QtConcurrent blockingMappedReduced v.s MappedReduced

Question

根据我的理解QtConcurrent::blockingMappedReducedreturns最终结果，而QtConcurrent::MappedReducedreturns一个QFuture对象，但在这个例子中http://doc.qt.io/qt-5/qtconcurrent-wordcount-main-cpp.html我看到这样的代码：

WordCount total = QtConcurrent::mappedReduced(files, countWords, reduce);

QtConcurrent::mappedReduced函数也是returns最终结果。我错过了什么吗？如果这是错误的，那么使用 QtConcurrent::mappedReduced 返回的结果的正确方法是什么？在什么情况下我应该 QtConcurrent::mappedReduced 而不是 QtConcurrent::blockingMappedReduced？请指教

Answer 1

在示例中 QFuture 对象被 return 直接编辑到 WordCount 使用 QFuture 对象的 conversion operator to its template parameter type 阻塞并等待结果可用。

typedef QMap<QString, int> WordCount;
WordCount total = mappedReduced(files, countWords, reduce);

实际上，如果您从异步 mappedReduced 调用函数 blockingMappedReduced 或 return QFuture 对象的阻塞版本并阻塞 return 立即编辑 QFuture 对象。请注意，调用 result() 或 resultAt(0) 也会阻塞。

WordCount total = blockingMappedReduced(files, countWords, reduce);

QFuture<WordCount> future = mappedReduced(files, countWords, reduce);
WordCount total = future.result();

如果您想与 QFuture 对象交互（暂停、恢复、检查结果是否准备就绪），那么您可以通过调用 mappedReduced 和 不使用阻塞函数来异步处理它.

QFuture<WordCount> future = mappedReduced(files, countWords, reduce);
qDebug() << future.isResultReadyAt(0); // returns false

QtConcurrent blockingMappedReduced v.s MappedReduced

QtConcurrent blockingMappedReduced v.s MappedReduced

c++

qt

qtconcurrent