.nil? can be used on any object and is true if the object is nil.
.empty? can be used on strings, arrays and hashes and returns true if:
- String length == 0
- Array length == 0
- Hash length == 0
Running .empty? on something that is nil will throw a NoMethodError.
That is where .blank? comes in. It is implemented by Rails and will operate on any object as well as work like .empty? on strings, arrays and hashes.
nil.blank? == true
false.blank? == true
[].blank? == true
{}.blank? == true
"".blank? == true
5.blank? == false
0.blank? == false
.blank? also evaluates true on strings which are non-empty but contain only whitespace:
" ".blank? == true
" ".empty? == false
Rails also provides .present?, which returns the negation of .blank?.
Array gotcha: blank? will return false even if all elements of an array are blank. To determine blankness in this case, use all? with blank?, for example:
[ nil, '' ].blank? == false
[ nil, '' ].all? &:blank? == true
Here is how I got this working.
- Use the collectiveidea fork of delayed_job besides being actively maintained, this version has a nice
script/delayed_job daemon you can use with monit. Railscasts has a good episode about this version of delayed_job (ASCIICasts version). This script also has some other nice features, like the ability to run multiple workers. I don't cover that here.
- Install monit. I installed from source because Ubuntu's version is so ridiculously out of date. I followed these instructions to get the standard init.d scripts that come with the Ubuntu packages. I also needed to configure with
./configure --sysconfdir=/etc/monit so the standard Ubuntu configuration dir was picked up.
Write a monit script. Here's what I came up with:
check process delayed_job with pidfile /var/www/app/shared/pids/delayed_job.pid
start program = "/var/www/app/current/script/delayed_job -e production start"
stop program = "/var/www/app/current/script/delayed_job -e production stop"
I store this in my soucre control system and point monit at it with include /var/www/app/current/config/monit in the /etc/monit/monitrc file.
- Configure monit. These instructions are laden with ads but otherwise OK.
- Write a task for capistrano to stop and start.
monit start delayed_job and monit stop delayed_job is what you want to run. I also reload monit when deploying to pick up any config file changes.
Problems I ran into:
daemons gem must be installed for script/delayed_job to run. - You must pass the Rails environment to
script/delayed_job with -e production (for example). This is documented in the README file but not in the script's help output.
- I use Ruby Enterprise Edition, so I needed to get monit to start with that copy of Ruby. Because of the way sudo handles the PATH in Ubuntu, I ended up symlinking
/usr/bin/ruby and /usr/bin/gem to the REE versions.
When debugging monit, I found it helps to stop the init.d version and run it from the th command line, so you can get error messages. Otherwise it is very difficult to figure out why things are going wrong.
sudo /etc/init.d/monit stop
sudo monit start delayed_job
Hopefully this helps the next person who wants to monitor delayed_job with monit.
Best Answer
God leaks memory pretty badly so I chose Monit for my VPS. Monit runs at about 2MB of RAM constantly, whereas my god install running on Ruby 1.8.6 leaked out to about 60MB of RAM in about 36 hours. I didn't want to monitor my system monitoring tool so I scrapped God and went over to Monit and have had absolutely no problems.