processor.py

#!/usr/bin/env python
# -*- coding: utf-8 -*-
#
# OMERO Grid Processor
# Copyright 2008 Glencoe Software, Inc.  All Rights Reserved.
# Use is subject to license terms supplied in LICENSE.txt
#

import os
import time
import signal
import uuid
from omero_ext import killableprocess as subprocess

from path import path

import Ice
import omero
import omero.clients
import omero.scripts
import omero.util
import omero.util.concurrency

from omero.util import load_dotted_class
from omero.util.temp_files import create_path, remove_path
from omero.util.decorators import remoted, perf, locked, wraps
from omero.rtypes import rint, rlong

sys = __import__("sys")


def with_context(func, context):
    """ Decorator for invoking Ice methods with a context """
    def handler(*args, **kwargs):
        args = list(args)
        args.append(context)
        return func(*args, **kwargs)
    handler = wraps(func)(handler)
    return handler


class WithGroup(object):
    """
    Wraps a ServiceInterfacePrx instance and applies
    a "omero.group" to the passed context on every
    invocation.

    For example, using a job handle as root requires logging
    manually into the group. (ticket:2044)
    """

    def __init__(self, service, group_id):
        self._service = service
        self._group_id = str(group_id)

    def _get_ctx(self, group=None):
        ctx = self._service.ice_getCommunicator()\
            .getImplicitContext().getContext()
        ctx = dict(ctx)
        ctx["omero.group"] = group
        return ctx

    def __getattr__(self, name):
        if name.startswith("_"):
            return self.__dict__[name]
        elif hasattr(self._service, name):
            method = getattr(self._service, name)
            ctx = self._get_ctx(self._group_id)
            return with_context(method, ctx)
        raise AttributeError(
            "'%s' object has no attribute '%s'" % (self.service, name))


class ProcessI(omero.grid.Process, omero.util.SimpleServant):
    """
    Wrapper around a subprocess.Popen instance. Returned by ProcessorI
    when a job is submitted. This implementation uses the given
    interpreter to call a file that must be named "script" in the
    generated temporary directory.

    Call is equivalent to:

    cd TMP_DIR
    ICE_CONFIG=./config interpreter ./script >out 2>err &

    The properties argument is used to generate the ./config file.

    The params argument may be null in which case this process
    is being used solely to calculate the parameters for the script
    ("omero.scripts.parse=true")

    If iskill is True, then on cleanup, this process will reap the
    attached session completely.
    """

    def __init__(self, ctx, interpreter, properties, params, iskill=False,
                 Popen=subprocess.Popen,
                 callback_cast=omero.grid.ProcessCallbackPrx.uncheckedCast,
                 omero_home=path.getcwd()):
        """
        Popen and callback_Cast are primarily for testing.
        """
        omero.util.SimpleServant.__init__(self, ctx)
        self.omero_home = omero_home  #: Location for OMERO_HOME/lib/python
        #: Executable which will be used on the script
        self.interpreter = interpreter
        #: Properties used to create an Ice.Config
        self.properties = properties
        #: JobParams for this script. Possibly None if a ParseJob
        self.params = params
        #: Whether or not, cleanup should kill the session
        self.iskill = iskill
        #: Function which should be used for creating processes
        self.Popen = Popen
        #: Function used to cast all ProcessCallback proxies
        self.callback_cast = callback_cast
        # Non arguments (mutable state)
        self.rcode = None  #: return code from popen
        self.callbacks = {}  #: dictionary from id strings to callback proxies
        self.popen = None  #: process. if None then this instance isn't alive.
        self.pid = None  #: pid of the process. Once set, isn't nulled.
        self.started = None  #: time the process started
        self.stopped = None  #: time of deactivation
        #: status which will be sent on set_job_status
        self.final_status = None
        # Non arguments (immutable state)
        #: session this instance is tied to
        self.uuid = properties["omero.user"]

        # More fields set by these methods
        self.make_files()
        self.make_env()
        self.make_config()
        self.logger.info("Created %s in %s" % (self.uuid, self.dir))

    #
    # Initialization methods
    #

    def make_env(self):
        self.env = omero.util.Environment(
            "CLASSPATH",
            "DISPLAY",
            "DYLD_LIBRARY_PATH",
            "HOME",
            "JYTHON_HOME",
            "LD_LIBRARY_PATH",
            "MLABRAW_CMD_STR",
            "OMERO_TEMPDIR",
            "OMERO_TMPDIR",
            "PATH",
            "PYTHONPATH",
        )

        # Since we know the location of our OMERO, we're going to
        # force the value for OMERO_HOME. This is useful in scripts
        # which want to be able to find their location.
        self.env.set("OMERO_HOME", self.omero_home)

        # WORKAROUND
        # Currently duplicating the logic here as in the PYTHONPATH
        # setting of the grid application descriptor (see etc/grid/*.xml)
        # This should actually be taken care of in the descriptor itself
        # by having setting PYTHONPATH to an absolute value. This is
        # not currently possible with IceGrid (without using icepatch --
        # see 39.17.2 "node.datadir).
        self.env.append("PYTHONPATH", str(self.omero_home / "lib" / "python"))
        self.env.set("ICE_CONFIG", str(self.config_path))
        # Also actively adding all jars under lib/server to the CLASSPATH
        lib_server = self.omero_home / "lib" / "server"
        for jar_file in lib_server.walk("*.jar"):
            self.env.append("CLASSPATH", str(jar_file))

    def make_files(self):
        self.dir = create_path("process", ".dir", folder=True)
        self.script_path = self.dir / "script"
        self.config_path = self.dir / "config"
        self.stdout_path = self.dir / "out"
        self.stderr_path = self.dir / "err"

    def make_config(self):
        """
        Creates the ICE_CONFIG file used by the client.
        """
        config_file = open(str(self.config_path), "w")
        try:
            for key in self.properties.iterkeys():
                config_file.write("%s=%s\n" % (key, self.properties[key]))
        finally:
            config_file.close()

    def tmp_client(self):
        """
        Create a client for performing cleanup operations.
        This client should be closed as soon as possible
        by the process
        """
        try:
            client = omero.client(["--Ice.Config=%s" % str(self.config_path)])
            client.setAgent("OMERO.process")
            client.createSession().detachOnDestroy()
            self.logger.debug("client: %s" % client.sf)
            return client
        except:
            self.logger.error("Failed to create client for %s" % self.uuid)
            return None

    #
    # Activation / Deactivation
    #

    @locked
    def activate(self):
        """
        Process creation has to wait until all external downloads, etc
        are finished.
        """

        if self.isActive():
            raise omero.ApiUsageException(None, None, "Already activated")

        self.stdout = open(str(self.stdout_path), "w")
        self.stderr = open(str(self.stderr_path), "w")
        self.popen = self.Popen(
            self.command(),
            cwd=str(self.dir), env=self.env(),
            stdout=self.stdout, stderr=self.stderr)
        self.pid = self.popen.pid
        self.started = time.time()
        self.stopped = None
        self.status("Activated")

    def command(self):
        """
        Method to allow subclasses to override the launch
        behavior by changing the command passed to self.Popen
        """
        return [self.interpreter, "./script"]

    @locked
    def deactivate(self):
        """
        Cleans up the temporary directory used by the process, and terminates
        the Popen process if running.
        """

        if not self.isActive():
            raise omero.ApiUsageException(None, None, "Not active")

        if self.stopped:
            # Prevent recursion since we are reusing kill & cancel
            return

        self.stopped = time.time()
        d_start = time.time()
        self.status("Deactivating")

        # None of these should throw, but just in case
        try:

            self.shutdown()     # Calls cancel & kill which recall this method!
            self.popen = None   # Now we are finished

            client = self.tmp_client()
            try:
                self.set_job_status(client)
                self.cleanup_output()
                self.upload_output(client)  # Important!
                self.cleanup_tmpdir()
            finally:
                if client:
                    client.__del__()  # Safe closeSession

        except Exception:
            self.logger.error(
                "FAILED TO CLEANUP pid=%s (%s)",
                self.pid, self.uuid, exc_info=True)

        d_stop = time.time()
        elapsed = int(self.stopped - self.started)
        d_elapsed = int(d_stop - d_start)
        self.status("Lived %ss. Deactivation took %ss." % (elapsed, d_elapsed))

    @locked
    def isActive(self):
        """
        Tests only if this instance has a non-None popen attribute. After
        activation this method will return True until the popen itself returns
        a non-None value (self.rcode) at which time it will be nulled and this
        method will again return False
        """
        return self.popen is not None

    @locked
    def wasActivated(self):
        """
        Returns true only if this instance has either a non-null
        popen or a non-null rcode field.
        """
        return self.popen is not None or self.rcode is not None

    @locked
    def isRunning(self):
        return self.popen is not None and self.rcode is None

    @locked
    def isFinished(self):
        return self.rcode is not None

    @locked
    def alreadyDone(self):
        """
        Allows short-cutting various checks if we already
        have a rcode for this popen. A non-None return value
        implies that a process was started and returned
        the given non-None value itself.
        """
        if not self.wasActivated:
            raise omero.InternalException(
                None, None, "Process never activated")
        return self.isFinished()

    #
    # Cleanup methods
    #

    def __del__(self):
        self.cleanup()

    @perf
    @locked
    def check(self):
        """
        Called periodically to keep the session alive. Returns
        False if this resource can be cleaned up. (Resources API)
        """

        if not self.wasActivated():
            return True  # This should only happen on startup, so ignore

        try:
            self.poll()
            self.ctx.getSession().getSessionService().getSession(self.uuid)
            return True
        except:
            self.status("Keep alive failed")
            return False

    @perf
    @locked
    def cleanup(self):
        """
        Deactivates the process (if active) and cleanups the server
        connection. (Resources API)
        """

        if self.isRunning():
            self.deactivate()

        if not self.iskill:
            return

        try:
            sf = self.ctx.getSession(recreate=False)
        except:
            self.logger.debug("Can't get session for cleanup")
            return

        self.status("Killing session")
        svc = sf.getSessionService()
        obj = omero.model.SessionI()
        obj.uuid = omero.rtypes.rstring(self.uuid)
        try:
            while svc.closeSession(obj) > 0:
                pass
            # No action to be taken when iskill == False if
            # we don't have an actual client to worry with.
        except:
            self.logger.error(
                "Error on session cleanup, kill=%s" %
                self.iskill, exc_info=True)

    def cleanup_output(self):
        """
        Flush and close the stderr and stdout streams.
        """
        try:
            if hasattr(self, "stderr"):
                self.stderr.flush()
                self.stderr.close()
        except:
            self.logger.error("cleanup of sterr failed", exc_info=True)
        try:
            if hasattr(self, "stdout"):
                self.stdout.flush()
                self.stdout.close()
        except:
            self.logger.error("cleanup of sterr failed", exc_info=True)

    def set_job_status(self, client):
        """
        Sets the job status
        """
        if not client:
            self.logger.error(
                "No client: Cannot set job status for pid=%s (%s)",
                self.pid, self.uuid)
            return

        gid = client.sf.getAdminService().getEventContext().groupId
        handle = WithGroup(client.sf.createJobHandle(), gid)
        try:
            status = self.final_status
            if status is None:
                status = (self.rcode == 0 and "Finished" or "Error")
            handle.attach(long(self.properties["omero.job"]))
            oldStatus = handle.setStatus(status)
            self.status(
                "Changed job status from %s to %s" % (oldStatus, status))
        finally:
            handle.close()

    def upload_output(self, client):
        """
        If this is not a params calculation (i.e. parms != null) and the
        stdout or stderr are non-null, they they will be uploaded and
        attached to the job.
        """
        if not client:
            self.logger.error(
                "No client: Cannot upload output for pid=%s (%s)",
                self.pid, self.uuid)
            return

        if self.params:
            out_format = self.params.stdoutFormat
            err_format = self.params.stderrFormat
        else:
            out_format = "text/plain"
            err_format = out_format

        self._upload(client, self.stdout_path, "stdout", out_format)
        self._upload(client, self.stderr_path, "stderr", err_format)

    def _upload(self, client, filename, name, format):

        if not format:
            return

        filename = str(filename)  # Might be path.path
        sz = os.path.getsize(filename)
        if not sz:
            self.status("No %s" % name)
            return

        try:
            ofile = client.upload(filename, name=name, type=format)
            jobid = long(client.getProperty("omero.job"))
            link = omero.model.JobOriginalFileLinkI()
            if self.params is None:
                link.parent = omero.model.ParseJobI(rlong(jobid), False)
            else:
                link.parent = omero.model.ScriptJobI(rlong(jobid), False)
            link.child = ofile.proxy()
            client.getSession().getUpdateService().saveObject(link)
            self.status(
                "Uploaded %s bytes of %s to %s" %
                (sz, filename, ofile.id.val))
        except:
            self.logger.error(
                "Error on upload of %s for pid=%s (%s)",
                filename, self.pid, self.uuid, exc_info=True)

    def cleanup_tmpdir(self):
        """
        Remove all known files and finally the temporary directory.
        If other files exist, an exception will be raised.
        """
        try:
            remove_path(self.dir)
        except:
            self.logger.error(
                "Failed to remove dir %s" % self.dir, exc_info=True)

    #
    # popen methods
    #

    def status(self, msg=""):
        if self.isRunning():
            self.rcode = self.popen.poll()
        self.logger.info("%s : %s", self, msg)

    @perf
    @remoted
    def poll(self, current=None):
        """
        Checks popen.poll() (if active) and notifies all callbacks
        if necessary. If this method returns a non-None value, then
        the process will be marked inactive.
        """

        if self.alreadyDone():
            return rint(self.rcode)

        self.status("Polling")
        if self.rcode is None:
            # Haven't finished yet, so do nothing.
            return None
        else:
            self.deactivate()
            rv = rint(self.rcode)
            self.allcallbacks("processFinished", self.rcode)
            return rv

    @perf
    @remoted
    def wait(self, current=None):
        """
        Waits on popen.wait() to return (if active) and notifies
        all callbacks. Marks this process as inactive.
        """

        if self.alreadyDone():
            return self.rcode

        self.status("Waiting")
        self.rcode = self.popen.wait()
        self.deactivate()
        self.allcallbacks("processFinished", self.rcode)
        return self.rcode

    def _term(self):
        """
        Attempts to cancel the process by sending SIGTERM
        (or similar)
        """
        try:
            self.status("os.kill(TERM)")
            os.kill(self.popen.pid, signal.SIGTERM)
        except AttributeError:
            self.logger.debug("No os.kill(TERM). Skipping cancel")

    def _send(self, iskill):
        """
        Helper method for sending signals. This method only
        makes a call is the process is active.
        """
        if self.isRunning():
            try:
                if self.popen.poll() is None:
                    if iskill:
                        self.status("popen.kill(True)")
                        self.popen.kill(True)
                    else:
                        self._term()

                else:
                    self.status("Skipped signal")
            except OSError, oserr:
                self.logger.debug(
                    "err on pid=%s iskill=%s : %s", self.popen.pid, iskill,
                    oserr)

    @perf
    @remoted
    def cancel(self, current=None):
        """
        Tries to cancel popen (if active) and notifies callbacks.
        """

        if self.alreadyDone():
            return True

        self.final_status = "Cancelled"
        self._send(iskill=False)
        finished = self.isFinished()
        if finished:
            self.deactivate()
        self.allcallbacks("processCancelled", finished)
        return finished

    @perf
    @remoted
    def kill(self, current=None):

        if self.alreadyDone():
            return True

        self.final_status = "Cancelled"
        self._send(iskill=True)
        finished = self.isFinished()
        if finished:
            self.deactivate()
        self.allcallbacks("processKilled", finished)
        return finished

    @perf
    @remoted
    def shutdown(self, current=None):
        """
        If self.popen is active, then first call cancel, wait a period of
        time, and finally call kill.
        """

        if self.alreadyDone():
            return

        self.status("Shutdown")
        try:
            for i in range(5, 0, -1):
                if self.cancel():
                    break
                else:
                    self.logger.warning(
                        "Shutdown: %s (%s). Killing in %s seconds.", self.pid,
                        self.uuid, 6*(i-1)+1)
                    self.stop_event.wait(6)
            self.kill()
        except:
            self.logger.error(
                "Shutdown failed: %s (%s)", self.pid, self.uuid,
                exc_info=True)

    #
    # Callbacks
    #

    @remoted
    @locked
    def registerCallback(self, callback, current=None):
        try:
            id = callback.ice_getIdentity()
            key = "%s/%s" % (id.category, id.name)
            callback = callback.ice_oneway()
            callback = self.callback_cast(callback)
            if not callback:
                e = "Callback is invalid"
            else:
                self.callbacks[key] = callback
                self.logger.debug("Added callback: %s", key)
                return
        except Exception, ex:
            e = ex
        # Only reached on failure
        msg = "Failed to add callback: %s. Reason: %s" % (callback, e)
        self.logger.debug(msg)
        raise omero.ApiUsageException(None, None, msg)

    @remoted
    @locked
    def unregisterCallback(self, callback, current=None):
        try:
            id = callback.ice_getIdentity()
            key = "%s/%s" % (id.category, id.name)
            if key not in self.callback:
                raise omero.ApiUsageException(
                    None, None, "No callback registered with id: %s" % key)
            del self.callbacks[key]
            self.logger.debug("Removed callback: %s", key)
        except Exception, e:
            msg = "Failed to remove callback: %s. Reason: %s" % (callback, e)
            self.logger.debug(msg)
            raise omero.ApiUsageException(None, None, msg)

    @locked
    def allcallbacks(self, method, arg):
        self.status("Callback %s" % method)
        for key, cb in self.callbacks.items():
            try:
                m = getattr(cb, method)
                m(arg)
            except Ice.LocalException:
                self.logger.debug(
                    "LocalException calling callback %s on pid=%s (%s)"
                    % (key, self.pid, self.uuid), exc_info=False)
            except:
                self.logger.error(
                    "Error calling callback %s on pid=%s (%s)"
                    % (key, self.pid, self.uuid), exc_info=True)

    def __str__(self):
        return "<proc:%s,rc=%s,uuid=%s>" % (
            self.pid, (self.rcode is None and "-" or self.rcode), self.uuid)


class MATLABProcessI(ProcessI):

    def make_files(self):
        """
        Modify the script_path field from ProcessI.make_files
        in ordert to append a ".m"
        """
        ProcessI.make_files(self)
        self.script_path = self.dir / "script.m"

    def command(self):
        """
        Overrides ProcessI to call MATLAB idiosyncratically.
        """
        r = "try, cd('%s'); script; " % self.dir
        r += "catch e, disp(e.identifier); disp(e.message); exit(1); "
        r += "end, exit(0)"
        matlab_cmd = [
            self.interpreter, "-nosplash", "-nodisplay", "-nodesktop", "-r", r,
        ]
        return matlab_cmd


class UseSessionHolder(object):

    def __init__(self, sf):
        self.sf = sf

    def check(self):
        try:
            self.sf.keepAlive(None)
            return True
        except:
            return False

    def cleanup(self):
        pass


class ProcessorI(omero.grid.Processor, omero.util.Servant):

    def __init__(self, ctx, needs_session=True, use_session=None,
                 accepts_list=None, cfg=None, omero_home=path.getcwd(),
                 category=None):

        if accepts_list is None:
            accepts_list = []

        self.category = category  #: Category to be used w/ ProcessI
        self.omero_home = omero_home

        # Extensions for user-mode processors (ticket:1672)

        self.use_session = use_session
        """
        If set, this session will be returned from internal_session and
        the "needs_session" setting ignored.
        """

        if self.use_session:
            needs_session = False

        self.accepts_list = accepts_list
        """
        A list of contexts which will be accepted by this user-mode
        processor.
        """

        omero.util.Servant.__init__(self, ctx, needs_session=needs_session)
        if cfg is None:
            self.cfg = os.path.join(omero_home, "etc", "ice.config")
            self.cfg = os.path.abspath(self.cfg)
        else:
            self.cfg = cfg

        # Keep this session alive until the processor is finished
        self.resources.add(UseSessionHolder(use_session))

    def setProxy(self, prx):
        """
        Overrides the default action in order to register this proxy
        with the session's sharedResources to register for callbacks.
        The on_newsession handler will also keep new sessions informed.

        See ticket:2304
        """
        omero.util.Servant.setProxy(self, prx)
        session = self.internal_session()
        self.register_session(session)

        # Keep other session informed
        self.ctx.on_newsession = self.register_session

    def user_client(self, agent):
        """
        Creates an omero.client instance for use by
        users.
        """
        args = ["--Ice.Config=%s" % (self.cfg)]
        rtr = self.internal_session().ice_getRouter()
        if rtr:
            # FIXME : How do we find an internal router?
            args.insert(0, "--Ice.Default.Router=%s" % rtr)
        client = omero.client(args)
        client.setAgent(agent)
        return client

    def internal_session(self):
        """
        Returns the session which should be used for lookups by this instance.
        Some methods will create a session based on the session parameter.
        In these cases, the session will belong to the user who is running a
        script.
        """
        if self.use_session:
            return self.use_session
        else:
            return self.ctx.getSession()

    def register_session(self, session):
        self.logger.info("Registering processor %s", self.prx)
        prx = omero.grid.ProcessorPrx.uncheckedCast(self.prx)
        session.sharedResources().addProcessor(prx)

    def lookup(self, job):
        sf = self.internal_session()
        gid = job.details.group.id.val
        handle = WithGroup(sf.createJobHandle(), gid)
        try:
            handle.attach(job.id.val)
            if handle.jobFinished():
                handle.close()
                raise omero.ApiUsageException("Job already finished.")

            prx = WithGroup(sf.getScriptService(), gid)
            file = prx.validateScript(job, self.accepts_list)

        except omero.SecurityViolation:
            self.logger.debug(
                "SecurityViolation on validate job %s from group %s",
                job.id.val, gid)
            file = None

        return file, handle

    @remoted
    def willAccept(self, userContext, groupContext, scriptContext, cb,
                   current=None):

        userID = None
        if userContext is not None:
            userID = userContext.id.val

        groupID = None
        if groupContext is not None:
            groupID = groupContext.id.val

        scriptID = None
        if scriptContext is not None:
            scriptID = scriptContext.id.val

        if scriptID:
            try:
                file, handle = self.lookup(scriptContext)
                handle.close()
                valid = (file is not None)
            except:
                self.logger.error(
                    "File lookup failed: user=%s, group=%s, script=%s",
                    userID, groupID, scriptID, exc_info=1)
                return  # EARlY EXIT !
        else:
            valid = False
            for x in self.accepts_list:
                if isinstance(x, omero.model.Experimenter) and \
                        x.id.val == userID:
                    valid = True
                elif isinstance(x, omero.model.ExperimenterGroup) and \
                        x.id.val == groupID:
                    valid = True

        self.logger.debug(
            "Accepts called on: user:%s group:%s scriptjob:%s - Valid: %s",
            userID, groupID, scriptID, valid)

        try:
            id = self.internal_session().ice_getIdentity().name
            cb = cb.ice_oneway()
            cb = omero.grid.ProcessorCallbackPrx.uncheckedCast(cb)
            prx = omero.grid.ProcessorPrx.uncheckedCast(self.prx)
            cb.isProxyAccepted(valid, id, prx)
        except Exception, e:
            self.logger.warn(
                "callback failed on willAccept: %s Exception:%s", cb, e)

        return valid

    @remoted
    def requestRunning(self, cb, current=None):

        try:
            cb = cb.ice_oneway()
            cb = omero.grid.ProcessorCallbackPrx.uncheckedCast(cb)
            servants = list(self.ctx.servant_map.values())
            rv = []

            for x in servants:
                try:
                    rv.append(long(x.properties["omero.job"]))
                except:
                    pass
            cb.responseRunning(rv)
        except Exception, e:
            self.logger.warn(
                "callback failed on requestRunning: %s Exception:%s", cb, e)

    @remoted
    def parseJob(self, session, job, current=None):
        self.logger.info(
            "parseJob: Session = %s, JobId = %s" % (session, job.id.val))
        client = self.user_client("OMERO.parseJob")

        try:
            iskill = False
            client.joinSession(session).detachOnDestroy()
            properties = {}
            properties["omero.scripts.parse"] = "true"
            prx, process = self.process(
                client, session, job, current, None, properties, iskill)
            process.wait()
            rv = client.getOutput("omero.scripts.parse")
            if rv is not None:
                return rv.val
            else:
                self.logger.warning(
                    "No output found for omero.scripts.parse. Keys: %s"
                    % client.getOutputKeys())
                return None
        finally:
            client.closeSession()
            del client

    @remoted
    def processJob(self, session, params, job, current=None):
        """
        """
        self.logger.info("processJob: Session = %s, JobId = %s"
                         % (session, job.id.val))
        client = self.user_client("OMERO.processJob")
        try:
            client.joinSession(session).detachOnDestroy()
            prx, process = self.process(
                client, session, job, current, params, iskill=True)
            return prx
        finally:
            client.closeSession()
            del client

    @perf
    def process(self, client, session, job, current, params, properties=None,
                iskill=True):
        """
        session: session uuid, used primarily if client is None
        client: an omero.client object which should be attached to a session
        """

        if properties is None:
            properties = {}

        if not session or not job or not job.id:
            raise omero.ApiUsageException("No null arguments")

        file, handle = self.lookup(job)

        try:
            if not file:
                raise omero.ApiUsageException(
                    None, None,
                    "Job should have one executable file attached.")

            sf = self.internal_session()
            if params:
                self.logger.debug("Checking params for job %s" % job.id.val)
                svc = sf.getSessionService()
                inputs = svc.getInputs(session)
                errors = omero.scripts.validate_inputs(
                    params, inputs, svc, session)
                if errors:
                    errors = "Invalid parameters:\n%s" % errors
                    raise omero.ValidationException(None, None, errors)

            properties["omero.job"] = str(job.id.val)
            properties["omero.user"] = session
            properties["omero.pass"] = session
            properties["Ice.Default.Router"] = \
                client.getProperty("Ice.Default.Router")

            launcher, ProcessClass = self.find_launcher(current)
            process = ProcessClass(self.ctx, launcher, properties, params,
                                   iskill, omero_home=self.omero_home)
            self.resources.add(process)

            # client.download(file, str(process.script_path))
            scriptText = sf.getScriptService().getScriptText(file.id.val)
            process.script_path.write_bytes(scriptText)

            self.logger.info("Downloaded file: %s" % file.id.val)
            s = client.sha1(str(process.script_path))
            if not s == file.hash.val:
                msg = "Sha1s don't match! expected %s, found %s" \
                    % (file.hash.val, s)
                self.logger.error(msg)
                process.cleanup()
                raise omero.InternalException(None, None, msg)
            else:
                process.activate()
                handle.setStatus("Running")

            id = None
            if self.category:
                id = Ice.Identity()
                id.name = "Process-%s" % uuid.uuid4()
                id.category = self.category
            prx = self.ctx.add_servant(current, process, ice_identity=id)
            return omero.grid.ProcessPrx.uncheckedCast(prx), process

        finally:
            handle.close()

    def find_launcher(self, current):
        launcher = ""
        process_class = ""
        if current.ctx:
            launcher = current.ctx.get("omero.launcher", "")
            process_class = current.ctx.get(
                "omero.process", "omero.process.ProcessI")

        if not launcher:
            launcher = sys.executable

        self.logger.info("Using launcher: %s", launcher)
        self.logger.info("Using process: %s", process_class)

        # Imports in omero.util don't work well for this class
        # Handling classes from this module specially.
        internal = False
        parts = process_class.split(".")
        if len(parts) == 3:
            if parts[0:2] == ("omero", "processor"):
                internal = True

        if not process_class:
            ProcessClass = ProcessI
        elif internal:
            ProcessClass = globals()[parts[-1]]
        else:
            ProcessClass = load_dotted_class(process_class)
        return launcher, ProcessClass


def usermode_processor(client, serverid="UsermodeProcessor", cfg=None,
                       accepts_list=None, stop_event=None,
                       omero_home=path.getcwd()):
    """
    Creates and activates a usermode processor for the given client.
    It is the responsibility of the client to call "cleanup()" on
    the ProcessorI implementation which is returned.

    cfg is the path to an --Ice.Config-valid file or files. If none
    is given, the value of ICE_CONFIG will be taken from the environment
    if available. Otherwise, all properties will be taken from the client
    instance.

    accepts_list is the list of IObject instances which will be passed to
    omero.api.IScripts.validateScript. If none is given, only the current
    Experimenter's own object will be passed.

    stop_event is an threading.Event. One will be acquired from
    omero.util.concurrency.get_event if none is provided.
    """

    if cfg is None:
        cfg = os.environ.get("ICE_CONFIG")

    if accepts_list is None:
        uid = client.sf.getAdminService().getEventContext().userId
        accepts_list = [omero.model.ExperimenterI(uid, False)]

    if stop_event is None:
        stop_event = omero.util.concurrency.get_event(name="UsermodeProcessor")

    id = Ice.Identity()
    id.name = "%s-%s" % (serverid, uuid.uuid4())
    id.category = client.getCategory()

    ctx = omero.util.ServerContext(serverid, client.ic, stop_event)
    impl = omero.processor.ProcessorI(
        ctx, use_session=client.sf, accepts_list=accepts_list, cfg=cfg,
        omero_home=omero_home, category=id.category)
    ctx.add_servant(client.adapter, impl, ice_identity=id)
    return impl