Windows下boost::process长启动目录异常问题求助

问题背景 #

在Windows 10系统中使用boost::process启动子进程时，当子进程的工作目录路径过长，会抛出异常：CreateProcess failed: The directory name is invalid.

为调试该问题，编写了如下测试程序：

#include <boost/process.hpp>
#include <boost/process/async.hpp>
#include <boost/asio/high_resolution_timer.hpp>
#include <iostream>
#include <iomanip>
#include <thread>
#include <string>
#include <filesystem>

namespace bp = boost::process;

void test(const std::filesystem::path& wdir)
{
  boost::asio::io_context io;
  bp::child child;
  try
  {
    std::filesystem::create_directories(wdir);
    std::cout << "exists " << std::filesystem::exists(wdir) << " len " << wdir.generic_wstring().size() << '\n';
    std::cout << "start proc\n";
    child = bp::child(
      "C:/WINDOWS/System32/WindowsPowerShell/v1.0/powershell.exe",
      std::vector<std::string> { "ls" },
      io,
      boost::process::start_dir = LR"(\\?\)" + wdir.generic_wstring());
    std::this_thread::sleep_for(std::chrono::seconds{ 3 });
    child.wait();
  }
  catch (const std::exception& e)
  {
    std::cout << "EXCEPTION " << e.what() << "\n";
  }
  std::cout << "done\n";
}

int main()
{
  std::cout << "short path\n";
  test("D:/tmp/10378020400asdfasdfqw4retf");

  std::cout << "\nlong path\n";
  test("D:/tmp/10378020400826168668/unicode/qwe/aaaqqqwwwiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii/aaaqqqwwwiiiiertzertz/aaaqqqwwwiiiiertzertz/eertz/"
    "iiiiiiiiiiiiiiiiiiiiiiiiiiii/aaaqqqwwwiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii/aaaqqqwwwiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii/aaaqqqwwwiiiiiiiiiiiii"
    "iiiiiiiiiiiiiiiiiii/aaaqqqwwwiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii/aaaqqqwwwiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii/aaaqqqwwwiiiiiiiiiiiiiiiiiiiiii"
    "iiiiiiiiii/aaaqqqwwwiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii/aaaqqqwwwiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii/aaaqqqwwwiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii"
    "i/aaaqqqwwwiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii/aaaqqqwwwiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii/aaaqqqwwwiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii/aaaqqqw"
    "wwiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii/aaaqqqwwwiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii/aaaqqqwwwiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii/aaaqqqwwwiiiiiii"
    "iiiiiiiiiiiiiiiiiiiiiiiii/aaaqqqwwwiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii/aaaqqqwwwiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii/aaaqqqwwwiiiiiiiiiiiiiiii"
    "iiiiiiiiiiiiiiii/aaaqqqwwwiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii/aaaqqqwwwiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii/aaaqqqwwwiiiiiiiiiiiiiiiiiiiiiiiii"
    "iiiiiii/aaaqqqwwwiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii/aaaqqqwwwiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii/aaaqqqwwwiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii/a"
    "aaqqqwwwiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii/aaaqqqwwwiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii/aaaqqqwwwiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii/aaaqqqwwwi"
    "iiiiiiiiiiiiiiiiiiiiiiiiiiiiiii/aaaqqqwwwiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii/aaaqqqwwwiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii/aaaqqqwwwiiiiiiiiii"
    "iiiiiiiiiiiiiiiiiiiiii/aaaqqqwwwiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii/aaaqqqwwwiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii/aaaqqqwwwiiiiiiiiiiiiiiiiiii"
    "iiiiiiiiiiiii/aaaqqqwwwiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii/aaaqqqwwwiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii/aaaqqqwwwiiiiiiiiiiiiiiiiiiiiiiiiiiii"
    "iiii/aaaqqqwwwiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii/aaaqqqwwwiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii/aaaqqqwwwiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii/aaaq"
    "qqwwwiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii/aaaqqqwwwiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii/aaaqqqwwwiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii/aaaqqqwwwiiii"
    "iiiiiiiiiiiiiiiiiiiiiiiiiiii/aaaqqqwwwiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii/aaaqqqwwwiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii/aaaqqqwwwiiiiiiiiiiiii"
    "iiiiiiiiiiiiiiiiiii/");
  return 0;
}

程序输出如下：

short path
exists 1 len 33
start proc
done

long path
exists 1 len 2177
start proc
EXCEPTION  CreateProcess failed: The directory name is invalid.
done

疑问与尝试 #

问题根源似乎在于内部调用的CreateProcessW API，其文档未提及lpCurrentDirectory的长度限制，且已尝试添加\\?\前缀（UNC路径格式）但无效果。现咨询以下问题：

• 这是Windows的固有限制吗？
• 能否通过boost规避该限制？
• 是否有其他Win32 API函数可规避此限制？

已尝试的方案：使用常规路径与UNC路径。

内容的提问来源于stack exchange，提问作者Raphael Grimm