Cache compiled classes between scripts

[gbrail]

Rhino generates bytecode every time a script is compiled, and that bytecode goes into the PermGen nutil the script is no longer used and it gets GCed. In a server with hundreds of node.js scripts running, if each is using a large set of modules such as Express, then we end up with hundreds of megabytes of bytecode sitting in PermGen.

We can drastically reduce the memory usage in large deployments by caching bytecode. For instance:

• SHA1 hash each script before compiling it
• Check a thread-safe cache to see if the same script has already been compiled
• Only compile if the bytecode is not cached
• Make the cache use weak / soft / whatever references so that it will be GCed on memory pressure and not grow forever.

[gbrail]

Fixed in 0.7.1.