我一直在阅读C++ 并发实践 https://rads.stackoverflow.com/amzn/click/com/1933988770第四章(又名“我刚刚完成的章节”)描述了一个解决方案。
简短版本
有一个共享的std::deque<std::packaged_task<void()>>
(或类似的消息/任务队列)。你的std::async
-启动的函数可以将任务推送到队列,并且您的 GUI 线程可以在循环期间处理它们。
确实没有很长的版本,但这里有一个例子
共享数据
std::deque<std::packaged_task<void()>> tasks;
std::mutex tasks_mutex;
std::atomic<bool> gui_running;
The std::async
功能
void one_off()
{
std::packaged_task<void()> task(FUNCTION TO RUN ON GUI THREAD); //!!
std::future<void> result = task.get_future();
{
std::lock_guard<std::mutex> lock(tasks_mutex);
tasks.push_back(std::move(task));
}
// wait on result
result.get();
}
图形用户界面线程
void gui_thread()
{
while (gui_running) {
// process messages
{
std::unique_lock<std::mutex> lock(tasks_mutex);
while (!tasks.empty()) {
auto task(std::move(tasks.front()));
tasks.pop_front();
// unlock during the task
lock.unlock();
task();
lock.lock();
}
}
// "do gui work"
std::this_thread::sleep_for(std::chrono::milliseconds(1000));
}
}
Notes:
我(总是)在学习,所以我的代码很有可能不是很好。不过这个概念至少是合理的。
返回值的析构函数std::async
(a std::future<>
)将阻塞,直到操作启动std::async
完成(参见std::async http://en.cppreference.com/w/cpp/thread/async),所以等待任务的结果(就像我在我的例子中所做的那样)one_off
可能不是一个好主意。
您可能想要(至少我会)创建自己的线程安全 MessageQueue 类型以提高代码可读性/可维护性/等等等等。
我发誓我还想指出一件事,但现在我想不起来了。
完整示例
#include <atomic>
#include <chrono>
#include <deque>
#include <iostream>
#include <mutex>
#include <future>
#include <thread>
// shared stuff:
std::deque<std::packaged_task<void()>> tasks;
std::mutex tasks_mutex;
std::atomic<bool> gui_running;
void message()
{
std::cout << std::this_thread::get_id() << std::endl;
}
void one_off()
{
std::packaged_task<void()> task(message);
std::future<void> result = task.get_future();
{
std::lock_guard<std::mutex> lock(tasks_mutex);
tasks.push_back(std::move(task));
}
// wait on result
result.get();
}
void gui_thread()
{
std::cout << "gui thread: "; message();
while (gui_running) {
// process messages
{
std::unique_lock<std::mutex> lock(tasks_mutex);
while (!tasks.empty()) {
auto task(std::move(tasks.front()));
tasks.pop_front();
// unlock during the task
lock.unlock();
task();
lock.lock();
}
}
// "do gui work"
std::this_thread::sleep_for(std::chrono::milliseconds(1000));
}
}
int main()
{
gui_running = true;
std::cout << "main thread: "; message();
std::thread gt(gui_thread);
for (unsigned i = 0; i < 5; ++i) {
// note:
// these will be launched sequentially because result's
// destructor will block until one_off completes
auto result = std::async(std::launch::async, one_off);
// maybe do something with result if it is not void
}
// the for loop will not complete until all the tasks have been
// processed by gui_thread
// ...
// cleanup
gui_running = false;
gt.join();
}
数据输出
$ ./messages
main thread: 140299226687296
gui thread: 140299210073856
140299210073856
140299210073856
140299210073856
140299210073856
140299210073856