I guess it depends what Writer is used.
StringBuilderWriter.append(CharSequence) is overloaded.
I thought that Velocity is using a pool of VelocityWriter instances, not an
OutputStreamWriter. If that is so you can overload append(CharSequence) as
needed in VelocityWriter.
JDK default implementation is very poor (creating potentially two copies of
data in subSequence and toString).
public Writer append(CharSequence csq, int start, int end) throws
IOException {
CharSequence cs = (csq == null ? "null" : csq);
write(cs.subSequence(start, end).toString());
return this;
}
On Tue, Dec 13, 2016 at 8:48 AM, Claude Brisson <cla...@renegat.net> wrote:
> Reducing useless synchronizations by using a StringBuilderWriter was easy.
>
> But about using CharSequences instead of Strings, after a quick look, it
> doesn't look so promising: did you know that Writer.append(CharSequence)
> does call Writer.write(sequence.toString()), which will itself use
> string.getChars(), at leats in its default version?!
>
> The most frightening about this code in java.io.Writer is that whenever
> you pass big strings to it, it will each time allocate big buffers instead
> of, for instance, copy small portions to output inside a loop. Time needed
> for memory copy is often negligible, whereas time needed to allocate big
> chunks of memory is rather annoying. Twice as annoying when done twice.
>
> There is no point in trying to avoid the toString() call in Velocity if
> the i/o lower layer will call it anyway.
>
> Claude
>
>
>
> On 12/12/2016 18:15, Alex Fedotov wrote:
>
>> I don't know if something like this is in scope fro 2.0, but for more
>> advanced manipulation of AST it would be helpful if creation of all AST
>> nodes would be delegated to some kind of configurable factory class.
>>
>> This way if I wanted to replace ASTStringLiteral with a subclass of
>> ASTStringLiteral for optimization purposes (say use a chunked buffer, or
>> something similar) I could then setup my own factory and create an
>> instance
>> of a subclass.
>>
>> Alex
>>
>>
>> On Mon, Dec 12, 2016 at 11:52 AM, Claude Brisson <cla...@renegat.net>
>> wrote:
>>
>> Yes, I also thought of that. But a particular care must be taken in
>>> upstream code that may expect to encounter String values and may
>>> otherwise
>>> call toString(), voiding the benefice. Worth looking at, though ; it must
>>> not be too difficult to have this code take CharSequence values into
>>> account.
>>>
>>> Claude
>>>
>>>
>>>
>>> On 12/12/2016 15:58, Alex Fedotov wrote:
>>>
>>> I am not sure if it's possible to assume that ASTStringLiteral.value()
>>>> returns a CharSequence and not a String. If that was the case you could
>>>> just return the StringBuilder directly (StringBuilder implements
>>>> CharSequence) without calling StringBuilder.toString(). This would avoid
>>>> making one more copy of the data.
>>>>
>>>> Same may apply in other places.
>>>>
>>>> Alex
>>>>
>>>>
>>>> On Sun, Dec 11, 2016 at 12:28 PM, Claude Brisson <cla...@renegat.net>
>>>> wrote:
>>>>
>>>> Thanks. I'll review those StringBuffer uses.
>>>>
>>>>> For the ASTStringLiteral, I see there's already a StringBuilderWriter
>>>>> in
>>>>> commons-io that I may borrow...
>>>>>
>>>>>
>>>>>
>>>>> On 11/12/2016 17:07, Alex Fedotov wrote:
>>>>>
>>>>> Great thank you.
>>>>>
>>>>>> Actually I would recommend removing the StringWriter. StringWriter is
>>>>>> using
>>>>>> StringBuffer inside which is synchronized.
>>>>>> In case of ASTStringLiteral there is no need to synchronize anything.
>>>>>> There
>>>>>> must be a Writer implementation based on StringBuilder instead.
>>>>>>
>>>>>> I have a run a search on the latest 2.0 code and it seems like there
>>>>>> is
>>>>>> a
>>>>>> number of places where StringBuffer is used.
>>>>>> Unless synchronization is required those usages should really be
>>>>>> replaced
>>>>>> with StringBuilder(s).
>>>>>>
>>>>>>
>>>>>> ============================================================
>>>>>> =================
>>>>>>
>>>>>> As far our usage of large string literal it was in a legacy framework
>>>>>> that
>>>>>> we had.
>>>>>> It was creating a system of macros to render "tiles" on a page.
>>>>>>
>>>>>> Similar to this syntax (not real):
>>>>>>
>>>>>> @#PageSection(param1, param2....)
>>>>>> @#SubSection("tileName1")
>>>>>> some html
>>>>>> #end
>>>>>> @#SubSection("tileName2")
>>>>>> some other html
>>>>>> #end
>>>>>> #SubSection("tileName3", "/blah/blah/section.vtl")
>>>>>> #end
>>>>>>
>>>>>> Velocity macros with body allow only one body block (special parameter
>>>>>> really).
>>>>>> We needed multiple named body blocks which we could render in the
>>>>>> correct
>>>>>> spots inside of the macro.
>>>>>>
>>>>>> We are no longer using this framework, but that is where we had large
>>>>>> string literals appearing.
>>>>>> I think we replaced the StringBuffer with some unsynchronized chunked
>>>>>> implementation to avoid allocation of very large strings and
>>>>>> unnecessary
>>>>>> synchronzation.
>>>>>>
>>>>>> Alex
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>> On Sun, Dec 11, 2016 at 7:18 AM, Claude Brisson <cla...@renegat.net>
>>>>>> wrote:
>>>>>>
>>>>>> FYI, we got rid of the Executor pattern in the events API, and we now
>>>>>>
>>>>>> always provide the current Context when calling handlers.
>>>>>>>
>>>>>>>
>>>>>>> On 29/11/2016 23:25, Alex Fedotov wrote:
>>>>>>> [...]
>>>>>>>
>>>>>>> We have run into some other inefficient places. For example
>>>>>>>
>>>>>>> ASTStringLiteral is buffering the entire content in the StringWriter.
>>>>>>>> It
>>>>>>>> does not work very well for large templates.
>>>>>>>> That code creates a writer which buffers up the whole thing, then
>>>>>>>> does a
>>>>>>>> toString() on it creating another copy. Then in some cases calls
>>>>>>>> substring() that creates yet another copy.
>>>>>>>>
>>>>>>>> The substring belonged to an old workaround, it has been removed.
>>>>>>>>
>>>>>>>> The StringWriter buffering is only done when interpolation is needed
>>>>>>> (that
>>>>>>> is, when the string literal is enclosed in double quotes and has
>>>>>>> some $
>>>>>>> or
>>>>>>> # inside). There could be some tricky ways of introducing some kind
>>>>>>> of
>>>>>>> lazy
>>>>>>> evaluation, that would resort to using the provided final writer when
>>>>>>> the
>>>>>>> value is meant to be rendered or to a buffered writer otherwise. But
>>>>>>> I'm
>>>>>>> not sure it is worth it, because it looks rather fragile and
>>>>>>> convoluted.
>>>>>>> Plus, you can generally avoid having big string literals. I don't
>>>>>>> know
>>>>>>> about your use case, but why can't something as:
>>>>>>>
>>>>>>> #set($foo = "#parse('big.vtl')") $foo
>>>>>>>
>>>>>>> be rewritten as:
>>>>>>>
>>>>>>> #parse('big.vtl')
>>>>>>>
>>>>>>> to avoid the buffering?
>>>>>>>
>>>>>>>
>>>>>>> Claude
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> ------------------------------------------------------------
>>>>>>> ---------
>>>>>>>
>>>>>> To unsubscribe, e-mail: dev-unsubscr...@velocity.apache.org
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>>>>>
>>>>>
>>>>>
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>>>
>>>
>
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