On Thu, 4 Apr 2013, Frank Shearar wrote:

> So this isn't exactly a common use case, except on build.squeak.org:
>
> You have a bunch of network tests, so in your #setUp you start up a
> server on some port and in #tearDown you shut down the server. What
> port do you use? Well, it doesn't really matter too much, as long as
> the port's available. So you choose some probably-not-used port, like
> 7799. (WebClient's test suite uses this.) All is almost always well,
> because tests only fail when something's using 7799, which is almost
> never.
>
> build.squeak.org has two executors, which means it can run two builds
> concurrently. Suddenly, if you build SqueakTrunk, you'll trigger
> ExternalPackages, ExternalPackages-Squeak4.3 and External-Squeak4.4.
> Which means you will often execute the same test suite in different
> images at the same time. Suddenly those tests using a hard-coded port
> all fail, causing noise. (Xtreams' test suite is also vulnerable to
> this problem: look at the  XTSocketReadingWritingTest failures in
> http://build.squeak.org/job/ExternalPackages/43/testReport/)
>
> So what do we do?
>
> One approach that I can think of is, like WebClient's test suite, to
> use a method #port returning the port to use in a test. However, #port
> should not return a constant but rather attempt to open a port within
> some range, and return _some_ open port. The problem here is a
> time-of-check-time-of-use race.
>
> Now that might nearly always work. Can anyone think of a better method?

The current socket implementation does exactly what you need. If a port 
is being used, the socket will listen on a random free port. So the 
solution is to ask the created Socket instance for which port it's 
listening on.

Code showing the behavior:

s := Socket newTCP.
s listenOn: 1234 backlogSize: 10.
s port.
s2 := Socket newTCP.
s2 listenOn: 1234 backlogSize: 10.
{ s port. s2 port } "==> #(1234 50542)"


Levente

>
> frank
>
>