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git-remote-testgit: fix race when spawning fast-import

Test "pushing to local repo" in t5800-remote-helpers can hang
due to a race condition in git-remote-testgit.  Fix it by
setting stdin to unbuffered.

On the writer side, "git push" invokes push_refs_with_export(),
which sends to stdout the command "export\n" and immediately
starts up "git fast-export".  The latter writes its output stream
to the same stdout.

On the reader side, remote helper "git-remote-testgit" reads from
stdin to get its next command.  It uses getc() to read characters
from libc up until \n.  Libc has buffered a potentially much
larger chunk of stdin.  When it sees the "export\n" command, it
forks "git fast-import" to read the stream.

If fast-export finishes before git fast-import starts, the
fast-export output can end up in libc's buffer in
git-remote-testgit, rather than in git fast-import.  The latter
hangs indefinitely on a now-empty stdin.

Signed-off-by: Pete Wyckoff <pw@padd.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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1 parent fdec2eb commit 7fb8e163bdfdc5ffb69b98f3f05ef0dbade4e677 Pete Wyckoff committed with gitster Apr 22, 2012
Showing with 20 additions and 0 deletions.
  1. +7 −0 git-remote-testgit.py
  2. +13 −0 t/t5800-remote-helpers.sh
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@@ -22,6 +22,7 @@
_digest = sha.new
import sys
import os
+import time
sys.path.insert(0, os.getenv("GITPYTHONLIB","."))
from git_remote_helpers.util import die, debug, warn
@@ -204,6 +205,11 @@ def read_one_line(repo):
"""Reads and processes one command.
"""
+ sleepy = os.environ.get("GIT_REMOTE_TESTGIT_SLEEPY")
+ if sleepy:
+ debug("Sleeping %d sec before readline" % int(sleepy))
+ time.sleep(int(sleepy))
+
line = sys.stdin.readline()
cmdline = line
@@ -258,6 +264,7 @@ def main(args):
more = True
+ sys.stdin = os.fdopen(sys.stdin.fileno(), 'r', 0)
while (more):
more = read_one_line(repo)
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@@ -72,6 +72,19 @@ test_expect_success 'pushing to local repo' '
compare_refs localclone HEAD server HEAD
'
+# Generally, skip this test. It demonstrates a now-fixed race in
+# git-remote-testgit, but is too slow to leave in for general use.
+: test_expect_success 'racily pushing to local repo' '
+ test_when_finished "rm -rf server2 localclone2" &&
+ cp -a server server2 &&
+ git clone "testgit::${PWD}/server2" localclone2 &&
+ (cd localclone2 &&
+ echo content >>file &&
+ git commit -a -m three &&
+ GIT_REMOTE_TESTGIT_SLEEPY=2 git push) &&
+ compare_refs localclone2 HEAD server2 HEAD
+'
+
test_expect_success 'synch with changes from localclone' '
(cd clone &&
git pull)

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