status: improve parallel execution stability

The status command runs a bunch of jobs in parallel, and each one
is responsible for writing to stdout directly.  When running many
noisy jobs in parallel, output can get intermingled.  Pass down a
StringIO buffer for writing to so we can return the entire output
as a string so the main job can handle displaying it.  This fixes
interleaved output as well as making the output stable: we always
display results in the same project order now.  By switching from
map to imap, this ends up not really adding any overhead.

Bug: https://crbug.com/gerrit/12231
Change-Id: Ic18b07c8074c046ff36e306eb8d392fb34fb6eca
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/297242
Tested-by: Mike Frysinger <vapier@google.com>
Reviewed-by: Chris Mcdonald <cjmcdonald@google.com>

1 files changed, 1 insertions, 9 deletions

diff --git a/subcmds/branches.py b/subcmds/branches.py
index 9665e85f..d5ea580c 100644
--- a/subcmds/branches.py
+++ b/subcmds/branches.py
@@ -16,15 +16,7 @@ import itertools
 import multiprocessing
 import sys
 from color import Coloring
-from command import Command, DEFAULT_LOCAL_JOBS
-
-# Number of projects to submit to a single worker process at a time.
-# This number represents a tradeoff between the overhead of IPC and finer
-# grained opportunity for parallelism. This particular value was chosen by
-# iterating through powers of two until the overall performance no longer
-# improved. The performance of this batch size is not a function of the
-# number of cores on the system.
-WORKER_BATCH_SIZE = 32
+from command import Command, DEFAULT_LOCAL_JOBS, WORKER_BATCH_SIZE
 
 
 class BranchColoring(Coloring):