Break the function `ref_transaction_commit()` into two functions,
`ref_transaction_prepare()` and `ref_transaction_finish()`, with a
third function, `ref_transaction_abort()`, that can be used to abort
the transaction. Break up the `ref_store` methods similarly.
This split will make it easier to implement compound reference stores,
where a transaction might have to span multiple underlying stores. In
that case, we would first want to "prepare" the sub-transactions in
each of the reference stores. If any of the "prepare" steps fails, we
would "abort" all of the sub-transactions. Only if all of the
"prepare" steps succeed would we "finish" each of them.
Signed-off-by: Michael Haggerty <mhag...@alum.mit.edu>
---
refs.c | 34 ++++++++++++++++++++++---
refs.h | 37 ++++++++++++++++++++++++++-
refs/files-backend.c | 71 +++++++++++++++++++++++++++++++++++++++++-----------
refs/refs-internal.h | 42 ++++++++++++++++++++++++-------
4 files changed, 157 insertions(+), 27 deletions(-)
diff --git a/refs.c b/refs.c
index 14dec88e7f..689362db1e 100644
--- a/refs.c
+++ b/refs.c
@@ -1689,8 +1689,8 @@ int create_symref(const char *ref_target, const char
*refs_heads_master,
refs_heads_master, logmsg);
}
-int ref_transaction_commit(struct ref_transaction *transaction,
- struct strbuf *err)
+int ref_transaction_prepare(struct ref_transaction *transaction,
+ struct strbuf *err)
{
struct ref_store *refs = transaction->ref_store;
@@ -1700,7 +1700,35 @@ int ref_transaction_commit(struct ref_transaction
*transaction,
return -1;
}
- return refs->be->transaction_commit(refs, transaction, err);
+ return refs->be->transaction_prepare(refs, transaction, err);
+}
+
+int ref_transaction_finish(struct ref_transaction *transaction,
+ struct strbuf *err)
+{
+ struct ref_store *refs = transaction->ref_store;
+
+ return refs->be->transaction_finish(refs, transaction, err);
+}
+
+int ref_transaction_abort(struct ref_transaction *transaction,
+ struct strbuf *err)
+{
+ struct ref_store *refs = transaction->ref_store;
+
+ return refs->be->transaction_abort(refs, transaction, err);
+}
+
+int ref_transaction_commit(struct ref_transaction *transaction,
+ struct strbuf *err)
+{
+ int ret;
+
+ ret = ref_transaction_prepare(transaction, err);
+ if (ret)
+ return ret;
+
+ return ref_transaction_finish(transaction, err);
}
int refs_verify_refname_available(struct ref_store *refs,
diff --git a/refs.h b/refs.h
index b2d9626be6..4139e917f5 100644
--- a/refs.h
+++ b/refs.h
@@ -525,7 +525,10 @@ int ref_transaction_verify(struct ref_transaction
*transaction,
/*
* Commit all of the changes that have been queued in transaction, as
- * atomically as possible.
+ * atomically as possible. This is equivalent to calling
+ * `ref_transaction_prepare()` then `ref_transaction_finish()` (see
+ * below), which you can call yourself if you want finer control over
+ * reference updates.
*
* Returns 0 for success, or one of the below error codes for errors.
*/
@@ -536,6 +539,38 @@ int ref_transaction_verify(struct ref_transaction
*transaction,
int ref_transaction_commit(struct ref_transaction *transaction,
struct strbuf *err);
+/*
+ * Perform the preparatory stages of commiting `transaction`. Acquire
+ * any needed locks, check preconditions, etc.; basically, do as much
+ * as possible to ensure that the transaction will be able to go
+ * through, stopping just short of making any irrevocable or
+ * user-visible changes. Anything that this function does should be
+ * able to be finished up by calling `ref_transaction_finish()` or
+ * rolled back by calling `ref_transaction_abort()`.
+ *
+ * On success, return 0 and leave the transaction in "prepared" state.
+ * On failure, abort the transaction and return one of the
+ * `TRANSACTION_*` constants.
+ *
+ * Callers who don't need such fine-grained control over commiting
+ * reference transactions should just call `ref_transaction_commit()`.
+ */
+int ref_transaction_prepare(struct ref_transaction *transaction,
+ struct strbuf *err);
+
+/*
+ * Perform the final commit of `transaction`, which has already been
+ * prepared.
+ */
+int ref_transaction_finish(struct ref_transaction *transaction,
+ struct strbuf *err);
+
+/*
+ * Abort `transaction`, which has already been prepared.
+ */
+int ref_transaction_abort(struct ref_transaction *transaction,
+ struct strbuf *err);
+
/*
* Like ref_transaction_commit(), but optimized for creating
* references when originally initializing a repository (e.g., by "git
diff --git a/refs/files-backend.c b/refs/files-backend.c
index 7ddd4f87d5..f48409132d 100644
--- a/refs/files-backend.c
+++ b/refs/files-backend.c
@@ -2867,27 +2867,24 @@ 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);
if (transaction->state != REF_TRANSACTION_OPEN)
- die("BUG: commit called for transaction that is not open");
+ die("BUG: prepare called for transaction that is not open");
if (!transaction->nr)
goto cleanup;
@@ -2949,6 +2946,8 @@ 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];
@@ -2956,7 +2955,41 @@ 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->state != REF_TRANSACTION_PREPARED)
+ die("BUG: finish called for transaction that is not prepared");
+
+ if (!transaction->nr) {
+ transaction->state = REF_TRANSACTION_CLOSED;
+ return 0;
}
/* Perform updates first so live commits remain referenced */
@@ -3037,7 +3070,6 @@ 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];
@@ -3054,13 +3086,22 @@ static int files_transaction_commit(struct ref_store
*ref_store,
}
}
+ 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)
+{
+ if (transaction->state != REF_TRANSACTION_PREPARED)
+ die("BUG: abort called for transaction that is not prepared");
+
+ files_transaction_cleanup(transaction);
+ return 0;
+}
+
static int ref_present(const char *refname,
const struct object_id *oid, int flags, void *cb_data)
{
@@ -3327,7 +3368,9 @@ 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,
diff --git a/refs/refs-internal.h b/refs/refs-internal.h
index 9ed4387c8c..2ff65d3ebd 100644
--- a/refs/refs-internal.h
+++ b/refs/refs-internal.h
@@ -185,17 +185,26 @@ struct ref_update *ref_transaction_add_update(
/*
* Transaction states.
- * OPEN: The transaction is in a valid state and can accept new updates.
- * An OPEN transaction can be committed.
- * CLOSED: A closed transaction is no longer active and no other operations
- * than free can be used on it in this state.
- * A transaction can either become closed by successfully committing
- * an active transaction or if there is a failure while building
- * the transaction thus rendering it failed/inactive.
+ *
+ * OPEN: The transaction is in a valid state and new updates can be
+ * added to it. An OPEN transaction can be prepared or
+ * committed.
+ *
+ * PREPARED: ref_transaction_prepare(), which locks all of the
+ * references involved in the update and checks that the
+ * update has no errors, has been called successfully for the
+ * transaction.
+ *
+ * CLOSED: The transaction is no longer active. No other operations
+ * than free can be used on it in this state. A transaction
+ * becomes closed if there is a failure while building the
+ * transaction, if an active transaction is committed, or if a
+ * prepared transaction is finished.
*/
enum ref_transaction_state {
REF_TRANSACTION_OPEN = 0,
- REF_TRANSACTION_CLOSED = 1
+ REF_TRANSACTION_PREPARED = 1,
+ REF_TRANSACTION_CLOSED = 2
};
/*
@@ -497,6 +506,18 @@ typedef struct ref_store *ref_store_init_fn(const char
*gitdir,
typedef int ref_init_db_fn(struct ref_store *refs, struct strbuf *err);
+typedef int ref_transaction_prepare_fn(struct ref_store *refs,
+ struct ref_transaction *transaction,
+ struct strbuf *err);
+
+typedef int ref_transaction_finish_fn(struct ref_store *refs,
+ struct ref_transaction *transaction,
+ struct strbuf *err);
+
+typedef int ref_transaction_abort_fn(struct ref_store *refs,
+ struct ref_transaction *transaction,
+ struct strbuf *err);
+
typedef int ref_transaction_commit_fn(struct ref_store *refs,
struct ref_transaction *transaction,
struct strbuf *err);
@@ -599,7 +620,10 @@ struct ref_storage_be {
const char *name;
ref_store_init_fn *init;
ref_init_db_fn *init_db;
- ref_transaction_commit_fn *transaction_commit;
+
+ ref_transaction_prepare_fn *transaction_prepare;
+ ref_transaction_finish_fn *transaction_finish;
+ ref_transaction_abort_fn *transaction_abort;
ref_transaction_commit_fn *initial_transaction_commit;
pack_refs_fn *pack_refs;
--
2.11.0
