StringTemplates deferred evaluation

Sun Mar 17 19:41:41 UTC 2024

I guess it is not fair to think about it in terms of premature
optimization. I am trying to look at it from a logging-framework developer
point of view. As a library developer I should give the smallest overhead
possible. So library users could safely do
  LOGGER.debug("Some thing={}, another={}", hugeObject, expensiveObject);
and don't care about anything at all as debug is usually disabled. So the
debug statement could be used even in a tight computation loop without
worries. In other words, logger devs could not assume anything about how
their framework would be used, but they will fight for the easiest to use
api with the fastest performance.
The idea is that the trace is usually disabled and an app could chew-up
gigs of data, but while debugging/investigating, the trace could be
temporarily enabled and expected to degrade performance.

On Sun, 17 Mar 2024 at 17:36, David Alayachew <davidalayachew at gmail.com>
wrote:

> Thank you for the code example. That helps clarify your desired behaviour.
>
> Ok, if your intent is to have absolutely no garbage collection whatsoever,
> then yes, my solution does not guarantee that. How much the JIT will help
> or optimize, I cannot say.
>
> That said, a String is a "blessed type" in Java. It has a handful of
> optimizations that are specific to it and it alone. I am actually expecting
> that StringTemplates will receive at least a small taste of this sort of
> optimization.
>
> Furthermore, the cost of creating a StringTemplate is rarely, if ever, the
> expensive part of the operation. In fact, I am certain it is trivial, if
> not optimized away like you were asking.
>
> I won't presume to call this premature optimization -- perhaps your
> application needs require it. But if so, I would first wait and see (or
> better yet, calculate!) the performance metrics of these StringTemplates.
> If they fail to meet your performance needs, then communicate your
> performance needs to this mailing list, with a hard example (and ideally
> metrics!) in tow.
>
> On Sun, Mar 17, 2024 at 1:07 PM Anatoly Kupriyanov <kan.izh at gmail.com>
> wrote:
>
>> Classically (how it was done a decade or so ago) the logger method would
>> look like:
>> void debug(String template, Object arg1, Object arg2) {
>>   if(!enabled) return;
>>   writeLog(interpolate(template, arg1.toString(), arg2.toString()));
>> }
>>
>> That allows that  if enabled==false, then it will be zero-gc, guaranteed.
>> It even used a lot of overrides with zero args, one arg, two args to
>> avoid ...-ellipsis array allocation. E.g. see
>> https://www.slf4j.org/api/org/slf4j/Logger.html
>>
>> There is a C# hacky approach the String Interpolation Handler (
>> https://learn.microsoft.com/en-us/dotnet/csharp/whats-new/tutorials/interpolated-string-handler
>> ) to use struct (allocated on stack) and magical isEnabled flags to cover
>> logging effectively.
>>
>> I don't see how it would be possible to use the StringTemplate to achieve
>> the similar effectiveness, unless there are some good and reliable
>> optimizations in JIT to avoid allocations.
>>
>> On Sun, 17 Mar 2024 at 16:41, David Alayachew <davidalayachew at gmail.com>
>> wrote:
>>
>>> The cost would be no different than evaluating a StringTemplate lazily.
>>> Utlimately, log.debug(blah) is still a method call, and therefore, some
>>> object is going into the method. Whether we evaluate the StringTemplate
>>> lazily or the Supplier<StringTemplate> lazily is largely the same thing.
>>>
>>> Or am I misunderstanding you?
>>>
>>> On Sun, Mar 17, 2024 at 12:28 PM Anatoly Kupriyanov <kan.izh at gmail.com>
>>> wrote:
>>>
>>>> But the "() ->" thing is still a runtime object to be allocated on the
>>>> heap... or is the JIT smart enough to always optimize it out?
>>>>
>>>> On Sun, 17 Mar 2024 at 16:17, David Alayachew <davidalayachew at gmail.com>
>>>> wrote:
>>>>
>>>>> I feel like that would be on the logging libraries to provide, not so
>>>>> much the language.
>>>>>
>>>>> Let's say that your problem (as I understand it) is like this.
>>>>>
>>>>> log.debug("metrics =
>>>>> \{this.expensiveComputationThatNormallyWouldntRunUnlessYouActivateDebug()}");
>>>>>
>>>>> Sounds to me like the solution is this instead.
>>>>>
>>>>> log.debug(() -> "metrics =
>>>>> \{this.expensiveComputationThatNormallyWouldntRunUnlessYouActivateDebug()}"
>>>>> )
>>>>>
>>>>> So, your logging library just needs to add a new overload for a
>>>>> Supplier<StringTemplate>, and then this problem is solved entirely outside
>>>>> of the language. Log4J and friends are pretty good about keeping up with
>>>>> new additions, so it should not take long.
>>>>>
>>>>> I know it's a little less convenient, but doing it this way helps keep
>>>>> out complexity from the feature, and only introduces it where necessary
>>>>> (and it's only necessary at use-site).
>>>>>
>>>>> Would this meet your needs?
>>>>>
>>>>> On Sun, Mar 17, 2024 at 11:15 AM Justin Spindler <
>>>>> justin.spindler at gmail.com> wrote:
>>>>>
>>>>>> I was toying around with the second preview of StringTemplates and I
>>>>>> had a question regarding their design.  I was wondering if it had been
>>>>>> considered for the embedded expressions to be evaluated lazily?
>>>>>>
>>>>>> One of the first use cases that came to mind when I was exploring
>>>>>> StringTemplates is logging.  That is an extremely common case where we want
>>>>>> to produce a form of interpolated value, and the current syntax generally
>>>>>> has the same concerns that a formatted string would, in that the inputs are
>>>>>> removed from where they are defined within the message format.  However, if
>>>>>> the log message is below the log level threshold you generally don't want
>>>>>> to incur the cost of building the message, including evaluating those
>>>>>> embedded expressions.  Log libraries typically offer a mechanism to defer
>>>>>> evaluation via Suppliers, but that feels like it would be a challenge to
>>>>>> use within StringTemplate.
>>>>>>
>>>>>> C# is an example of a language that offers this functionality via
>>>>>> FormattableString, which gives a method the ability to choose whether or
>>>>>> not to interpret the template or evaluate the expressions.  That allows
>>>>>> logging below threshold to be more or less a no-op.
>>>>>>
>>>>>>
>>>>>>
>>>>
>>>> --
>>>> WBR, Anatoly.
>>>>
>>>
>>
>> --
>> WBR, Anatoly.
>>
>

-- 
WBR, Anatoly.
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