RFR: 8333211: NMT Reports: replace manual indentation handling with auto indent

[David Holmes]

On Wed, 29 May 2024 16:10:07 GMT, Thomas Stuefe <stuefe at openjdk.org> wrote:

> Hi,
> 
> this is the first of a few patches I plan to reduce NMT code complexity.
> 
> In NMT reporting, indentations are manually hard-coded. That makes the code brittle and frustrating to maintain. One cannot, e.g., re-use a printing subfunction in differently aligned portions without some awkward gymnastics (e.g. handing indentation as argument to the sub routine).
> 
> This patch adds a simple automatic indentation feature to `outputStream` and then uses that feature to simplify NMT reporting. NMT reporting becomes more malleable and easier to change. 
> 
> I plan to reuse this feature for a couple of non-NMT things.
> 
> ---
> 
> The new "autoindent" mode in `outputStream` is off by default. If enabled, the stream automatically adds indentations at new lines.
> 
> The added code is small and minimally invasive. It builds atop the existing manual indentation. It trades completeness for simplicity: 
> - it only works for a selected set of APIs (`print`, `print_cr`, `print_raw`, `print_raw_cr`). 
> - it does not work for multiline output: `print("line\nline\nline")` needs to be broken up into individual `print` calls
> 
> Despite these limitations, the feature works fine and I expect covers 99% of all use cases.
> 
> In the NMT reports, I replaced the many manual indentations with a few incarnations of `streamIndentor`. The changes in detail:
> 
> - to prevent backward compatibility issues, I am careful to limit the autoindent mode to NMT reporting.
> - I replaced manual indentation with a few `streamIndentor` placements
> - I removed the now useless `print_(malloc|virtual_memory|arena)_line`
> 
> - Some minor cleanups:
>   - merged the `outputStream` constructors into one
>   - moved indentation level and autoindent flag to the private section of `outputStream`
>   - removed some unused accessors in `outputStream`
>   - tightened printing code in NMT reporting, e.g. replaced `print_cr(" ")` with `cr()`
>   - removed the now unused `NativeCallStack::print_on(outputStream* out, int indent)` which hands in indentation. 
> 
> The last point I see as the real benefit of autoindent; we now don't have to manually hand indentation levels to printing subroutines. Subroutines can be oblivious to indentation - their printouts will be correctly indented regardless of indentation level.
> 
> -----
> 
> Testing:
> 
> - GHAs
> - I ran NMT jtreg tests manually
> - I was careful to preserve the formatting of the existing reports. Therefore I tested all four variants: summary, summary.diff, detail, detail.diff , compared with outputs from mainline, an...

Hi Thomas,
I'm only looking at the auto-indent aspect of this as I'm also working on the stream code and reviewing another change using indentation. To be honest I cannot understand how outputstream's indentation works because to me indentation is always/only something that applies at the start of a new line - hence "auto-indent" would always be the case. I mean "indentation" in the middle of a line is a meaningless concept, so the logic in `indent` has me really bemused.

src/hotspot/share/utilities/ostream.hpp line 83:

> 81:    void dec(int n) { _indentation -= n; };
> 82:    int  indentation() const    { return _indentation; }
> 83:    void set_indentation(int i) { _indentation = i;    }

Why have you deleted these?

src/hotspot/share/utilities/ostream.hpp line 106:

> 104:    void print_raw(const char* str, size_t len);
> 105:    void print_raw_cr(const char* str)             { print_raw(str); cr(); }
> 106:    void print_raw_cr(const char* str, size_t len) { print_raw(str, len); cr(); }

Can these be simplified if we have a default value for len? i.e.

void print_raw(const char* str, size_t len = strlen(str));

-------------

PR Review: https://git.openjdk.org/jdk/pull/19461#pullrequestreview-2095410597
PR Review Comment: https://git.openjdk.org/jdk/pull/19461#discussion_r1625408785
PR Review Comment: https://git.openjdk.org/jdk/pull/19461#discussion_r1625413709