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src/subversion/subversion/libsvn_fs_fs/tree.c  view on Meta::CPAN

   that is null, TXN's base node.

   If the merge is successful, TXN's base will become
   SOURCE_NODE, and its root node will have a new ID, a
   successor of SOURCE_NODE.

   If a conflict results, update *CONFLICT to the path in the txn that
   conflicted; see the CONFLICT_P parameter of merge() for details. */
static svn_error_t *
merge_changes(dag_node_t *ancestor_node,
              dag_node_t *source_node,
              svn_fs_txn_t *txn,
              svn_stringbuf_t *conflict,
              apr_pool_t *pool)
{
  dag_node_t *txn_root_node;
  svn_fs_t *fs = txn->fs;
  const char *txn_id = txn->id;

  SVN_ERR(svn_fs_fs__dag_txn_root(&txn_root_node, fs, txn_id, pool));

  if (ancestor_node == NULL)
    {
      SVN_ERR(svn_fs_fs__dag_txn_base_root(&ancestor_node, fs,
                                           txn_id, pool));
    }

  if (svn_fs_fs__id_eq(svn_fs_fs__dag_get_id(ancestor_node),
                       svn_fs_fs__dag_get_id(txn_root_node)))
    {
      /* If no changes have been made in TXN since its current base,
         then it can't conflict with any changes since that base.
         The caller isn't supposed to call us in that case. */
      SVN_ERR_MALFUNCTION();
    }
  else
    SVN_ERR(merge(conflict, "/", txn_root_node,
                  source_node, ancestor_node, txn_id, NULL, pool));

  return SVN_NO_ERROR;
}


svn_error_t *
svn_fs_fs__commit_txn(const char **conflict_p,
                      svn_revnum_t *new_rev,
                      svn_fs_txn_t *txn,
                      apr_pool_t *pool)
{
  /* How do commits work in Subversion?
   *
   * When you're ready to commit, here's what you have:
   *
   *    1. A transaction, with a mutable tree hanging off it.
   *    2. A base revision, against which TXN_TREE was made.
   *    3. A latest revision, which may be newer than the base rev.
   *
   * The problem is that if latest != base, then one can't simply
   * attach the txn root as the root of the new revision, because that
   * would lose all the changes between base and latest.  It is also
   * not acceptable to insist that base == latest; in a busy
   * repository, commits happen too fast to insist that everyone keep
   * their entire tree up-to-date at all times.  Non-overlapping
   * changes should not interfere with each other.
   *
   * The solution is to merge the changes between base and latest into
   * the txn tree [see the function merge()].  The txn tree is the
   * only one of the three trees that is mutable, so it has to be the
   * one to adjust.
   *
   * You might have to adjust it more than once, if a new latest
   * revision gets committed while you were merging in the previous
   * one.  For example:
   *
   *    1. Jane starts txn T, based at revision 6.
   *    2. Someone commits (or already committed) revision 7.
   *    3. Jane's starts merging the changes between 6 and 7 into T.
   *    4. Meanwhile, someone commits revision 8.
   *    5. Jane finishes the 6-->7 merge.  T could now be committed
   *       against a latest revision of 7, if only that were still the
   *       latest.  Unfortunately, 8 is now the latest, so...
   *    6. Jane starts merging the changes between 7 and 8 into T.
   *    7. Meanwhile, no one commits any new revisions.  Whew.
   *    8. Jane commits T, creating revision 9, whose tree is exactly
   *       T's tree, except immutable now.
   *
   * Lather, rinse, repeat.
   */

  svn_error_t *err = SVN_NO_ERROR;
  svn_stringbuf_t *conflict = svn_stringbuf_create_empty(pool);
  svn_fs_t *fs = txn->fs;

  /* Limit memory usage when the repository has a high commit rate and
     needs to run the following while loop multiple times.  The memory
     growth without an iteration pool is very noticeable when the
     transaction modifies a node that has 20,000 sibling nodes. */
  apr_pool_t *iterpool = svn_pool_create(pool);

  /* Initialize output params. */
  *new_rev = SVN_INVALID_REVNUM;
  if (conflict_p)
    *conflict_p = NULL;

  while (1729)
    {
      svn_revnum_t youngish_rev;
      svn_fs_root_t *youngish_root;
      dag_node_t *youngish_root_node;

      svn_pool_clear(iterpool);

      /* Get the *current* youngest revision.  We call it "youngish"
         because new revisions might get committed after we've
         obtained it. */

      SVN_ERR(svn_fs_fs__youngest_rev(&youngish_rev, fs, iterpool));
      SVN_ERR(svn_fs_fs__revision_root(&youngish_root, fs, youngish_rev,
                                       iterpool));

      /* Get the dag node for the youngest revision.  Later we'll use