来标志testFunc是否执行完吗？
#include <QCoreApplication>
#include <QtConcurrent>
....... (2019-07-26 22:30) 

非常感谢你的回复，你的代码应该也是可以解决问题的，只是我们实现的方式不一样而已，我的代码应该是没有问题的。我只是想向各位学习一下，看有没有更好的实现方式。你的这种方法给我提供了一种新的思路，我学习了。谢谢。如果我的代码有纰漏，还望指点一二。
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离线songhuirong1
侠客
只看该作者 3楼 发表于: 2019-09-23
新的例子代码，更加简洁。
    template <typename Type>
    bool common_kit::RemoteControlHelper::readRequest(int varid, int vartype, Type &data, int offset /*= 0*/)
    {
        if (m_dataStream.isNull())
        {
            Q_ASSERT(false);

            return false;
        }

        if (gdp::core::INVALID_ID == m_mtManualId)
        {
            Q_ASSERT(false);

            return false;
        }

        mn::common_title common_title_;
        mn::common_title_item common_title_item_;
        common_title_item_.varid = varid;
        common_title_item_.offset = offset;
        common_title_item_.vartype = vartype;
        common_title_item_.length = sizeof(data);
        common_title_.items.push_back(common_title_item_);
        bool bOk = false;
        QMutex mutex;
        QMutexLocker mutexLocker(&mutex);
        QWaitCondition wc;
        int ret = m_dataStream->mt_post_common_read_request_by_id(m_mtManualId, common_title_, [&](uint32_t mtManualId, const void *pdata){
            QMutexLocker mutextLocker(&mutex);
            [&](){
                if (mtManualId != m_mtManualId)
                {
                    qDebug() << Q_FUNC_INFO << "\nmt manual id is not match!mtManualId:" << mtManualId << "\tm_mtManualId:" << m_mtManualId
                        << "\tvarid:" << varid << "\tvartype:" << vartype << "\toffset:" << offset;

                    return;
                }

                if (Q_NULLPTR == pdata)
                {
                    qDebug() << Q_FUNC_INFO << "\npdata is null!mtManualId:" << mtManualId
                        << "\tvarid:" << varid << "\tvartype:" << vartype << "\toffset:" << offset;

                    return;
                }

                mn::asio_t *pasio_t = (mn::asio_t *)pdata;

                if (Q_NULLPTR == pasio_t)
                {
                    qDebug() << Q_FUNC_INFO << "\npasio_t is null!mtManualId:" << mtManualId
                        << "\tvarid:" << varid << "\tvartype:" << vartype << "\toffset:" << offset;

                    return;
                }

                int err_ = pasio_t->err_;

                if (err_ < 0)
                {
                    qDebug() << Q_FUNC_INFO << "\nread request failed!mtManualId:" << mtManualId
                        << "\terr_:" << err_ << "\tvarid:" << varid << "\tvartype:" << vartype
                        << "\toffset:" << offset;

                    return;
                }

                mn::common_data *pcommon_data = (mn::common_data *)pdata;

                if (Q_NULLPTR == pcommon_data)
                {
                    qDebug() << Q_FUNC_INFO << "\npcommon_data is null!mtManualId:" << mtManualId
                        << "\tvarid:" << varid << "\tvartype:" << vartype << "\toffset:" << offset;

                    return;
                }

                if (pcommon_data->items.empty())
                {
                    qDebug() << Q_FUNC_INFO << "\npcommon_data's items is empty!mtManualId:" << mtManualId
                        << "\tvarid:" << varid << "\tvartype:" << vartype << "\toffset:" << offset;

                    return;
                }

                mn::common_data_item ack = pcommon_data->items[0];
                char *pack_data = (char *)(ack.data.data());

                if (Q_NULLPTR == pack_data)
                {
                    qDebug() << Q_FUNC_INFO << "\npack_data is null!mtManualId:" << mtManualId
                        << "\tvarid:" << varid << "\tvartype:" << vartype << "\toffset:" << offset;

                    return;
                }

                data = *(Type *)pack_data;
                bOk = true;
            }();

            wc.wakeAll();
        });

        if (ret < 0)
        {
            return false;
        }

        if (!wc.wait(&mutex, READ_REQUEST_TIMEOUT))
        {
            qDebug() << Q_FUNC_INFO << "\nQWaitCondition wait failed!m_mtManualId:" << m_mtManualId;

            return false;
        }

        return bOk;
    }
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离线songhuirong1
侠客
只看该作者 4楼 发表于: 2019-09-23
新的例子代码，更加简洁。
复制代码
  1. template <typename Type>
  2.     bool common_kit::RemoteControlHelper::readRequest(int varid, int vartype, Type &data, int offset /*= 0*/)
  3.     {
  4.         if (m_dataStream.isNull())
  5.         {
  6.             Q_ASSERT(false);
  8.             return false;
  9.         }
  11.         if (gdp::core::INVALID_ID == m_mtManualId)
  12.         {
  13.             Q_ASSERT(false);
  15.             return false;
  16.         }
  18.         mn::common_title common_title_;
  19.         mn::common_title_item common_title_item_;
  20.         common_title_item_.varid = varid;
  21.         common_title_item_.offset = offset;
  22.         common_title_item_.vartype = vartype;
  23.         common_title_item_.length = sizeof(data);
  24.         common_title_.items.push_back(common_title_item_);
  25.         bool bOk = false;
  26.         QMutex mutex;
  27.         QMutexLocker mutexLocker(&mutex);
  28.         QWaitCondition wc;
  29.         int ret = m_dataStream->mt_post_common_read_request_by_id(m_mtManualId, common_title_, [&](uint32_t mtManualId, const void *pdata){
  30.             QMutexLocker mutextLocker(&mutex);
  31.             [&](){
  32.                 if (mtManualId != m_mtManualId)
  33.                 {
  34.                     qDebug() << Q_FUNC_INFO << "\nmt manual id is not match!mtManualId:" << mtManualId << "\tm_mtManualId:" << m_mtManualId
  35.                         << "\tvarid:" << varid << "\tvartype:" << vartype << "\toffset:" << offset;
  37.                     return;
  38.                 }
  40.                 if (Q_NULLPTR == pdata)
  41.                 {
  42.                     qDebug() << Q_FUNC_INFO << "\npdata is null!mtManualId:" << mtManualId
  43.                         << "\tvarid:" << varid << "\tvartype:" << vartype << "\toffset:" << offset;
  45.                     return;
  46.                 }
  48.                 mn::asio_t *pasio_t = (mn::asio_t *)pdata;
  50.                 if (Q_NULLPTR == pasio_t)
  51.                 {
  52.                     qDebug() << Q_FUNC_INFO << "\npasio_t is null!mtManualId:" << mtManualId
  53.                         << "\tvarid:" << varid << "\tvartype:" << vartype << "\toffset:" << offset;
  55.                     return;
  56.                 }
  58.                 int err_ = pasio_t->err_;
  60.                 if (err_ < 0)
  61.                 {
  62.                     qDebug() << Q_FUNC_INFO << "\nread request failed!mtManualId:" << mtManualId
  63.                         << "\terr_:" << err_ << "\tvarid:" << varid << "\tvartype:" << vartype
  64.                         << "\toffset:" << offset;
  66.                     return;
  67.                 }
  69.                 mn::common_data *pcommon_data = (mn::common_data *)pdata;
  71.                 if (Q_NULLPTR == pcommon_data)
  72.                 {
  73.                     qDebug() << Q_FUNC_INFO << "\npcommon_data is null!mtManualId:" << mtManualId
  74.                         << "\tvarid:" << varid << "\tvartype:" << vartype << "\toffset:" << offset;
  76.                     return;
  77.                 }
  79.                 if (pcommon_data->items.empty())
  80.                 {
  81.                     qDebug() << Q_FUNC_INFO << "\npcommon_data's items is empty!mtManualId:" << mtManualId
  82.                         << "\tvarid:" << varid << "\tvartype:" << vartype << "\toffset:" << offset;
  84.                     return;
  85.                 }
  87.                 mn::common_data_item ack = pcommon_data->items[0];
  88.                 char *pack_data = (char *)(ack.data.data());
  90.                 if (Q_NULLPTR == pack_data)
  91.                 {
  92.                     qDebug() << Q_FUNC_INFO << "\npack_data is null!mtManualId:" << mtManualId
  93.                         << "\tvarid:" << varid << "\tvartype:" << vartype << "\toffset:" << offset;
  95.                     return;
  96.                 }
  98.                 data = *(Type *)pack_data;
  99.                 bOk = true;
  100.             }();
  102.             wc.wakeAll();
  103.         });
  105.         if (ret < 0)
  106.         {
  107.             return false;
  108.         }
  110.         if (!wc.wait(&mutex, READ_REQUEST_TIMEOUT))
  111.         {
  112.             qDebug() << Q_FUNC_INFO << "\nQWaitCondition wait failed!m_mtManualId:" << m_mtManualId;
  114.             return false;
  115.         }
  117.         return bOk;
  118.     }
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