[SPARK-9140][MLlib] Replace TimeTracker by Stopwatch

[hhbyyh]

jira: https://issues.apache.org/jira/browse/SPARK-9140
We can replace TImeTracker in tree implementations by Stopwatch. The initial PR could use local stopwatches only.
With the current API of MultiStopwatch:

1. The typical invoking sequence is not reenterable (causes exception)

 multiTimer.addLocal("total")
multiTimer("total").start()
...
multiTimer("total").stop()

1. Maybe we can have a new API combining

 multiTimer.addLocal("total")
multiTimer("total").start()

just for simplification.

next: Shall we keep TimeTracker ?

[SparkQA]

Test build #39431 has finished for PR 7871 at commit 60366ac.

• This patch fails Scala style tests.
• This patch merges cleanly.
• This patch adds no public classes.

[SparkQA]

Test build #39433 has finished for PR 7871 at commit 40f3931.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[mengxr]

@hhbyyh Could you post the exception you saw?

[hhbyyh]

Oh I should have made it more clear. @mengxr An example:

 def run(): Unit ={
val conf = new SparkConf().setMaster("local").setAppName("ss")
val sc = new SparkContext(conf)
val multiTimer = new MultiStopwatch(sc)
for(i <- 0 to 2) {
someFunction(multiTimer)
}
}
def someFunction(multiTimer: MultiStopwatch): Unit ={
multiTimer.addLocal("total")
multiTimer("total").start()
// ...
multiTimer("total").stop()
}

will throw Exception in thread "main" java.lang.IllegalArgumentException: requirement failed: Stopwatch with name total already exists.
This is probably by design, yet it's not quite handy. Since users will have to:

1. avoid passing MultiStopwatch around as a parameter
2. or avoid invoking someFunction multiple times.

[rxin]

@hhbyyh thanks for the pull request. I'm going through a list of pull requests to cut them down since the sheer number is breaking some of the tooling we have. Due to lack of activity on this pull request, I'm going to push a commit to close it. Feel free to reopen it or create a new one.

[MechCoder]

@hhbyyh What is your opinion about renaming addLocal to addOrGetLocal which returns a local stopwatch if it already exists? That should solve your concerns.