From 30173b8851bb7203de938a638386cb9e6d7c501b Mon Sep 17 00:00:00 2001 From: Michael Haggerty Date: Mon, 22 May 2017 16:17:44 +0200 Subject: 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 Signed-off-by: Junio C Hamano --- refs/files-backend.c | 63 +++++++++++++++++++++++++++++++++++++++++----------- 1 file changed, 50 insertions(+), 13 deletions(-) (limited to 'refs/files-backend.c') diff --git a/refs/files-backend.c b/refs/files-backend.c index a4261d4683..19842d2e56 100644 --- a/refs/files-backend.c +++ b/refs/files-backend.c @@ -2855,22 +2855,19 @@ static void files_transaction_cleanup(struct ref_transaction *transaction) transaction->state = REF_TRANSACTION_CLOSED; } -static int files_transaction_commit(struct ref_store *ref_store, - struct ref_transaction *transaction, - struct strbuf *err) +static int files_transaction_prepare(struct ref_store *ref_store, + struct ref_transaction *transaction, + struct strbuf *err) { struct files_ref_store *refs = files_downcast(ref_store, REF_STORE_WRITE, - "ref_transaction_commit"); + "ref_transaction_prepare"); size_t i; int ret = 0; - struct string_list refs_to_delete = STRING_LIST_INIT_NODUP; - struct string_list_item *ref_to_delete; struct string_list affected_refnames = STRING_LIST_INIT_NODUP; char *head_ref = NULL; int head_type; struct object_id head_oid; - struct strbuf sb = STRBUF_INIT; assert(err); @@ -2934,6 +2931,8 @@ static int files_transaction_commit(struct ref_store *ref_store, * that new values are valid, and write new values to the * lockfiles, ready to be activated. Only keep one lockfile * open at a time to avoid running out of file descriptors. + * Note that lock_ref_for_update() might append more updates + * to the transaction. */ for (i = 0; i < transaction->nr; i++) { struct ref_update *update = transaction->updates[i]; @@ -2941,7 +2940,38 @@ static int files_transaction_commit(struct ref_store *ref_store, ret = lock_ref_for_update(refs, update, transaction, head_ref, &affected_refnames, err); if (ret) - goto cleanup; + break; + } + +cleanup: + free(head_ref); + string_list_clear(&affected_refnames, 0); + + if (ret) + files_transaction_cleanup(transaction); + else + transaction->state = REF_TRANSACTION_PREPARED; + + return ret; +} + +static int files_transaction_finish(struct ref_store *ref_store, + struct ref_transaction *transaction, + struct strbuf *err) +{ + struct files_ref_store *refs = + files_downcast(ref_store, 0, "ref_transaction_finish"); + size_t i; + int ret = 0; + struct string_list refs_to_delete = STRING_LIST_INIT_NODUP; + struct string_list_item *ref_to_delete; + struct strbuf sb = STRBUF_INIT; + + assert(err); + + if (!transaction->nr) { + transaction->state = REF_TRANSACTION_CLOSED; + return 0; } /* Perform updates first so live commits remain referenced */ @@ -3022,7 +3052,6 @@ static int files_transaction_commit(struct ref_store *ref_store, cleanup: files_transaction_cleanup(transaction); - strbuf_release(&sb); for (i = 0; i < transaction->nr; i++) { struct ref_update *update = transaction->updates[i]; @@ -3039,13 +3068,19 @@ cleanup: } } + strbuf_release(&sb); string_list_clear(&refs_to_delete, 0); - free(head_ref); - string_list_clear(&affected_refnames, 0); - return ret; } +static int files_transaction_abort(struct ref_store *ref_store, + struct ref_transaction *transaction, + struct strbuf *err) +{ + files_transaction_cleanup(transaction); + return 0; +} + static int ref_present(const char *refname, const struct object_id *oid, int flags, void *cb_data) { @@ -3316,7 +3351,9 @@ struct ref_storage_be refs_be_files = { "files", files_ref_store_create, files_init_db, - files_transaction_commit, + files_transaction_prepare, + files_transaction_finish, + files_transaction_abort, files_initial_transaction_commit, files_pack_refs, -- cgit v1.2.3