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QThreadPool Class
https://doc.qt.io/qt-5/qthreadpool.html#expiryTimeout-prop
QThreadPool(QObject *parent = nullptr)
QThreadPool manages and recyles individual QThread objects to help reduce thread creation costs in programs that use threads. Each Qt application has one global QThreadPool object, which can be accessed by calling globalInstance().
To use one of the QThreadPool threads, subclass QRunnable and implement the run() virtual function. Then create an object of that class and pass it to QThreadPool::start().
Qt 线程池QThreadPool类、QRunnable类
https://my.oschina.net/u/4328928/blog/3315428
Qt 多线程编程之降低线程的开销
https://zhuanlan.zhihu.com/p/55081052
Qt 多线程编程之敲开 QThread 类的大门
https://zhuanlan.zhihu.com/p/53270619
Qt 中的多线程技术
https://zhuanlan.zhihu.com/p/52612180