Fibers 1.0.0 has a bug in run-fibers in which peer schedulers aren't destroyed -
so if you had 4 cores, 1 would be destroyed when run-fibers returned, but the
other 3 would stay around.  Each scheduler uses 3 file descriptors, so for
machines with many cores, this resource leak adds up quickly - quickly enough
that the test suite can even fail because of it.

See https://github.com/wingo/fibers/issues/36.

This fixes that.  It should be safe to destroy the peer schedulers at the given
point because the threads that could be running them are all either dead or the
current thread.

As of May 21, 2020, this bug still existed in the 1.0.0 (latest) release and in
git master.
--- a/fibers.scm	2020-05-21 18:38:06.890690154 -0500
+++ b/fibers.scm	2020-05-21 18:38:56.395686693 -0500
@@ -137,5 +137,6 @@
              (%run-fibers scheduler hz finished? affinity))
            (lambda ()
              (stop-auxiliary-threads scheduler)))))
+      (for-each destroy-scheduler (scheduler-remote-peers scheduler))
       (destroy-scheduler scheduler)
       (apply values (atomic-box-ref ret))))))

4616ff5315050b0'>refs</a><a class='active' href='/guix/log/nix/libstore/gc.cc'>log</a><a href='/guix/tree/nix/libstore/gc.cc?id=2fa0ec238c2cd79aa025f2cd54616ff5315050b0'>tree</a><a href='/guix/commit/nix/libstore/gc.cc?id=2fa0ec238c2cd79aa025f2cd54616ff5315050b0'>commit</a><a href='/guix/diff/nix/libstore/gc.cc?id=2fa0ec238c2cd79aa025f2cd54616ff5315050b0'>diff</a></td><td class='form'><form class='right' method='get' action='/guix/log/nix/libstore/gc.cc'>
<input type='hidden' name='id' value='2fa0ec238c2cd79aa025f2cd54616ff5315050b0'/><select name='qt'>
<option value='grep'>log msg</option>
<option value='author'>author</option>
<option value='committer'>committer</option>
<option value='range'>range</option>
</select>
<input class='txt' type='search' size='10' name='q' value=''/>
<input type='submit' value='search'/>
</form>
</td></tr></table>
<div class='path'>path: <a href='/guix/log/?id=2fa0ec238c2cd79aa025f2cd54616ff5315050b0'>root</a>/<a href='/guix/log/nix?id=2fa0ec238c2cd79aa025f2cd54616ff5315050b0'>nix</a>/<a href='/guix/log/nix/libstore?id=2fa0ec238c2cd79aa025f2cd54616ff5315050b0'>libstore</a>/<a href='/guix/log/nix/libstore/gc.cc?id=2fa0ec238c2cd79aa025f2cd54616ff5315050b0'>gc.cc</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/nix/libstore/gc.cc?id=2fa0ec238c2cd79aa025f2cd54616ff5315050b0&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2021-11-16 14:34:28 +0100'>2021-11-16</span></td><td><a href='/guix/commit/nix/libstore/gc.cc?id=472a0e82a52a3d5d841e1dfad6b13e26082a5750'>daemon: Do not deduplicate files smaller than 8 KiB.</a><span class='msg-avail'>...<span class='msg-tooltip'>Files smaller than 8 KiB typically represent ~70% of the entries in
/gnu/store/.links but only contribute to ~4% of the space savings
afforded by deduplication.

Not considering these files for deduplication speeds up file insertion
in the store and, more importantly, leaves 'removeUnusedLinks' with
fewer entries to traverse, thereby speeding it up proportionally.

Partly fixes &lt;https://issues.guix.gnu.org/24937&gt;.

* config-daemon.ac: Remove symlink hard link check and CAN_LINK_SYMLINK
definition.
* guix/store/deduplication.scm (%deduplication-minimum-size): New
variable.
(deduplicate)[loop]: Do not recurse when FILE's size is below
%DEDUPLICATION-MINIMUM-SIZE.
(dump-port): New procedure.
(dump-file/deduplicate)[hash]: Turn into...
[dump-and-compute-hash]: ... this thunk.
Call 'deduplicate' only when SIZE is greater than
%DEDUPLICATION-MINIMUM-SIZE; otherwise call 'dump-port'.
* nix/libstore/gc.cc (LocalStore::removeUnusedLinks): Drop files where
st.st_size &lt; deduplicationMinSize.
* nix/libstore/local-store.hh (deduplicationMinSize): New declaration.
* nix/libstore/optimise-store.cc (deduplicationMinSize): New variable.
(LocalStore::optimisePath_): Return when PATH is a symlink or smaller
than 'deduplicationMinSize'.
* tests/derivations.scm ("identical files are deduplicated"): Produce
files bigger than %DEDUPLICATION-MINIMUM-SIZE.
* tests/nar.scm ("restore-file-set with directories (signed, valid)"):
Likewise.
* tests/store-deduplication.scm ("deduplicate, below %deduplication-minimum-size"):
New test.
("deduplicate", "deduplicate, ENOSPC"): Produce files bigger than
%DEDUPLICATION-MINIMUM-SIZE.
* tests/store.scm ("substitute, deduplication"): Likewise.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2020-06-06 15:43:35 -0700'>2020-06-06</span></td><td><a href='/guix/commit/nix/libstore/gc.cc?id=d445c30ea6f9693454ca96bae9089ba8738a6f78'>daemon: Handle EXDEV when moving to trash directory.</a><span class='msg-avail'>...<span class='msg-tooltip'>Fixes &lt;https://bugs.gnu.org/41607&gt;.
Reported by Stephen Scheck &lt;singularsyntax@gmail.com&gt;.

* nix/libstore/gc.cc (LocalStore::deletePathRecursive): When we try to
move a dead directory into the trashDir using rename(2) but it returns
an EXDEV error, just delete the directory instead.  This can happen in a
Docker container when the directory is not on the "top layer".
</span></span></td><td>Chris Marusich</td></tr>
<tr><td><span title='2020-02-26 22:05:56 +0100'>2020-02-26</span></td><td><a href='/guix/commit/nix/libstore/gc.cc?id=513c0a0f4602018a49d8fd2dfa24670a3fa08ac9'>daemon: Drop 'AT_STATX_DONT_SYNC' flag upon EINVAL.</a><span class='msg-avail'>...<span class='msg-tooltip'>Fixes &lt;https://bugs.gnu.org/39727&gt;.
Reported by Paul Garlick &lt;pgarlick@tourbillion-technology.com&gt;.

* nix/libstore/gc.cc (LocalStore::removeUnusedLinks) [HAVE_STATX]: Add
'statx_flags' static variables.  Clear 'AT_STATX_DONT_SYNC' flag from
'statx_flags' when 'statx' returns EINVAL.
</span></span></td><td>Ludovic Courtès</td></tr>