RFR: 8304020: Speed up test/jdk/java/util/zip/ZipFile/TestTooManyEntries.java and clarify its purpose [v10]

[Jaikiran Pai]

On Mon, 30 Oct 2023 15:50:49 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.
>> - By writing sparse 'holes' until the last CEN entry, we can reduce required disk space.
>> 
>> These speedups reduced the runtime from 4 min 17 sec to 3 seconds on my Macbook Pro. The produced ZIP size was reduced from 5.7 GB to ~4K. Memory consumption is down from 8GB to something like 12MB.
>
> Eirik Bjorsnos has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Replace the 'afterLastCEN' boolean with a 'sparse' state variable

Overall, this is a very good improvement to the test and looks good to me. I just a have a trivial comment about a typo in a code comment, which I've added inline.

test/jdk/java/util/zip/ZipFile/CenSizeTooLarge.java line 78:

> 76:     public static final int NAME_LENGTH = 10;
> 77: 
> 78:     // Use a shared LocalDataTime on all entries to save processing time

Hello Eirik, there appears to be a typo in the comment here. It should have been `LocalDateTime`.

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Marked as reviewed by jpai (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/12991#pullrequestreview-1731410663
PR Review Comment: https://git.openjdk.org/jdk/pull/12991#discussion_r1393773103