Delete Jenkins job workspaces left after renaming

Tim Pizey from Tim Pizey

When renaming a job or moving one from slave to slave Jenkins copies it and does not delete the original. This script can fix that.

#!/usr/bin/env python
import urllib, json, os, sys
from shutil import rmtree

url = 'http://jenkins/api/python?pretty=true'

data = eval(urllib.urlopen(url).read())
jobnames = []
for job in data['jobs']:

def clean(path):
builds = os.listdir(path)
for build in builds:
if build not in jobnames:
build_path = os.path.join(path, build)
print "removing dir: %s " % build_path


Event Processing with Transducers

Rob Smallshire from Good With Computers

In the previous article in this series on transducers we looked at lazily evaluating transducers. This time we'll look not at pulling output through a transducer chain from downstream, but at pushing input items into the chain from upstream.

All of the uses of transducers we've demonstrated in Python so far are probably better handled by existing and well established Python programming techniques, such as generator expressions and generator functions. At this point in the series, we move definitely beyond that into new territory where transducers bring completely new capabilities to Python.

One the key selling points of transducers is that they abstract the essence of a transformation away from the details of the data series that is being transformed. We'll show this in Python by using transducers to transform a series of events modelled using Python coroutines.

Coroutines in Python

Coroutines in Python are little-used, and their workings are not widely known, so their implementation bears repeating here. If you're familiar with the notion of coroutines in general, and the specifics of how they're implemented in Python, you can skim over this section.

Coroutines are like generator functions insofar as they are resumable functions. In fact, coroutines in Python are generator functions which use yield as an expression rather than a statement. What this means in practice is that generator function objects sport a send() method which allows the client of the generator function to transmit information to a running generator and for the generator to receive this data as the value of the yield expression. As usual, an example will serve to make things clearer.

We'll start by defining a generator function which enters an infinite loop, waits at the yield expression for a value to be received, and then prints this value to the console.

>>> def event_receiver():
...     while True:
...         message = (yield)
...         print("Message:", message)

We create a generator object just the same as we would with any other generator:

>>> r = event_receiver()
>>> r

Now we'll try to send it a message, using the send() method of the generator object:

>>> r.send("message")
Traceback (most recent call last):
  File "", line 1, in
TypeError: can't send non-None value to a just-started generator

This actually fails, because the generator code has not yet been executed at all. We need to prime the pump, so to speak, by advancing execution to the first occurrence of yield. We can do this by passing the generator to the next() built-in:

>>> next(r)

We'll fix this pump-priming annoyance of generator based coroutines shortly.

Now we can send messages:

>>> r.send("message")
Message: message
>>> r.send("another message")
Message: another message

When we're done, we terminate the coroutine by calling the close() method. (This actually raises a GeneratorExit exception at the site of the yield expression, which allows control flow to exit the otherwise infinite loop; this special exception is intercepted by the Python runtime system, so it isn't seen by us at the console).

>>> r.close()

Any further attempts to send() messages into the generator function cause StopIteration to be raised. This, of course, is the normal means of indicating that a generator is exhausted:

>>> r.send("message")
Traceback (most recent call last):
  File "", line 1, in

Priming generator-based coroutines

Now to address the awkwardness of having to prime coroutine generator functions by initially passing them to next(). We can improve this with a function decorator which creates the generator object and calls next on our behalf. We'll call the decorator @coroutine:

def coroutine(func):
    def start(*args, **kwargs):
        g = func(*args, **kwargs)
        return g
    return start

We'll use our new decorator to assist in defining a slightly more sophisticated coroutine for printing, called rprint():

import sys

def rprint(sep='\n', end=''):
    """A coroutine sink which prints received items to stdout

      sep: Optional separator to be printed between received items.
      end: Optional terminator to be printed after the last item.
        first_item = (yield)
        while True:
            item = (yield)
    except GeneratorExit:

In this implementation, we intercept GeneratorExit explicitly to give us the opportunity to print a terminator. We also regularly flush the stream so we get immediate feedback for our following experiments.

Event sources

The opposite of a sink is a source. Until now, we've been sourcing 'events' ourself by sending them from the REPL, but to make this a little more interesting, we'll cook up a function – just a plain old function, not a generator – which takes values from an iterable series and intermittently sends them, after a delay, to anything with a send() method such as our coroutine generators. For fun, the random delay has a so-called Poisson distribution which mimics a radioactive source; imagine a device with a geiger counter which sends the next item from an iterable series each time an atom decays:

def poisson_source(rate, iterable, target):
    """Send events at random times with uniform probability.

      rate: The average number of events to send per second.

      iterable: A series of items which will be sent to the target
          one by one.

      target: The target coroutine or sink.

        The completed value, or None if iterable was exhausted
        and the target was closed.
    for item in iterable:
        duration = random.expovariate(rate)
        except StopIteration as e:
            return e.value
    return None

When either the iterable series is exhausted or the target signals it has terminated (by raising StopIteration) we call close() on the target. Note that by supplying an infinite iterable series we could make the source send events forever.

Let's hook our source and sink together at the REPL:

>>> printer = rprint(sep=', ', end='\nDONE!\n')
>>> count_to_nine = range(10)
>>> poisson_source(rate=0.5, iterable=count_to_nine, target=printer)
0, 1, 2, 3, 4, 5, 6, 7, 8, 9

Combined event sources and event sinks

Of course, we can build functions which act as both sinks and sources, transforming the messages they receive in some way and forwarding the processed results onwards to another sink. Here's a combined source and sink function, which simply doubles the values it receives:

def doubler(target):
    while True:
        item = (yield)
        doubled_item = item * 2
        except StopIteration as e:
            return e.value

To use, doubler() we chain the components of the pipeline together

>>> printer = rprint(sep=', ', end='\nDONE!\n')
>>> count_to_nine = range(10)
>>> poisson_source(rate=0.5,
...                iterable=count_to_nine,
...                target=doubler(target=printer))
0, 2, 4, 6, 8, 10, 12, 14, 16, 18

From doubler() it's but a short hop to a more general mapper() which accepts an arbitrary transforming function:

def mapper(transform, target):
    while True:
        item = (yield)
        transformed_item = transform(item)
        except StopIteration as e:
            return e.value

Used like so,

>>> printer = rprint(sep=', ', end='\nDONE!\n')
>>> count_to_nine = range(10)
>>> poisson_source(rate=0.5, iterable=count_to_nine, target=mapper(transform=square, target=printer))
0, 1, 4, 9, 16, 25, 36, 49, 64, 81

From here, you can see how we could also implement equivalents of filter(), reduce() and so on to operate on the 'push' event stream modelled by Python coroutines.

The point here is that we can't just re-use any existing functions which process 'pull' data series – such as the functions in itertools – with 'push' data series. Each and every function needs to be reimplemented to accept values pushed from upstream, and send processed results downstream.

Transducing events

Transducers provide a way out of this quandary. We've demonstrated earlier in this series that 'reduce' is a fundamental operation, and by reimagining reduce() into a more general transduce() we were able to use the same transducers to operate on both eager and lazy data series. We can do the same with coroutine-based push events, by implementing a version of transduce() which allows us to use any transducer to process a stream of such events.

Our reactive_transduce() is a coroutine which accepts two arguments: a transducer and a target sink to which the transduced results will be sent:

def reactive_transduce(transducer, target=None):
    reducer = transducer(sending())
    accumulator = target if (target is not None) else reducer.initial()
        while True:
            item = (yield)
            accumulator = reducer.step(accumulator, item)
            if isinstance(accumulator, Reduced):
                accumulator = accumulator.value
    except GeneratorExit:
    return reducer.complete(accumulator)

The reactive_transduce() function connects to the upstream end of a transducer chain, adapting from the coroutine protocol to the reducer interface. At the downstream end of the transducer chain, we need to adapt the other way, from the reducer interface to the coroutine protocol. To do this we use a reducer called Sending, which we hard-wire as the 'bottom' reducer on the first line of reactive_transduce(). The Sending reducer looks like this:

class Sending:
    def initial(self):
        return null_sink()

    def step(self, result, item):
        except StopIteration:
            return Reduced(result)
            return result

    def complete(result):
        return result

The step() method literally sends the next item to the result – which must therefore be a legitimate event sink. Should the sink indicate that it can't accept a further item, by raising StopIteration we return the result wrapped in the Reduced sentinel. The initial() method provides a legitimate sink – just a simple do-nothing sink defined as:

def null_sink():
    while True:
        _ = (yield)

Going back to reactive_transduce() the main loop continues to iterate, receiving new values via a yield expression, until such time as GeneratorExit is signalled by the client or the reducer signals termination by returning Reduced.

When the main loop is exited by whatever means, we give the reducer opportunity to complete(), and the Sending.complete() method ensures that close() is called on the target.

With these pieces in place, let's look at how to use reactive_transduce(). We'll reproduce our previous example where we squared the output from poisson_source(), but this time using the mapping() transducer to do the work:

>>> poisson_source(rate=0.5,
...                iterable=range(10),
...                target=transduce(transducer=mapping(square),
...                target=printer))
0, 1, 4, 9, 16, 25, 36, 49, 64, 81

The key point here is that we can now take an arbitrary transducer and reuse it with eager collections, lazy iterables, and push-events! In fact, simply by devising an appropriate transduce function we can use re-use our transducers in an arbitrary data-series processing context.

This is the true power of transducers: Data processing components completely abstracted away from how the input data arrives, or to where the output results are sent.

Useful regular expressions for searching C++ code with Visual Studio

The Lone C++ Coder's Blog from The Lone C++ Coder's Blog

I’m generally more of a grep person but sometimes it’s easier to just use the built-in search in Visual Studio, especially if you want to be able to restrict the search to parts of your Visual Studio solution. Visual Studio does have pretty powerful search built in if you do use regular expressions instead of the default text matching. Here are a couple of regexes to get you started: Find all shared_ptr calls that use “new” instead of the recommended make_shared: shared_ptr<.

Merging two sets of Jacoco Integration Test Coverage Reports for Sonar using Gradle

Tim Pizey from Tim Pizey

In a Jenkins build:

./gradlew cukeTest
./gradlew integTest
./gradlew sonarrunner

This leaves three .exec files behind. SonarQube can only use two. So we merge the two integration tests results.

task integCukeMerge(type: JacocoMerge) {
description = 'Merge test code coverage results from feign and cucumber'
// This assumes cuketests have already been run in a separate gradle session

doFirst {
delete destinationFile
// Wait until integration tests have actually finished
println start.process != null ? start.process.waitFor() : "In integCukeMerge tomcat is null"

executionData fileTree("${buildDir}/jacoco/it/")


sonarRunner {
tasks.sonarRunner.dependsOn integCukeMerge
sonarProperties {
property "sonar.projectDescription", "A legacy codebase."
property "sonar.exclusions", "**/fakes/**/*.java, **/domain/**.java, **/*"

properties["sonar.tests"] += sourceSets.integTest.allSource.srcDirs

property "sonar.jdbc.url", "jdbc:postgresql://localhost/sonar"
property "sonar.jdbc.driverClassName", "org.postgresql.Driver"
property "sonar.jdbc.username", "sonar"
property "", "http://sonar.we7.local:9000"

def jenkinsBranchName = System.getenv("GIT_BRANCH")
if (jenkinsBranchName != null) {
jenkinsBranchName = jenkinsBranchName.substring(jenkinsBranchName.lastIndexOf('/') + 1)
def branch = jenkinsBranchName ?: ('git rev-parse --abbrev-ref HEAD'.execute().text ?: 'unknown').trim()

def buildName = System.getenv("JOB_NAME")
if (buildName == null) {
property "sonar.projectKey", "${name}"
def username = System.getProperty('')
property "sonar.projectName", "~${name.capitalize()} (${username})"
property "sonar.branch", "developer"
} else {
property "sonar.projectKey", "$buildName"
property "sonar.projectName", name.capitalize()
property "sonar.branch", "${branch}"
property "", "http://jenkins/job/${buildName}/"

property "sonar.projectVersion", "git describe --abbrev=0".execute().text.trim()

property "", "jacoco"
property "sonar.jacoco.reportPath", "$project.buildDir/jacoco/test.exec"
// feign results
//property "sonar.jacoco.itReportPath", "$project.buildDir/jacoco/it/integTest.exec"
// Cucumber results
//property "sonar.jacoco.itReportPath", "$project.buildDir/jacoco/it/cukeTest.exec"
// Merged results
property "sonar.jacoco.itReportPath", "$project.buildDir/jacoco/integCukeMerge.exec"

property "sonar.links.homepage", "${org}/${name}"

Remember to use Overall Coverage in any Sonar Quality Gates!

Writing: Coders Causing Conflict

Pete Goodliffe from Pete Goodliffe

My latest Becoming a Better Programmer column is published in the March issue of C Vu magazine (27.1). It's called Coders Causing Conflict and investigates how "conflict" can be a driving force for good in software development. It's quite an interesting topic, and one worth thinking about.

I realise that I failed to announce my previous few C Vu columns here. So, as a recap:
  • In January (C Vu 26.6) I published Advice for the Young at Heart, considering how to give career advice to new programmers.
  • In November 2014 (C Vu 26.5) I published Playing by the Rules which looks at developing "tribal rules" for your development team to help it work most effectively.

C Vu is a magazine produced by the ACCU - an excellent organisation for programmers. It has a great community, great publications, and an awesome conference. Check it out.

Setting up Emacs spell checking on OS X

The Lone C++ Coder's Blog from The Lone C++ Coder&#039;s Blog

As I mentioned in yesterday’s post, I’m trying to improve my blogging workflow by using org2blog to draft my posts before pushing them to my WordPress blog. When I posted yesterday I had the basic workflow going, could edit posts in Emacs, save them, update drafts and push them to WordPress. The last piece that was missing was getting spell checking to work. I’ve actually never spent much time thinking about spell checkers until I discovered that OS X doesn’t come with a spell checker that ispell recognises.

Improving my blogging workflow using Emacs (of course)

The Lone C++ Coder's Blog from The Lone C++ Coder&#039;s Blog

I try not to post too many metablogging posts. Other people do it better and I’m trying to focus on journalling what I learn as a software engineer and manager, not what tools I use for blogging. However after losing another post to WordPress’s built-in editor I decided Something Must Be Done. I think this is only the second post I lost, but it’s a fairly regular occurrence for a journalist friend of mine and I really don’t have that much time to retype blog entries that ended up in Bit Nirvana.