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>

1 files changed, 7 insertions, 0 deletions

diff --git a/git-remote-testgit.py b/git-remote-testgit.py
index 3dc4851..5f3ebd2 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 +205,11 @@ 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)