(DISTFILES): Comment out a few missing files.

[mono-project.git] / mcs / class / corlib / System.Threading / ReaderWriterLock.cs

//
// System.Threading.ReaderWriterLock.cs
//
// Author:
//   Dick Porter (dick@ximian.com)
//   Jackson Harper (jackson@ximian.com)
//   Lluis Sanchez Gual (lluis@ximian.com)
//
// (C) Ximian, Inc.  http://www.ximian.com
// (C) 2004 Novell, Inc (http://www.novell.com)
//

//
// Copyright (C) 2004 Novell, Inc (http://www.novell.com)
//
// Permission is hereby granted, free of charge, to any person obtaining
// a copy of this software and associated documentation files (the
// "Software"), to deal in the Software without restriction, including
// without limitation the rights to use, copy, modify, merge, publish,
// distribute, sublicense, and/or sell copies of the Software, and to
// permit persons to whom the Software is furnished to do so, subject to
// the following conditions:
// 
// The above copyright notice and this permission notice shall be
// included in all copies or substantial portions of the Software.
// 
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
// NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
// LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
// OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
// WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
//

using System.Collections;

namespace System.Threading
{
        public sealed class ReaderWriterLock
        {
                private int seq_num = 1;
                private int state = 0;
                private int readers = 0;
                private LockQueue writer_queue;
                private Hashtable reader_locks;
                private int writer_lock_owner;
                private int readyWaitingReaders = 0;

                public ReaderWriterLock()
                {
                        writer_queue = new LockQueue (this);
                        reader_locks = new Hashtable ();
                }

                public bool IsReaderLockHeld {
                        get {
                                lock (this) return reader_locks.ContainsKey (Thread.CurrentThreadId);
                        }
                }

                public bool IsWriterLockHeld {
                        get {
                                lock (this) return (state < 0 && Thread.CurrentThreadId == writer_lock_owner);
                        }
                }

                public int WriterSeqNum {
                        get {
                                lock (this) return seq_num;
                        }
                }

                public void AcquireReaderLock (int millisecondsTimeout) 
                {
                        AcquireReaderLock (millisecondsTimeout, 1);
                }
                
                void AcquireReaderLock (int millisecondsTimeout, int initialLockCount) 
                {
                        lock (this) {
                                if (HasWriterLock ()) {
                                        AcquireWriterLock (millisecondsTimeout, initialLockCount);
                                        return;
                                }
                                
                                object nlocks = reader_locks [Thread.CurrentThreadId];
                                if (nlocks == null)
                                {
                                        // Not currently holding a reader lock
                                        // Wait if there is a write lock
                                        readers++;
                                        try {
                                                if (state < 0 || !writer_queue.IsEmpty) {
                                                        if (!Monitor.Wait (this, millisecondsTimeout))
                                                                throw new ApplicationException ("Timeout expired");
                                                }
                                                readyWaitingReaders--;
                                        }
                                        finally {
                                                readers--;
                                        }
                                        
                                        reader_locks [Thread.CurrentThreadId] = initialLockCount;
                                        state += initialLockCount;
                                }
                                else {
                                        reader_locks [Thread.CurrentThreadId] = ((int)nlocks) + 1;
                                        state++;
                                }
                        }
                }

                public void AcquireReaderLock(TimeSpan timeout)
                {
                        int ms = CheckTimeout (timeout);
                        AcquireReaderLock ((int) timeout.TotalMilliseconds, 1);
                }

                public void AcquireWriterLock (int millisecondsTimeout)
                {
                        AcquireWriterLock (millisecondsTimeout, 1);
                }
                
                void AcquireWriterLock (int millisecondsTimeout, int initialLockCount)
                {
                        lock (this) {
                                if (HasWriterLock ()) {
                                        state--;
                                        return;
                                }
                                
                                // wait while there are reader locks or another writer lock, or
                                // other threads waiting for the writer lock
                                if (state != 0 || !writer_queue.IsEmpty || readers > 0) {
                                        if (!writer_queue.Wait (millisecondsTimeout))
                                                throw new ApplicationException ("Timeout expited");
                                }

                                state = -initialLockCount;
                                writer_lock_owner = Thread.CurrentThreadId;
                                seq_num++;
                        }
                }

                public void AcquireWriterLock(TimeSpan timeout) {
                        int ms = CheckTimeout (timeout);
                        AcquireWriterLock (ms, 1);
                }

                public bool AnyWritersSince(int seqNum) {
                        lock (this) {
                                return (this.seq_num > seqNum);
                        }
                }

                public void DowngradeFromWriterLock(ref LockCookie lockCookie)
                {
                        lock (this) {
                                if (!HasWriterLock())
                                        throw new ApplicationException ("The thread does not have the writer lock.");
                                
                                state = lockCookie.ReaderLocks;
                                reader_locks [Thread.CurrentThreadId] = state;
                                if (readers > 0) {
                                        readyWaitingReaders = readers;
                                        Monitor.PulseAll (this);
                                }
                                
                                // MSDN: A thread does not block when downgrading from the writer lock, 
                                // even if other threads are waiting for the writer lock
                        }
                }

                public LockCookie ReleaseLock()
                {
                        LockCookie cookie;
                        lock (this) {
                                cookie = GetLockCookie ();
                                if (cookie.WriterLocks != 0)
                                        ReleaseWriterLock (cookie.WriterLocks);
                                else if (cookie.ReaderLocks != 0) {
                                        ReleaseReaderLock (cookie.ReaderLocks, cookie.ReaderLocks);
                                }
                        }
                        return cookie;
                }
                
                public void ReleaseReaderLock()
                {
                        lock (this) {
                                if (HasWriterLock ()) {
                                        ReleaseWriterLock ();
                                        return;
                                }
                                else if (state > 0) {
                                        object read_lock_count = reader_locks [Thread.CurrentThreadId];
                                        if (read_lock_count != null) {
                                                ReleaseReaderLock ((int)read_lock_count, 1);
                                                return;
                                        }
                                }
                                throw new ApplicationException ("The thread does not have any reader or writer locks.");
                        }
                }

                void ReleaseReaderLock (int currentCount, int releaseCount)
                {
                        int new_count = currentCount - releaseCount;
                        
                        if (new_count == 0)
                                reader_locks.Remove (Thread.CurrentThreadId);
                        else
                                reader_locks [Thread.CurrentThreadId] = new_count;
                                
                        state -= releaseCount;
                        if (state == 0 && (readers == 0 || readyWaitingReaders <= 0) && !writer_queue.IsEmpty)
                                writer_queue.Pulse ();
                }

                public void ReleaseWriterLock()
                {
                        lock (this) {
                                if (!HasWriterLock())
                                        throw new ApplicationException ("The thread does not have the writer lock.");
                                
                                ReleaseWriterLock (1);
                        }
                }

                void ReleaseWriterLock (int releaseCount)
                {
                        state += releaseCount;
                        if (state == 0) {
                                if (readers > 0) {
                                        readyWaitingReaders = readers;
                                        Monitor.PulseAll (this);
                                }
                                else if (!writer_queue.IsEmpty)
                                        writer_queue.Pulse ();
                        }
                }
                
                public void RestoreLock(ref LockCookie lockCookie)
                {
                        lock (this) {
                                if (lockCookie.WriterLocks != 0)
                                        AcquireWriterLock (-1, lockCookie.WriterLocks);
                                else if (lockCookie.ReaderLocks != 0)
                                        AcquireReaderLock (-1, lockCookie.ReaderLocks);
                        }
                }

                public LockCookie UpgradeToWriterLock(int millisecondsTimeout)
                {
                        LockCookie cookie;
                        lock (this) {
                                cookie = GetLockCookie ();
                                if (cookie.WriterLocks != 0) {
                                        state--;
                                        return cookie;
                                }
                                
                                if (cookie.ReaderLocks != 0)
                                        ReleaseReaderLock (cookie.ReaderLocks, cookie.ReaderLocks);
                        }
                        
                        // Don't do this inside the lock, since it can cause a deadlock.
                        AcquireWriterLock (millisecondsTimeout);
                        return cookie;
                }
                
                public LockCookie UpgradeToWriterLock(TimeSpan timeout)
                {
                        int ms = CheckTimeout (timeout);
                        return UpgradeToWriterLock (ms);
                }
                
                LockCookie GetLockCookie ()
                {
                        LockCookie cookie = new LockCookie (Thread.CurrentThreadId);
                        
                        if (HasWriterLock())
                                cookie.WriterLocks = -state;
                        else {
                                object locks = reader_locks [Thread.CurrentThreadId];
                                if (locks != null) cookie.ReaderLocks = (int)locks;
                        }
                        return cookie;
                }

                bool HasWriterLock ()
                {
                        return (state < 0 && Thread.CurrentThreadId == writer_lock_owner);
                }
                
                private int CheckTimeout (TimeSpan timeout)
                {
                        int ms = (int) timeout.TotalMilliseconds;

                        if (ms < -1)
                                throw new ArgumentOutOfRangeException ("timeout",
                                                "Number must be either non-negative or -1");
                        return ms;
                }
        }
}