RFR: 8304020: Speed up test/jdk/java/util/zip/ZipFile/TestTooManyEntries.java and clarify its purpose [v6]

[Martin Buchholz]

On Sun, 12 Mar 2023 21:25:46 GMT, Eirik Bjorsnos <duke at openjdk.org> wrote:

>> Please review this PR which speeds up TestTooManyEntries and clarifies its purpose:
>> 
>> - The name 'TestTooManyEntries' does not clearly convey the purpose of the test. What is tested is the validation that the total CEN size fits in a Java byte array. Suggested rename: CenSizeTooLarge
>> - The test creates DEFLATED entries which incurs zlib costs and File Data / Data Descriptors for no additional benefit. We can use STORED instead.
>> - By creating a single LocalDateTime and setting it with `ZipEntry.setTimeLocal`, we can avoid repeated time zone calculations. 
>> - The name of entries is generated by calling UUID.randomUUID, we could use simple counter instead.
>> - The produced file is unnecessarily large. We know how large a CEN entry is, let's take advantage of that to create a file with the minimal size.
>> - By adding a maximally large extra field to the CEN entries, we get away with fewer CEN records and save memory
>> - The summary and comments of the test can be improved to help explain the purpose of the test and how we reach the limit being tested.
>> 
>> These speedups reduced the runtime from 4 min 17 sec to 4 seconds on my Macbook Pro. The produced ZIP size was reduced from 5.7 GB to 2 GB. Memory consumption is down from 8GB to something like 12MB.
>
> Eirik Bjorsnos has updated the pull request incrementally with two additional commits since the last revision:
> 
>  - MAX_EXTRA_FIELD_SIZE can be better expressed as 0xFFFF
>  - Bring back '@requires sun.arch.data.model == 64' for now

test/jdk/java/util/zip/ZipFile/CenSizeTooLarge.java line 53:

> 51: 
> 52:     // Maximum size (unsigned short) of an extra field allowed by the standard
> 53:     static final int MAX_EXTRA_FIELD_SIZE = 0XFFFF;

4.4.10 file name length: (2 bytes)
   4.4.11 extra field length: (2 bytes)
   4.4.12 file comment length: (2 bytes)

       The length of the file name, extra field, and comment
       fields respectively.  The combined length of any
       directory record and these three fields SHOULD NOT
       generally exceed 65,535 bytes.

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PR: https://git.openjdk.org/jdk/pull/12991