使用BOOST进程在单独的线程中读取子进程标准输出 [英] Read child process stdout in a separate thread with BOOST process
问题描述
我有一个主程序，该程序使用boost进程库来生成可打印的子进程
I have a main program that uses boost process library to spawn a child process that prints
Hello World !
每5秒在其标准输出上
我想在子进程的标准输出中读取/监视子进程的标准输出，并在主程序中执行其他操作.
I would like to read/monitor the stdout of the child process in the main process when it becomes available along with performing other operations within the main program.
我已经尝试了boost asynchronous IO的示例(
I have tried out the examples for boost asynchronous IO (http://www.boost.org/doc/libs/1_66_0/doc/html/boost_process/tutorial.html) but all these seem to block the main program until the child process has exited.
我们是否需要在单独的线程中读取childs stdout?有人可以提供一个示例，在该示例中主程序可以同时执行其他操作，而不是阻止孩子的stdout吗?
Do we need to read the childs stdout in a separate thread ? Can someone please provide an example where the main program can do other things at the same time instead of blocking for stdout from th child ?
推荐答案
I have tried out the examples for boost asynchronous IO (http://www.boost.org/doc/libs/1_66_0/doc/html/boost_process/tutorial.html) but all these seem to block the main program until the child process has exited.
再看一次. 异步I下的所有示例/O 应该可以帮助您选择一种适合您的方法.
Look again. All the samples under Asynchronous I/O should help you select a method that works for you.
我们是否需要在单独的线程中读取childs stdout?有人可以提供一个示例，说明主程序可以同时执行其他操作，而不是阻止孩子的stdout吗?
Do we need to read the childs stdout in a separate thread ? Can someone please provide an example where the main program can do other things at the same time instead of blocking for stdout from th child ?
不，您不需要 .尽管您可以，并且取决于要实现的目标，但这可能是最容易的事情.
No, you don't need to. Though you can and depending on what you're trying to achieve, it might be the easiest thing to do.
您没有告诉我们您想做什么，所以让我们假设您只想打印输出:
You failed to tell us what you want to be able to do, so let's assume you just want the output printed:
bp::child c("/bin/bash", std::vector<std::string> { "-c", "for a in {1..10}; do sleep 2; echo 'Hello World !'; done" });
c.wait();
那是同步的，因此您不能同时进行工作
That's synchronous, so you can't do work in the meantime
就像:
#include <boost/process.hpp>
#include <boost/process/async.hpp>
#include <iostream>
namespace bp = boost::process;
int main() {
bp::ipstream output;
std::thread reader([&output] {
std::string line;
while (std::getline(output, line))
std::cout << "Received: '" << line << "'" << std::endl;
});
bp::child c("/bin/bash",
std::vector<std::string> { "-c", "for a in {1..10}; do sleep 2; echo 'Hello World ('$a')!'; done" },
bp::std_out > output);
while (c.running()) {
std::this_thread::sleep_for(std::chrono::milliseconds(2793));
std::cout << "(main thread working)" << std::endl;
}
std::cout << "(done)" << std::endl;
c.wait();
output.pipe().close();
reader.join();
}
打印( 在Coliru上直播 ):
Received: 'Hello World (1)!'
(main thread working)
Received: 'Hello World (2)!'
(main thread working)
Received: 'Hello World (3)!'
Received: 'Hello World (4)!'
(main thread working)
Received: 'Hello World (5)!'
(main thread working)
Received: 'Hello World (6)!'
(main thread working)
Received: 'Hello World (7)!'
Received: 'Hello World (8)!'
(main thread working)
Received: 'Hello World (9)!'
(main thread working)
Received: 'Hello World (10)!'
(main thread working)
(done)
异步IO
不使用任何线程(好吧，只是主线程)，就像这样:
Asynchronous IO
Using no threads (well, just the main thread), could look like:
#include <boost/process.hpp>
#include <boost/process/async.hpp>
#include <boost/asio/high_resolution_timer.hpp>
#include <iostream>
#include <iomanip>
namespace bp = boost::process;
struct OtherWork {
using clock = std::chrono::high_resolution_clock;
OtherWork(boost::asio::io_context& io) : timer(io) { }
void start() {
timer.expires_at(clock::time_point::max());
loop();
}
void stop() {
timer.expires_at(clock::time_point::min());
}
private:
void loop() {
if (timer.expires_at() == clock::time_point::min()) {
std::cout << "(done)" << std::endl;
return;
}
timer.expires_from_now(std::chrono::milliseconds(2793));
timer.async_wait([=](boost::system::error_code ec) {
if (!ec) {
std::cout << "(other work in progress)" << std::endl;
start();
} else {
std::cout << "(" << ec.message() << ")" << std::endl;
}
});
}
boost::asio::high_resolution_timer timer;
};
int main() {
boost::asio::io_context io;
bp::async_pipe output(io);
OtherWork mainwork{io};
bp::child c("/bin/bash", std::vector<std::string> { "-c", "for a in {1..10}; do sleep 2; echo 'Hello World ('$a')!'; done" },
bp::std_out > output, io, bp::on_exit([&mainwork,&output](auto...) {
output.close();
mainwork.stop();
}));
std::function<void()> readloop = [&,buffer=std::array<char, 32>{}]() mutable {
output.async_read_some(bp::buffer(buffer), [&](boost::system::error_code ec, size_t transferred) {
if (transferred) {
std::cout << "Received: '";
while (transferred && buffer[transferred-1] == '\n') // strip newline(s)
--transferred;
std::cout.write(buffer.data(), transferred);
std::cout << "'" << std::endl;
}
if (ec)
std::cout << "Output pipe: " << ec.message() << std::endl;
else
readloop();
});
};
mainwork.start();
readloop();
io.run();
}
打印 在Coliru上直播
Received: 'Hello World (1)!'
(other work in progress)
Received: 'Hello World (2)!'
(other work in progress)
Received: 'Hello World (3)!'
Received: 'Hello World (4)!'
(other work in progress)
Received: 'Hello World (5)!'
(other work in progress)
Received: 'Hello World (6)!'
(other work in progress)
Received: 'Hello World (7)!'
Received: 'Hello World (8)!'
(other work in progress)
Received: 'Hello World (9)!'
(other work in progress)
Received: 'Hello World (10)!'
Output pipe: End of file
Child exited with code=0(Success)
(Operation canceled)
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