Guice Servlet should allow for on-demand instantiation of servlets

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When using guice-servlet on AppEngine, you can incur a startup penalty on the 
first request as Guice attempts to instantiate all bound servlets and 
dependencies, potentially forcing a large number of class loads.

It would be useful if guice-servlet allowed a configuration mode where servlets 
were loaded on-demand. This would let us amortize the startup costs of the 
application over the first few requests, rather than paying it all upfront on 
the first request.

Original issue reported on code.google.com by mmast...@gmail.com on 24 Jun 2010 at 10:10

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What would the advantage of this be? I think the first request is really where 
you want to take the hit, correct? I mean, I can only think of development 
speed being an issue, but you develop mostly on the local devserver anyway.

The reason I say this is that it's quite complex to split up the lifecycle this 
way--particularly because servlets can depend on each other (how do I know it 
has been initialized if it is called from another servlet?)

Original comment by dha...@gmail.com on 5 Jul 2010 at 7:26

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When running on AppEngine, the first request after a JVM shutdown always 
includes this Guice startup time.  Unfortunately, for low-volume applications, 
this first request can happen as often as once per minute. In the case of our 
application, the total time to run the Guice module code, load all required 
classes from everything in the module, bind the servlets and serve the first 
request ends up being around 10s. The end result of this is that the first 
person to hit our application every minute basically has to wait 10s for it to 
come alive.

I used YourKit and Guice's stopwatch logs to profile my application's startup 
and there's not much going on there beyond simple classloading. I hacked up a 
filter that lived in front of GuiceFilter (and subclassed GuiceFilter to lazily 
initialize the module on the first request rather than using a servlet context 
listener). This filter manages to serve the first request in under 3s. This is 
probably around the fastest you can get a JVM to come back to life on AppEngine.

I believe that solving this would cut down our application's startup time by 
approximately 50% by not initializing every class to serve the first request 
(which is likely the homepage and can be served by memcache in most cases). 

Original comment by mmast...@gmail.com on 5 Jul 2010 at 5:05

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Original comment by sberlin on 22 Feb 2011 at 1:44

• Added labels: Extension-Servlet