Optimize route collecting: Reduce memory usage when there's no routes.cache

[ngocdaothanh]

1 - Problem

When running from console:

java.lang.OutOfMemoryError: PermGen space
Dumping heap to java_pid32500.hprof ...
Heap dump file created [107664867 bytes in 0.659 secs]

When running inside Eclipse, Eclipse will freeze the process.

When there's no routes.cache, Xitrum currently has to load all classes in classpath in order to collect routes from annotations.

When running from console:

• It seems that although there's OutOfMemoryError, routes.cache is still created, so the next run will be OK.
• Increasing MaxMetaspaceSize/MaxPermSize seems to solve the problem.

2 - Solution

• Optimize route collecting: Ignore more packages that obviously don't contain routes #459 Optimize route collecting: Ignore more packages that obviously don't contain routes
• Only load classes that are descendants of xitrum.Action
• Find a way to extract data from Scala annotations without having to load class: https://github.com/json4s/json4s/pull/180/files (maybe it's scalap: https://github.com/scala/scala/tree/2.11.x/src/scalap/scala/tools/scalap/scalax/rules/scalasig)

[ngocdaothanh]

See https://github.com/scala/scala/tree/2.11.x/src/scalap/scala/tools/scalap

xitrum-new is used for the below examples.

---

From command line:

scalap SiteIndex
=>

package quickstart.action
@xitrum.annotation.GET("")
class SiteIndex extends scala.AnyRef with quickstart.action.DefaultLayout {
  def this() = { /* compiled code */ }
  def execute(): scala.Unit = { /* compiled code */ }
}

---

From SBT console:

import scala.tools.scalap.scalax.rules.scalasig._

val b = ByteCode.forClass(classOf[quickstart.action.SiteIndex])  // ByteCode
val c = ClassFileParser.parse(b)  // ClassFile
val s = ScalaSigParser.parse(c).get  // ScalaSig

scala.tools.scalap.Main.parseScalaSignature(s, false)
=>
package quickstart.action
@xitrum.annotation.GET("")
class SiteIndex extends scala.AnyRef with quickstart.action.DefaultLayout {
  def this() = { /* compiled code */ }
  def execute(): scala.Unit = { /* compiled code */ }
}

The above is printed from ScalaSigPrinter's printClass:
https://github.com/scala/scala/blob/2.11.x/src/scalap/scala/tools/scalap/scalax/rules/scalasig/ScalaSigPrinter.scala

To get a ClassSymbol:

val cs = s.topLevelClasses(0)