[Python-Dev] Portable "spawn" module for core?

[Greg Ward]

On 30 August 1999, To python-dev@python.org said:
> The module as it's currently in the Distutils code is attached.  Let me
> know what you think...

New definition of "attached": I'll just reply to my own message with the 
code I meant to attach.  D'oh!

------------------------------------------------------------------------
"""distutils.spawn

Provides the 'spawn()' function, a front-end to various platform-
specific functions for launching another program in a sub-process."""

# created 1999/07/24, Greg Ward

__rcsid__ = "$Id: spawn.py,v 1.2 1999/08/29 18:20:56 gward Exp $"

import sys, os, string
from distutils.errors import *


def spawn (cmd,
           search_path=1,
           verbose=0,
           dry_run=0):

    """Run another program, specified as a command list 'cmd', in a new
       process.  'cmd' is just the argument list for the new process, ie.
       cmd[0] is the program to run and cmd[1:] are the rest of its
       arguments.  There is no way to run a program with a name different
       from that of its executable.

       If 'search_path' is true (the default), the system's executable
       search path will be used to find the program; otherwise, cmd[0] must
       be the exact path to the executable.  If 'verbose' is true, a
       one-line summary of the command will be printed before it is run.
       If 'dry_run' is true, the command will not actually be run.

       Raise DistutilsExecError if running the program fails in any way;
       just return on success."""

    if os.name == 'posix':
        _spawn_posix (cmd, search_path, verbose, dry_run)
    elif os.name in ( 'nt', 'windows' ):          # ???
        _spawn_nt (cmd, search_path, verbose, dry_run)
    else:
        raise DistutilsPlatformError, \
              "don't know how to spawn programs on platform '%s'" % os.name

# spawn ()

def _spawn_nt ( cmd,
                search_path=1,
                verbose=0,
                dry_run=0):
    import string
    executable = cmd[0]
    if search_path:
        paths = string.split( os.environ['PATH'], os.pathsep)
        base,ext = os.path.splitext(executable)
        if (ext != '.exe'):
            executable = executable + '.exe'
        if not os.path.isfile(executable):
            paths.reverse()         # go over the paths and keep the last one
            for p in paths:
                f = os.path.join( p, executable )
                if os.path.isfile ( f ):
                    # the file exists, we have a shot at spawn working
                    executable = f
    if verbose:
        print string.join ( [executable] + cmd[1:], ' ')
    if not dry_run:
        # spawn for NT requires a full path to the .exe
        rc = os.spawnv (os.P_WAIT, executable, cmd)
        if rc != 0:
            raise DistutilsExecError("command failed: %d" % rc) 

    
                
def _spawn_posix (cmd,
                  search_path=1,
                  verbose=0,
                  dry_run=0):

    if verbose:
        print string.join (cmd, ' ')
    if dry_run:
        return
    exec_fn = search_path and os.execvp or os.execv

    pid = os.fork ()

    if pid == 0:                        # in the child
        try:
            #print "cmd[0] =", cmd[0]
            #print "cmd =", cmd
            exec_fn (cmd[0], cmd)
        except OSError, e:
            sys.stderr.write ("unable to execute %s: %s\n" %
                              (cmd[0], e.strerror))
            os._exit (1)
            
        sys.stderr.write ("unable to execute %s for unknown reasons" % cmd[0])
        os._exit (1)

    
    else:                               # in the parent
        # Loop until the child either exits or is terminated by a signal
        # (ie. keep waiting if it's merely stopped)
        while 1:
            (pid, status) = os.waitpid (pid, 0)
            if os.WIFSIGNALED (status):
                raise DistutilsExecError, \
                      "command %s terminated by signal %d" % \
                      (cmd[0], os.WTERMSIG (status))

            elif os.WIFEXITED (status):
                exit_status = os.WEXITSTATUS (status)
                if exit_status == 0:
                    return              # hey, it succeeded!
                else:
                    raise DistutilsExecError, \
                          "command %s failed with exit status %d" % \
                          (cmd[0], exit_status)
        
            elif os.WIFSTOPPED (status):
                continue

            else:
                raise DistutilsExecError, \
                      "unknown error executing %s: termination status %d" % \
                      (cmd[0], status)
# _spawn_posix ()
------------------------------------------------------------------------

-- 
Greg Ward - software developer                    gward@cnri.reston.va.us
Corporation for National Research Initiatives    
1895 Preston White Drive                           voice: +1-703-620-8990
Reston, Virginia, USA  20191-5434                    fax: +1-703-620-0913