Re: master: t5800-remote-helpers.sh hangs on test "pulling from remote remote"
- From
- Pete Wyckoff <pw@padd.com>
- Date
- Apr 21, 2012, 20:15 UTC
- Message-ID
- <20120421201524.GA18419@padd.com>
- In-Reply-To
- <4F9145A1.6020201@gmail.com>
stefano.lattarini@gmail.com wrote on Fri, 20 Apr 2012 13:16 +0200:
Show 51 quoted lines
> On 04/20/2012 01:34 AM, Pete Wyckoff wrote: > > drizzd@aon.at wrote on Sun, 15 Apr 2012 14:51 +0200: > >> The 'pushing to local repo' test of t5800 which pushes using > >> git-remote-testgit.py results in a deadlock for Stefano. Invoking > >> fast-export/fast-import manually seems to work, however. I don't know > >> what else to try at this point. > >> > >> I am pasting some relevant results below. > >> > >>> expecting success: > >>> (cd localclone && > >>> echo content >>file && > >>> git commit -a -m three && > >>> GIT_TRACE=1 GIT_TRANSPORT_HELPER_DEBUG=1 GIT_DEBUG_TESTGIT=1 git push) && > >>> compare_refs localclone HEAD server HEAD > > > > fast-export should say to fd 1 "feature done\nblob\n..." > > > > fast-import is probably blocked on reading fd 0, hoping to find a > > sequence of commands > > > > I too cannot reproduce the problem. Stefano, can you try this > > bigger hammer? We'll see if anything sticks out. > > > > GIT_TRACE=1 GIT_TRANSPORT_HELPER_DEBUG=1 GIT_DEBUG_TESTGIT=1 strace -vf -s 2000 -o /tmp/strace.out git push > > > > Then "bzip2 /tmp/strace.out" and attach /tmp/strace.out.bz2, please. > > > > -- Pete > > > Here it is. Details of the git version I've used to do this test: > > $ git describe > v1.7.10-207-g0bb2ee1 > > $ git diff > diff --git a/t/t5800-remote-helpers.sh b/t/t5800-remote-helpers.sh > index 1c62001..770cda6 100755 > --- a/t/t5800-remote-helpers.sh > +++ b/t/t5800-remote-helpers.sh > @@ -68,7 +68,10 @@ test_expect_success 'pushing to local repo' ' > (cd localclone && > echo content >>file && > git commit -a -m three && > - git push) && > + GIT_TRACE=1 \ > + GIT_TRANSPORT_HELPER_DEBUG=1 \ > + GIT_DEBUG_TESTGIT=1 \ > + strace -vf -s 2000 -o /tmp/strace.out git push) && > compare_refs localclone HEAD server HEAD > '
Thank you. Adding the strace made that test work, and a later one hung with the same race condition. Here's a patch that describes the race, and adds a strategic sleep to make it easily reproducible.
Not sure yet what is the right way to fix this. And I don't know if it's just git-remote-testgit that has the problem because it forks an importer, or if other remote helpers would be similarly affected.
The easiest fix is to invoke "python -u" in git-remote-testgit.py, or do
sys.stdin = os.fdopen(sys.stdin.fileno(), 'r', 0)
But I'm not sure if this works on all systems. We could also consider adding a handshake after "export", to give the helper time to get ready.
-- Pete
--8<--
>From 4179e326d86b6ab9f9c7f79a9dbd03b8d81b6a6a Mon Sep 17 00:00:00 2001
From: Pete Wyckoff <pw@padd.com> Date: Sat, 21 Apr 2012 14:57:31 -0400 Subject: [PATCH] demonstrate git-remote-testgit race
Test t5800-remote-helpers "pushing to local repo" can hang in a race condition between git push and git-remote-testgit.
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 is faster than git-remote-testgit + git fast-import, the fast-export output can end up in libc's buffer, rather than in git fast-import. The latter blocks on a now-empty stdin.
This patch demonstates the problem.
Signed-off-by: Pete Wyckoff <pw@padd.com> --- git-remote-testgit.py | 7 +++++++ t/t5800-remote-helpers.sh | 17 +++++++++++++++++ 2 files changed, 24 insertions(+)
diff --git a/git-remote-testgit.py b/git-remote-testgit.py index 3dc4851..616e772 100644 --- a/git-remote-testgit.py +++ b/git-remote-testgit.py @@ -22,6 +22,7 @@ except ImportError: _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 +205,12 @@ 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)) + debug("Awake, to readline") + line = sys.stdin.readline() cmdline = line diff --git a/t/t5800-remote-helpers.sh b/t/t5800-remote-helpers.sh index 1c62001..7555be6 100755 --- a/t/t5800-remote-helpers.sh +++ b/t/t5800-remote-helpers.sh @@ -72,6 +72,23 @@ test_expect_success 'pushing to local repo' ' compare_refs localclone HEAD server HEAD ' +test_expect_failure 'racily pushing to local repo' ' + cp -a server server2 && + git clone "testgit::${PWD}/server2" localclone2 && + test_when_finished "rm -rf server2 localclone2" && + (cd localclone2 && + echo content >>file && + git commit -a -m three && + GIT_TRANSPORT_HELPER_DEBUG=1 GIT_REMOTE_TESTGIT_SLEEPY=2 timeout 10 strace -o trace.out -f git push + ret=$? && + if [ $ret -eq 124 ]; then + echo "Check for too much input in export line" && + grep "read(0, .export" trace.out ; true + fi && + exit $ret) && + compare_refs localclone2 HEAD server2 HEAD +' + test_expect_success 'synch with changes from localclone' ' (cd clone && git pull)
-- 1.7.10.57.g7fa2a.dirty