__init__(self, reactor, command, args, environment, path, proto, uid=None, gid=None, childFDs=None)
(Constructor)

Spawn an operating-system process.

This is where the hard work of disconnecting all currently open
files / forking / executing the new process happens.  (This is
executed automatically when a Process is instantiated.)

This will also run the subprocess as a given user ID and group ID, if
specified.  (Implementation Note: this doesn't support all the arcane
nuances of setXXuid on UNIX: it will assume that either your effective
or real UID is 0.)

@param childFDs: a dictionary mapping
    fd_in_child -> current_fd_in_parent/'r'/'w'

     If the value is a number, it specifies one of the parent's fds
     that will be remapped to the child's fd. This is useful for
     things like inetd and shell-like file redirection.

     If it is the string 'r', a pipe will be created and attached to
     the child at that fd number, and the parent will be able to
     read from the pipe. This is useful for the child's stdout and
     stderr.

     If it is the string 'w', a pipe will be created and attached,
     and the parent will be able to write into that pipe. This is
     useful for the child's stdin.

    If childFDs is not passed, the default behaviour is to use a
    mapping that opens the usual stdin/stdout/stderr pipes.

_setupChild(self, fdmap)

fdmap[childFD] = parentFD

The child wants to end up with 'childFD' attached to what used to be
the parent's parentFD. As an example, a bash command run like
'command 2>&1' would correspond to an fdmap of {0:0, 1:1, 2:1}.
'command >foo.txt' would be {0:0, 1:os.open('foo.txt'), 2:2}.

Step 1: close all file descriptors that aren't values of fdmap.
This means 0 .. maxfds.

Step 2: for each childFD:
 if fdmap[childFD] == childFD, the descriptor is already in place.
 Make sure the CLOEXEC flag is not set, then delete the entry from
 fdmap.

 if childFD is in fdmap.values(), then the target descriptor is
 busy. Use os.dup() to move it elsewhere, update all fdmap[childFD]
 items that point to it, then close the original. Then fall through
 to the next case.

 now fdmap[childFD] is not in fdmap.values(), and is free. Use
 os.dup2() to move it to the right place, then close the original.

closeStdin(self)

reapProcess(self)

Try to reap a process (without blocking) via waitpid.

This is called when sigchild is caught or a Process object loses its "connection" (stdout is closed) This ought to result in reaping all zombie processes, since it will be called twice as often as it needs to be.

write(self, data)