Service Name and PID of a Zope Instance

In certain situations it can be quite useful to discern the service name and the PID (process identifier) of a Zope instance - in order to monitor the instance, to control memory usage, or to start a new service, for example. This article descripes a Python program that assists to restart the service via a batch file.

The Zope Windows Service

In order to start or stop a Zope service with standard Windows utilities it is first necessary to discern the name. Looking into the service properties gives us a one-glance chance to do so. The name is composed of the string Zope_ and a number that at first glance might seem rather cryptic.

Typing out the name is annoying and leads to errors. It is a lot easier to have the name generated from the hashcode of the relevant INSTANCE_HOME path. This code fragment provides the service name to the respective Zope service as shown in the screenshot above:

The following Python script generates a batch file entitled restart.bat in the \bin directory of the defined instance. This file stops and starts the Zope service with assistance of Windows' own net start/stop command.

This is the content of the generated batch file:

The PID of an operational Zope process is contained within the \\var\Z2.pid file in the INSTANCE_HOME directory. This script provides the PID as a numerical value. If the process is not running it should return '0'.

Zope Process Memory Usage

The following script returns the current memory usage as pertains the Zope process. The path to the INSTANCE_HOME directory suffices as handoff parameter.

import os

def _getPid(INSTANCE_HOME):
    """
        Returns the PID found in the Z2.pid
        of INSTANCE_HOME as an integer or
        0 if the process is not running.

"""
    filepath = INSTANCE_HOME + '\\var\\Z2.pid'
    try:
        pidfile = file(filepath)
        pid = int(pidfile.read())
    except:
        pid = 0
    return pid

def _executeCmd(cmd):
    """
        Executes a Windows command line programm.
    """
    pipe = os.popen(cmd + ' 2>&1','r')
    txt  = pipe.read()
    pipe.close()
    return txt

def _getTaskList(pid):
	"""
	   Calls a the Windows tasklist command and
	   returns the information for the given PID as an array of lines.
	   The first line contains the column names.
    """
	cmd = """tasklist /FI "PID eq %d" /FO CSV /V""" % (pid)
	result =  _executeCmd(cmd).strip()
	return result.split('\n')

def getRamUsage(INSTANCE_HOME=None):
    """ returns the RAM consumed by this Zope instance """
    pid = _getPid(INSTANCE_HOME)
    ram = _getTaskList(pid)[1].split(",")[4]
    return ram

print getRamUsage("""d:\\testinstance\\instance-9999""")

Conclusion

The functions described above, such as the start / stop function for a Zope isntance or the return of the memory usage value for a particular instance can be used, for example, to stop an instance for a nightly backup of the "Data.fs" files or to monitor the memory usage of a particular instance. It is possible, for example, to forward the value of the current memory being used as a string onto a HTML page. This could be used as a so-called "HTTP Advanced sensor" when using a server monitoring program, such as IPCheck. When surpassing a defined threshold it would thus be possible to trigger an alarm.

Furthermore, these functions can be used in order to display detailed information about the instance, as well as start/stop functions within the ZMI.