import os
import sys
import string

MAXFD = 256     # Max number of file descriptors (os.getdtablesize()???)

_active = []

def _cleanup():
    for inst in _active[:]:
        inst.poll()

class Popen3:
    def __init__(self, cmd, capturestderr=0, bufsize=-1):
        if type(cmd) == type(''):
            cmd = ['/bin/sh', '-c', cmd]
        p2cread, p2cwrite = os.pipe()
        c2pread, c2pwrite = os.pipe()
        if capturestderr:
            errout, errin = os.pipe()
        self.pid = os.fork()
        if self.pid == 0:
            # Child
            os.close(0)
            os.close(1)
            if os.dup(p2cread) <> 0:
                sys.stderr.write('popen2: bad read dup\n')
            if os.dup(c2pwrite) <> 1:
                sys.stderr.write('popen2: bad write dup\n')
            if capturestderr:
                os.close(2)
                if os.dup(errin) <> 2: pass
            for i in range(3, MAXFD):
                try:
                    os.close(i)
                except: pass
            try:
                os.execvp(cmd[0], cmd)
            finally:
                os._exit(1)
            # Shouldn't come here, I guess
            os._exit(1)
        os.close(p2cread)
        self.tochild = os.fdopen(p2cwrite, 'w', bufsize)
        os.close(c2pwrite)
        self.fromchild = os.fdopen(c2pread, 'r', bufsize)
        if capturestderr:
            os.close(errin)
            self.childerr = os.fdopen(errout, 'r', bufsize)
        else:
            self.childerr = None
        self.sts = -1 # Child not completed yet
        _active.append(self)
    def poll(self):
        if self.sts < 0:
            try:
                pid, sts = os.waitpid(self.pid, os.WNOHANG)
                if pid == self.pid:
                    self.sts = sts
                    _active.remove(self)
            except os.error:
                pass
        return self.sts
    def wait(self):
        pid, sts = os.waitpid(self.pid, 0)
        if pid == self.pid:
            self.sts = sts
            _active.remove(self)
        return self.sts

def popen2(cmd, bufsize=-1):
    _cleanup()
    inst = Popen3(cmd, 0, bufsize)
    return inst.fromchild, inst.tochild

def popen3(cmd, bufsize=-1):
    _cleanup()
    inst = Popen3(cmd, 1, bufsize)
    return inst.fromchild, inst.tochild, inst.childerr

def _test():
    teststr = "abc\n"
    print "testing popen2..."
    r, w = popen2('cat')
    w.write(teststr)
    w.close()
    assert r.read() == teststr
    print "testing popen3..."
    r, w, e = popen3(['cat'])
    w.write(teststr)
    w.close()
    assert r.read() == teststr
    assert e.read() == ""
    _cleanup()
    assert not _active
    print "All OK"

if __name__ == '__main__':
    _test()