演示如何使用 map-reduce (映射缩减) 算法。
The Qt Concurrent Word Count example demonstrates the use of the map-reduce algorithm when applied to the problem of counting words in a collection of files.
First, the Application starts a QFileDialog to select a starting path, and then prints the output to the console.
要运行范例从 Qt Creator ，打开 Welcome 模式，然后选择范例从 Examples 。更多信息，拜访 构建和运行范例 .
Compare a single-threaded, sequential approach to counting the words in the text files to a multithreaded approach with mappedReduced():
...
WordCount total = singleThreadedWordCount(files);
...
WordCount total = QtConcurrent::mappedReduced(files, countWords, reduce).result();
...
The first argument to the
mappedReduced
function is the container to operate on. The second argument is the mapping function
countWords()
. It is called in parallel by multiple threads. The third argument is the reducing function
reduce()
. It is called once for each result returned by the mapping function, and generates the final computation result.
函数返回
QFuture
object of type
WordCount
. Call the
result
function immediately on this
QFuture
to block further execution until the result becomes available.
注意： The mapping function must be thread-safe since it is called from multiple threads.