"ExceptionBlob"

[Russ P.]

I just ran with Java -Xprof profiling enabled, and here is a small sample of what I get:

     Compiled + native   Method                        

 82.7%    86  +     0    ExceptionBlob

  2.9%     3  +     0    scala.collection.mutable.WrappedArray.reduceLeft

  1.9%     2  +     0    scala.collection.mutable.ArrayBuffer.foreach

What is "ExceptionBlob," and what I should look for in my code to stop it from gobbling up so much time? I don't use exceptions much. Thanks.

[Naftoli Gugenheim]

What is your code?

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[Russ P.]

On Tuesday, February 2, 2016 at 2:00:15 PM UTC-8, nafg wrote:

What is your code?

It's an application of many thousands of lines of code. I'm just looking for some general guidance on this "ExceptionBlob" thing. I generally try to steer clear of "blobs" of any sort if possible.

[Jason Zaugg]

That might be an indication that the runtime of your benchmark is dominated by the overhead of throwing/catching exceptions.

See http://erikengbrecht.blogspot.com.au/2009/02/scala-actors-versus-exceptionblob.html and http://erikengbrecht.blogspot.com.au/2009/02/profiling-exceptionblob.html for a discussion on how using exceptions for "regular" control flow can hurt performance. There are some cases where the JVM has gotten quite good at optimizing this away: https://blogs.oracle.com/jrose/entry/longjumps_considered_inexpensive, though.

-jason

[Russ P.]

On Tuesday, February 2, 2016 at 2:43:20 PM UTC-8, Jason Zaugg wrote:

On Wed, Feb 3, 2016 at 7:44 AM Russ P. <russ.p...@gmail.com> wrote:

I just ran with Java -Xprof profiling enabled, and here is a small sample of what I get:

     Compiled + native   Method                        

 82.7%    86  +     0    ExceptionBlob

  2.9%     3  +     0    scala.collection.mutable.WrappedArray.reduceLeft

  1.9%     2  +     0    scala.collection.mutable.ArrayBuffer.foreach

What is "ExceptionBlob," and what I should look for in my code to stop it from gobbling up so much time? I don't use exceptions much. Thanks.

That might be an indication that the runtime of your benchmark is dominated by the overhead of throwing/catching exceptions.

That is why I am baffled. The words "catch,", "throw," and "Exception" barely appear in my code (and not in any critical area).

Could this possibly have something to do with early return statements? I recall hearing some warnings about them several years ago, and I do use them.

[Naftoli Gugenheim]

Return inside a function (not a method) works by throwing an exception.

--

[Jason Zaugg]

def foo: Int = {
  if (condition) return 1 // early return is still efficient, although many people claim they hamper code readability
  val function = () => return 2 // non-local return. this is compiled into `throw new NonLocalReturnException(2) ...
  function()
  34
  // ... and an exception handler is added here to catch that exception and return the value from this method
}

​

-jason

[Russ P.]

I'm glad to hear that early returns are efficient, but that still leaves me wondering why my code is spending 80% of its time in the "ExceptionBlob." I don't do any non-local returns. The Java -Xprof option doesn't seem to tell me where the exceptions are that are eating up so much time. Am I missing something?

[Juha Heljoranta]

Perhaps using more advanced profiling tools such as Mission Control
(http://www.oracle.com/technetwork/java/javaseproducts/mission-control/index.html) or VisualVM (http://visualvm.java.net/) would help?

Cheers,
Juha