//*******************************************************************************************************//  ReaderWriterSpinLock.cs - Gbtc////  Tennessee Valley Authority, 2011//  No copyright is claimed pursuant to 17 USC § 105.  All Other Rights Reserved.////  This software is made freely available under the TVA Open Source Agreement (see below).//  Code in this file licensed to GSF under one or more contributor license agreements listed below.////  Code Modification History://  -----------------------------------------------------------------------------------------------------//  03/21/2011 - Ritchie//       Generated original version of source code based on Joe Duffy's Weblog articles://           "A single-word reader/writer spin lock", January 29, 2009//              http://www.bluebytesoftware.com/blog/2009/01/30/ASinglewordReaderwriterSpinLock.aspx//           "A more scalable reader/writer lock, and a bit less harsh consideration of the idea", February 20, 2009//              http://www.bluebytesoftware.com/blog/2009/02/21/AMoreScalableReaderwriterLockAndABitLessHarshConsiderationOfTheIdea.aspx////******************************************************************************************************* #region [ TVA Open Source Agreement ]/*  THIS OPEN SOURCE AGREEMENT ("AGREEMENT") DEFINES THE RIGHTS OF USE,REPRODUCTION, DISTRIBUTION, MODIFICATION AND REDISTRIBUTION OF CERTAIN COMPUTER SOFTWARE ORIGINALLY RELEASED BY THE TENNESSEE VALLEY AUTHORITY, A CORPORATE AGENCY AND INSTRUMENTALITY OF THE UNITED STATES GOVERNMENT ("GOVERNMENT AGENCY"). GOVERNMENT AGENCY IS AN INTENDED THIRD-PARTY BENEFICIARY OF ALL SUBSEQUENT DISTRIBUTIONS OR REDISTRIBUTIONS OF THE SUBJECT SOFTWARE. ANYONE WHO USES, REPRODUCES, DISTRIBUTES, MODIFIES OR REDISTRIBUTES THE SUBJECT SOFTWARE, AS DEFINED HEREIN, OR ANY PART THEREOF, IS, BY THAT ACTION, ACCEPTING IN FULL THE RESPONSIBILITIES AND OBLIGATIONS CONTAINED IN THIS AGREEMENT.  Original Software Designation: openPDC Original Software Title: The GSF Open Source Phasor Data Concentrator User Registration Requested. Please Visit https://naspi.tva.com/Registration/ Point of Contact for Original Software: J. Ritchie Carroll <mailto:jrcarrol@tva.gov>  1. DEFINITIONS  A. "Contributor" means Government Agency, as the developer of the Original Software, and any entity that makes a Modification.  B. "Covered Patents" mean patent claims licensable by a Contributor that are necessarily infringed by the use or sale of its Modification alone or when combined with the Subject Software.  C. "Display" means the showing of a copy of the Subject Software, either directly or by means of an image, or any other device.  D. "Distribution" means conveyance or transfer of the Subject Software, regardless of means, to another.  E. "Larger Work" means computer software that combines Subject Software, or portions thereof, with software separate from the Subject Software that is not governed by the terms of this Agreement.  F. "Modification" means any alteration of, including addition to or deletion from, the substance or structure of either the Original Software or Subject Software, and includes derivative works, as that term is defined in the Copyright Statute, 17 USC § 101. However, the act of including Subject Software as part of a Larger Work does not in and of itself constitute a Modification.  G. "Original Software" means the computer software first released under this Agreement by Government Agency entitled openPDC, including source code, object code and accompanying documentation, if any.  H. "Recipient" means anyone who acquires the Subject Software under this Agreement, including all Contributors.  I. "Redistribution" means Distribution of the Subject Software after a Modification has been made.  J. "Reproduction" means the making of a counterpart, image or copy of the Subject Software.  K. "Sale" means the exchange of the Subject Software for money or equivalent value.  L. "Subject Software" means the Original Software, Modifications, or any respective parts thereof.  M. "Use" means the application or employment of the Subject Software for any purpose.  2. GRANT OF RIGHTS  A. Under Non-Patent Rights: Subject to the terms and conditions of this Agreement, each Contributor, with respect to its own contribution to the Subject Software, hereby grants to each Recipient a non-exclusive, world-wide, royalty-free license to engage in the following activities pertaining to the Subject Software:  1. Use  2. Distribution  3. Reproduction  4. Modification  5. Redistribution  6. Display  B. Under Patent Rights: Subject to the terms and conditions of this Agreement, each Contributor, with respect to its own contribution to the Subject Software, hereby grants to each Recipient under Covered Patents a non-exclusive, world-wide, royalty-free license to engage in the following activities pertaining to the Subject Software:  1. Use  2. Distribution  3. Reproduction  4. Sale  5. Offer for Sale  C. The rights granted under Paragraph B. also apply to the combination of a Contributor's Modification and the Subject Software if, at the time the Modification is added by the Contributor, the addition of such Modification causes the combination to be covered by the Covered Patents. It does not apply to any other combinations that include a Modification.   D. The rights granted in Paragraphs A. and B. allow the Recipient to sublicense those same rights. Such sublicense must be under the same terms and conditions of this Agreement.  3. OBLIGATIONS OF RECIPIENT  A. Distribution or Redistribution of the Subject Software must be made under this Agreement except for additions covered under paragraph 3H.   1. Whenever a Recipient distributes or redistributes the Subject Software, a copy of this Agreement must be included with each copy of the Subject Software; and  2. If Recipient distributes or redistributes the Subject Software in any form other than source code, Recipient must also make the source code freely available, and must provide with each copy of the Subject Software information on how to obtain the source code in a reasonable manner on or through a medium customarily used for software exchange.  B. Each Recipient must ensure that the following copyright notice appears prominently in the Subject Software:           No copyright is claimed pursuant to 17 USC § 105.  All Other Rights Reserved.  C. Each Contributor must characterize its alteration of the Subject Software as a Modification and must identify itself as the originator of its Modification in a manner that reasonably allows subsequent Recipients to identify the originator of the Modification. In fulfillment of these requirements, Contributor must include a file (e.g., a change log file) that describes the alterations made and the date of the alterations, identifies Contributor as originator of the alterations, and consents to characterization of the alterations as a Modification, for example, by including a statement that the Modification is derived, directly or indirectly, from Original Software provided by Government Agency. Once consent is granted, it may not thereafter be revoked.  D. A Contributor may add its own copyright notice to the Subject Software. Once a copyright notice has been added to the Subject Software, a Recipient may not remove it without the express permission of the Contributor who added the notice.  E. A Recipient may not make any representation in the Subject Software or in any promotional, advertising or other material that may be construed as an endorsement by Government Agency or by any prior Recipient of any product or service provided by Recipient, or that may seek to obtain commercial advantage by the fact of Government Agency's or a prior Recipient's participation in this Agreement.  F. In an effort to track usage and maintain accurate records of the Subject Software, each Recipient, upon receipt of the Subject Software, is requested to register with Government Agency by visiting the following website: https://naspi.tva.com/Registration/. Recipient's name and personal information shall be used for statistical purposes only. Once a Recipient makes a Modification available, it is requested that the Recipient inform Government Agency at the web site provided above how to access the Modification.  G. Each Contributor represents that that its Modification does not violate any existing agreements, regulations, statutes or rules, and further that Contributor has sufficient rights to grant the rights conveyed by this Agreement.  H. A Recipient may choose to offer, and to charge a fee for, warranty, support, indemnity and/or liability obligations to one or more other Recipients of the Subject Software. A Recipient may do so, however, only on its own behalf and not on behalf of Government Agency or any other Recipient. Such a Recipient must make it absolutely clear that any such warranty, support, indemnity and/or liability obligation is offered by that Recipient alone. Further, such Recipient agrees to indemnify Government Agency and every other Recipient for any liability incurred by them as a result of warranty, support, indemnity and/or liability offered by such Recipient.  I. A Recipient may create a Larger Work by combining Subject Software with separate software not governed by the terms of this agreement and distribute the Larger Work as a single product. In such case, the Recipient must make sure Subject Software, or portions thereof, included in the Larger Work is subject to this Agreement.  J. Notwithstanding any provisions contained herein, Recipient is hereby put on notice that export of any goods or technical data from the United States may require some form of export license from the U.S. Government. Failure to obtain necessary export licenses may result in criminal liability under U.S. laws. Government Agency neither represents that a license shall not be required nor that, if required, it shall be issued. Nothing granted herein provides any such export license.  4. DISCLAIMER OF WARRANTIES AND LIABILITIES; WAIVER AND INDEMNIFICATION  A. No Warranty: THE SUBJECT SOFTWARE IS PROVIDED "AS IS" WITHOUT ANY WARRANTY OF ANY KIND, EITHER EXPRESSED, IMPLIED, OR STATUTORY, INCLUDING, BUT NOT LIMITED TO, ANY WARRANTY THAT THE SUBJECT SOFTWARE WILL CONFORM TO SPECIFICATIONS, ANY IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, OR FREEDOM FROM INFRINGEMENT, ANY WARRANTY THAT THE SUBJECT SOFTWARE WILL BE ERROR FREE, OR ANY WARRANTY THAT DOCUMENTATION, IF PROVIDED, WILL CONFORM TO THE SUBJECT SOFTWARE. THIS AGREEMENT DOES NOT, IN ANY MANNER, CONSTITUTE AN ENDORSEMENT BY GOVERNMENT AGENCY OR ANY PRIOR RECIPIENT OF ANY RESULTS, RESULTING DESIGNS, HARDWARE, SOFTWARE PRODUCTS OR ANY OTHER APPLICATIONS RESULTING FROM USE OF THE SUBJECT SOFTWARE. FURTHER, GOVERNMENT AGENCY DISCLAIMS ALL WARRANTIES AND LIABILITIES REGARDING THIRD-PARTY SOFTWARE, IF PRESENT IN THE ORIGINAL SOFTWARE, AND DISTRIBUTES IT "AS IS."  B. Waiver and Indemnity: RECIPIENT AGREES TO WAIVE ANY AND ALL CLAIMS AGAINST GOVERNMENT AGENCY, ITS AGENTS, EMPLOYEES, CONTRACTORS AND SUBCONTRACTORS, AS WELL AS ANY PRIOR RECIPIENT. IF RECIPIENT'S USE OF THE SUBJECT SOFTWARE RESULTS IN ANY LIABILITIES, DEMANDS, DAMAGES, EXPENSES OR LOSSES ARISING FROM SUCH USE, INCLUDING ANY DAMAGES FROM PRODUCTS BASED ON, OR RESULTING FROM, RECIPIENT'S USE OF THE SUBJECT SOFTWARE, RECIPIENT SHALL INDEMNIFY AND HOLD HARMLESS  GOVERNMENT AGENCY, ITS AGENTS, EMPLOYEES, CONTRACTORS AND SUBCONTRACTORS, AS WELL AS ANY PRIOR RECIPIENT, TO THE EXTENT PERMITTED BY LAW.  THE FOREGOING RELEASE AND INDEMNIFICATION SHALL APPLY EVEN IF THE LIABILITIES, DEMANDS, DAMAGES, EXPENSES OR LOSSES ARE CAUSED, OCCASIONED, OR CONTRIBUTED TO BY THE NEGLIGENCE, SOLE OR CONCURRENT, OF GOVERNMENT AGENCY OR ANY PRIOR RECIPIENT.  RECIPIENT'S SOLE REMEDY FOR ANY SUCH MATTER SHALL BE THE IMMEDIATE, UNILATERAL TERMINATION OF THIS AGREEMENT.  5. GENERAL TERMS  A. Termination: This Agreement and the rights granted hereunder will terminate automatically if a Recipient fails to comply with these terms and conditions, and fails to cure such noncompliance within thirty (30) days of becoming aware of such noncompliance. Upon termination, a Recipient agrees to immediately cease use and distribution of the Subject Software. All sublicenses to the Subject Software properly granted by the breaching Recipient shall survive any such termination of this Agreement.  B. Severability: If any provision of this Agreement is invalid or unenforceable under applicable law, it shall not affect the validity or enforceability of the remainder of the terms of this Agreement.  C. Applicable Law: This Agreement shall be subject to United States federal law only for all purposes, including, but not limited to, determining the validity of this Agreement, the meaning of its provisions and the rights, obligations and remedies of the parties.  D. Entire Understanding: This Agreement constitutes the entire understanding and agreement of the parties relating to release of the Subject Software and may not be superseded, modified or amended except by further written agreement duly executed by the parties.  E. Binding Authority: By accepting and using the Subject Software under this Agreement, a Recipient affirms its authority to bind the Recipient to all terms and conditions of this Agreement and that Recipient hereby agrees to all terms and conditions herein.  F. Point of Contact: Any Recipient contact with Government Agency is to be directed to the designated representative as follows: J. Ritchie Carroll <mailto:jrcarrol@tva.gov>. */#endregion #region [ Contributor License Agreements ] //******************************************************************************************************////  Copyright © 2011, Grid Protection Alliance.  All Rights Reserved.////  The GPA licenses this file to you under the Eclipse Public License -v 1.0 (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.opensource.org/licenses/eclipse-1.0.php////  Unless agreed to in writing, the subject software distributed under the License is distributed on an//  "AS-IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. Refer to the//  License for the specific language governing permissions and limitations.////****************************************************************************************************** #endregion using System;using System.Runtime.InteropServices;using System.Threading; // We use plenty of interlocked operations on volatile fields below.  Safe.#pragma warning disable 0420 namespace GSF.Threading{    /// <summary>    /// Represents a fast, lightweight reader/writer lock that uses spinning to perform locking with no thread affinity. No recursive    /// acquires or upgradable locks are allowed (i.e., all entered locks must be exited before entering another lock).    /// </summary>    /// <remarks>    /// <para>    /// <see cref="ReaderWriterSpinLock"/> uses a single word of memory and only spins when contention arises so no events are necessary.    /// </para>    /// <para>    /// This reader/writer lock uses <see cref="SpinWait"/> to spin the CPU instead of engaging event based locking. As a result it    /// should only be used in cases where lock times are expected to be very small, reads are very frequent and writes are rare.    /// If hold times for write locks can be lengthy, it will be better to use <see cref="ReaderWriterLockSlim"/> instead to avoid    /// unnecessary CPU utilization due to spinning incurred by waiting reads.    /// </para>    /// </remarks>    public class ReaderWriterSpinLock    {        #region [ Members ]         // Nested Types        [StructLayout(LayoutKind.Sequential, Size = 128)]        struct ReadEntry        {            internal volatile int m_taken;        }         // Fields        private volatile int m_writer;        private volatile ReadEntry[] m_readers = new ReadEntry[Environment.ProcessorCount * 16];         #endregion         #region [ Properties ]         private int ReadLockIndex        {            get            {                return Thread.CurrentThread.ManagedThreadId % m_readers.Length;            }        }         #endregion         #region [ Methods ]         /// <summary>        /// Enters the lock in write mode.        /// </summary>        /// <remarks>        /// Upon successful aquistion of a write lock, use the <c>finally</c> block of a <c>try/finally</c> statement to call <see cref="ExitWriteLock"/>.        /// One <see cref="ExitWriteLock"/> should be called for each <see cref="EnterWriteLock"/>.        /// </remarks>        public void EnterWriteLock()        {            SpinWait sw = new SpinWait();             while (true)            {                if (m_writer == 0 && Interlocked.Exchange(ref m_writer, 1) == 0)                {                    // We now hold the write lock, and prevent new readers -                    // but we must ensure no readers exist before proceeding.                    for (int i = 0; i < m_readers.Length; i++)                    {                        while (m_readers[i].m_taken != 0)                            sw.SpinOnce();                    }                     break;                }                 // We failed to take the write lock; wait a bit and retry.                sw.SpinOnce();            }        }         /// <summary>        /// Exits write mode.        /// </summary>        public void ExitWriteLock()        {            // No need for a CAS.            m_writer = 0;        }         /// <summary>        /// Enters the lock in read mode.        /// </summary>        /// <remarks>        /// Upon successful aquistion of a read lock, use the <c>finally</c> block of a <c>try/finally</c> statement to call <see cref="ExitReadLock"/>.        /// One <see cref="ExitReadLock"/> should be called for each <see cref="EnterReadLock"/>.        /// </remarks>        public void EnterReadLock()        {            SpinWait sw = new SpinWait();            int tid = ReadLockIndex;             // Wait until there are no writers.            while (true)            {                while (m_writer == 1)                    sw.SpinOnce();                 // Try to take the read lock.                Interlocked.Increment(ref m_readers[tid].m_taken);                 if (m_writer == 0)                {                    // Success, no writer, proceed.                    break;                }                 // Back off, to let the writer go through.                Interlocked.Decrement(ref m_readers[tid].m_taken);            }        }         /// <summary>        /// Exits read mode.        /// </summary>        /// <exception cref="InvalidOperationException">Cannot exit read lock when there are no readers.</exception>        public void ExitReadLock()        {            // Just note that the current reader has left the lock.            Interlocked.Decrement(ref m_readers[ReadLockIndex].m_taken);        }         #endregion    }}