Posted by Jim Morris
on Sun Sep 19 17:26:42 -0700 2010
Recently I needed to deploy an Erlang OTP application to a production
server, and was surprised at the lack of official documentation on how
to do that. My requirements are to have the application run on system
startup, and if the application crashes to have it automatically be
restarted, some optional requirements are to have rotated logs and
to get email notifications if the application does crash.
Erlang itself has several layers of supervision to keep its processes
running, however on occasion the VM itself may crash, if it runs out
of memory for instance. I would want the entire appliction to be
restarted in that case.
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Posted in
Erlang
|
Tags
erlang,OTP,daemon
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2 comments
Posted by Jim Morris
on Wed Nov 11 13:59:07 -0800 2009
I started playing with Grails, and I am planning to rewrite the blog
engine I use for this blog in Grails. As noted
earlier
I wrote it in Merb originally. Although Merb is nice and lite it seems
to be having difficulty keeping up with the gems it is dependent on. A
case in point is Cucumber which it says is its recommended way of
doing integration tests. The current version of Cucumber is very
difficult to get working with Merb. See the
Git source to see how I
finally did it.
While I was learning Grails, I hooked up Postgresql 8.2 to Grails
using the Datasource.groovy file. I turned on SQL logging, and to my
horror saw how it was handling the id's. I have been using Postgresql
for quite a while now, and used to run into problems with the creation
and retrieval of the automatically generated IDs. It seems a lot of
people run into these hard to describe problems, as it appears to
happen rarely and is probably a race condition. With version >= 8.2
Postgresql introduced a way of inserting a new record and returning
the automatically generated id in one atomic statement. This solves
all the problems and is more efficient as it does not require two
queries for each insert.
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Posted in
Grails
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Tags
grails,hibernate,postgresql
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11 comments
Posted by Jim Morris
on Sat Oct 24 14:50:02 -0700 2009
In playing with my new Rovio I decided that my Old MS Sidewinder 3D
Pro Joystick would be an excellent way to control it, as it has the
twist which can rotate the Rovio, and the joystick up/left/down/right
can move the Rovio in those directions while still facing forward.
The problem is that the joystick has a game port connector, and my
Linux workstation does not have a game-port. After doing the obligatory
Googling I found
this Exactly what I
needed, except this was for Windows not Linux. Thinking I would have
to modify the code I contacted Grendel who graciously sent me the
source code for the project, however it turns out the code he wrote
was so good it works as is on Linux, I just needed to modprobe
sidewinder and it worked.
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Posted in
Linux,Embedded,Robotics
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Tags
joystick,usb,soldering
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1 comments
Posted by Jim Morris
on Wed Oct 21 01:32:16 -0700 2009
Around 10 years ago I was playing with some home robotics, built a
simple robot, with some sensors and an on-board Linux-based PC. The
purpose was to experiment with Robot AI, a continuation of my PhD
thesis I started on some 30 years ago, but did not complete.
The robot had a camera, a digital compass, a sonar scanner and a short
range IR range detector, plus some bump detectors. I could control
it over a wifi connection, that was a Orinoco PCMCIA board plugged
into the PC104, 586 based Linux PC that was on-board. All powered by
several batteries.
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Posted in
Linux,Embedded
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Tags
linux,pc104,wpa_supplicant,microdrive
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no comments
Posted by Jim Morris
on Sat Sep 12 16:07:22 -0700 2009
In the process of rewriting my voice server in
Erlang,
I decided a new web-based Javascript UI would also be welcome. One problem of
course is my voice server requires a TCP connection and a UDP socket
for sending voice, not to mention the whole voice capture, playback
thing.
In order for this to work the voice and playback would need to be
written in a Java Applet, so it made sense to put the whole TCP/UDP
communications stuff in there too.
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Posted in
Java,Javascript
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Tags
java,javascript,applet
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no comments
Posted by Jim Morris
on Sat May 02 00:09:36 -0700 2009
Background
I've been using cucumber to do all my integration testing. Usually
testing over the wire to a live system, regardless of what the target
system is written in (Ruby Rails, Merb, Java etc).
... Show more ...
Posted in
Erlang,Cucumber
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Tags
erlang,cucumber,bdd
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8 comments
Posted by Jim Morris
on Mon Apr 13 01:11:57 -0700 2009
In Erlang they have a very neat way of reading TCP packets that have a
header that specifies how big the following packet is. So long as you
send that header as a big-endian integer, you can use the built-in
mechanism. Then gen_tcp, takes care of making sure the entire packet
is read before passing it onto you.
Here is an example of a simple server getting packets from a client
using some simple binary protocol... For instance sending this binary
packet,
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Posted in
Erlang
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Tags
erlang,gen_tcp
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3 comments
Posted by Jim Morris
on Sun Apr 12 16:56:50 -0700 2009
Background
I recently undertook a project to rewrite a voice conference server I
wrote over 10 years ago. This server was written in C++ running on a
Windows Server (originally NT and then win2k). The reason it was
written for win2k was to use
I/O Completion Ports
which were not (and still are not) available on Linux.
Solaris has an equivalent AIO feature but not quite the same. I/O
Completion Ports make very efficient use of multiple CPU's, and the
conference server had to be very fast and handle a large number of
concurrent connections.
... Show more ...
Posted in
Erlang
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Tags
erlang,jinterface
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5 comments
Posted by Jim Morris
on Sun Apr 12 01:26:06 -0700 2009
I haven't blogged much about Java even though it is my primary
programming language. Since I have been doing a lot of Java recently I
thought I'd post something about some of the Java idioms I've used
over the years.
One I have been using a lot recently is a command dispatcher where the
command is text.
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Posted in
Java
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Tags
java,enum,dispatcher
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2 comments
Posted by Jim Morris
on Fri Feb 06 15:04:54 -0800 2009
There is a raging debate in many forums about how to do fixture-like
things. Basically how do you populate a database with test data so you
can run your Specs/Tests/Features.
There are several libraries out there to do this like FactoryGirl,
FixtureReplacement, Machinist, Fixjour etc etc. If you use Rails and
ActiveRecord pick the one you like and be happy ;)
... Show more ...
Posted in
Rails,Merb,Sequel
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Tags
merb,sequel,fixtures
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1 comments
