a1d308a316
Task-number: QTBUG-116071 Pick-to: 6.5 6.6 Change-Id: I7413a0d8085eec38e6480f6aa21c85620ca68f54 Reviewed-by: Topi Reiniö <topi.reinio@qt.io>
46 lines
1.6 KiB
Plaintext
46 lines
1.6 KiB
Plaintext
// Copyright (C) 2023 The Qt Company Ltd.
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// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only
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/*!
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\example wordcount
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\meta tags {threads, console}
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\title Word Count
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\ingroup qtconcurrentexamples
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\examplecategory {Data Processing & I/O}
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\brief Demonstrates how to use the map-reduce algorithm.
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The Qt Concurrent \e {Word Count} example demonstrates the use of the
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map-reduce algorithm when applied to the problem of counting words in a
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collection of files.
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First, the Application starts a QFileDialog to select a starting
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path, and then prints the output to the console.
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\include examples-run.qdocinc
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\section1 Comparing the operations
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Compare a single-threaded, sequential approach to counting the words in
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the text files to a multithreaded approach with mappedReduced():
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\dots
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\snippet wordcount/main.cpp 1
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\dots
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\snippet wordcount/main.cpp 2
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\dots
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The first argument to the \l {QtConcurrent::}{mappedReduced} function is the
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container to operate on. The second argument is the mapping function
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\c {countWords()}. It is called in parallel by multiple threads. The
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third argument is the reducing function \c {reduce()}. It is called
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once for each result returned by the mapping function, and generates the
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final computation result.
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The function returns a QFuture object of type \c WordCount. Call the
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\l {QFuture::}{result} function immediately on this QFuture to block further
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execution until the result becomes available.
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\note The mapping function must be thread-safe since it is called from
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multiple threads.
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*/
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