src/Utils/ReaderWriterLock.h

   1 /*********************************************************************
   2 CReaderWriterLock: A simple and fast reader-writer lock class in C++
   3 has characters of .NET ReaderWriterLock class
   4 Copyright (C) 2006 Quynh Nguyen Huu
   5
   6 This library is free software; you can redistribute it and/or
   7 modify it under the terms of the GNU Lesser General Public
   8 License as published by the Free Software Foundation; either
   9 version 2.1 of the License, or (at your option) any later version.
  10
  11 This library is distributed in the hope that it will be useful,
  12 but WITHOUT ANY WARRANTY; without even the implied warranty of
  13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14 Lesser General Public License for more details.
  15
  16 Email questions, comments or suggestions to quynhnguyenhuu@gmail.com
  17 *********************************************************************/
  18
  19 /*********************************************************************
  20 Introduction:
  21 This implementation is inspired by System.Threading.ReaderWriterLock in
  22 .NET framework. Following are some important statements I excerpted
  23 (with some words modified) from .NET document.
  24
  25 http://msdn.microsoft.com/library/default.asp?url=/library/en-us/cpref/html/frlrfSystemThreadingReaderWriterLockClassTopic.asp
  26
  27 "ReaderWriterLock is used to synchronize access to a resource.
  28 At any given time, it allows either concurrent read access for
  29 multiple threads, or write access for a single thread.
  30 In a situation where a resource is changed infrequently, a
  31 ReaderWriterLock provides better throughput than a simple
  32 one-at-a-time lock, such as CriticalSection or Mutex.
  33
  34 This library works best where most accesses are reads, while
  35 writes are infrequent and of short duration.
  36
  37 While a writer is waiting for active reader locks to be released,
  38 threads requesting new reader locks will have to wait in the reader
  39 queue. Their requests are not granted, even though they could share
  40 concurrent access with existing reader-lock holders; this helps
  41 protect writers against indefinite blockage by readers..."
  42 *********************************************************************/
  43
  44 #pragma once
  45
  46 #include <windows.h>
  47 #include <map>
  48
  49 #if (_WIN32_WINNT >= 0x0403)
  50 //////////////////////////////////////////////////////////////////
  51 // On multiprocessor systems, this value define number of times
  52 // that a thread tries to spin before actually performing a wait
  53 // operation (see InitializeCriticalSectionAndSpinCount API)
  54 #ifndef READER_WRITER_SPIN_COUNT
  55 #define READER_WRITER_SPIN_COUNT 400
  56 #endif READER_WRITER_SPIN_COUNT
  57 #endif _WIN32_WINNT
  58
  59 // Forward reference
  60 class CReaderWriterLock;
  61
  62 //////////////////////////////////////////////////////////////////
  63 // CReaderWriterLockNonReentrance class
  64 // NOTE: This class doesn't support reentrance & lock escalation.
  65 // May be deadlock in one of following situations:
  66 //  1) Call AcquireReaderLock twice (reentrance)
  67 //     --> Revise execution flow.
  68 //  2) Call AcquireWriterLock twice (reentrance)
  69 //     --> Revise execution flow.
  70 //  3) Call AcquireReaderLock then AcquireWriterLock (lock escalation)
  71 //     --> Use ReleaseReaderAndAcquireWriterLock method
  72 //  4) Call AcquireWriterLock then AcquireReaderLock (lock deescalation)
  73 //     --> Use DowngradeFromWriterLock method
  74 class CReaderWriterLockNonReentrance
  75 {
  76 public:
  77         CReaderWriterLockNonReentrance() noexcept;
  78         ~CReaderWriterLockNonReentrance() noexcept;
  79         bool AcquireReaderLock(DWORD dwTimeout = INFINITE) noexcept;
  80         void ReleaseReaderLock() noexcept;
  81         bool AcquireWriterLock(DWORD dwTimeout = INFINITE) noexcept;
  82         void ReleaseWriterLock() noexcept;
  83         void DowngradeFromWriterLock() noexcept;
  84
  85         // When a thread calls UpgradeToWriterLock, the reader lock is released,
  86         // and the thread goes to the end of the writer queue. Thus, other threads
  87         // might write to resources before this method returns
  88         bool UpgradeToWriterLock(DWORD dwTimeout = INFINITE) noexcept;
  89 protected:
  90         // A critical section to guard all the other members
  91         mutable CRITICAL_SECTION m_cs;
  92         // Auto-reset event, will be dynamically created/destroyed on demand
  93         volatile HANDLE m_hSafeToWriteEvent = nullptr;
  94         // Manual-reset event, will be dynamically created/destroyed on demand
  95         volatile HANDLE m_hSafeToReadEvent = nullptr;
  96         // Total number of writers on this object
  97         volatile INT m_iNumOfWriter = 0;
  98         // Total number of readers have already owned this object
  99         volatile INT m_iNumOfReaderEntered = 0;
 100         // Total number of readers are waiting to be owners of this object
 101         volatile INT m_iNumOfReaderWaiting = 0;
 102         // Internal/Real implementation
 103         void EnterCS() const noexcept;
 104         void LeaveCS() const noexcept;
 105         bool _ReaderWait(ULONGLONG dwTimeout) noexcept;
 106         bool _WriterWaitAndLeaveCSIfSuccess(ULONGLONG dwTimeout) noexcept;
 107         bool _UpgradeToWriterLockAndLeaveCS(ULONGLONG dwTimeout) noexcept;
 108         void _ReaderRelease() noexcept;
 109         void _WriterRelease(bool blDowngrade) noexcept;
 110
 111         friend CReaderWriterLock;
 112 };
 113
 114 //////////////////////////////////////////////////////////////////
 115 // CReaderWriterLock class
 116 // This class supports reentrance & lock escalation
 117 class CReaderWriterLock
 118 {
 119 public:
 120         CReaderWriterLock();
 121         ~CReaderWriterLock();
 122
 123         bool AcquireReaderLock(DWORD dwTimeout = INFINITE) noexcept;
 124         void ReleaseReaderLock() noexcept;
 125
 126         // If current thread was already a reader
 127         // it will be upgraded to be writer automatically.
 128         // BE CAREFUL! Other threads might write to the resource
 129         // before current thread is successfully upgraded.
 130         bool AcquireWriterLock(DWORD dwTimeout = INFINITE) noexcept;
 131         void ReleaseWriterLock() noexcept;
 132
 133         // Regardless of how many times current thread acquired reader
 134         // or writer locks, a call to this method will release all locks.
 135         // After that, any call to ReleaseWriterLock or ReleaseReaderLock
 136         // will raise exception in DEBUG mode.
 137         void ReleaseAllLocks() noexcept;
 138
 139         // Query thread's status
 140         DWORD GetCurrentThreadStatus() const noexcept;
 141         void GetCurrentThreadStatus(DWORD* lpdwReaderLockCounter,
 142                 DWORD* lpdwWriterLockCounter) const noexcept;
 143 protected:
 144         CReaderWriterLockNonReentrance m_impl;
 145
 146         using CMapThreadToState = std::map<DWORD,DWORD>;
 147         CMapThreadToState m_map;
 148 };
 149
 150 //////////////////////////////////////////////////////////////////
 151 // CAutoReadLockT & CAutoWriteLockT classes
 152 // Couple of template helper classes which would let one acquire a lock
 153 // in a body of code and not have to worry about explicitly releasing
 154 // that lock if an exception is encountered in that piece of code or
 155 // if there are multiple return points out of that piece.
 156
 157 template<typename T>
 158 class CAutoReadLockT
 159 {
 160 public:
 161         CAutoReadLockT(T& objLock) noexcept : m_lock(objLock)
 162         {
 163                 m_lock.AcquireReaderLock();
 164         }
 165         ~CAutoReadLockT() noexcept
 166         {
 167                 m_lock.ReleaseReaderLock();
 168         }
 169         CAutoReadLockT(CAutoReadLockT&) = delete;
 170         CAutoReadLockT(CAutoReadLockT&& that) = default;
 171         CAutoReadLockT& operator=(const CAutoReadLockT&) = delete;
 172 protected:
 173         T& m_lock;
 174 };
 175
 176 template<typename T>
 177 class CAutoWriteLockT
 178 {
 179 public :
 180         CAutoWriteLockT(T& objLock) noexcept : m_lock(objLock)
 181         {
 182                 m_lock.AcquireWriterLock();
 183         }
 184         ~CAutoWriteLockT() noexcept
 185         {
 186                 m_lock.ReleaseWriterLock();
 187         }
 188         CAutoWriteLockT(CAutoWriteLockT&) = delete;
 189         CAutoWriteLockT(CAutoWriteLockT&&) = default;
 190         CAutoWriteLockT& operator=(const CAutoWriteLockT&) = delete;
 191 protected:
 192         T& m_lock;
 193 };
 194
 195 template<typename T>
 196 class CAutoReadWeakLockT
 197 {
 198 public:
 199         CAutoReadWeakLockT(T& objLock, DWORD timeout = 1) noexcept : m_lock(objLock)
 200         {
 201                 isAcquired = m_lock.AcquireReaderLock(timeout);
 202         }
 203         ~CAutoReadWeakLockT() noexcept
 204         {
 205                 if (isAcquired)
 206                         m_lock.ReleaseReaderLock();
 207         }
 208         bool IsAcquired() const
 209         {
 210                 return isAcquired;
 211         }
 212         CAutoReadWeakLockT(CAutoReadWeakLockT&) = delete;
 213         CAutoReadWeakLockT(CAutoReadWeakLockT&&) = default;
 214         CAutoReadWeakLockT& operator=(const CAutoReadWeakLockT&) = delete;
 215 protected:
 216         T& m_lock;
 217         bool isAcquired;
 218 };
 219
 220 template<typename T>
 221 class CAutoWriteWeakLockT
 222 {
 223 public :
 224         CAutoWriteWeakLockT(T& objLock, DWORD timeout = 1) noexcept : m_lock(objLock)
 225         {
 226                 isAcquired = m_lock.AcquireWriterLock(timeout);
 227         }
 228         ~CAutoWriteWeakLockT() noexcept
 229         {
 230                 release();
 231         }
 232         void Release()
 233         {
 234                 release();
 235         }
 236         bool IsAcquired() const
 237         {
 238                 return isAcquired;
 239         }
 240         CAutoWriteWeakLockT(CAutoWriteWeakLockT&) = delete;
 241         CAutoWriteWeakLockT(CAutoWriteWeakLockT&&) = default;
 242         CAutoWriteWeakLockT& operator=(const CAutoWriteWeakLockT&) = delete;
 243 protected:
 244         T& m_lock;
 245         bool isAcquired;
 246
 247         void release()
 248         {
 249                 if (isAcquired)
 250                 {
 251                         m_lock.ReleaseWriterLock();
 252                         isAcquired = false;
 253                 }
 254         }
 255 };
 256
 257 //////////////////////////////////////////////////////////////////
 258 // Instances of above template helper classes
 259
 260 using CAutoReadLock = CAutoReadLockT<CReaderWriterLock>;
 261 using CAutoWriteLock = CAutoWriteLockT<CReaderWriterLock>;
 262 using CAutoReadWeakLock = CAutoReadWeakLockT<CReaderWriterLock>;
 263 using CAutoWriteWeakLock = CAutoWriteWeakLockT<CReaderWriterLock>;
 264
 265 //////////////////////////////////////////////////////////////////
 266 // Inline methods
 267
 268 __forceinline
 269         void CReaderWriterLockNonReentrance::EnterCS() const noexcept {
 270                 ::EnterCriticalSection(&m_cs);
 271 }
 272
 273 __forceinline
 274         void CReaderWriterLockNonReentrance::LeaveCS() const noexcept {
 275                 ::LeaveCriticalSection(&m_cs);
 276 }