RFR: 8330532: Improve line-oriented text parsing in HotSpot

[Matias Saavedra Silva]

On Thu, 18 Apr 2024 11:59:51 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:

>> (This PR is an alternative to https://github.com/openjdk/jdk/pull/18669 with a better API for reading lines of text)
>> 
>> HotSpot has a few cases where information is parsed from a file, or from a memory buffer, one line at a time. Example:
>> 
>> - https://github.com/openjdk/jdk/blob/064628471b83616b4463baa78618d1b7a66d0c7c/src/hotspot/share/cds/classListParser.cpp#L169
>> - https://github.com/openjdk/jdk/blob/064628471b83616b4463baa78618d1b7a66d0c7c/src/hotspot/share/compiler/compilerOracle.cpp#L1059-L1066
>> 
>> Common problems:
>> - They use a fixed buffer for reading a line, so long (but valid) lines will cause errors.
>> - There's ad-hoc code that deals with `FILE*` differently than from memory.
>> 
>> This RFE implements a common utility, `inputStream`, for reading lines from different sources of input (see `FileInput` and `MemoryInput`). We fixed only `ClassListParser` and `CompilerOracle` in this RFE, but we can fix other readers in follow-up RFEs.
>> 
>> The API allows other source of input to be implemented. For example, one could implement a `SocketInput` if there's a use case for it.
>> 
>> In the future, `inputStream` can be extended (or encapsulated in a higher-level reader class) to read typed input tokens (for example, integers, strings, etc.)
>> 
>> Credit:
>> The `inputStream` class and friends are contributed by @rose00 . See https://mail.openjdk.org/pipermail/hotspot-dev/2024-April/087077.html .
>> 
>> John's original version is in the draft PR https://github.com/openjdk/jdk/pull/18773. In order to minimize the size of this PR, I have kept only the functionalities for reading a line and a time. Other features, such as pushing back contents into the `inputStream`, could be added in follow-up PRs. (These removed features can be found in the commit history of this PR).
>
> src/hotspot/share/cds/classListParser.cpp line 436:
> 
>> 434: }
>> 435: 
>> 436: void ClassListParser::check_class_name(const char* class_name) {
> 
> Did we not already have code to check the length of the class name for the class list parser?  There's similar code in systemDictionary.

There is `SystemDictionary::class_name_symbol()` which checks if a class name is valid but it creates a new symbol instead of solely checking the name. Maybe it's worth abstracting the check into its own method and using it here and in SystemDictionary?

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PR Review Comment: https://git.openjdk.org/jdk/pull/18833#discussion_r1575291232