[SPARK-10001] Consolidate Signaling and SignalLogger.

[rxin]

What changes were proposed in this pull request?

This is a follow-up to #12557, with the following changes:

1. Fixes some of the style issues.
2. Merges Signaling and SignalLogger into a new class called SignalUtils. It was pretty confusing to have Signaling and Signal in one file, and it was also confusing to have two classes named Signaling and one called the other.
3. Made logging registration idempotent.

How was this patch tested?

N/A.

[rxin]

cc @jodersky

[rxin]

can you write a short description here on what this is doing? it's not very straightforward (especially the forall and boolean inversion)

[jodersky]

sure, I initially had comments but thought they were overkill since the behaviour can be deducted from the comments in the register() method. I'll add some more info

[jodersky]

how should I add the comments? Just post them here and you'll update the PR?

[rxin]

sounds good

[jodersky]

/**
     * Called when this handler's signal is received. Note that if the same signal is received
     * before this method returns, it is escalated to the previous handler.
     */
    override def handle(sig: Signal): Unit = {
      // register old handler, will receive incoming signals while this handler is running
      Signal.handle(signal, prevHandler)

      // run all actions, escalate to parent handler if no action says the signal was caught
      // (i.e. all actions return false) 
      val escalate = actions.asScala.forall { action => !action() }
      if (escalate) {
        prevHandler.handle(sig)
      }

      // re-register this handler
      Signal.handle(signal, this)
    }

is this better? I can add even more if you prefer

[rxin]

OK updated.

[SparkQA]

Test build #56673 has finished for PR 12605 at commit fa1c83a.

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

[SparkQA]

Test build #56682 has finished for PR 12605 at commit 9a8f93c.

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

[rxin]

Merging in master.