ln.types/odb/ng/storage/bases/StorageBase.cs

using System;
using System.Collections.Generic;
using ln.types.odb.values;
using System.Linq;
using ln.types.btree;
using System.Threading;
using System.Runtime.ConstrainedExecution;

namespace ln.types.odb.ng.storage.bases
{
	public abstract class StorageBase : IStorage
	{
		BTree<Guid> lockedDocuments = new BTree<Guid>();

		public StorageBase()
		{
		}
		public abstract bool Open();
		public abstract void Close();
		public abstract bool IsOpen { get; }


		public abstract Document Load(Guid documentID);
		public abstract void Save(Document document);
		public abstract void Delete(Guid documentID);

		public virtual bool GetDocumentLocked(Guid documentID)
		{
			lock (this)
			{
				return lockedDocuments.ContainsKey(documentID);
			}
		}

		public virtual bool LockDocument(Guid documentID)
		{
			lock (this)
			{
				if (lockedDocuments.ContainsKey(documentID))
					return false;

				lockedDocuments.Add(documentID);
				return true;
			}
		}
		public virtual bool ReleaseDocument(Guid documentID)
		{
			lock (this)
			{
				lockedDocuments.Remove(documentID);
				return true;
			}
		}
		public virtual void SaveRelease(Document document)
		{
			lock (this)
			{
				ReleaseDocument(document.ID);
				Save(document);
			}
		}


		public virtual DateTime GetStorageTimestamp(Guid documentID)
		{
			Document doc = Load(documentID);
			return doc.StorageTimeStamp;
		}

		/* Enumeration */
		public abstract IEnumerable<Guid> GetDocumentIDs();
		public abstract IEnumerable<Guid> GetDocumentIDs(string path, Predicate<ODBEntity> predicate);

		/* Indeces */
		public abstract void EnsureIndex(params string[] path);

		public virtual void Dispose()
		{
			if (IsOpen)
				Close();
		}

		public virtual bool Contains(Guid documentID)
		{
			return GetDocumentIDs().Contains(documentID);
		}

		class LockedDocumentID
		{
			public Guid DocumentID { get; }
			int waiting;

			public LockedDocumentID(Guid documentID)
			{
				DocumentID = documentID;
			}

			public void Lock()
			{
				waiting++;
				Monitor.Enter(this);
			}
			public bool Release()
			{
				waiting--;
				Monitor.Exit(this);

				return waiting > 0;
			}


			public override bool Equals(object obj)
			{
				return (obj is LockedDocumentID) && DocumentID.Equals((obj as LockedDocumentID).DocumentID);
			}
			public override int GetHashCode() => DocumentID.GetHashCode();
		}
	}
}