Executing pipelines

[magicant]

• Opening a pipe
• Duplicating an FD
• Closing an FD
• Put pipeline commands in Rc Executing pipeline #66
• Running subshells simultaneously (starting a subshell asynchronously) Executing pipeline #66
• Complete partially unimplemented test (pipe_connects_commands_in_pipeline) Selecting in child processes #70
  • Requires select in cat_builtin_main
  • SharedSystem::select should wait until the condition is met (rather than immediately returning 0). Pipes should have some condition variable to wake it up.
    • Can we make System::select async for that?
  • Calling a parent Env's select should also select in child Envs
    • Keep child SharedSystems in parent SharedSystem or in parent VirtualSystem?
    • Call select repeatedly in DummyChildProcess::run?
• Handle Divert in subshell cfa9849
• Convert signal number to exit status for signaled child process
• Handle all wait statuses 856a30d
• Inverting the exit status with the ! keyword
• Method to test I/O on pipes with VirtualSystem
  • System::read
  • System::write
  • Virtual pipe
  • Virtual open file description (pipe reader)
  • Virtual open file description (pipe writer)
  • Virtual open file description (file reader/writer)
  • Virtual file descriptor
  • Default stdin/stdout
  • Dummy cat built-in or something alike

In the minimum implementation of pipeline execution, the shell is not required to wait for all the subshells of a pipeline. It suffices to waiting only for the last subshell, so it is out of scope of this issue to manage all the child processes of a pipeline in the environment. (Do we need to add a pid parameter to System::wait_sync so we can wait for a particular child process?)

[magicant]

Pipeline commands are run in a subshell concurrently, so the command cannot be just borrowed and passed to the subshell. Probably Pipeline should be redefined as:

pub struct Pipeline<H = HereDoc> {
    pub commands: Rc<Vec<Command<H>>>,
    pub negation: bool,
}