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

[Thomas Stuefe]

On Wed, 17 May 2023 19:55:59 GMT, Ioi Lam <iklam at openjdk.org> wrote:

>> I extracted the `get_line()` code from `CompileReplay` and put it in a utility class so that it can be used by `ClassListParser` as well. A few notable changes:
>> 
>> - Simplified the API
>> - Changed the buffer size to a size_t
>> - Added size overflow and OOM checks
>> - Brought over the `fdopen` logic from `ClassListParser` for handling long path names on Windows. (I don't know how valid this is nowadays, but I don't want to drop it in a refactoring PR).
>
> Ioi Lam has updated the pull request incrementally with one additional commit since the last revision:
> 
>   fixed typo in comments

What would cool would be a closure that gets each line, optionally with the ability to stop iteration prematurely. Or even better, a lambda that does the same.

src/hotspot/share/cds/classListParser.cpp line 63:

> 61:   if (!_reader.is_opened()) {
> 62:     char errmsg[JVM_MAXPATHLEN];
> 63:     os::lasterror(errmsg, JVM_MAXPATHLEN);

_reader should buffer errno after the failing OS call. We should not have to rely on os::lasterror() being called right after whatever OS API failed inside the reader. Neither is os::lasterror() necessary, we can just use os::strerror since reader only uses Posix file APIs.

src/hotspot/share/utilities/lineReader.cpp line 30:

> 28: #include "utilities/lineReader.hpp"
> 29: 
> 30: LineReader::LineReader(const char* filename) : _filename(filename), _stream(nullptr) {

Maybe strdup the file name to be sure? Up to you. We usually just feed literals, so this may be ok.

src/hotspot/share/utilities/lineReader.cpp line 44:

> 42:     }
> 43:   } else {
> 44:     _stream = nullptr;

unnecessary

src/hotspot/share/utilities/lineReader.cpp line 65:

> 63: // \n is treated as the line separator.
> 64: // All occurrences of \r are stripped.
> 65: char* LineReader::get_line() {

I would return const char* here, this is an internal buffer.

src/hotspot/share/utilities/lineReader.cpp line 71:

> 69:   size_t buffer_pos = 0;
> 70:   int c;
> 71:   while ((c = getc(_stream)) != EOF) {

Lets not read individual characters. Lets use fgets or fread() or just plain read(). Preferably the first.

src/hotspot/share/utilities/lineReader.cpp line 76:

> 74:       if (new_length < _buffer_length) {
> 75:         // This could happen on 32-bit. On 64-bit, the VM would have exited
> 76:         // due to OOM before we ever get to here.

This is scary. I don't like a general utility to use half my address space on 32-bit if bad things happen. I would cap the max. buffer size to something sensible, e.g. 1K or 64K.

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Changes requested by stuefe (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/14025#pullrequestreview-1432366585
PR Review Comment: https://git.openjdk.org/jdk/pull/14025#discussion_r1197607457
PR Review Comment: https://git.openjdk.org/jdk/pull/14025#discussion_r1197616845
PR Review Comment: https://git.openjdk.org/jdk/pull/14025#discussion_r1197617824
PR Review Comment: https://git.openjdk.org/jdk/pull/14025#discussion_r1197626049
PR Review Comment: https://git.openjdk.org/jdk/pull/14025#discussion_r1197623702
PR Review Comment: https://git.openjdk.org/jdk/pull/14025#discussion_r1197624433