Michael Haggerty 30173b8851 ref_transaction_prepare(): new optional step for reference updates ... In the future, compound reference stores will sometimes need to modify references in two different reference stores at the same time, meaning that a single logical reference transaction might have to be implemented as two internal sub-transactions. They won't want to call `ref_transaction_commit()` for the two sub-transactions one after the other, because that wouldn't be atomic (the first commit could succeed and the second one fail). Instead, they will want to prepare both sub-transactions (i.e., obtain any necessary locks and do any pre-checks), and only if both prepare steps succeed, then commit both sub-transactions. Start preparing for that day by adding a new, optional `ref_transaction_prepare()` step to the reference transaction sequence, which obtains the locks and does any prechecks, reporting any errors that occur. Also add a `ref_transaction_abort()` function that can be used to abort a sub-transaction even if it has already been prepared. That is on the side of the public-facing API. On the side of the `ref_store` VTABLE, get rid of `transaction_commit` and instead add methods `transaction_prepare`, `transaction_finish`, and `transaction_abort`. A `ref_transaction_commit()` now basically calls methods `transaction_prepare` then `transaction_finish`. Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu> Signed-off-by: Junio C Hamano <gitster@pobox.com>		2017-05-23 14:29:55 +09:00
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files-backend.c	ref_transaction_prepare(): new optional step for reference updates	2017-05-23 14:29:55 +09:00
iterator.c	prefix_ref_iterator: don't trim too much	2017-05-23 14:29:52 +09:00
ref-cache.c	refs/files-backend: convert many internals to struct object_id	2017-05-08 15:12:58 +09:00
ref-cache.h	refs/files-backend: convert many internals to struct object_id	2017-05-08 15:12:58 +09:00
refs-internal.h	ref_transaction_prepare(): new optional step for reference updates	2017-05-23 14:29:55 +09:00