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Asmichi.ChildProcess

A .NET library that provides functionality for creating child processes. Easier, less error-prone, more flexible than System.Diagnostics.Process at creating and interacting with child processes.

This library can be obtained via NuGet.

See the Wiki for the goals and the roadmap.

Comparison with System.Diagnostics.Process

• Concentrates on creating a child process and obtaining its output.
  • Cannot query status of a process.
  • Cannot create a resident process.
• More destinations of redirection:
  • NUL
  • File (optionally appended)
  • Pipe
  • Handle
• Less error-prone default values for redirection:
  • stdin to NUL
  • stdout to the current stdout
  • stderr to the current stderr
• Pipes are asynchronous; asynchronous reads and writes will be handled by IO completion ports.
• Ensures termination of child processes

License

The MIT License

Supported Runtimes

• .NET Core 3.1 or later

RIDs:

• win10-x86 (not tested)
• win10-x64 (1809 or later; tested on 1809)
• win10-arm (not tested)
• win10-arm64 (not tested)
• linux-x64 (tested on Ubuntu 18.04)
• linux-arm (not tested)
• linux-arm64 (not tested)
• linux-musl-arm64 (not tested)
• linux-musl-x64 (tested on Alpine 3.20)
• osx-x64 (macOS 10.15 Catalina or later; tested on 12)
• osx-arm64 (macOS 11.0 Big Sur or later; not tested)

NOTE: On glibc-based Linux, the system must have glibc 2.27 or later and libstdc++ 3.4.25 or later.

Known Issues

• On Windows prior to Windows 11 24H2, each ChildProcess.Start execution leaks one process handle to conhost.exe (except when the child process is successfully attached to the current console using ChildProcessFlags.AttachToCurrentConsole).
  • This is due to a Kernel32 issue.
• On Windows 10 1809 (including Windows Server 2019), SignalTermination just forcibly kills the process tree (the same operation as Kill).
  • This is due to a Windows pseudoconsole bug where ClosePseudoConsole does not terminate applications attached to the pseudoconsole.
• On macOS prior to 11.0, ExitCode for processes killed by a signal will always be -1.
  • This is due to a waitid bug where it returns 0 in siginfo_t.si_status for such processes.

Notes

• When completely rewriting environment variables with ChildProcessCreationContext or ChildProcessFlags.DisableEnvironmentVariableInheritance, it is recommended that you include basic environment variables such as SystemRoot, etc.

Limitations

• More than 2^63 processes cannot be created.

Assumptions on Runtimes

This library assumes that the underlying runtime has the following characteristics:

• Windows
  • The inner value of a SafeFileHandle is a file handle.
  • The inner value of a SafeWaitHandle is a handle that WaitForSingleObject can wait for.
  • The inner value of a SafeProcessHandle is a process handle.
• *nix
  • The inner value of a SafeFileHandle is a file descriptor.
  • The inner value of a SafeProcessHandle is a process id.
  • Socket.Handle returns a socket file descriptor.

Examples

Open ChildProcessExample.sln or see ChildProcess.Example for more examples.

Basic

You can read the output of a child, optionally combining stdout and stderr.

var si = new ChildProcessStartInfo("cmd", "/C", "echo", "foo")
{
    StdOutputRedirection = OutputRedirection.OutputPipe,
    // Works like 2>&1
    StdErrorRedirection = OutputRedirection.OutputPipe,
    // DisableArgumentQuoting: See ChildProcessExamplesWindows.cs for details
    Flags = ChildProcessFlags.DisableArgumentQuoting,
};

using (var p = ChildProcess.Start(si))
{
    using (var sr = new StreamReader(p.StandardOutput))
    {
        // "foo"
        Console.Write(await sr.ReadToEndAsync());
    }
    await p.WaitForExitAsync();
    // ExitCode: 0
    Console.WriteLine("ExitCode: {0}", p.ExitCode);
}

Redirection to File

You can redirect the output of a child into a file without ever reading the output.

var tempFile = Path.GetTempFileName();

var si = new ChildProcessStartInfo("cmd", "/C", "set")
{
    ExtraEnvironmentVariables = new Dictionary<string, string> { { "A", "A" } },
    StdOutputRedirection = OutputRedirection.File,
    StdErrorRedirection = OutputRedirection.File,
    StdOutputFile = tempFile,
    StdErrorFile = tempFile,
    // DisableArgumentQuoting: See ChildProcessExamplesWindows.cs for details
    Flags = ChildProcessFlags.UseCustomCodePage | ChildProcessFlags.DisableArgumentQuoting,
    CodePage = Encoding.Default.CodePage, // UTF-8 on .NET Core
};

using (var p = ChildProcess.Start(si))
{
    await p.WaitForExitAsync();
}

// A=A
// ALLUSERSPROFILE=C:\ProgramData
// ...
Console.WriteLine(File.ReadAllText(tempFile));
File.Delete(tempFile);

True piping

You can pipe the output of a child into another child without ever reading the output.

// Create an anonymous pipe.
using var inPipe = new AnonymousPipeServerStream(PipeDirection.In);

var si1 = new ChildProcessStartInfo("cmd", "/C", "set")
{
    // Connect the output to writer side of the pipe.
    StdOutputRedirection = OutputRedirection.Handle,
    StdErrorRedirection = OutputRedirection.Handle,
    StdOutputHandle = inPipe.ClientSafePipeHandle,
    StdErrorHandle = inPipe.ClientSafePipeHandle,
    // DisableArgumentQuoting: See ChildProcessExamplesWindows.cs for details
    Flags = ChildProcessFlags.UseCustomCodePage | ChildProcessFlags.DisableArgumentQuoting,
    CodePage = Encoding.Default.CodePage, // UTF-8 on .NET Core
};

var si2 = new ChildProcessStartInfo("findstr", "Windows")
{
    // Connect the input to the reader side of the pipe.
    StdInputRedirection = InputRedirection.Handle,
    StdInputHandle = inPipe.SafePipeHandle,
    StdOutputRedirection = OutputRedirection.OutputPipe,
    StdErrorRedirection = OutputRedirection.OutputPipe,
    Flags = ChildProcessFlags.UseCustomCodePage,
    CodePage = Encoding.Default.CodePage, // UTF-8 on .NET Core
};

using var p1 = ChildProcess.Start(si1);
using var p2 = ChildProcess.Start(si2);

// Close our copy of the pipe handles. (Otherwise p2 will get stuck while reading from the pipe.)
inPipe.DisposeLocalCopyOfClientHandle();
inPipe.Close();

using (var sr = new StreamReader(p2.StandardOutput))
{
    // ...
    // OS=Windows_NT
    // ...
    Console.Write(await sr.ReadToEndAsync());
}

await p1.WaitForExitAsync();
await p2.WaitForExitAsync();