RFC: 8357183: Improving efficiency of Writer::append(CharSequence) and Writer::append(CharSequence, int, int) / Sub Task of 8356679: Using CharSequence::getChars internally

[Markus KARG]

Roger,

thank you for your comments.

Following your advice I have splitted the larger work of JDK-8356679 
into sub tasks.

I would like to start with a first PR implementing the *foundational* 
work, i. e. optimizing Writer::append for efficiency (JDK-8357183). For 
convenience, attached below is a copy of the description.

Comments Welcome!

If everybody is fine with this, I would be happy to get some +1 to 
publish the PR for JDK-8357183!

-Markus


This sub task of JDK-8356679 proposes implementation-only changes to 
java.io.Writer. No API is changed. Implementation behavior is slightly 
changed w.r.t to self-calls to non-private methods.

The target is to make the Writer::append(CharSequence) and 
Writer::append(CharSequence, int, int) methods *in the non-String* case 
be as efficient as they are already *in the String* case.

This is achived by now handling CharSequence in *the exact same* 
optimized way as String was specifically handled before. This 
generalization of the previously String-specific optimization is 
possible since Java 25, thanks to the new CharSequence::getChars(int, 
int, char[], int) bulk-read method.

Prior to the proposed change, the code was unefficient, as ontop of what 
the String-case did, the text content of other CharSequences (like 
StringBuilder and CharBuffer) had to be copied *once or multiply*, 
before it was finally processed *as* a String.

The changes in detail are:
* Extract the original implementation of Writer::write(String, int, int) 
to become a newly introduced, internal method 
Writer::implWrite(CharSequence, int, int). This allows making use of 
that exact original implementation by other methods, particularly 
CharSequence::append, but potentially also sub classes in the same 
package (for subsequent enhancement of specific Writers).
* Writer::append(CharSequence) prevents the previously implied creation 
of an intermediate String representation in the non-String case (which 
implied creating another temporary object on the heap, and duplicating 
full text content), ontop of what the String case did
* Writer::append(CharSequence, int, int), in addition to the 
optimization of the single-arg case, also prevents the previously 
implied creation of a sub sequence (which always meant to create another 
temporary object on the heap, and in many cases meant to duplicate 
partial text content).
* As a benefit, the JavaDocs of these methods can be simplified thanks 
to the reduced number of self-calls. While this changes the internal 
behavior slightly, it is finally clarifying that these JavaDoc sections 
were originally meant as explanatory notes what *the default code* does, 
but not as as mandatory specs what *subclasses* have to do.

This work is foundational to subsequent enhancements of specific 
Writers, as the new implWrite(CharSequence, int, int) method is to be 
called by them *instead* of the previously called write(String, int, 
int) method, to allow for the same efficiency optimiziation now found in 
the new default code. Due to that, no other Writers are changed in this 
first step; these Writers will follow in subsequent JBS / PRs.


Am 14.05.2025 um 15:57 schrieb Roger Riggs:
> Hi Markus,
>
> Starting out with the common case is a good idea for the first PR.
>
> I much prefer a PR with a single goal and that comes to a conclusion 
> and does not add new features or changes after the PR is submitted.
> I tend to lose interest in PRs with lots of churn, it means I have to 
> re-review the bulk of it when there is a change and may wait days to 
> let it settle down before coming back to it.
>
> I tend to think the PR was not really ready to be reviewed if simple 
> issues and corrections have to be made frequently.
> Do your own checking for typos and copyrights and simple refactoring 
> before opening the PR.
> Quality before quantity or speed.
>
> I'm fine with separate Jira issues that clearly delineate a specific 
> scope and goal.
>
> The title of this issue (8356679) doesn't identify the real goal.
> It seems to be to improve performance or memory usage, not just to use 
> a new API.
>
> These are my personal opinions about contributions and process.
>
> Regards, Roger
>
>
> On 5/14/25 6:48 AM, Markus KARG wrote:
>> Many of the modified classes derive from a common super class and 
>> share one needed common change (which is one of the points which are 
>> easy to see once you see all of those classes in a single PR, but 
>> hard to explain in plaint-text pre-PR mailing list threads), so at 
>> least those need to be discussed *together*. But to spare JBS and 
>> PRs, I can open the PR with just the first set of changes, and once 
>> we agree that this set is fine, I can push the next commit *in the 
>> same PR*. Otherwise we would need endless JBS, mailing list threads, 
>> and PRs, just to fixe a dozen internal code lines.
>>
>> Having said that, does the current state of this thread count as 
>> "reached common agreement to file a PR" or do I still have to wait 
>> until more people chime in?
>>
>> -Markus
>>
>>
>> Am 13.05.2025 um 15:10 schrieb Roger Riggs:
>>> Hi Markus,
>>>
>>> A main point was to avoid trying to do everything at once.
>>> The PR comments become hard to follow and intermingled and it takes 
>>> longer to get agreement because of the thrash in the PR.
>>>
>>> Roger
>>>
>>> On 5/13/25 5:05 AM, Markus KARG wrote:
>>>> Thank you, Roger.
>>>>
>>>> Actually the method helps in the "toString()" variants, too, as in 
>>>> some places we could *get rid* of "toString()" (which is more work 
>>>> than "just" a buffer due to the added compression complexity).
>>>>
>>>> In fact, I already took the time to rewrite *all* of them while 
>>>> waiting for the approval of this list posting. In *all* cases 
>>>> *less* buffering / copying is needed, and *less* "toString()" 
>>>> conversion (which is a copy under the hood) is needed. So if I 
>>>> would be allowed to show the code as a PR, it would be much easier 
>>>> to explain and discuss.
>>>>
>>>> A PR is the best place to discuss "how to code would change". In 
>>>> the worst case, let's drop it if we see that it is actually a bad 
>>>> thing.
>>>>
>>>> -Markus
>>>>
>>>>
>>>> Am 12.05.2025 um 20:18 schrieb Roger Riggs:
>>>>> Hi Markus,
>>>>>
>>>>> On the surface, its looks constructive.
>>>>> I suspect that many of these cases will turn into discussions 
>>>>> about the right/best/better way to buffer the characters.
>>>>> The getChars method only helps when extracting to a char array, 
>>>>> many of the current implementations create strings as the 
>>>>> intermediary. The advantage of the 1 character at a time technique 
>>>>> is not needing a (separated allocated) buffer.
>>>>> Consider taking a few at a time before launching into the whole set.
>>>>>
>>>>> $.02, Roger
>>>>>
>>>>> On 5/11/25 2:45 AM, Markus KARG wrote:
>>>>>> Dear Core Libs Team,
>>>>>>
>>>>>> I am hereby requesting comments on JDK-8356679.
>>>>>>
>>>>>> I would like to invest some time and set up a PR implementing 
>>>>>> Chen Liangs's proposal laid out in 
>>>>>> https://bugs.openjdk.org/browse/JDK-8356679. For your 
>>>>>> convenience, the text of that JBS is copied below. According to 
>>>>>> the Developer's Guide I do need to get broad agreement BEFORE 
>>>>>> filing a PR. Therefore, I kindly ask everybody to briefly show 
>>>>>> consent, so I may file a PR.
>>>>>>
>>>>>> Thanks
>>>>>> -Markus
>>>>>>
>>>>>>
>>>>>> Copy from https://bugs.openjdk.org/browse/JDK-8356679:
>>>>>>
>>>>>> Recently OpenJDK adopted the new method 
>>>>>> CharSequence::getChars(int, int, char[], int) for inclusion in 
>>>>>> Java 25. As a bulk reader method, it allows potentially improved 
>>>>>> efficiency over the previously available char-by-char reader 
>>>>>> method CharSequence::charAt(int).
>>>>>>
>>>>>> Chen Liang suggested on March 23rd on the core-lib-dev mailing 
>>>>>> list to use the new method within the internal source code of 
>>>>>> OpenJDK for the implementation of Appendables (see 
>>>>>> https://mail.openjdk.org/pipermail/core-libs-dev/2025-March/141521.html). 
>>>>>> The idea behind this is that the implementations might be more 
>>>>>> efficient then.
>>>>>>
>>>>>> A quick analysis of the OpenJDK source code identified (at least) 
>>>>>> the following classes which could potentially run more efficient 
>>>>>> when using CharSequence::getChars internally, thanks to bulk 
>>>>>> reading and / or prevention of internal copies / toString() 
>>>>>> conversions:
>>>>>> * java.io.Writer
>>>>>> * java.io.StringWriter
>>>>>> * java.io.PrintWriter
>>>>>> * java.io.BufferedWriter
>>>>>> * java.io.CharArrayWriter
>>>>>> * java.io.FileWriter
>>>>>> * java.io.OutputStreamWriter
>>>>>> * sun.nio.cs.StreamEncoder
>>>>>> * java.io.PrintStream
>>>>>> * java.nio.CharBuffer
>>>>>>
>>>>>> In the sense of "eat your own dog food", it makes sense to 
>>>>>> implement Chen's idea in (at least) those classes. Possibly more 
>>>>>> classes could get identified when taking a deeper look. Besides 
>>>>>> the potential efficiency improvements, it would be a good show 
>>>>>> case for the usage of the new API.
>>>>>>
>>>>>> The risk of this change should be low, as test coverage exists, 
>>>>>> and as the intended changes are solely internal to the 
>>>>>> implementation. No API will get changed. In some cases the 
>>>>>> JavaDocs will get slightly adapted where it currently exposes the 
>>>>>> actual implementation (to not lie in future).
>>>>>>
>>>>>
>>>
>