I reported a couple of times that t5552 is not passing reliably. It has now reached next, and will no doubt infect master soon. Turns out that it is not a Windows-specific issue, even if it occurs a lot more often on Windows than elsewhere. The culprit is that two processes try simultaneously to write to the same file specified via GIT_TRACE_PACKET, and it is not well defined how that should work, even on Linux. This patch series addresses that by locking the trace fd. I chose to use flock() instead of fcntl() because the Win32 API LockFileEx() [https://docs.microsoft.com/en-us/windows/desktop/api/fileapi/nf-fileapi-lockfileex] (which does exactly what I want in this context) has much more similar semantics to the former than the latter. Of course, I have to admit that I am not super solid on flock() semantics, and I also do not know which conditional blocks in config.mak.uname should grow a HAVE_FLOCK = YesWeDo line, still. Reviewers knowledgeable in flock() semantics: I would be much indebted if you helped me there. Also: is it safe to call flock() on file descriptors referring not to files, but, say, pipes or an interactive terminal? Johannes Schindelin (4): Introduce a function to lock/unlock file descriptors when appending mingw: implement lock_or_unlock_fd_for_appending() trace: lock the trace file to avoid racy trace_write() calls trace: verify that locking works Makefile | 1 + compat/mingw.c | 19 ++++++ compat/mingw.h | 3 + config.mak.uname | 3 + git-compat-util.h | 2 + t/helper/test-tool.c | 1 + t/helper/test-tool.h | 1 + t/helper/test-trace.c | 130 +++++++++++++++++++++++++++++++++++++++++ t/t0070-fundamental.sh | 6 ++ trace.c | 11 +++- wrapper.c | 14 +++++ 11 files changed, 190 insertions(+), 1 deletion(-) create mode 100644 t/helper/test-trace.c base-commit: 42cc7485a2ec49ecc440c921d2eb0cae4da80549 Published-As: https://github.com/gitgitgadget/git/releases/tags/pr-17%2Fdscho%2Ffetch-negotiator-skipping-v1 Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-17/dscho/fetch-negotiator-skipping-v1 Pull-Request: https://github.com/gitgitgadget/git/pull/17 -- gitgitgadget
