allow Histograms and Summaries to time Callables

[yarosla]

@brian-brazil

Another usability enhancement allowing instead of:

    String v;
    try (Summary.Timer timer = summary.startTimer()) {
      v = someMethod();
    }

to write:

    String v = summary.time(this::someMethod);

This is especially useful when programming (reactive) streams.

Trying to make metric code as unobtrusive as possible.

BTW Micrometer already does that.

[brian-brazil]

e.g.

[yarosla]

There is no example in existing time() method, but I can certainly add one here.

[brian-brazil]

I meant that i.e. is incorrect as it can be any Callable, not just a Java 8 Lambda.

[yarosla]

I see. Then on old method this should also be corrected, as I copied text from there.

[brian-brazil]

Yes, I must have missed that back when that was added.

[brian-brazil]

Gauge also has a time() method

[yarosla]

I can add that too.

[brian-brazil]

Why are you wrapping this exception rather than just letting it propagate naturally?

[yarosla]

Cause in most cases there will be no checked exceptions within that Callable.

And I would not make time() method throw checked exception, as this will require try-catch around it, which makes usage in streams quite painful.

Supplier class would be much more appropriate for this method but there is only a Callable alternative in Java 6.

[brian-brazil]

Okay

[yarosla]

I've fixed all the comments. Don't know how to deal with this DCO thing.

[brian-brazil]

The easiest thing to do is to squash the commits with rebase, and make sure the remaining commit has the signoff.

[yarosla]

I've created new PR #378 from squashed branch.