文章目录
-
- [一、QtConcurrent 简介](#一、QtConcurrent 简介)
- 二、常用功能分类
-
- [2.1 异步运行一个函数(无返回值)](#2.1 异步运行一个函数(无返回值))
- [2.2 异步运行一个带参数的函数(有返回值)](#2.2 异步运行一个带参数的函数(有返回值))
- [2.3 绑定类成员函数](#2.3 绑定类成员函数)
- [2.4 容器并行处理(map)](#2.4 容器并行处理(map))
- 三、线程池控制
- 四、取消任务
- 五、典型应用场景
- 六、完整示例:并发下载图片
一、QtConcurrent 简介
QtConcurrent 是 Qt 提供的一个高级并发编程模块,属于 QtConcurrent 命名空间,旨在简化多线程任务的执行。它支持并行执行算法(如 map、filter、reduce),还支持异步任务运行和结果管理,不需要显式管理 QThread。
模块介绍
头文件包含:
cpp
#include <QtConcurrent>
模块依赖:
cpp
QT += concurrent
常用功能:
二、常用功能分类
2.1 异步运行一个函数(无返回值)
cpp
QtConcurrent::run([]() {
qDebug() << "后台线程中执行任务:" << QThread::currentThread();
});
2.2 异步运行一个带参数的函数(有返回值)
cpp
int add(int a, int b) {
return a + b;
}
QFuture<int> future = QtConcurrent::run(add, 3, 5);
// 后续获取结果
int result = future.result(); // 阻塞直到完成
qDebug() << "结果是:" << result;
2.3 绑定类成员函数
cpp
class Worker {
public:
int multiply(int x, int y) {
return x * y;
}
};
Worker worker;
QFuture<int> future = QtConcurrent::run(&worker, &Worker::multiply, 4, 6);
2.4 容器并行处理(map)
并发修改容器元素(原地修改)
cpp
QList<int> numbers = {1, 2, 3, 4, 5};
auto doubleIt = [](int &n) {
n *= 2;
};
QtConcurrent::map(numbers, doubleIt);
// 输出: 2 4 6 8 10
并发映射容器到新容器(mapped)
cpp
QList<int> numbers = {1, 2, 3};
auto square = [](int n) {
return n * n;
};
QList<int> squares = QtConcurrent::mapped(numbers, square).results();
// 输出: 1 4 9
并发过滤(filtered)
cpp
QStringList names = {"Alice", "Bob", "Eve"};
auto isShort = [](const QString &name) {
return name.length() <= 3;
};
QStringList shortNames = QtConcurrent::filtered(names, isShort).results();
// 输出: Bob, Eve
2.5 使用 QFutureWatcher 监听结果(推荐与 UI 配合)
cpp
QFutureWatcher<QString> *watcher = new QFutureWatcher<QString>(this);
connect(watcher, &QFutureWatcher<QString>::finished, this, [=]() {
QString result = watcher->result();
qDebug() << "计算完成,结果为:" << result;
});
QFuture<QString> future = QtConcurrent::run([]() {
QThread::sleep(2);
return QString("Hello from thread");
});
watcher->setFuture(future);
三、线程池控制
QtConcurrent 默认使用全局 QThreadPool,可通过如下方式调整:
cpp
QThreadPool::globalInstance()->setMaxThreadCount(8);
或者使用局部线程池:
cpp
QThreadPool pool;
QtConcurrent::run(&pool, someFunction);
四、取消任务
可通过 QFuture 中的 cancel() 方法取消任务:
cpp
QFuture<void> future = QtConcurrent::run([]{
for (int i = 0; i < 100; ++i) {
if (QThread::currentThread()->isInterruptionRequested()) {
return;
}
QThread::msleep(100);
}
});
// 取消任务
future.cancel();
五、典型应用场景

六、完整示例:并发下载图片
效果目标:
核心类:ImageDownloader
cpp
// ImageDownloader.h
#ifndef IMAGEDOWNLOADER_H
#define IMAGEDOWNLOADER_H
#include <QObject>
#include <QNetworkAccessManager>
#include <QNetworkReply>
#include <QSemaphore>
class ImageDownloader : public QObject
{
Q_OBJECT
public:
explicit ImageDownloader(QObject *parent = nullptr);
void setMaxConcurrent(int count); // 设置最大并发数
void downloadImages(const QStringList &urls, const QString &saveDir);
signals:
void imageDownloaded(const QString &url, const QString &filePath);
void downloadFailed(const QString &url, const QString &error);
void allFinished();
private:
void downloadOne(const QString &url, const QString &saveDir, int retryCount = 3);
QSemaphore m_semaphore; // 控制并发数
int m_maxConcurrent = 5;
};
#endif // IMAGEDOWNLOADER_H
cpp
// ImageDownloader.cpp
#include "ImageDownloader.h"
#include <QDir>
#include <QFile>
#include <QFileInfo>
#include <QNetworkRequest>
#include <QThread>
#include <QDebug>
#include <QtConcurrent>
ImageDownloader::ImageDownloader(QObject *parent)
: QObject(parent), m_semaphore(m_maxConcurrent)
{}
void ImageDownloader::setMaxConcurrent(int count)
{
m_maxConcurrent = count;
m_semaphore = QSemaphore(m_maxConcurrent);
}
void ImageDownloader::downloadImages(const QStringList &urls, const QString &saveDir)
{
for (const QString &url : urls) {
QtConcurrent::run([=]() {
m_semaphore.acquire(); // 限制并发
downloadOne(url, saveDir);
m_semaphore.release();
});
}
// 可选:全部下载完再发信号(略)
}
void ImageDownloader::downloadOne(const QString &urlStr, const QString &saveDir, int retryCount)
{
QNetworkAccessManager manager;
QNetworkRequest request(QUrl(urlStr));
QNetworkReply *reply = manager.get(request);
QEventLoop loop;
QObject::connect(reply, &QNetworkReply::finished, &loop, &QEventLoop::quit);
loop.exec();
if (reply->error() == QNetworkReply::NoError) {
QByteArray data = reply->readAll();
QUrl url(urlStr);
QString fileName = QFileInfo(url.path()).fileName();
QString fullPath = QDir(saveDir).filePath(fileName);
QFile file(fullPath);
if (file.open(QIODevice::WriteOnly)) {
file.write(data);
file.close();
emit imageDownloaded(urlStr, fullPath);
} else {
emit downloadFailed(urlStr, "文件保存失败");
}
} else {
if (retryCount > 0) {
qDebug() << "下载失败,重试:" << urlStr;
downloadOne(urlStr, saveDir, retryCount - 1);
} else {
emit downloadFailed(urlStr, reply->errorString());
}
}
reply->deleteLater();
}
使用示例:
cpp
ImageDownloader *downloader = new ImageDownloader(this);
downloader->setMaxConcurrent(5); // 最多5张图同时下载
QStringList urls = {
"https://example.com/a.jpg",
"https://example.com/b.jpg",
"https://example.com/c.jpg"
};
QString savePath = QDir::currentPath() + "/images";
connect(downloader, &ImageDownloader::imageDownloaded, this, [](const QString &url, const QString &path){
qDebug() << "下载成功:" << url << " -> " << path;
});
connect(downloader, &ImageDownloader::downloadFailed, this, [](const QString &url, const QString &error){
qWarning() << "下载失败:" << url << error;
});
downloader->downloadImages(urls, savePath);