LockingQueue.cs

Go to the documentation of this file.

// 
//  Copyright 2010-2015 Deveel
// 
//    Licensed under the Apache License, Version 2.0 (the "License");
//    you may not use this file except in compliance with the License.
//    You may obtain a copy of the License at
// 
//        http://www.apache.org/licenses/LICENSE-2.0
// 
//    Unless required by applicable law or agreed to in writing, software
//    distributed under the License is distributed on an "AS IS" BASIS,
//    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
//    See the License for the specific language governing permissions and
//    limitations under the License.
//

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading;

namespace Deveel.Data.Transactions {
    public sealed class LockingQueue {
        private readonly List<Lock> locks;

        internal LockingQueue(ILockable lockable) {
            Lockable = lockable;
            locks = new List<Lock>();
        }

        public ILockable Lockable { get; private set; }

        public bool IsEmpty {
            get {
                lock (this) {
                    return !locks.Any();
                }
            }
        }

        public void Acquire(Lock @lock) {
            lock (this) {
                locks.Add(@lock);
            }
        }

        public void Release(Lock @lock) {
            lock (this) {
                locks.Remove(@lock);
                Lockable.Released(@lock);
                Monitor.PulseAll(this);
            }
        }

        internal void CheckAccess(Lock @lock) {
            lock (this) {
                // Error checking.  The queue must contain the Lock.
                if (!locks.Contains(@lock))
                    throw new InvalidOperationException("Queue does not contain the given Lock");

                // If 'READ'
                bool blocked;
                int index;
                if (@lock.AccessType == AccessType.Read) {
                    do {
                        blocked = false;

                        index = locks.IndexOf(@lock);

                        int i;
                        for (i = index - 1; i >= 0 && !blocked; --i) {
                            var testLock = locks[i];
                            if (testLock.AccessType == AccessType.Write)
                                blocked = true;
                        }

                        if (blocked) {
                            Monitor.Wait(this);
                        }
                    } while (blocked);
                } else {
                    do {
                        blocked = false;

                        index = locks.IndexOf(@lock);

                        if (index != 0) {
                            blocked = true;

                            Monitor.Wait(this);
                        }

                    } while (blocked);
                }

                // Notify the Lock table that we've got a lock on it.
                // TODO: Lock.Table.LockAcquired(Lock);
            }
        }
    }
}