private async Task<Errorable<Stage>> persistStage(Stage stg)
        {
            FileInfo tmpFile = system.getTemporaryFile();
            using (var fs = new FileStream(tmpFile.FullName, FileMode.OpenOrCreate, FileAccess.Write, FileShare.None, bufferSize: 16386, useAsync: true))
            {
                await fs.WriteRawAsync(stg.WriteTo(new StringBuilder()).ToString());
            }

            lock (FileSystem.SystemLock)
            {
                FileInfo fi = system.getStagePathByStageName(stg.Name);
                if (fi.Exists)
                    fi.Delete();

                // Create directory if it doesn't exist:
                if (!fi.Directory.Exists)
                {
                    Debug.WriteLine(String.Format("New DIR '{0}'", fi.Directory.FullName));
                    fi.Directory.Create();
                }

                // Write the contents to the file:
                Debug.WriteLine(String.Format("New STAGE '{0}'", fi.FullName));
                File.Move(tmpFile.FullName, fi.FullName);
            }

            return stg;
        }
        private async Task<Errorable<Ref>> persistRef(Ref rf)
        {
            FileInfo tmpFile = system.getTemporaryFile();

            // Write the ref's contents to the temporary file:
            using (var fs = new FileStream(tmpFile.FullName, FileMode.OpenOrCreate, FileAccess.Write, FileShare.None, 16384, true))
                await fs.WriteRawAsync(rf.WriteTo(new StringBuilder()).ToString());

            lock (FileSystem.SystemLock)
            {
                // TODO: would love to see FileInfo.DeleteAsync, DirectoryInfo.CreateAsync, etc.
                FileInfo fi = system.getRefPathByRefName(rf.Name);
                if (fi.Exists) fi.Delete();
                else
                    // Create directory if it doesn't exist:
                    if (!fi.Directory.Exists)
                    {
                        Debug.WriteLine(String.Format("New DIR '{0}'", fi.Directory.FullName));
                        fi.Directory.Create();
                    }

                // Move the temp file to the real file:
                Debug.WriteLine(String.Format("New REF '{0}'", fi.FullName));
                File.Move(tmpFile.FullName, fi.FullName);
            }

            return rf;
        }
        private async Task<Errorable<Commit>> persistCommit(Commit cm)
        {
            FileInfo tmpFile = system.getTemporaryFile();

            // Write the commit contents to the file:
            using (var fs = new FileStream(tmpFile.FullName, FileMode.CreateNew, FileAccess.Write, FileShare.None, bufferSize: 16834, useAsync: true))
            {
                await fs.WriteRawAsync(cm.WriteTo(new StringBuilder()).ToString());
            }

            lock (FileSystem.SystemLock)
            {
                FileInfo fi = system.getPathByID(cm.ID);

                // NOTE: if the record already exists we can either error out or overwrite the existing file with contents known to be good in the case the existing file got corrupt.
                // Let's stick with the self-repair scenario since erroring out doesn't help anyone.
                if (fi.Exists)
                {
                    Debug.WriteLine(String.Format("Self-repair scenario: overwriting old CommitID {0} with new contents", cm.ID));
                    fi.Delete();
                }

                // Create directory if it doesn't exist:
                if (!fi.Directory.Exists)
                {
                    Debug.WriteLine(String.Format("New DIR '{0}'", fi.Directory.FullName));
                    fi.Directory.Create();
                }

                Debug.WriteLine(String.Format("New COMMIT '{0}'", fi.FullName));
                File.Move(tmpFile.FullName, fi.FullName);
            }

            return cm;
        }
        private async Task<Errorable<TreeNode>> persistTree(TreeNode tr)
        {
            Debug.Assert(tr != null);

            // Check that all referenced blobs are already persisted:
            foreach (var trbl in tr.Blobs)
            {
                if (!system.getPathByID(trbl.BlobID).Exists)
                    return new BlobIDRecordDoesNotExistError(trbl.BlobID);
            }

            // Check that all referenced blobs are already persisted:
            foreach (var trtr in tr.Trees)
            {
                if (!system.getPathByID(trtr.TreeID).Exists)
                    return new TreeIDRecordDoesNotExistError(trtr.TreeID);
            }

            // Write the tree contents to the file:
            FileInfo tmpFile = system.getTemporaryFile();
            using (var fs = new FileStream(tmpFile.FullName, FileMode.CreateNew, FileAccess.Write, FileShare.None, bufferSize: 16384, useAsync: true))
            {
                await fs.WriteRawAsync(tr.WriteTo(new StringBuilder()).ToString());
            }

            lock (FileSystem.SystemLock)
            {
                FileInfo fi = system.getPathByID(tr.ID);

                // NOTE: if the record already exists we can either error out or overwrite the existing file with contents known to be good in the case the existing file got corrupt.
                // Let's stick with the self-repair scenario since erroring out doesn't help anyone.
                if (fi.Exists)
                {
                    Debug.WriteLine(String.Format("Self-repair scenario: overwriting old TreeID {0} with new contents", tr.ID));
                    fi.Delete();
                    File.Move(tmpFile.FullName, fi.FullName);
                    return tr;
                }

                // Create directory if it doesn't exist:
                if (!fi.Directory.Exists)
                {
                    Debug.WriteLine(String.Format("New DIR '{0}'", fi.Directory.FullName));
                    fi.Directory.Create();
                }

                Debug.WriteLine(String.Format("New TREE '{0}'", fi.FullName));
                File.Move(tmpFile.FullName, fi.FullName);
            }

            return tr;
        }
        private async Task<Errorable<Tag>> persistTag(Tag tg)
        {
            // Write the commit contents to the file:
            FileInfo tmpFile = system.getTemporaryFile();
            using (var fs = new FileStream(tmpFile.FullName, FileMode.CreateNew, FileAccess.Write, FileShare.None))
            {
                await fs.WriteRawAsync(tg.WriteTo(new StringBuilder()).ToString());
            }

            lock (FileSystem.SystemLock)
            {
                FileInfo fi = system.getPathByID(tg.ID);

                // NOTE: if the record already exists we can either error out or overwrite the existing file with contents known to be good in the case the existing file got corrupt.
                // Let's stick with the self-repair scenario since erroring out doesn't help anyone.
                if (fi.Exists)
                {
                    Debug.WriteLine(String.Format("Self-repair scenario: overwriting old TagID {0} with new contents", tg.ID));
                    fi.Delete();
                }

                // Create directory if it doesn't exist:
                if (!fi.Directory.Exists)
                {
                    Debug.WriteLine(String.Format("New DIR '{0}'", fi.Directory.FullName));
                    fi.Directory.Create();
                }

                Debug.WriteLine(String.Format("New TAG '{0}'", fi.FullName));
                File.Move(tmpFile.FullName, fi.FullName);
            }

            // Now keep track of the tag by its name:
            tmpFile = system.getTemporaryFile();
            using (var fs = new FileStream(tmpFile.FullName, FileMode.CreateNew, FileAccess.Write, FileShare.None))
            {
                await fs.WriteRawAsync(tg.ID.ToString());
            }

            lock (FileSystem.SystemLock)
            {
                FileInfo fiTracker = system.getTagPathByTagName(tg.Name);
                // Does this tag name exist already?
                if (fiTracker.Exists)
                {
                    tmpFile.Delete();
                    return new TagNameAlreadyExistsError(tg.Name);
                }

                // Create directory if it doesn't exist:
                if (!fiTracker.Directory.Exists)
                {
                    Debug.WriteLine(String.Format("New DIR '{0}'", fiTracker.Directory.FullName));
                    fiTracker.Directory.Create();
                }

                Debug.WriteLine(String.Format("New TAG '{0}'", fiTracker.FullName));
                File.Move(tmpFile.FullName, fiTracker.FullName);
            }

            return tg;
        }