Spoon

An Ada 2012 library for posix_spawn() to spawn processes without a fork(). See the paper A fork() in the road why fork() should not be used.

Usage

The package Spoon provides the function Spawn which can either return a Result or a Process. Calling the function which returns a Result will spawn a process, wait for it to exit, and return the exit result. The exit result contains the exit status, signal that caused the process to crash or terminate, or the error code if the process could not be spawned. The function which returns a Process does not wait and returns immediately.

An object of the type Process provides the function Wait_For_Exit, which waits for the process to exit and then return a Result. Additionally, a Process or its process group can be terminated with the procedures Terminate_Process and Terminate_Group.

To capture the standard output and error, provide a pointer to an object implementing the protected interface Output_Capturer. The package Spoon.Output provides the protected type Text_Capturer, which can return an unbounded string.

The parameter Attributes of the function Spawn can be used to reset the effective user and group if the parent process is a setuid binary, or to let the spawned process have its own process group (so that Terminate_Group can be called).

with Ada.Text_IO;
with Spoon.Output;

procedure Example is
   use all type Spoon.Exit_State;
   use type Spoon.Exit_Status;

   Arg_1 : aliased Spoon.Argument := Spoon.To_Argument ("2");

   Result : constant Spoon.Result :=
     Spoon.Spawn ("/bin/sleep", (1 => Arg_1'Unchecked_Access));
begin
   Ada.Text_IO.Put (Result.State'Image & " ");

   case Result.State is
      when Exited =>
         if Result.Exit_Status = Spoon.Success then
            Ada.Text_IO.Put_Line ("OK");
         else
            Ada.Text_IO.Put_Line ("with status" & Result.Exit_Status'Image);
         end if;
      when Crashed | Terminated =>
         Ada.Text_IO.Put_Line ("with signal" & Result.Signal'Image);
      when Error =>
         Ada.Text_IO.Put_Line ("with error" & Result.Error_Code'Image);
   end case;

   declare
      Text : aliased Spoon.Output.Text_Capturer;

      Process : constant Spoon.Process :=
        Spoon.Spawn ("whoami", Output => Text'Access, Kind => Spoon.Name);

      use Spoon.Output;
   begin
      if Process.Wait_For_Exit.State = Exited then
         Ada.Text_IO.Put_Line ("OK: '" & (+Text.Get (Spoon.Standard_Output)) & "'");
      else
         Ada.Text_IO.Put_Line ("not OK");
      end if;
   end;
end Example;

Dependencies

In order to build the library, you need to have:

• An Ada 2012 compiler

• Alire package manager

License

The Ada code is licensed under the Apache License 2.0. The first line of each Ada file should contain an SPDX license identifier tag that refers to this license:

SPDX-License-Identifier: Apache-2.0