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Avoid blocking on CloseHandle #1850

Merged
merged 2 commits into from
May 18, 2019
Merged

Avoid blocking on CloseHandle #1850

merged 2 commits into from
May 18, 2019

Commits on May 18, 2019

  1. Customisable tracker units 

    Files are in bytes, but other things we may track are not.
    @rbtcollins
    rbtcollins committed May 18, 2019
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  2. Avoid blocking on CloseHandle 

    On Windows closing a file involves CloseHandle, which can be quite
slow (6+ms) for various reasons, including circumstances outside our
control such as virus scanners, content indexing, device driver cache
write-back synchronisation and so forth. Rather than having a super
long list of all the things users need to do to optimise the performance
of CloseHandle, use a small threadpool to avoid blocking package
extraction when closing file handles.

This does run a risk of resource exhaustion, but as we only have 20k
files in the largest package today that should not be a problem in
practice.

https://www.mercurial-scm.org/pipermail/mercurial-devel/2016-January/078404.html
provided inspiration for this.

My benchmark system went from 21/22s to 11s with this change with both
4 or 8 threads.
    @rbtcollins
    rbtcollins committed May 18, 2019
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