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authorLibravatar Patrick Steinhardt <ps@pks.im>2020-04-02 09:10:02 +0200
committerLibravatar Junio C Hamano <gitster@pobox.com>2020-04-02 11:09:49 -0700
commite48cf33b61b8fecf1558fb32fcf5ee2987e82890 (patch)
tree39e57596523fdf5bc71b71e6f047a4e0f9f9f642 /pack-bitmap-write.c
parentupdate-ref: read commands in a line-wise fashion (diff)
downloadtgif-e48cf33b61b8fecf1558fb32fcf5ee2987e82890.tar.xz
update-ref: implement interactive transaction handling
The git-update-ref(1) command can only handle queueing transactions right now via its "--stdin" parameter, but there is no way for users to handle the transaction itself in a more explicit way. E.g. in a replicated scenario, one may imagine a coordinator that spawns git-update-ref(1) for multiple repositories and only if all agree that an update is possible will the coordinator send a commit. Such a transactional session could look like > start < start: ok > update refs/heads/master $OLD $NEW > prepare < prepare: ok # All nodes have returned "ok" > commit < commit: ok or > start < start: ok > create refs/heads/master $OLD $NEW > prepare < fatal: cannot lock ref 'refs/heads/master': reference already exists # On all other nodes: > abort < abort: ok In order to allow for such transactional sessions, this commit introduces four new commands for git-update-ref(1), which matches those we have internally already with the exception of "start": - start: start a new transaction - prepare: prepare the transaction, that is try to lock all references and verify their current value matches the expected one - commit: explicitly commit a session, that is update references to match their new expected state - abort: abort a session and roll back all changes By design, git-update-ref(1) will commit as soon as standard input is being closed. While fine in a non-transactional world, it is definitely unexpected in a transactional world. Because of this, as soon as any of the new transactional commands is used, the default will change to aborting without an explicit "commit". To avoid a race between queueing updates and the first "prepare" that starts a transaction, the "start" command has been added to start an explicit transaction. Add some tests to exercise this new functionality. Signed-off-by: Patrick Steinhardt <ps@pks.im> Signed-off-by: Junio C Hamano <gitster@pobox.com>
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