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Spawnling News Spawnling Installation git rubygem configure Usage Options be nice fork me kill or be killed a process by any other name Forking vs. Threading Acknowledgements
Spawnling
Also, now runs with ruby 1.9 (and later). Because ruby “stole” the name “spawn”, this gemnow has been redefined to use “Spawnling.new(&block)” instead of “spawn(&block)”. Otherthan that nothing has changed in the basic usage. Read below for detailed usage.
SpawnlingThis gem provides a “Spawnling” class to easily fork OR thread long-running sections ofcode so that your application can return results to your users more quickly.It works by creating new database connections in ActiveRecord::Base for thespawned block so that you don”t have to worry about database connections working,they just do.
The gem also patches ActiveRecord::Base to handle some known bugs when usingthreads if you prefer using the threaded model over forking.
Installation
The name of the gem is “spawnling” (unfortunately somebody took the name “spawn” beforeI was able to convert this to a gem).
git
If you want to live on the latest master branch, add this to your Gemfile,
gem “spawnling”, :git => “https://travelhome.vn/tra/spawnling”
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and use bundler to manage it (bundle install, bundle update).
rubygem
If you”d rather install from the latest gem,
gem “spawnling”, “~>2.1”
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configure
Make sure that ActiveRecord reconnects to your database automatically when needed,for instance put
production/development: … reconnect: true
into your config/database.yml.
Usage
Here”s a simple example of how to demonstrate the spawn plugin.In one of your controllers, insert this code (after installing the plugin of course):
Spawnling.new do logger.info(“I feel sleepy…”) sleep 11 logger.info(“Time to wake up!”)end
If everything is working correctly, your controller should finish quickly then you”ll seethe last log message several seconds later.
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If you need to wait for the spawned processes/threads, then pass the objects returned byspawn to Spawnling.wait(), like this:
spawns = <>N.times do |i| # spawn N blocks of code spawns Spawnling.new do something(i) endend# wait for all N blocks of code to finish runningSpawnling.wait(spawns)
Options
The options you can pass to spawn are:
| :method | :fork, :thread, :yield |
| :nice | integer value 0-19, 19 = really nice |
| :kill | boolean value indicating whether the parent should kill the spawned process when it exits (only valid when :method => :fork) |
| :argv | string to override the process name |
| :detach | boolean value indicating whether the parent should Process.detach the spawned processes. (defaults to true). You *must* Spawnling.wait or Process.wait if you use this. Changing this allows you to wait for the first child to exit instead of waiting for all of them. |
Any option to spawn can be set as a default so that you don”t have to pass them into every call of spawn. To configure the spawn default options, add a line toyour configuration file(s) like this:
Spawnling::default_options :method => :thread
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If you don”t set any default options, the :method will default to :fork. Tospecify different values for different environments, add the default_options call tohe appropriate environment file (development.rb, test.rb). For testing you can setthe default :method to :yield so that the code is run inline.
# in environment.rb Spawnling::default_options :method => :fork, :nice => 7 # in test.rb, will override the environment.rb setting Spawnling::default_options :method => :yield
:fork, :nice => 7 # in test.rb, will override the environment.rb setting Spawnling::default_options :method => :yield” aria-label=”Copy” class=”ClipboardButton btn js-clipboard-copy m-2 p-0 tooltipped-no-delay” data-copy-feedback=”Copied!” data-tooltip-direction=”w”>
This allows you to set your production and development environments to use differentmethods according to your needs.
be nice
If you want your forked child to run at a lower priority than the parent process, pass inthe :nice option like this:
Spawnling.new(:nice => 7) do do_something_nicelyend
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fork me
By default, spawn will use the fork to spawn child processes. You can configure it todo threading either by telling the spawn method when you call it or by configuring yourenvironment.For example, this is how you can tell spawn to use threading on the call,
Spawnling.new(:method => :thread) do somethingend
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When you use threaded spawning, make sure that your application is thread-safe. Railscan be switched to thread-safe mode with (not sure if this is needed anymore)
# Enable threaded mode config.threadsafe!
in environments/your_environment.rb
kill or be killed
Depending on your application, you may want the children processes to go away whenthe parent process exits. By default spawn lets the children live after theparent dies. But you can tell it to kill the children by setting the :kill optionto true.
a process by any other name
If you”d like to be able to identify which processes are spawned by looking at theoutput of ps then set the :argv option with a string of your choice.You should then be able to see this string as the process name whenlisting the running processes (ps).
For example, if you do something like this,
3.times do |i| Spawnling.new(:argv => “spawn -#{i}-“) do something(i) endend
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then in the shell,
$ ps -ef | grep spawn502 2645 2642 0 0:00.01 ttys002 0:00.02 spawn -0-502 2646 2642 0 0:00.02 ttys002 0:00.02 spawn -1-502 2647 2642 0 0:00.02 ttys002 0:00.03 spawn -2-
The length of the process name may be limited by your OS so you might want to experimentto see how long it can be (it may be limited by the length of the original process name).
Forking vs. Threading
There are several tradeoffs for using threading vs. forking. Forking was chosen as thedefault primarily because it requires no configuration to get it working out of the box.
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Forking advantages:
more reliable? – the ActiveRecord code is generally not deemed to be thread-safe.Even though spawn attempts to patch known problems with the threaded implementation,there are no guarantees. Forking is heavier but should be fairly reliable.keep running – this could also be a disadvantage, but you may find you want to forkoff a process that could have a life longer than its parent. For example, maybe youwant to restart your server without killing the spawned processes.We don”t necessarily condone this (i.e. haven”t tried it) but it”s technically possible.easier – forking works out of the box with spawn, threading requires you setallow_concurrency=true (for older versions of Rails).Also, beware of automatic reloading of classes in developmentmode (config.cache_classes = false).
Threading advantages:
less filling – threads take less resources… how much less? it depends. Someflavors of Unix are pretty efficient at forking so the threading advantage may notbe as big as you think… but then again, maybe it”s more than you think.
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