Michael Haggerty <mhag...@alum.mit.edu> writes:
> Build out the API for dealing with a bunch of reference checks and
> changes within a transaction. Define an opaque ref_transaction type
> that is managed entirely within refs.c. Introduce functions for
> beginning a transaction, adding updates to a transaction, and
> committing/rolling back a transaction.
>
> This API will soon replace update_refs().
>
> Signed-off-by: Michael Haggerty <mhag...@alum.mit.edu>
> ---
> refs.c | 96
> ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> refs.h | 65 +++++++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 161 insertions(+)
>
> diff --git a/refs.c b/refs.c
> index 1305eb1..e788c27 100644
> --- a/refs.c
> +++ b/refs.c
> @@ -3267,6 +3267,93 @@ static int update_ref_write(const char *action, const
> char *refname,
> return 0;
> }
>
> +/*
> + * Data structure for holding a reference transaction, which can
> + * consist of checks and updates to multiple references, carried out
> + * as atomically as possible. This structure is opaque to callers.
> + */
> +struct ref_transaction {
> + struct ref_update **updates;
Don't we try to name an array update[] (not plural updates[]) so
that we can say update[7] to mean the seventh update?
> + size_t alloc;
> + size_t nr;
> +};
> +
> +struct ref_transaction *ref_transaction_begin(void)
> +{
> + return xcalloc(1, sizeof(struct ref_transaction));
> +}
> +
> +static void ref_transaction_free(struct ref_transaction *transaction)
> +{
> + int i;
> +
> + for (i = 0; i < transaction->nr; i++) {
> + struct ref_update *update = transaction->updates[i];
> +
> + free((char *)update->ref_name);
> + free(update);
> + }
> +
> + free(transaction->updates);
> + free(transaction);
> +}
OK.
> +void ref_transaction_rollback(struct ref_transaction *transaction)
> +{
> + ref_transaction_free(transaction);
> +}
OK.
> +static struct ref_update *add_update(struct ref_transaction *transaction,
> + const char *refname)
> +{
> + struct ref_update *update = xcalloc(1, sizeof(*update));
> +
> + update->ref_name = xstrdup(refname);
> + ALLOC_GROW(transaction->updates, transaction->nr + 1,
> transaction->alloc);
> + transaction->updates[transaction->nr++] = update;
> + return update;
> +}
> +
> +void ref_transaction_update(struct ref_transaction *transaction,
> + const char *refname,
> + unsigned char *new_sha1, unsigned char *old_sha1,
> + int flags, int have_old)
> +{
> + struct ref_update *update = add_update(transaction, refname);
> +
> + hashcpy(update->new_sha1, new_sha1);
> + update->flags = flags;
> + update->have_old = have_old;
> + if (have_old)
> + hashcpy(update->old_sha1, old_sha1);
> +}
> +
> +void ref_transaction_create(struct ref_transaction *transaction,
> + const char *refname,
> + unsigned char *new_sha1,
> + int flags)
> +{
> + struct ref_update *update = add_update(transaction, refname);
> +
> + hashcpy(update->new_sha1, new_sha1);
> + hashclr(update->old_sha1);
> + update->flags = flags;
> + update->have_old = 1;
> +}
> +
> +void ref_transaction_delete(struct ref_transaction *transaction,
> + const char *refname,
> + unsigned char *old_sha1,
> + int flags, int have_old)
> +{
> + struct ref_update *update = add_update(transaction, refname);
> +
> + update->flags = flags;
> + update->have_old = have_old;
> + if (have_old)
> + hashcpy(update->old_sha1, old_sha1);
> +}
> +
I can see that the chosen set of primitives update/create/delete
mirrors what update-ref allows us to do, but given the explanation
of "update" in refs.h, wouldn't it make more sense to implement the
others in terms of it?
> int update_ref(const char *action, const char *refname,
> const unsigned char *sha1, const unsigned char *oldval,
> int flags, enum action_on_err onerr)
> @@ -3378,6 +3465,15 @@ cleanup:
> return ret;
> }
>
> +int ref_transaction_commit(struct ref_transaction *transaction,
> + const char *msg, enum action_on_err onerr)
> +{
> + int ret = update_refs(msg, transaction->updates, transaction->nr,
> + onerr);
> + ref_transaction_free(transaction);
> + return ret;
> +}
OK.
> char *shorten_unambiguous_ref(const char *refname, int strict)
> {
> int i;
> diff --git a/refs.h b/refs.h
> index 08e60ac..476a923 100644
> --- a/refs.h
> +++ b/refs.h
> @@ -24,6 +24,8 @@ struct ref_update {
> int have_old; /* 1 if old_sha1 is valid, 0 otherwise */
> };
>
> +struct ref_transaction;
> +
> /*
> * Bit values set in the flags argument passed to each_ref_fn():
> */
> @@ -220,6 +222,69 @@ enum action_on_err {
> UPDATE_REFS_QUIET_ON_ERR
> };
>
> +/*
> + * Begin a reference transaction. The reference transaction must
> + * eventually be commited using ref_transaction_commit() or rolled
> + * back using ref_transaction_rollback().
> + */
> +struct ref_transaction *ref_transaction_begin(void);
> +
> +/*
> + * Roll back a ref_transaction and free all associated data.
> + */
> +void ref_transaction_rollback(struct ref_transaction *transaction);
> +
> +
> +/*
> + * The following functions add a reference check or update to a
> + * ref_transaction. In all of them, refname is the name of the
> + * reference to be affected. The functions make internal copies of
> + * refname, so the caller retains ownership of the parameter. flags
Good to see the ownership rules described.
> + * can be REF_NODEREF; it is passed to update_ref_lock().
> + */
> +
> +
> +/*
> + * Add a reference update to transaction. new_sha1 is the value that
> + * the reference should have after the update, or zeros if it should
> + * be deleted. If have_old is true, then old_sha1 holds the value
> + * that the reference should have had before the update, or zeros if
> + * it must not have existed beforehand.
> + */
> +void ref_transaction_update(struct ref_transaction *transaction,
> + const char *refname,
> + unsigned char *new_sha1, unsigned char *old_sha1,
> + int flags, int have_old);
> +
> +/*
> + * Add a reference creation to transaction. new_sha1 is the value
> + * that the reference should have after the update, or zeros if it
> + * should be deleted. It is verified that the reference does not
> + * exist already.
> + */
Sounds a bit crazy that you can ask "create", which verifies the
absense of the thing, to delete a thing.
> +void ref_transaction_create(struct ref_transaction *transaction,
> + const char *refname,
> + unsigned char *new_sha1,
> + int flags);
> +
> +/*
> + * Add a reference deletion to transaction. If have_old is true, then
> + * old_sha1 holds the value that the reference should have had before
> + * the update.
> + */
> +void ref_transaction_delete(struct ref_transaction *transaction,
> + const char *refname,
> + unsigned char *old_sha1,
> + int flags, int have_old);
> +
> +/*
> + * Commit all of the changes that have been queued in transaction, as
> + * atomically as possible. Return a nonzero value if there is a
> + * problem. The ref_transaction is freed by this function.
> + */
> +int ref_transaction_commit(struct ref_transaction *transaction,
> + const char *msg, enum action_on_err onerr);
> +
> /** Lock a ref and then write its file */
> int update_ref(const char *action, const char *refname,
> const unsigned char *sha1, const unsigned char *oldval,
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