commit 6a60296ca7ca9cc4705e62e22f6a0164b59452e3
author Bruce Dawson <brucedawson@chromium.org> Fri Apr 26 00:53:52 2019
committer Commit Bot <commit-bot@chromium.org> Fri Apr 26 00:53:52 2019
tree 58a835f8551c94c73aacb71ee8c4f012a96c52c2
parent 51eeb5e52adee36cec79d1e80613e63838d8260d

Use 31 instead of 15-bit int for temp dir names

unit_tests creates two temporary directories for each test process. When
run with --test-launcher-batch-limit=1 this means about 21,800
directories, 10,900 of each naming pattern.

This is a problem because CreateTemporaryDirInDir uses a 15-bit random
number to generate directory names. After we have generated just 214
names there is a greater than 50% probability of a collision and after
10,900 names there will have been thousands of collisions. These
collisions are handled but they harm startup performance (especially
when running with --test-launcher-batch-limit=1) and if we add enough
tests or if directory cleanup isn't perfect then the slowdown can go
asymptotic.

Using a GUID would avoid all collisions but causes failures because
a GUID is 36 characters - 31 longer - and we sometimes have nested
temp directories. The extra 62 characters hits path length limits. Using
31-bit ints means the dir names are only 5 characters longer.

Bug: 955038, 956723
Change-Id: Id8d921eba0a59a3e4031470ccb5ae5368f6144db
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1584743
Commit-Queue: Robert Liao <robliao@chromium.org>
Reviewed-by: Robert Liao <robliao@chromium.org>
Cr-Commit-Position: refs/heads/master@{#654287}