From: "phluid61 (Matthew Kerwin)" <matthew@...>
Date: 2013-07-19T08:00:02+09:00
Subject: [ruby-core:56082] [CommonRuby - Feature #8640] Add Time#elapsed to return nanoseconds since creation


Issue #8640 has been updated by phluid61 (Matthew Kerwin).


rosenfeld (Rodrigo Rosenfeld Rosas) wrote:
> Em 18-07-2013 03:03, Aaron Patterson escreveu:
>  >> In that case, would #8096 be a better proposal?  Since that one doesn't even allocate a Time object.
>  > I don't think so.  We need subsecond resolution, which (if we used
>  > #8096) would require a possible bignum allocation (from what I gather in
>  > the ticket).
>  
>  But I believe he has a point, Aaron. Maybe we should avoid allocating a 
>  time object (Time.now) and instead introduce something like Java's 
>  System.currentTimeMillis():
>  
>  start = Benchmark.start
>  operation
>  report start.since_beginning
>  other_operation
>  report start.since_beginning # from start= on
>  report start.since_last_report # since operation
>  
>  This new object would be lighter than Time as it would only contain the 
>  start absolute nanoseconds or millis since epoch, maybe.
>  
>  I haven't given the names much of a thought, but that would be the idea. 
>  Makes sense?

Actually the supplied patch uses clock_gettime(CLOCK_REALTIME), which is already the C equivalent of System.currentTimeMillis().  The only issue is that it allocates a Time object (although it doesn't matter because that happens before the benchmarking commences).  Since the getting of the final time and the calculation of the elapsed duration all happen in C-land, there's very little cost involved, even when the numbers are very large.

However, one of the threads of discussion on #8096 suggested using clock_gettime(CLOCK_MONOTONIC)* or System.nanoTime(), which count from an arbitrary epoch (so the number would usually be smaller and thus more likely to fit into a Fixnum).  It would be quite light to do:

    start = Time.timestamp # clock_gettime(CLOCK_MONOTONIC) => Fixnum
    # ... stuff ...
    delta = start - Time.timestamp # => Fixnum

..even if you have to do more of the logic yourself.

I'm +0 for the original proposal, just because of the naming/kwarg issue, otherwise I'd be +1.


* or CLOCK_PROCESS_CPUTIME_ID or CLOCK_THREAD_CPUTIME_ID if they're available, and that's what you need.
----------------------------------------
Feature #8640: Add Time#elapsed to return nanoseconds since creation
https://bugs.ruby-lang.org/issues/8640#change-40580

Author: tenderlovemaking (Aaron Patterson)
Status: Open
Priority: Normal
Assignee: 
Category: 
Target version: 


Hi,

We time many things in Rails (and so does lots of other code), and I've found that we spend lots of time allocating and subtracting time objects.  For example:

start = Time.now
##  do stuff we want to time
finish = Time.now - start

It would be nice if we could just create one time object and grab the nanoseconds elapsed since the time object was created like so:

start = Time.now
## do stuff we want to time
finished = start.elapsed # => nanoseconds elapsed.

I've attached a patch that implements this feature.


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