[launchd-dev] Launching a process on demand?

[Damien Sorresso]

On Jul 6, 2009, at 10:11 PM, Conrad Taylor wrote:
> Hi, I'm attempting to configure the MySQL launchd plist file to  
> launch MySQL process only when needed.  At this time, it's launched  
> at boot/startup and it stays alive.  At this time, the script looks  
> as follows:
>
> BEGIN org.macports.mysql5.plist:
>
> <?xml version="1.0" encoding="UTF-8"?>
> <!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd 
> ">
> <plist version="1.0">
> <dict>
> 	<key>Debug</key>
> 	<false/>
> 	<key>Label</key>
> 	<string>org.macports.mysql5</string>
> 	<key>OnDemand</key>
> 	<false/>
> 	<key>ProgramArguments</key>
> 	<array>
> 		<string>/opt/local/bin/daemondo</string>
> 		<string>--label=mysql5</string>
> 		<string>--start-cmd</string>
> 		<string>/opt/local/etc/LaunchDaemons/org.macports.mysql5/ 
> mysql5.wrapper</string>
> 		<string>start</string>
> 		<string>;</string>
> 		<string>--stop-cmd</string>
> 		<string>/opt/local/etc/LaunchDaemons/org.macports.mysql5/ 
> mysql5.wrapper</string>
> 		<string>stop</string>
> 		<string>;</string>
> 		<string>--restart-cmd</string>
> 		<string>/opt/local/etc/LaunchDaemons/org.macports.mysql5/ 
> mysql5.wrapper</string>
> 		<string>restart</string>
> 		<string>;</string>
> 		<string>--pid=none</string>
> 	</array>
> 	<key>RunAtLoad</key>
> 	<false/>
> </dict>
> </plist>
>
> END org.macports.mysql5.plist:

When you start inserting semi-colons into your ProgramArguments, it's  
time to wrap it all up in a simple shell script.

> I changed the above key/value pair to OnDemand/true.  Now, the  
> process doesn't start when I try to access it by doing the following:

OnDemand is deprecated. If you want the job launched on-demand, you  
can define a Sockets dictionary or a MachServices dictionary. Though  
since you're dealing with MySQL, I'm guessing you want the former. To  
see an example of a job that's launched on-demand when there is a  
connection to a socket, check out the SampleD example and  
BetterAuthorizationSample.

> Is there a manual which clearly describes these key/value pairs?  I  
> guess I'm interested in the key/value pair, OnDemand, and when/how  
> it works.

launchd.plist(5)
-- 
Damien Sorresso
BSD Engineering
Apple Inc.

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