refs: add a concept of a reference transaction

diff --git a/refs.c b/refs.c
index 1305eb1fcff6d9e6f9f9563fe691c8a0914ace24..f0b5764b34d7eb94207b1cc7fecc747fe1eb510b 100644 (file)
--- a/refs.c
+++ b/refs.c
@@ -3267,6 +3267,96 @@ 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;
+       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);
+}
+
+void ref_transaction_rollback(struct ref_transaction *transaction)
+{
+       ref_transaction_free(transaction);
+}
+
+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);
+
+       assert(!is_null_sha1(new_sha1));
+       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) {
+               assert(!is_null_sha1(old_sha1));
+               hashcpy(update->old_sha1, old_sha1);
+       }
+}
+
 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 +3468,15 @@ int update_refs(const char *action, struct ref_update * const *updates_orig,
        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;
+}
+
 char *shorten_unambiguous_ref(const char *refname, int strict)
 {
        int i;