RFR: 8256828: ostream::print_cr() truncates buffer in copy-through case

[Thomas Stuefe]

On Sun, 2 Jun 2024 22:05:40 GMT, David Holmes <dholmes at openjdk.org> wrote:

> Clarifies the behaviour of this function in regards to truncation when adding a CR. Ensures a truncation warning is always issued.
> 
> Adds unit testing for the specialized cases.
> 
> See JBS for discussion of other suggestions.
> 
> Testing: - tiers 1-4
> 
> Thanks

So, just to clarify, this is a behavioral change, right?

Where before we would not truncate raw strings, now we do, since result_len is used to determine how many bytes we will write to the output sink.

src/hotspot/share/utilities/ostream.cpp line 109:

> 107:       result_len = buflen - 1;
> 108:     }
> 109:   } else if (format[0] == '%' && format[1] == 's' && format[2] == '\0') {

nit, preexisting: why not just `strncmp(format, "%s", 3) == 0`?

src/hotspot/share/utilities/ostream.hpp line 74:

> 72:   // of the returned string.
> 73:   //
> 74:   // In a debug build, if truncation occurs a VM warning is issued.

I had to think a bit (I am not a native English speaker) about what the "Nominally" means, but I think it is supposed to contrast the second paragraph? As in "Normally we do that, but in the case of ... we do... ?". Same for "idiomatically" - what does that signify?

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PR Review: https://git.openjdk.org/jdk/pull/19512#pullrequestreview-2092883626
PR Review Comment: https://git.openjdk.org/jdk/pull/19512#discussion_r1623841035
PR Review Comment: https://git.openjdk.org/jdk/pull/19512#discussion_r1623850806