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authorJiyoung Yun <jy910.yun@samsung.com>2017-04-13 14:17:19 +0900
committerJiyoung Yun <jy910.yun@samsung.com>2017-04-13 14:17:19 +0900
commita56e30c8d33048216567753d9d3fefc2152af8ac (patch)
tree7e5d979695fc4a431740982eb1cfecc2898b23a5 /src/mscorlib/src/System/Threading/ReaderWriterLockSlim.cs
parent4b11dc566a5bbfa1378d6266525c281b028abcc8 (diff)
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Imported Upstream version 2.0.0.11353upstream/2.0.0.11353
Diffstat (limited to 'src/mscorlib/src/System/Threading/ReaderWriterLockSlim.cs')
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diff --git a/src/mscorlib/src/System/Threading/ReaderWriterLockSlim.cs b/src/mscorlib/src/System/Threading/ReaderWriterLockSlim.cs
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+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using Internal.Runtime.Augments;
+using System.Diagnostics; // for TraceInformation
+using System.Threading;
+using System.Runtime.CompilerServices;
+
+namespace System.Threading
+{
+ public enum LockRecursionPolicy
+ {
+ NoRecursion = 0,
+ SupportsRecursion = 1,
+ }
+
+ //
+ // ReaderWriterCount tracks how many of each kind of lock is held by each thread.
+ // We keep a linked list for each thread, attached to a ThreadStatic field.
+ // These are reused wherever possible, so that a given thread will only
+ // allocate N of these, where N is the maximum number of locks held simultaneously
+ // by that thread.
+ //
+ internal class ReaderWriterCount
+ {
+ // Which lock does this object belong to? This is a numeric ID for two reasons:
+ // 1) We don't want this field to keep the lock object alive, and a WeakReference would
+ // be too expensive.
+ // 2) Setting the value of a long is faster than setting the value of a reference.
+ // The "hot" paths in ReaderWriterLockSlim are short enough that this actually
+ // matters.
+ public long lockID;
+
+ // How many reader locks does this thread hold on this ReaderWriterLockSlim instance?
+ public int readercount;
+
+ // Ditto for writer/upgrader counts. These are only used if the lock allows recursion.
+ // But we have to have the fields on every ReaderWriterCount instance, because
+ // we reuse it for different locks.
+ public int writercount;
+ public int upgradecount;
+
+ // Next RWC in this thread's list.
+ public ReaderWriterCount next;
+ }
+
+ /// <summary>
+ /// A reader-writer lock implementation that is intended to be simple, yet very
+ /// efficient. In particular only 1 interlocked operation is taken for any lock
+ /// operation (we use spin locks to achieve this). The spin lock is never held
+ /// for more than a few instructions (in particular, we never call event APIs
+ /// or in fact any non-trivial API while holding the spin lock).
+ /// </summary>
+ public class ReaderWriterLockSlim : IDisposable
+ {
+ //Specifying if locked can be reacquired recursively.
+ private bool _fIsReentrant;
+
+ // Lock specification for myLock: This lock protects exactly the local fields associated with this
+ // instance of ReaderWriterLockSlim. It does NOT protect the memory associated with
+ // the events that hang off this lock (eg writeEvent, readEvent upgradeEvent).
+ private int _myLock;
+
+ //The variables controlling spinning behavior of Mylock(which is a spin-lock)
+
+ private const int LockSpinCycles = 20;
+ private const int LockSpinCount = 10;
+ private const int LockSleep0Count = 5;
+
+ // These variables allow use to avoid Setting events (which is expensive) if we don't have to.
+ private uint _numWriteWaiters; // maximum number of threads that can be doing a WaitOne on the writeEvent
+ private uint _numReadWaiters; // maximum number of threads that can be doing a WaitOne on the readEvent
+ private uint _numWriteUpgradeWaiters; // maximum number of threads that can be doing a WaitOne on the upgradeEvent (at most 1).
+ private uint _numUpgradeWaiters;
+
+ //Variable used for quick check when there are no waiters.
+ private bool _fNoWaiters;
+
+ private int _upgradeLockOwnerId;
+ private int _writeLockOwnerId;
+
+ // conditions we wait on.
+ private EventWaitHandle _writeEvent; // threads waiting to acquire a write lock go here.
+ private EventWaitHandle _readEvent; // threads waiting to acquire a read lock go here (will be released in bulk)
+ private EventWaitHandle _upgradeEvent; // thread waiting to acquire the upgrade lock
+ private EventWaitHandle _waitUpgradeEvent; // thread waiting to upgrade from the upgrade lock to a write lock go here (at most one)
+
+ // Every lock instance has a unique ID, which is used by ReaderWriterCount to associate itself with the lock
+ // without holding a reference to it.
+ private static long s_nextLockID;
+ private long _lockID;
+
+ // See comments on ReaderWriterCount.
+ [ThreadStatic]
+ private static ReaderWriterCount t_rwc;
+
+ private bool _fUpgradeThreadHoldingRead;
+
+ private const int MaxSpinCount = 20;
+
+ //The uint, that contains info like if the writer lock is held, num of
+ //readers etc.
+ private uint _owners;
+
+ //Various R/W masks
+ //Note:
+ //The Uint is divided as follows:
+ //
+ //Writer-Owned Waiting-Writers Waiting Upgraders Num-Readers
+ // 31 30 29 28.......0
+ //
+ //Dividing the uint, allows to vastly simplify logic for checking if a
+ //reader should go in etc. Setting the writer bit will automatically
+ //make the value of the uint much larger than the max num of readers
+ //allowed, thus causing the check for max_readers to fail.
+
+ private const uint WRITER_HELD = 0x80000000;
+ private const uint WAITING_WRITERS = 0x40000000;
+ private const uint WAITING_UPGRADER = 0x20000000;
+
+ //The max readers is actually one less then its theoretical max.
+ //This is done in order to prevent reader count overflows. If the reader
+ //count reaches max, other readers will wait.
+ private const uint MAX_READER = 0x10000000 - 2;
+
+ private const uint READER_MASK = 0x10000000 - 1;
+
+ private bool _fDisposed;
+
+ private void InitializeThreadCounts()
+ {
+ _upgradeLockOwnerId = -1;
+ _writeLockOwnerId = -1;
+ }
+
+ public ReaderWriterLockSlim()
+ : this(LockRecursionPolicy.NoRecursion)
+ {
+ }
+
+ public ReaderWriterLockSlim(LockRecursionPolicy recursionPolicy)
+ {
+ if (recursionPolicy == LockRecursionPolicy.SupportsRecursion)
+ {
+ _fIsReentrant = true;
+ }
+ InitializeThreadCounts();
+ _fNoWaiters = true;
+ _lockID = Interlocked.Increment(ref s_nextLockID);
+ }
+
+ [MethodImpl(MethodImplOptions.AggressiveInlining)]
+ private static bool IsRWEntryEmpty(ReaderWriterCount rwc)
+ {
+ if (rwc.lockID == 0)
+ return true;
+ else if (rwc.readercount == 0 && rwc.writercount == 0 && rwc.upgradecount == 0)
+ return true;
+ else
+ return false;
+ }
+
+ private bool IsRwHashEntryChanged(ReaderWriterCount lrwc)
+ {
+ return lrwc.lockID != _lockID;
+ }
+
+ /// <summary>
+ /// This routine retrieves/sets the per-thread counts needed to enforce the
+ /// various rules related to acquiring the lock.
+ ///
+ /// DontAllocate is set to true if the caller just wants to get an existing
+ /// entry for this thread, but doesn't want to add one if an existing one
+ /// could not be found.
+ /// </summary>
+ [MethodImpl(MethodImplOptions.AggressiveInlining)]
+ private ReaderWriterCount GetThreadRWCount(bool dontAllocate)
+ {
+ ReaderWriterCount rwc = t_rwc;
+ ReaderWriterCount empty = null;
+ while (rwc != null)
+ {
+ if (rwc.lockID == _lockID)
+ return rwc;
+
+ if (!dontAllocate && empty == null && IsRWEntryEmpty(rwc))
+ empty = rwc;
+
+ rwc = rwc.next;
+ }
+
+ if (dontAllocate)
+ return null;
+
+ if (empty == null)
+ {
+ empty = new ReaderWriterCount();
+ empty.next = t_rwc;
+ t_rwc = empty;
+ }
+
+ empty.lockID = _lockID;
+ return empty;
+ }
+
+ public void EnterReadLock()
+ {
+ TryEnterReadLock(-1);
+ }
+
+ //
+ // Common timeout support
+ //
+ private struct TimeoutTracker
+ {
+ private int _total;
+ private int _start;
+
+ public TimeoutTracker(TimeSpan timeout)
+ {
+ long ltm = (long)timeout.TotalMilliseconds;
+ if (ltm < -1 || ltm > (long)Int32.MaxValue)
+ throw new ArgumentOutOfRangeException(nameof(timeout));
+ _total = (int)ltm;
+ if (_total != -1 && _total != 0)
+ _start = Environment.TickCount;
+ else
+ _start = 0;
+ }
+
+ public TimeoutTracker(int millisecondsTimeout)
+ {
+ if (millisecondsTimeout < -1)
+ throw new ArgumentOutOfRangeException(nameof(millisecondsTimeout));
+ _total = millisecondsTimeout;
+ if (_total != -1 && _total != 0)
+ _start = Environment.TickCount;
+ else
+ _start = 0;
+ }
+
+ public int RemainingMilliseconds
+ {
+ get
+ {
+ if (_total == -1 || _total == 0)
+ return _total;
+
+ int elapsed = Environment.TickCount - _start;
+ // elapsed may be negative if TickCount has overflowed by 2^31 milliseconds.
+ if (elapsed < 0 || elapsed >= _total)
+ return 0;
+
+ return _total - elapsed;
+ }
+ }
+
+ public bool IsExpired
+ {
+ get
+ {
+ return RemainingMilliseconds == 0;
+ }
+ }
+ }
+
+ public bool TryEnterReadLock(TimeSpan timeout)
+ {
+ return TryEnterReadLock(new TimeoutTracker(timeout));
+ }
+
+ public bool TryEnterReadLock(int millisecondsTimeout)
+ {
+ return TryEnterReadLock(new TimeoutTracker(millisecondsTimeout));
+ }
+
+ private bool TryEnterReadLock(TimeoutTracker timeout)
+ {
+ return TryEnterReadLockCore(timeout);
+ }
+
+ private bool TryEnterReadLockCore(TimeoutTracker timeout)
+ {
+ if (_fDisposed)
+ throw new ObjectDisposedException(null);
+
+ ReaderWriterCount lrwc = null;
+ int id = Environment.CurrentManagedThreadId;
+
+ if (!_fIsReentrant)
+ {
+ if (id == _writeLockOwnerId)
+ {
+ //Check for AW->AR
+ throw new LockRecursionException(SR.LockRecursionException_ReadAfterWriteNotAllowed);
+ }
+
+ EnterMyLock();
+
+ lrwc = GetThreadRWCount(false);
+
+ //Check if the reader lock is already acquired. Note, we could
+ //check the presence of a reader by not allocating rwc (But that
+ //would lead to two lookups in the common case. It's better to keep
+ //a count in the structure).
+ if (lrwc.readercount > 0)
+ {
+ ExitMyLock();
+ throw new LockRecursionException(SR.LockRecursionException_RecursiveReadNotAllowed);
+ }
+ else if (id == _upgradeLockOwnerId)
+ {
+ //The upgrade lock is already held.
+ //Update the global read counts and exit.
+
+ lrwc.readercount++;
+ _owners++;
+ ExitMyLock();
+ return true;
+ }
+ }
+ else
+ {
+ EnterMyLock();
+ lrwc = GetThreadRWCount(false);
+ if (lrwc.readercount > 0)
+ {
+ lrwc.readercount++;
+ ExitMyLock();
+ return true;
+ }
+ else if (id == _upgradeLockOwnerId)
+ {
+ //The upgrade lock is already held.
+ //Update the global read counts and exit.
+ lrwc.readercount++;
+ _owners++;
+ ExitMyLock();
+ _fUpgradeThreadHoldingRead = true;
+ return true;
+ }
+ else if (id == _writeLockOwnerId)
+ {
+ //The write lock is already held.
+ //Update global read counts here,
+ lrwc.readercount++;
+ _owners++;
+ ExitMyLock();
+ return true;
+ }
+ }
+
+ bool retVal = true;
+
+ int spincount = 0;
+
+ for (; ;)
+ {
+ // We can enter a read lock if there are only read-locks have been given out
+ // and a writer is not trying to get in.
+
+ if (_owners < MAX_READER)
+ {
+ // Good case, there is no contention, we are basically done
+ _owners++; // Indicate we have another reader
+ lrwc.readercount++;
+ break;
+ }
+
+ if (spincount < MaxSpinCount)
+ {
+ ExitMyLock();
+ if (timeout.IsExpired)
+ return false;
+ spincount++;
+ SpinWait(spincount);
+ EnterMyLock();
+ //The per-thread structure may have been recycled as the lock is acquired (due to message pumping), load again.
+ if (IsRwHashEntryChanged(lrwc))
+ lrwc = GetThreadRWCount(false);
+ continue;
+ }
+
+ // Drat, we need to wait. Mark that we have waiters and wait.
+ if (_readEvent == null) // Create the needed event
+ {
+ LazyCreateEvent(ref _readEvent, false);
+ if (IsRwHashEntryChanged(lrwc))
+ lrwc = GetThreadRWCount(false);
+ continue; // since we left the lock, start over.
+ }
+
+ retVal = WaitOnEvent(_readEvent, ref _numReadWaiters, timeout, isWriteWaiter: false);
+ if (!retVal)
+ {
+ return false;
+ }
+ if (IsRwHashEntryChanged(lrwc))
+ lrwc = GetThreadRWCount(false);
+ }
+
+ ExitMyLock();
+ return retVal;
+ }
+
+ public void EnterWriteLock()
+ {
+ TryEnterWriteLock(-1);
+ }
+
+ public bool TryEnterWriteLock(TimeSpan timeout)
+ {
+ return TryEnterWriteLock(new TimeoutTracker(timeout));
+ }
+
+ public bool TryEnterWriteLock(int millisecondsTimeout)
+ {
+ return TryEnterWriteLock(new TimeoutTracker(millisecondsTimeout));
+ }
+
+ private bool TryEnterWriteLock(TimeoutTracker timeout)
+ {
+ return TryEnterWriteLockCore(timeout);
+ }
+
+ private bool TryEnterWriteLockCore(TimeoutTracker timeout)
+ {
+ if (_fDisposed)
+ throw new ObjectDisposedException(null);
+
+ int id = Environment.CurrentManagedThreadId;
+ ReaderWriterCount lrwc;
+ bool upgradingToWrite = false;
+
+ if (!_fIsReentrant)
+ {
+ if (id == _writeLockOwnerId)
+ {
+ //Check for AW->AW
+ throw new LockRecursionException(SR.LockRecursionException_RecursiveWriteNotAllowed);
+ }
+ else if (id == _upgradeLockOwnerId)
+ {
+ //AU->AW case is allowed once.
+ upgradingToWrite = true;
+ }
+
+ EnterMyLock();
+ lrwc = GetThreadRWCount(true);
+
+ //Can't acquire write lock with reader lock held.
+ if (lrwc != null && lrwc.readercount > 0)
+ {
+ ExitMyLock();
+ throw new LockRecursionException(SR.LockRecursionException_WriteAfterReadNotAllowed);
+ }
+ }
+ else
+ {
+ EnterMyLock();
+ lrwc = GetThreadRWCount(false);
+
+ if (id == _writeLockOwnerId)
+ {
+ lrwc.writercount++;
+ ExitMyLock();
+ return true;
+ }
+ else if (id == _upgradeLockOwnerId)
+ {
+ upgradingToWrite = true;
+ }
+ else if (lrwc.readercount > 0)
+ {
+ //Write locks may not be acquired if only read locks have been
+ //acquired.
+ ExitMyLock();
+ throw new LockRecursionException(SR.LockRecursionException_WriteAfterReadNotAllowed);
+ }
+ }
+
+ int spincount = 0;
+ bool retVal = true;
+
+ for (; ;)
+ {
+ if (IsWriterAcquired())
+ {
+ // Good case, there is no contention, we are basically done
+ SetWriterAcquired();
+ break;
+ }
+
+ //Check if there is just one upgrader, and no readers.
+ //Assumption: Only one thread can have the upgrade lock, so the
+ //following check will fail for all other threads that may sneak in
+ //when the upgrading thread is waiting.
+
+ if (upgradingToWrite)
+ {
+ uint readercount = GetNumReaders();
+
+ if (readercount == 1)
+ {
+ //Good case again, there is just one upgrader, and no readers.
+ SetWriterAcquired(); // indicate we have a writer.
+ break;
+ }
+ else if (readercount == 2)
+ {
+ if (lrwc != null)
+ {
+ if (IsRwHashEntryChanged(lrwc))
+ lrwc = GetThreadRWCount(false);
+
+ if (lrwc.readercount > 0)
+ {
+ //This check is needed for EU->ER->EW case, as the owner count will be two.
+ Debug.Assert(_fIsReentrant);
+ Debug.Assert(_fUpgradeThreadHoldingRead);
+
+ //Good case again, there is just one upgrader, and no readers.
+ SetWriterAcquired(); // indicate we have a writer.
+ break;
+ }
+ }
+ }
+ }
+
+ if (spincount < MaxSpinCount)
+ {
+ ExitMyLock();
+ if (timeout.IsExpired)
+ return false;
+ spincount++;
+ SpinWait(spincount);
+ EnterMyLock();
+ continue;
+ }
+
+ if (upgradingToWrite)
+ {
+ if (_waitUpgradeEvent == null) // Create the needed event
+ {
+ LazyCreateEvent(ref _waitUpgradeEvent, true);
+ continue; // since we left the lock, start over.
+ }
+
+ Debug.Assert(_numWriteUpgradeWaiters == 0, "There can be at most one thread with the upgrade lock held.");
+
+ retVal = WaitOnEvent(_waitUpgradeEvent, ref _numWriteUpgradeWaiters, timeout, isWriteWaiter: true);
+
+ //The lock is not held in case of failure.
+ if (!retVal)
+ return false;
+ }
+ else
+ {
+ // Drat, we need to wait. Mark that we have waiters and wait.
+ if (_writeEvent == null) // create the needed event.
+ {
+ LazyCreateEvent(ref _writeEvent, true);
+ continue; // since we left the lock, start over.
+ }
+
+ retVal = WaitOnEvent(_writeEvent, ref _numWriteWaiters, timeout, isWriteWaiter: true);
+ //The lock is not held in case of failure.
+ if (!retVal)
+ return false;
+ }
+ }
+
+ Debug.Assert((_owners & WRITER_HELD) > 0);
+
+ if (_fIsReentrant)
+ {
+ if (IsRwHashEntryChanged(lrwc))
+ lrwc = GetThreadRWCount(false);
+ lrwc.writercount++;
+ }
+
+ ExitMyLock();
+
+ _writeLockOwnerId = id;
+
+ return true;
+ }
+
+ public void EnterUpgradeableReadLock()
+ {
+ TryEnterUpgradeableReadLock(-1);
+ }
+
+ public bool TryEnterUpgradeableReadLock(TimeSpan timeout)
+ {
+ return TryEnterUpgradeableReadLock(new TimeoutTracker(timeout));
+ }
+
+ public bool TryEnterUpgradeableReadLock(int millisecondsTimeout)
+ {
+ return TryEnterUpgradeableReadLock(new TimeoutTracker(millisecondsTimeout));
+ }
+
+ private bool TryEnterUpgradeableReadLock(TimeoutTracker timeout)
+ {
+ return TryEnterUpgradeableReadLockCore(timeout);
+ }
+
+ private bool TryEnterUpgradeableReadLockCore(TimeoutTracker timeout)
+ {
+ if (_fDisposed)
+ throw new ObjectDisposedException(null);
+
+ int id = Environment.CurrentManagedThreadId;
+ ReaderWriterCount lrwc;
+
+ if (!_fIsReentrant)
+ {
+ if (id == _upgradeLockOwnerId)
+ {
+ //Check for AU->AU
+ throw new LockRecursionException(SR.LockRecursionException_RecursiveUpgradeNotAllowed);
+ }
+ else if (id == _writeLockOwnerId)
+ {
+ //Check for AU->AW
+ throw new LockRecursionException(SR.LockRecursionException_UpgradeAfterWriteNotAllowed);
+ }
+
+ EnterMyLock();
+ lrwc = GetThreadRWCount(true);
+ //Can't acquire upgrade lock with reader lock held.
+ if (lrwc != null && lrwc.readercount > 0)
+ {
+ ExitMyLock();
+ throw new LockRecursionException(SR.LockRecursionException_UpgradeAfterReadNotAllowed);
+ }
+ }
+ else
+ {
+ EnterMyLock();
+ lrwc = GetThreadRWCount(false);
+
+ if (id == _upgradeLockOwnerId)
+ {
+ lrwc.upgradecount++;
+ ExitMyLock();
+ return true;
+ }
+ else if (id == _writeLockOwnerId)
+ {
+ //Write lock is already held, Just update the global state
+ //to show presence of upgrader.
+ Debug.Assert((_owners & WRITER_HELD) > 0);
+ _owners++;
+ _upgradeLockOwnerId = id;
+ lrwc.upgradecount++;
+ if (lrwc.readercount > 0)
+ _fUpgradeThreadHoldingRead = true;
+ ExitMyLock();
+ return true;
+ }
+ else if (lrwc.readercount > 0)
+ {
+ //Upgrade locks may not be acquired if only read locks have been
+ //acquired.
+ ExitMyLock();
+ throw new LockRecursionException(SR.LockRecursionException_UpgradeAfterReadNotAllowed);
+ }
+ }
+
+ bool retVal = true;
+
+ int spincount = 0;
+
+ for (; ;)
+ {
+ //Once an upgrade lock is taken, it's like having a reader lock held
+ //until upgrade or downgrade operations are performed.
+
+ if ((_upgradeLockOwnerId == -1) && (_owners < MAX_READER))
+ {
+ _owners++;
+ _upgradeLockOwnerId = id;
+ break;
+ }
+
+ if (spincount < MaxSpinCount)
+ {
+ ExitMyLock();
+ if (timeout.IsExpired)
+ return false;
+ spincount++;
+ SpinWait(spincount);
+ EnterMyLock();
+ continue;
+ }
+
+ // Drat, we need to wait. Mark that we have waiters and wait.
+ if (_upgradeEvent == null) // Create the needed event
+ {
+ LazyCreateEvent(ref _upgradeEvent, true);
+ continue; // since we left the lock, start over.
+ }
+
+ //Only one thread with the upgrade lock held can proceed.
+ retVal = WaitOnEvent(_upgradeEvent, ref _numUpgradeWaiters, timeout, isWriteWaiter: false);
+ if (!retVal)
+ return false;
+ }
+
+ if (_fIsReentrant)
+ {
+ //The lock may have been dropped getting here, so make a quick check to see whether some other
+ //thread did not grab the entry.
+ if (IsRwHashEntryChanged(lrwc))
+ lrwc = GetThreadRWCount(false);
+ lrwc.upgradecount++;
+ }
+
+ ExitMyLock();
+
+ return true;
+ }
+
+ public void ExitReadLock()
+ {
+ ReaderWriterCount lrwc = null;
+
+ EnterMyLock();
+
+ lrwc = GetThreadRWCount(true);
+
+ if (lrwc == null || lrwc.readercount < 1)
+ {
+ //You have to be holding the read lock to make this call.
+ ExitMyLock();
+ throw new SynchronizationLockException(SR.SynchronizationLockException_MisMatchedRead);
+ }
+
+ if (_fIsReentrant)
+ {
+ if (lrwc.readercount > 1)
+ {
+ lrwc.readercount--;
+ ExitMyLock();
+ return;
+ }
+
+ if (Environment.CurrentManagedThreadId == _upgradeLockOwnerId)
+ {
+ _fUpgradeThreadHoldingRead = false;
+ }
+ }
+
+ Debug.Assert(_owners > 0, "ReleasingReaderLock: releasing lock and no read lock taken");
+
+ --_owners;
+
+ Debug.Assert(lrwc.readercount == 1);
+ lrwc.readercount--;
+
+ ExitAndWakeUpAppropriateWaiters();
+ }
+
+ public void ExitWriteLock()
+ {
+ ReaderWriterCount lrwc;
+ if (!_fIsReentrant)
+ {
+ if (Environment.CurrentManagedThreadId != _writeLockOwnerId)
+ {
+ //You have to be holding the write lock to make this call.
+ throw new SynchronizationLockException(SR.SynchronizationLockException_MisMatchedWrite);
+ }
+ EnterMyLock();
+ }
+ else
+ {
+ EnterMyLock();
+ lrwc = GetThreadRWCount(false);
+
+ if (lrwc == null)
+ {
+ ExitMyLock();
+ throw new SynchronizationLockException(SR.SynchronizationLockException_MisMatchedWrite);
+ }
+
+ if (lrwc.writercount < 1)
+ {
+ ExitMyLock();
+ throw new SynchronizationLockException(SR.SynchronizationLockException_MisMatchedWrite);
+ }
+
+ lrwc.writercount--;
+
+ if (lrwc.writercount > 0)
+ {
+ ExitMyLock();
+ return;
+ }
+ }
+
+ Debug.Assert((_owners & WRITER_HELD) > 0, "Calling ReleaseWriterLock when no write lock is held");
+
+ ClearWriterAcquired();
+
+ _writeLockOwnerId = -1;
+
+ ExitAndWakeUpAppropriateWaiters();
+ }
+
+ public void ExitUpgradeableReadLock()
+ {
+ ReaderWriterCount lrwc;
+ if (!_fIsReentrant)
+ {
+ if (Environment.CurrentManagedThreadId != _upgradeLockOwnerId)
+ {
+ //You have to be holding the upgrade lock to make this call.
+ throw new SynchronizationLockException(SR.SynchronizationLockException_MisMatchedUpgrade);
+ }
+ EnterMyLock();
+ }
+ else
+ {
+ EnterMyLock();
+ lrwc = GetThreadRWCount(true);
+
+ if (lrwc == null)
+ {
+ ExitMyLock();
+ throw new SynchronizationLockException(SR.SynchronizationLockException_MisMatchedUpgrade);
+ }
+
+ if (lrwc.upgradecount < 1)
+ {
+ ExitMyLock();
+ throw new SynchronizationLockException(SR.SynchronizationLockException_MisMatchedUpgrade);
+ }
+
+ lrwc.upgradecount--;
+
+ if (lrwc.upgradecount > 0)
+ {
+ ExitMyLock();
+ return;
+ }
+
+ _fUpgradeThreadHoldingRead = false;
+ }
+
+ _owners--;
+ _upgradeLockOwnerId = -1;
+
+ ExitAndWakeUpAppropriateWaiters();
+ }
+
+ /// <summary>
+ /// A routine for lazily creating a event outside the lock (so if errors
+ /// happen they are outside the lock and that we don't do much work
+ /// while holding a spin lock). If all goes well, reenter the lock and
+ /// set 'waitEvent'
+ /// </summary>
+ private void LazyCreateEvent(ref EventWaitHandle waitEvent, bool makeAutoResetEvent)
+ {
+#if DEBUG
+ Debug.Assert(MyLockHeld);
+ Debug.Assert(waitEvent == null);
+#endif
+ ExitMyLock();
+ EventWaitHandle newEvent;
+ if (makeAutoResetEvent)
+ newEvent = new AutoResetEvent(false);
+ else
+ newEvent = new ManualResetEvent(false);
+ EnterMyLock();
+ if (waitEvent == null) // maybe someone snuck in.
+ waitEvent = newEvent;
+ else
+ newEvent.Dispose();
+ }
+
+ /// <summary>
+ /// Waits on 'waitEvent' with a timeout
+ /// Before the wait 'numWaiters' is incremented and is restored before leaving this routine.
+ /// </summary>
+ private bool WaitOnEvent(
+ EventWaitHandle waitEvent,
+ ref uint numWaiters,
+ TimeoutTracker timeout,
+ bool isWriteWaiter)
+ {
+#if DEBUG
+ Debug.Assert(MyLockHeld);
+#endif
+ waitEvent.Reset();
+ numWaiters++;
+ _fNoWaiters = false;
+
+ //Setting these bits will prevent new readers from getting in.
+ if (_numWriteWaiters == 1)
+ SetWritersWaiting();
+ if (_numWriteUpgradeWaiters == 1)
+ SetUpgraderWaiting();
+
+ bool waitSuccessful = false;
+ ExitMyLock(); // Do the wait outside of any lock
+
+ try
+ {
+ waitSuccessful = waitEvent.WaitOne(timeout.RemainingMilliseconds);
+ }
+ finally
+ {
+ EnterMyLock();
+ --numWaiters;
+
+ if (_numWriteWaiters == 0 && _numWriteUpgradeWaiters == 0 && _numUpgradeWaiters == 0 && _numReadWaiters == 0)
+ _fNoWaiters = true;
+
+ if (_numWriteWaiters == 0)
+ ClearWritersWaiting();
+ if (_numWriteUpgradeWaiters == 0)
+ ClearUpgraderWaiting();
+
+ if (!waitSuccessful) // We may also be about to throw for some reason. Exit myLock.
+ {
+ if (isWriteWaiter)
+ {
+ // Write waiters block read waiters from acquiring the lock. Since this was the last write waiter, try
+ // to wake up the appropriate read waiters.
+ ExitAndWakeUpAppropriateReadWaiters();
+ }
+ else
+ ExitMyLock();
+ }
+ }
+ return waitSuccessful;
+ }
+
+ /// <summary>
+ /// Determines the appropriate events to set, leaves the locks, and sets the events.
+ /// </summary>
+ private void ExitAndWakeUpAppropriateWaiters()
+ {
+#if DEBUG
+ Debug.Assert(MyLockHeld);
+#endif
+ if (_fNoWaiters)
+ {
+ ExitMyLock();
+ return;
+ }
+
+ ExitAndWakeUpAppropriateWaitersPreferringWriters();
+ }
+
+ private void ExitAndWakeUpAppropriateWaitersPreferringWriters()
+ {
+ uint readercount = GetNumReaders();
+
+ //We need this case for EU->ER->EW case, as the read count will be 2 in
+ //that scenario.
+ if (_fIsReentrant)
+ {
+ if (_numWriteUpgradeWaiters > 0 && _fUpgradeThreadHoldingRead && readercount == 2)
+ {
+ ExitMyLock(); // Exit before signaling to improve efficiency (wakee will need the lock)
+ _waitUpgradeEvent.Set(); // release all upgraders (however there can be at most one).
+ return;
+ }
+ }
+
+ if (readercount == 1 && _numWriteUpgradeWaiters > 0)
+ {
+ //We have to be careful now, as we are dropping the lock.
+ //No new writes should be allowed to sneak in if an upgrade
+ //was pending.
+
+ ExitMyLock(); // Exit before signaling to improve efficiency (wakee will need the lock)
+ _waitUpgradeEvent.Set(); // release all upgraders (however there can be at most one).
+ }
+ else if (readercount == 0 && _numWriteWaiters > 0)
+ {
+ ExitMyLock(); // Exit before signaling to improve efficiency (wakee will need the lock)
+ _writeEvent.Set(); // release one writer.
+ }
+ else
+ {
+ ExitAndWakeUpAppropriateReadWaiters();
+ }
+ }
+
+ private void ExitAndWakeUpAppropriateReadWaiters()
+ {
+#if DEBUG
+ Debug.Assert(MyLockHeld);
+#endif
+
+ if (_numWriteWaiters != 0 || _numWriteUpgradeWaiters != 0 || _fNoWaiters)
+ {
+ ExitMyLock();
+ return;
+ }
+
+ Debug.Assert(_numReadWaiters != 0 || _numUpgradeWaiters != 0);
+
+ bool setReadEvent = _numReadWaiters != 0;
+ bool setUpgradeEvent = _numUpgradeWaiters != 0 && _upgradeLockOwnerId == -1;
+
+ ExitMyLock(); // Exit before signaling to improve efficiency (wakee will need the lock)
+
+ if (setReadEvent)
+ _readEvent.Set(); // release all readers.
+
+ if (setUpgradeEvent)
+ _upgradeEvent.Set(); //release one upgrader.
+ }
+
+ private bool IsWriterAcquired()
+ {
+ return (_owners & ~WAITING_WRITERS) == 0;
+ }
+
+ private void SetWriterAcquired()
+ {
+ _owners |= WRITER_HELD; // indicate we have a writer.
+ }
+
+ private void ClearWriterAcquired()
+ {
+ _owners &= ~WRITER_HELD;
+ }
+
+ private void SetWritersWaiting()
+ {
+ _owners |= WAITING_WRITERS;
+ }
+
+ private void ClearWritersWaiting()
+ {
+ _owners &= ~WAITING_WRITERS;
+ }
+
+ private void SetUpgraderWaiting()
+ {
+ _owners |= WAITING_UPGRADER;
+ }
+
+ private void ClearUpgraderWaiting()
+ {
+ _owners &= ~WAITING_UPGRADER;
+ }
+
+ private uint GetNumReaders()
+ {
+ return _owners & READER_MASK;
+ }
+
+ [MethodImpl(MethodImplOptions.AggressiveInlining)]
+ private void EnterMyLock()
+ {
+ if (Interlocked.CompareExchange(ref _myLock, 1, 0) != 0)
+ EnterMyLockSpin();
+ }
+
+ private void EnterMyLockSpin()
+ {
+ int pc = Environment.ProcessorCount;
+ for (int i = 0; ; i++)
+ {
+ if (i < LockSpinCount && pc > 1)
+ {
+ RuntimeThread.SpinWait(LockSpinCycles * (i + 1)); // Wait a few dozen instructions to let another processor release lock.
+ }
+ else if (i < (LockSpinCount + LockSleep0Count))
+ {
+ RuntimeThread.Sleep(0); // Give up my quantum.
+ }
+ else
+ {
+ RuntimeThread.Sleep(1); // Give up my quantum.
+ }
+
+ if (_myLock == 0 && Interlocked.CompareExchange(ref _myLock, 1, 0) == 0)
+ return;
+ }
+ }
+
+ private void ExitMyLock()
+ {
+ Debug.Assert(_myLock != 0, "Exiting spin lock that is not held");
+ Volatile.Write(ref _myLock, 0);
+ }
+
+#if DEBUG
+ private bool MyLockHeld { get { return _myLock != 0; } }
+#endif
+
+ private static void SpinWait(int SpinCount)
+ {
+ //Exponential back-off
+ if ((SpinCount < 5) && (Environment.ProcessorCount > 1))
+ {
+ RuntimeThread.SpinWait(LockSpinCycles * SpinCount);
+ }
+ else
+ {
+ RuntimeThread.Sleep(0);
+ }
+
+ // Don't want to Sleep(1) in this spin wait:
+ // - Don't want to spin for that long, since a proper wait will follow when the spin wait fails. The artifical
+ // delay introduced by Sleep(1) will in some cases be much longer than desired.
+ // - Sleep(1) would put the thread into a wait state, and a proper wait will follow when the spin wait fails
+ // anyway, so it's preferable to put the thread into the proper wait state
+ }
+
+ public void Dispose()
+ {
+ Dispose(true);
+ }
+
+ private void Dispose(bool disposing)
+ {
+ if (disposing && !_fDisposed)
+ {
+ if (WaitingReadCount > 0 || WaitingUpgradeCount > 0 || WaitingWriteCount > 0)
+ throw new SynchronizationLockException(SR.SynchronizationLockException_IncorrectDispose);
+
+ if (IsReadLockHeld || IsUpgradeableReadLockHeld || IsWriteLockHeld)
+ throw new SynchronizationLockException(SR.SynchronizationLockException_IncorrectDispose);
+
+ if (_writeEvent != null)
+ {
+ _writeEvent.Dispose();
+ _writeEvent = null;
+ }
+
+ if (_readEvent != null)
+ {
+ _readEvent.Dispose();
+ _readEvent = null;
+ }
+
+ if (_upgradeEvent != null)
+ {
+ _upgradeEvent.Dispose();
+ _upgradeEvent = null;
+ }
+
+ if (_waitUpgradeEvent != null)
+ {
+ _waitUpgradeEvent.Dispose();
+ _waitUpgradeEvent = null;
+ }
+
+ _fDisposed = true;
+ }
+ }
+
+ public bool IsReadLockHeld
+ {
+ get
+ {
+ if (RecursiveReadCount > 0)
+ return true;
+ else
+ return false;
+ }
+ }
+
+ public bool IsUpgradeableReadLockHeld
+ {
+ get
+ {
+ if (RecursiveUpgradeCount > 0)
+ return true;
+ else
+ return false;
+ }
+ }
+
+ public bool IsWriteLockHeld
+ {
+ get
+ {
+ if (RecursiveWriteCount > 0)
+ return true;
+ else
+ return false;
+ }
+ }
+
+ public LockRecursionPolicy RecursionPolicy
+ {
+ get
+ {
+ if (_fIsReentrant)
+ {
+ return LockRecursionPolicy.SupportsRecursion;
+ }
+ else
+ {
+ return LockRecursionPolicy.NoRecursion;
+ }
+ }
+ }
+
+ public int CurrentReadCount
+ {
+ get
+ {
+ int numreaders = (int)GetNumReaders();
+
+ if (_upgradeLockOwnerId != -1)
+ return numreaders - 1;
+ else
+ return numreaders;
+ }
+ }
+
+
+ public int RecursiveReadCount
+ {
+ get
+ {
+ int count = 0;
+ ReaderWriterCount lrwc = GetThreadRWCount(true);
+ if (lrwc != null)
+ count = lrwc.readercount;
+
+ return count;
+ }
+ }
+
+ public int RecursiveUpgradeCount
+ {
+ get
+ {
+ if (_fIsReentrant)
+ {
+ int count = 0;
+
+ ReaderWriterCount lrwc = GetThreadRWCount(true);
+ if (lrwc != null)
+ count = lrwc.upgradecount;
+
+ return count;
+ }
+ else
+ {
+ if (Environment.CurrentManagedThreadId == _upgradeLockOwnerId)
+ return 1;
+ else
+ return 0;
+ }
+ }
+ }
+
+ public int RecursiveWriteCount
+ {
+ get
+ {
+ if (_fIsReentrant)
+ {
+ int count = 0;
+
+ ReaderWriterCount lrwc = GetThreadRWCount(true);
+ if (lrwc != null)
+ count = lrwc.writercount;
+
+ return count;
+ }
+ else
+ {
+ if (Environment.CurrentManagedThreadId == _writeLockOwnerId)
+ return 1;
+ else
+ return 0;
+ }
+ }
+ }
+
+ public int WaitingReadCount
+ {
+ get
+ {
+ return (int)_numReadWaiters;
+ }
+ }
+
+ public int WaitingUpgradeCount
+ {
+ get
+ {
+ return (int)_numUpgradeWaiters;
+ }
+ }
+
+ public int WaitingWriteCount
+ {
+ get
+ {
+ return (int)_numWriteWaiters;
+ }
+ }
+ }
+}