[v2,1/3] common/rc: introduce _random_file() helper

Commit Message

Naohiro Aota Aug. 21, 2023, 6:37 a.m. UTC

Currently, we use "ls ... | sort -R | head -n1" (or tail) to choose a
random file in a directory.It sorts the files with "ls", sort it randomly
and pick the first line, which wastes the "ls" sort.

Also, using "sort -R | head -n1" is inefficient. For example, in a
directory with 1000000 files, it takes more than 15 seconds to pick a file.

  $ time bash -c "ls -U | sort -R | head -n 1 >/dev/null"
  bash -c "ls -U | sort -R | head -n 1 >/dev/null"  15.38s user 0.14s system 99% cpu 15.536 total

  $ time bash -c "ls -U | shuf -n 1 >/dev/null"
  bash -c "ls -U | shuf -n 1 >/dev/null"  0.30s user 0.12s system 138% cpu 0.306 total

So, we should just use "ls -U" and "shuf -n 1" to choose a random file.
Introduce _random_file() helper to do it properly.

Signed-off-by: Naohiro Aota <[e-mail]>
---
 common/rc | 7 +++++++
 1 file changed, 7 insertions(+)

Patch

diff --git a/common/rc b/common/rc
index 5c4429ed0425..2bdda30f497a 100644
--- a/common/rc
+++ b/common/rc
@@ -5224,6 +5224,13 @@  _soak_loop_running() {
 	return 0
 }
 
+# Return a random file in a directory. A directory is *not* followed
+# recursively.
+_random_file() {
+	local basedir=$1
+	ls -U "${basedir}" | shuf -n 1
+}
+
 init_rc
 
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