如何通过 boost 子进程的异步运行测试实例计数器？

Question

我已尝试将 boost::childprocess 与 async_pipe 一起使用，如下面的代码示例所示，同时期望因为有等待方法，所以对运行的调用不会等待被调用的可执行文件完成后再继续到我调用 wait() 的行。我的目标是多次启动同一个可执行文件，以便在 GTest 中测试实例计数方法（基于 boost 管理的共享内存段实现）。但在此之前我需要调用 io_service::运行()，而不是等待被调用的可执行文件完成现在。有人可以告诉我我在哪里使用错了吗？或者如果这是对我的功能进行单元测试的错误方法？我一直在努力寻找解决方案！这是我如何调用可执行文件的一个实例的示例：

int CallChildProcess_Style9() {

std::string strCmdLine = "E:\file.exe --Debug MainStartUps_Off --Lock 3";
boost::asio::io_service m_oIOS;
std::vector<char>       m_oAsyncBuffer_Out;
bp::async_pipe          m_oAsyncPipe_Out(m_oIOS);
std::error_code         build_ec;
size_t                  nReadSize(0);
boost::scoped_ptr<boost::process::child>  m_pChildProcess(nullptr);

m_pChildProcess.reset(new bp::child(strCmdLine.data(), bp::std_out > m_oAsyncPipe_Out, build_ec));

m_oAsyncBuffer_Out.resize(1024*8);

boost::asio::async_read(m_oAsyncPipe_Out, boost::asio::buffer(m_oAsyncBuffer_Out),
    [&](const boost::system::error_code &ec, std::size_t size) { nReadSize = size; });

size_t iii = m_oIOS.run();

m_pChildProcess->wait();
m_oAsyncBuffer_Out.resize(nReadSize);

std::string strBuf(m_oAsyncBuffer_Out.begin(), m_oAsyncBuffer_Out.begin() + nReadSize);

int         result = m_pChildProcess->exit_code();

m_oAsyncPipe_Out.close();

m_oIOS.reset();

return result;

}

Answer 1

使用`io_service`

要使用 async_pipe，您需要将 io_service 实例提供给 bp::child 的参数关键字：

#include <boost/asio.hpp>
#include <boost/process.hpp>
#include <boost/process/async.hpp>
#include <boost/scoped_ptr.hpp>
#include <iostream>

namespace bp = boost::process;

int CallChildProcess_Style9() {

    std::string strCmdLine = "/bin/cat";
    boost::asio::io_service m_oIOS;
    std::vector<char> m_oAsyncBuffer_Out;
    bp::async_pipe m_oAsyncPipe_Out(m_oIOS);
    std::error_code build_ec;

    size_t nReadSize(0);
    boost::scoped_ptr<boost::process::child> m_pChildProcess(nullptr);

    std::vector<std::string> const args = { "/home/sehe/Projects/Whosebug/test.cpp" };
    m_pChildProcess.reset(new bp::child(strCmdLine, args, bp::std_out > m_oAsyncPipe_Out, build_ec, m_oIOS));

    std::cout << "Launched: " << build_ec.message() << std::endl;

    m_oAsyncBuffer_Out.resize(1024 * 8);

    boost::asio::async_read(m_oAsyncPipe_Out, boost::asio::buffer(m_oAsyncBuffer_Out),
        [&](const boost::system::error_code &ec, std::size_t size) {
            std::cout << "read completion handler: size = " << size << " (" << ec.message() << ")" << std::endl;
            nReadSize = size;
        });

    std::cout << "read started" << std::endl;
    size_t iii = m_oIOS.run();

    std::cout << "io_service stopped" << std::endl;
    std::cout << "initiate child::wait" << std::endl;
    m_pChildProcess->wait();
    std::cout << "wait completed" << std::endl;

    std::string const strBuf(m_oAsyncBuffer_Out.data(), nReadSize);

    int result = m_pChildProcess->exit_code();

    m_oAsyncPipe_Out.close();

    m_oIOS.reset();

    return result;
}

int main() {
    CallChildProcess_Style9();
}

版画

http://coliru.stacked-crooked.com/a/8a9bc6bed3dd5e0a

Launched: Success
read started
read completion handler: size = 1589 (End of file)
io_service stopped
initiate child::wait
wait completed

挂断 Child

即使已修复，async_pipe::async_read 也只会读取直到缓冲区已满或达到 EOF。如果 child 进程输出超过缓冲区大小（在您的示例中为 8k），那么它将卡住并且永远不会完成。

例如：像这样替换命令：

std::string strCmdLine = "/usr/bin/yes";

结果

生活在 Coliru

Launched: Success
read started
read completion handler: size = 8192 (Success)
io_service stopped
initiate child::wait

它将挂到无穷大。这是 而不是 因为 yes 有无限输出。任何具有大输出的命令都会挂起（例如 /bin/cat /etc/dictionaries-common/words 以相同的方式挂起）。您可以通过查看 strace 输出来证明这一点：

$ sudo strace -p $(pgrep yes)

strace: Process 21056 attached
write(1, "/home/sehe/Projects/stackoverflo"..., 8170

"fix"最简单的方法是在填满输出缓冲区后关闭输出接收器：

boost::asio::async_read(m_oAsyncPipe_Out, boost::asio::buffer(m_oAsyncBuffer_Out),
    [&](const boost::system::error_code &ec, std::size_t size) {
        std::cout << "read completion handler: size = " << size << " (" << ec.message() << ")" << std::endl;
        nReadSize = size;
        m_oAsyncPipe_Out.close();
    });

这要求您在调用 wait() 之前预计 child 已退出，因此 wait() 可能会失败：

Live On Coliru

Launched: Success
read started
read completion handler: size = 8192 (Success)
io_service stopped
initiate child::wait
wait completed (Success)

退一步：您需要什么？

不过，看起来您可能把问题复杂化了。如果您乐于将输出限制为 8k，并且您所需要的只是拥有多个副本，那么为什么还要使用 async io？

任何child已经是异步的，你可以只传递缓冲区：

Live On Coliru

#include <boost/asio.hpp>
#include <boost/process.hpp>
#include <iostream>

namespace bp   = boost::process;
using Args     = std::vector<std::string>;
using Buffer8k = std::array<char, 8192>;

int main() {
    auto first_out  = std::make_unique<Buffer8k>(),
         second_out = std::make_unique<Buffer8k>();

    *first_out = {};
    *second_out = {};

    boost::asio::io_service svc;

    bp::child first("/bin/echo", Args{"-n", "first"}, bp::std_out > boost::asio::buffer(*first_out), svc);
    bp::child second("/bin/echo", Args{"-n", "second"}, bp::std_out >boost::asio::buffer(*second_out), svc);

    std::cout << "Launched" << std::endl;

    svc.run();
    first.wait();
    second.wait();

    std::string const strFirst(first_out->data()); // uses NUL-termination (assumes text output)
    std::string const strSecond(second_out->data()); // uses NUL-termination (assumes text output)

    std::cout << strFirst << "\n";
    std::cout << strSecond << "\n";

    return first.exit_code();
}

版画

Launched
first
second

如何通过 boost 子进程的异步运行测试实例计数器？

How to test an instance counter by asynchronous run of a boost childprocess?

boost

parallel-processing

boost-asio

boost-process

使用`io_service`

挂断 Child

退一步：您需要什么？

更多示例

如何通过 boost 子进程的异步 运行 测试实例计数器？

How to test an instance counter by asynchronous run of a boost childprocess?

boost

parallel-processing

boost-asio

boost-process

使用io_service

挂断 Child

退一步：您需要什么？

更多示例

如何通过 boost 子进程的异步运行测试实例计数器？

使用`io_service`