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()
