EOF to stdin when launching process asynchronously on macOS

[atraastrum]

On macOS 15.6.1 M3 the program below exits due to EOF flag being raised on std::cin after subprocess finishes.

#include <boost/process.hpp>
#include <boost/asio.hpp>
#include <cstdio>
#include <string>
#include <iostream>
#include <future>
#include <vector>

namespace asio = boost::asio;
namespace bp = boost::process::v2;

void runCommand(const std::string &cmd);

int main(int argc, char *argv[]) {
  std::vector<std::future<void>> tasks;
  std::string line;
  while(true) {
    if (!std::getline(std::cin, line)) {
      if (std::cin.eof()) {
        break;
      }
      std::printf("Error reading input?\n");
      std::cin.clear();
      continue;
    }

    if (line == "r") {
      tasks.push_back(std::async(std::launch::async, []() {
        runCommand("/bin/ls");
      }));
    }
  }

  return 0;
}

void runCommand(const std::string &cmd) {
  try {
    std::printf("Running subprocess: %s\n", cmd.c_str());
    asio::io_context ctx;
    bp::process subProcess(ctx, cmd, {}, bp::process_stdio{nullptr});
    subProcess.wait();

    std::printf("Finished running subprocess with exit code %d\n", subProcess.exit_code());
  } catch (const std::exception &ex) {
    std::printf("Error running subprocess: %s\n", ex.what());
  }
}

Compiler

Apple clang version 17.0.0 (clang-1700.0.13.5)
Target: arm64-apple-darwin24.6.0
Thread model: posix
InstalledDir: /Library/Developer/CommandLineTools/usr/bin

Boos version (from vcpkg)

1.89.0

Example run:

boost-process git:(cpp-boost-process) ✗ ./build/main
r
Running subprocess: /bin/ls
CMakeLists.txt	README.md	build		main.cpp	vcpkg.json	vcpkg_installed
Finished running subprocess with exit code 0

[klemens-morgenstern]

What do you expect to read from std::cin ?

[atraastrum]

What do you expect to read from std::cin ?

I expect not to get EOF after reading r\n from stdin and running the command. The program should continue waiting for another line instead of exiting.

[klemens-morgenstern]

Well, you're reading from the parent processes std::cin and redirecting the child process's stdout to the null device.

Every process has it's own set of stdio handles, so you're using the wrong one.

[atraastrum]

You probably meant redirecting stdin to null device.

I am reading command from stdin of parent process e.g. command r to run the ls as child process. Yes correct.

I don't actually care for stdin of child process. I am redirecting it null device just to make sure nothing comes from child process to main process.

Screen.Recording.2025-12-17.at.7.45.21.mov

[klemens-morgenstern]

OK, so why is this a question related to boost.process?

[atraastrum]

Using boost.process to run any child process using std::async with async launcher on macOS results in writing EOF to stdin.

This does not happen on Linux or Windows.

This might be a bug in boost.process.

[klemens-morgenstern]

It might be, even though I don't see how. What happens if you don't redirect the child's stdin to null?

[atraastrum]

What happens if you don't redirect the child's stdin to null?

Nothing changes. EOF is written to stdin.

If child process is launched from main thread no EOF is written and program behaves as expected:

-      tasks.push_back(std::async(std::launch::async, []() {
-        runCommand("/bin/ls");
-      }));
+      runCommand("/bin/ls");
     }
   }
```   

[klemens-morgenstern]

That is odd, it could be asio related. Are you sure the program does exit properly, i.e. reach the line with break?

[atraastrum]

Yes it does

Screen.Recording.2025-12-17.at.14.16.23.mov