Re: [PATCH v3 19/19] refs.c: pass **transaction to commit and have it clear the pointer

On Fri, Apr 25, 2014 at 6:31 PM, Michael Haggerty [off-list ref] wrote:

On 04/25/2014 06:14 PM, Ronnie Sahlberg wrote:

quoted

Change ref_transaction_commit to take a pointer to a pointer for the
transaction. This allows us to clear the transaction pointer from within
ref_transaction_commit so that it becomes NULL in the caller.

This makes transaction handling in the callers much nicer since instead of
having to write horrible code like :
      t = ref_transaction_begin();
      if ((!t ||
          ref_transaction_update(t, refname, sha1, oldval, flags,
                                 !!oldval)) ||
          (ref_transaction_commit(t, action, &err) && !(t = NULL))) {
              ref_transaction_rollback(t);

we can now just do the much nicer
      t = ref_transaction_begin();
      if (!t ||
          ref_transaction_update(t, refname, sha1, oldval, flags,
                                 !!oldval) ||
          ref_transaction_commit(&t, action, &err)) {
              ref_transaction_rollback(t);

I understand the motivation for this change, but passing
pointer-to-pointer is unconventional in a case like this.  Unfortunately
I ran out of steam for the night before I could think about alternatives.

I see.
Yes passing a pointer to pointer is not ideal.
But I still want to be able to use the pattern
       t = ref_transaction_begin();
       if (!t ||
           ref_transaction_update(t, ...) ||
           ref_transaction_commit(t, ...)) {
               ref_transaction_rollback(t);

Maybe the problem is that ref_transaction_commit() implicitely also
frees the transaction.


What about changing ref_transaction_commit() would NOT free the
transaction and thus a caller would
always have to explicitely free the transaction afterwards?

Something like this :
       t = ref_transaction_begin();
       if (!t ||
           ref_transaction_update(t, ...) ||
           ref_transaction_commit(&t, ...)) {
               ref_transaction_rollback(t);
       }
       ref_transaction_free(t);

Regarding patches 01-18, I agree with Jonathan's comments and made a few
of my own.  I definitely don't think that code like "!(t = NULL)" should
stay in our code base as more than a transitional state.  But I'd have
to play with the alternatives before I can form an opinion on your
suggestion in this patch.

Thanks for working on this!

Michael

quoted

Signed-off-by: Ronnie Sahlberg <redacted>
---
 branch.c             |  4 ++--
 builtin/commit.c     |  2 +-
 builtin/replace.c    |  2 +-
 builtin/tag.c        |  2 +-
 builtin/update-ref.c |  2 +-
 fast-import.c        |  7 +++----
 refs.c               | 18 ++++++++++--------
 refs.h               |  3 ++-
 sequencer.c          |  7 +++----
 9 files changed, 24 insertions(+), 23 deletions(-)

diff --git a/branch.c b/branch.c
index 23cde1e..5d68467 100644
--- a/branch.c
+++ b/branch.c

@@ -303,14 +303,14 @@ void create_branch(const char *head,
                      if (!transaction ||
                          ref_transaction_update(transaction, ref.buf, sha1,
                                                 NULL, 0, 0) ||
-                         ref_transaction_commit(transaction, msg, &err))
+                         ref_transaction_commit(&transaction, msg, &err))
                        die_errno(_("%s: failed to write ref: %s"),
                                  ref.buf, err);
              } else {
                      if (!transaction ||
                          ref_transaction_create(transaction, ref.buf, sha1,
                                                 0) ||
-                         ref_transaction_commit(transaction, msg, &err))
+                         ref_transaction_commit(&transaction, msg, &err))
                        die_errno(_("%s: failed to write ref: %s"),
                                  ref.buf, err);
              }

diff --git a/builtin/commit.c b/builtin/commit.c
index 7e4c306..3142827 100644
--- a/builtin/commit.c
+++ b/builtin/commit.c

@@ -1682,7 +1682,7 @@ int cmd_commit(int argc, const char **argv, const char *prefix)
                                 current_head ?
                                 current_head->object.sha1 : NULL,
                                 0, !!current_head) ||
-         ref_transaction_commit(transaction, sb.buf, &err)) {
+         ref_transaction_commit(&transaction, sb.buf, &err)) {
              rollback_index_files();
              die(_("HEAD: cannot update ref: %s"), err);
      }

diff --git a/builtin/replace.c b/builtin/replace.c
index cf0f56d..51e9ddf 100644
--- a/builtin/replace.c
+++ b/builtin/replace.c

@@ -162,7 +162,7 @@ static int replace_object(const char *object_ref, const char *replace_ref,
      if (!transaction ||
          ref_transaction_update(transaction, ref, repl, prev,
                                 0, !is_null_sha1(prev)) ||
-         ref_transaction_commit(transaction, NULL, &err))
+         ref_transaction_commit(&transaction, NULL, &err))
        die(_("%s: failed to replace ref: %s"), ref, err);

      return 0;

diff --git a/builtin/tag.c b/builtin/tag.c
index dd53fb4..60b57a1 100644
--- a/builtin/tag.c
+++ b/builtin/tag.c

@@ -646,7 +646,7 @@ int cmd_tag(int argc, const char **argv, const char *prefix)
      if (!transaction ||
          ref_transaction_update(transaction, ref.buf, object, prev,
                                 0, !is_null_sha1(prev)) ||
-         ref_transaction_commit(transaction, NULL, &err))
+         ref_transaction_commit(&transaction, NULL, &err))
        die(_("%s: cannot update the ref: %s"), ref.buf, err);
      if (force && !is_null_sha1(prev) && hashcmp(prev, object))
              printf(_("Updated tag '%s' (was %s)\n"), tag, find_unique_abbrev(prev, DEFAULT_ABBREV));

diff --git a/builtin/update-ref.c b/builtin/update-ref.c
index a600ab3..4a0901d 100644
--- a/builtin/update-ref.c
+++ b/builtin/update-ref.c

@@ -373,7 +373,7 @@ int cmd_update_ref(int argc, const char **argv, const char *prefix)
              if (end_null)
                      line_termination = '\0';
              update_refs_stdin();
-             if (ref_transaction_commit(transaction, msg, &err))
+             if (ref_transaction_commit(&transaction, msg, &err))
                      die("update_ref failed: %s", err);
              return 0;
      }

diff --git a/fast-import.c b/fast-import.c
index a2b05fa..3ce2f47 100644
--- a/fast-import.c
+++ b/fast-import.c

@@ -1703,11 +1703,10 @@ static int update_branch(struct branch *b)
              }
      }
      transaction = ref_transaction_begin();
-     if ((!transaction ||
+     if (!transaction ||
          ref_transaction_update(transaction, b->name, b->sha1, old_sha1,
-                                0, 1)) ||
-         (ref_transaction_commit(transaction, msg, &err) &&
-          !(transaction = NULL))) {
+                                0, 1) ||
+         ref_transaction_commit(&transaction, msg, &err)) {
              ref_transaction_rollback(transaction);
              return error("Unable to update branch %s: %s", b->name, err);
      }

diff --git a/refs.c b/refs.c
index ffa9c83..0b60250 100644
--- a/refs.c
+++ b/refs.c

@@ -3401,10 +3401,10 @@ int update_ref(const char *action, const char *refname,
      char *err = NULL;

      t = ref_transaction_begin();
-     if ((!t ||
+     if (!t ||
          ref_transaction_update(t, refname, sha1, oldval, flags,
-                                !!oldval)) ||
-         (ref_transaction_commit(t, action, &err) && !(t = NULL))) {
+                                !!oldval) ||
+         ref_transaction_commit(&t, action, &err)) {
           const char *str = "update_ref failed for ref '%s': %s";

              ref_transaction_rollback(t);

@@ -3444,16 +3444,17 @@ static int ref_update_reject_duplicates(struct ref_update **updates, int n,
      return 0;
 }

-int ref_transaction_commit(struct ref_transaction *transaction,
+int ref_transaction_commit(struct ref_transaction **transaction,
                         const char *msg, char **err)
 {
      int ret = 0, delnum = 0, i;
      const char **delnames;
-     int n = transaction->nr;
-     struct ref_update **updates = transaction->updates;
+     int n = (*transaction)->nr;
+     struct ref_update **updates = (*transaction)->updates;

      if (!n) {
-             ref_transaction_free(transaction);
+             ref_transaction_free(*transaction);
+             *transaction = NULL;
              return 0;
      }

@@ -3527,7 +3528,8 @@ cleanup:
              if (updates[i]->lock)
                      unlock_ref(updates[i]->lock);
      free(delnames);
-     ref_transaction_free(transaction);
+     ref_transaction_free(*transaction);
+     *transaction = NULL;
      return ret;
 }

diff --git a/refs.h b/refs.h
index 8135131..85127f2 100644
--- a/refs.h
+++ b/refs.h

@@ -270,8 +270,9 @@ int ref_transaction_delete(struct ref_transaction *transaction,
  * problem.  The ref_transaction is freed by this function.
  * If error is non-NULL it will return an error string that describes
  * why a commit failed. This string must be free()ed by the caller.
+ * *transaction is reset to NULL in this call.
  */
-int ref_transaction_commit(struct ref_transaction *transaction,
+int ref_transaction_commit(struct ref_transaction **transaction,
                         const char *msg, char **err);

 /** Lock a ref and then write its file */

diff --git a/sequencer.c b/sequencer.c
index 7d59f58..3f6eced 100644
--- a/sequencer.c
+++ b/sequencer.c

@@ -283,11 +283,10 @@ static int fast_forward_to(const unsigned char *to, const unsigned char *from,
      strbuf_addf(&sb, "%s: fast-forward", action_name(opts));

      transaction = ref_transaction_begin();
-     if ((!transaction ||
+     if (!transaction ||
          ref_transaction_update(transaction, "HEAD", to, from,
-                                0, !unborn)) ||
-         (ref_transaction_commit(transaction, sb.buf, &err) &&
-          !(transaction = NULL))) {
+                                0, !unborn) ||
+         ref_transaction_commit(&transaction, sb.buf, &err)) {
              ref_transaction_rollback(transaction);
              strbuf_release(&sb);
              return error(_("HEAD: Could not fast-forward: %s\n"), err);

--
Michael Haggerty
mhagger@alum.mit.edu
http://softwareswirl.blogspot.com/