RFR: 8257679: Improved unix compatibility layer in Windows build (winenv) [v5]

Fri Dec 4 18:23:16 UTC 2020

On Fri, 4 Dec 2020 17:34:33 GMT, Erik Joelsson <erikj at openjdk.org> wrote:

>> Ok, after looking at `set -x` output WSL seems to have a problem with the space in the path `/mnt/c/Program Files/Java/jdk-15` e.g. if I move the jdk to `/mnt/h/jdk-15` it works. Might be a missing fixup somewhere? (FWIW, that Program Files dir does have an 8dot3 name).
>> 
>> With that I can build `images` on both Cygwin and WSL. Build times are about 29 mins and 18 mins respectively.
>
> Do you see any significant difference in build times compared to before the patch?

@erikj79 The big difference is the shell script fixpath, as opposed to a native fixpath.exe. I've gone to great pains to make sure the "exec" pathway in fixpath.sh contains no external calls, but only native bash constructs, to avoid forks, which are expensive at Windows. With that said, fixpath.sh is still slower than fixpath.exe. A typical invocation with fixpath.sh is about 30 ms slower than fixpath.exe;  that is, in average 0.079 s instead of  0.047 s. (This is on Cygwin; on WSL fixpath.sh executes basically instantaneously.) This do translate to longer build times, but I have a hard time getting a proper value. The fluctuation in build times is so large so it's hard to say with certainty, but e.g. on GitHub Actions the build time increased from 53-57 minutes typically, to 58-62 minutes typically.  On my personal machine, I could get more reliable and repeatable results. There the time taken to build hotspot increased from 4 min 45 s to 4 min 53 s.

All these values are from running on Cygwin. The build times on WSL noticeably faster. (As a follow-up bug, I intend to migrate the GitHub Action script to running on WSL instead of Cygwin.) On machine, the build time decreased from over. 15 minutes, to under 13, when going from Cygwin to WSL.

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PR: https://git.openjdk.java.net/jdk/pull/1597