NestedLocks.cs

using System;
using System.Collections.Generic;
using Waher.Persistence.Serialization;
 
namespace Waher.Persistence.Files.Storage
{
    internal class NestedLocks
    {
        private readonly ObjectBTreeFile file;
        private int count;
        private Dictionary<ObjectBTreeFile, int> additionalLocks = null;
        private Dictionary<ObjectBTreeFile, bool> touched = null;
 
        public NestedLocks(ObjectBTreeFile File, bool WriteLock)
        {
            this.file = File;
            this.count = WriteLock ? 1 : -1;
        }
 
        public static NestedLocks CreateIfNested(ObjectBTreeFile File, bool WriteLock, IObjectSerializer Serializer)
        {
            if (Serializer is ObjectSerializer ObjectSerializer)
                return CreateIfNested(File, WriteLock, ObjectSerializer);
            else
                return null;
        }
 
        public static NestedLocks CreateIfNested(ObjectBTreeFile File, bool WriteLock, ObjectSerializer Serializer)
        {
            return Serializer.HasByReference ? new NestedLocks(File, WriteLock) : null;
        }
 
        public bool HasLock(ObjectBTreeFile File, out bool WriteLock)
        {
            if (this.touched is null)
                this.touched = new Dictionary<ObjectBTreeFile, bool>();
 
            this.touched[File] = true;
 
            if (File == this.file)
            {
                WriteLock = this.count > 0;
                return true;
            }
 
            if (this.additionalLocks is null)
            {
                WriteLock = false;
                return false;
            }
 
            if (this.additionalLocks.TryGetValue(File, out int i))
            {
                WriteLock = i > 0;
                return true;
            }
            else
            {
                WriteLock = false;
                return false;
            }
        }
 
        public void AddLock(ObjectBTreeFile File, bool WriteLock)
        {
            if (this.touched is null)
                this.touched = new Dictionary<ObjectBTreeFile, bool>();
 
            this.touched[File] = true;
 
            if (File == this.file)
            {
                if (WriteLock ^ (this.count > 0))
                    throw new InvalidOperationException("Mismatching lock state.");
 
                if (WriteLock)
                    this.count++;
                else
                    this.count--;
            }
            else
            {
                if (this.additionalLocks is null)
                {
                    if (this.additionalLocks is null)
                        this.additionalLocks = new Dictionary<ObjectBTreeFile, int>();
                }
 
                if (this.additionalLocks.TryGetValue(File, out int i))
                {
                    if (WriteLock ^ (i > 0))
                        throw new InvalidOperationException("Mismatching lock state.");
 
                    if (WriteLock)
                        i++;
                    else
                        i--;
                }
                else
                    i = WriteLock ? 1 : -1;
 
                this.additionalLocks[File] = i;
            }
        }
 
        public bool RemoveLock(ObjectBTreeFile File)
        {
            if (File == this.file)
            {
                if (this.count > 0)
                    this.count--;
                else
                    this.count++;
 
                return true;
            }
            else
            {
                if (this.additionalLocks is null)
                    return false;
 
                if (!this.additionalLocks.TryGetValue(File, out int i))
                    return false;
 
                if (i > 0)
                    i--;
                else
                    i++;
 
                if (i == 0)
                    this.additionalLocks.Remove(File);
                else
                    this.additionalLocks[File] = i;
 
                return true;
            }
        }
 
        public bool HasBeenTouched(ObjectBTreeFile File)
        {
            return this.touched?.ContainsKey(File) ?? false;
        }
 
    }
}