RFR: 8308252: Refactor line-by-line file reading code [v3]

[Thomas Stuefe]

On Tue, 23 May 2023 06:59:46 GMT, Ioi Lam <iklam at openjdk.org> wrote:

>> I can revert to the getc version and implement the fgets version in a separate RFE. I agree that keeping the logic unchanged in refactoring will make things more manageable.
>> 
>> getc is buffered I/O, so there shouldn't be much difference in performance when compared to fgets. And the code affected by this PR doesn't care too much about I/O performance.
>
> By the way, I think I should take out the handling of _max_buffer_length, which I actually haven't implemented. I don't know what the failure mode should be when the line width is longer than the specified max, and I don't want to write any test case when the max is set to a small number like 256.
> 
> So let's keep the existing 2x expansion and crash when OOM (which is the same as the numerous sites that use GrowableArray).

Okay, pity since that makes the code less reusable for cases I had in mind. For instance, reading and writing out gigantic mapping files. I recently had a customer with a 4TB heap and ZGC, where /proc/pid/maps alone was 20mio lines.

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PR Review Comment: https://git.openjdk.org/jdk/pull/14025#discussion_r1201874954