[PATCH v2 2/2] lock_packed_refs(): allow retries when acquiring the packed-refs lock
- From
Michael Haggerty <mhagger@alum.mit.edu>
- Date
- May 11, 2015, 10:35 UTC
- Message-ID
- <1431340526-24288-3-git-send-email-mhagger@alum.mit.edu>
- In-Reply-To
- <1431340526-24288-1-git-send-email-mhagger@alum.mit.edu>
Currently, there is only one attempt to acquire any lockfile, and if the lock is held by another process, the locking attempt fails immediately.
This is not such a limitation for loose reference files. First, they don't take long to rewrite. Second, most reference updates have a known "old" value, so if another process is updating a reference at the same moment that we are trying to lock it, then probably the expected "old" value will not longer be valid, and the update will fail anyway.
But these arguments do not hold for packed-refs:
* The packed-refs file can be large and take significant time to rewrite.
* Many references are stored in a single packed-refs file, so it could be that the other process was changing a different reference than the one that we are interested in.
Therefore, it is much more likely for there to be spurious lock conflicts in connection to the packed-refs file, resulting in unnecessary command failures.
So, if the first attempt to lock the packed-refs file fails, continue retrying for a configurable length of time before giving up. The default timeout is 1 second.
Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu> --- Documentation/config.txt | 6 ++++++ refs.c | 12 +++++++++++- t/t3210-pack-refs.sh | 17 +++++++++++++++++ 3 files changed, 34 insertions(+), 1 deletion(-)
diff --git a/Documentation/config.txt b/Documentation/config.txt index 2e5ceaf..3c24e10 100644 --- a/Documentation/config.txt +++ b/Documentation/config.txt @@ -622,6 +622,12 @@ core.commentChar:: If set to "auto", `git-commit` would select a character that is not the beginning character of any line in existing commit messages. +core.packedRefsTimeout:: + The length of time, in milliseconds, to retry when trying to + lock the `packed-refs` file. Value 0 means not to retry at + all; -1 means to try indefinitely. Default is 1000 (i.e., + retry for 1 second). + sequence.editor:: Text editor used by `git rebase -i` for editing the rebase instruction file. The value is meant to be interpreted by the shell when it is used. diff --git a/refs.c b/refs.c index 47e4e53..3f8ac63 100644 --- a/refs.c +++ b/refs.c @@ -2413,9 +2413,19 @@ static int write_packed_entry_fn(struct ref_entry *entry, void *cb_data) /* This should return a meaningful errno on failure */ int lock_packed_refs(int flags) { + static int timeout_configured = 0; + static int timeout_value = 1000; + struct packed_ref_cache *packed_ref_cache; - if (hold_lock_file_for_update(&packlock, git_path("packed-refs"), flags) < 0) + if (!timeout_configured) { + git_config_get_int("core.packedrefstimeout", &timeout_value); + timeout_configured = 1; + } + + if (hold_lock_file_for_update_timeout( + &packlock, git_path("packed-refs"), + flags, timeout_value) < 0) return -1; /* * Get the current packed-refs while holding the lock. If the diff --git a/t/t3210-pack-refs.sh b/t/t3210-pack-refs.sh index aa9eb3a..e5e3204 100755 --- a/t/t3210-pack-refs.sh +++ b/t/t3210-pack-refs.sh @@ -187,4 +187,21 @@ test_expect_success 'notice d/f conflict with existing ref' ' test_must_fail git branch foo/bar/baz/lots/of/extra/components ' +test_expect_success 'timeout if packed-refs.lock exists' ' + LOCK=.git/packed-refs.lock && + >$LOCK && + test_when_finished "rm -f $LOCK" && + test_must_fail git pack-refs --all --prune +' + +test_expect_success 'retry acquiring packed-refs.lock' ' + LOCK=.git/packed-refs.lock && + >$LOCK && + test_when_finished "wait; rm -f $LOCK" && + { + ( sleep 1 ; rm -f $LOCK ) & + } && + git -c core.packedrefstimeout=3000 pack-refs --all --prune +' + test_done
-- 2.1.4