Qt版本5.1.1
以HTTP操作为例
Qt中的HTTP操作都是异步的. 内部通过线程实现
创建线程的时机在QNetworkReplyHttpImplPrivate::postRequest()
void QNetworkReplyHttpImplPrivate::postRequest()
{Q_Q(QNetworkReplyHttpImpl);QThread *thread &＃61; 0;if (synchronous) {// A synchronous HTTP request uses its own threadthread &＃61; new QThread();thread->setObjectName(QStringLiteral("Qt HTTP synchronous thread"));QObject::connect(thread, SIGNAL(finished()), thread, SLOT(deleteLater()));thread->start();} else if (!managerPrivate->httpThread) {// We use the manager-global thread.// At some point we could switch to having multiple threads if it makes sense.managerPrivate->httpThread &＃61; new QThread();managerPrivate->httpThread->setObjectName(QStringLiteral("Qt HTTP thread"));managerPrivate->httpThread->start();thread &＃61; managerPrivate->httpThread;} else {// Asynchronous request, thread already existsthread &＃61; managerPrivate->httpThread;}..........// Move the delegate to the http threaddelegate->moveToThread(thread);// This call automatically moves the uploadDevice too for the asynchronous case............
}
分为两种情况:
(1) synchronous &＃61;&＃61; true 每次HTTP请求创建自己的线程, 并在finished后自动退出线程
在QNetworkRequest设置QNetworkRequest::SynchronousRequestAttribute 属性为真时, synchronous &＃61; true, 然而SynchronousRequestAttribute被Qt标记为internal. 以防止外部创建synchronous HTTP请求.
我在Qt的源码中找到一点说明, QNetworkReplyHttpImpl的构造函数中.
........// Internal code that does a HTTP reply for the synchronous Ajax// in Qt WebKit.QVariant synchronousHttpAttribute &＃61; request.attribute(static_cast
........
webkit的ajax请求使用
(2) synchronous &＃61;&＃61; false 则把所有http请求放置在一个线程中.
并且该线程在
QNetworkAccessManagerPrivate对象析构(即QNetworkAccessManager析构)或者调用QNetworkAccessManagerPrivate::clearCache 时退出
QNetworkAccessManagerPrivate::~QNetworkAccessManagerPrivate()
{if (httpThread) {httpThread->quit();httpThread->wait(5000);if (httpThread->isFinished())delete httpThread;elseQObject::connect(httpThread, SIGNAL(finished()), httpThread, SLOT(deleteLater()));httpThread &＃61; 0;}
}void QNetworkAccessManagerPrivate::clearCache(QNetworkAccessManager *manager)
{manager->d_func()->objectCache.clear();manager->d_func()->authenticationManager->clearCache();if (manager->d_func()->httpThread) {manager->d_func()->httpThread->quit();manager->d_func()->httpThread->wait(5000);if (manager->d_func()->httpThread->isFinished())delete manager->d_func()->httpThread;elseQObject::connect(manager->d_func()->httpThread, SIGNAL(finished()), manager->d_func()->httpThread, SLOT(deleteLater()));manager->d_func()->httpThread &＃61; 0;}
}
否则会一直HTTP 线程会一直存在. 另外, 每个QNetworkAccessManager对象对应自己的HTTP thread.
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