Code:
/ 4.0 / 4.0 / DEVDIV_TFS / Dev10 / Releases / RTMRel / ndp / fx / src / Core / System / Threading / ReaderWriterLockSlim / ReaderWriterLockSlim.cs / 1305376 / ReaderWriterLockSlim.cs
// optimize
using System; // for Basic system types
using System.IO; // for File, Path
using System.Diagnostics; // for TraceInformation ...
using System.Threading;
using System.Security.Permissions;
namespace System.Threading
{
public enum LockRecursionPolicy
{
NoRecursion = 0,
SupportsRecursion = 1,
}
internal class RecursiveCounts
{
public int writercount;
public int upgradecount;
}
//Ideally ReadCount should be part of recursivecount too.
//However,to avoid an extra lookup in the common case (readers only)
//we maintain the readercount in the common per-thread structure.
internal class ReaderWriterCount
{
public int threadid;
public int readercount;
public ReaderWriterCount next;
public RecursiveCounts rc;
public ReaderWriterCount(bool fIsReentrant)
{
threadid = -1;
if (fIsReentrant)
rc = new RecursiveCounts();
}
}
///
/// 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).
///
[HostProtection(SecurityAction.LinkDemand, Synchronization=true, ExternalThreading=true)]
[System.Security.Permissions.HostProtection(MayLeakOnAbort = true)]
public class ReaderWriterLockSlim : IDisposable
{
//Specifying if locked can be reacquired recursively.
bool fIsReentrant;
// Lock specifiation for myLock: This lock protects exactly the local fields associted
// instance of ReaderWriterLockSlim. It does NOT protect the memory associted with the
// the events that hang off this lock (eg writeEvent, readEvent upgradeEvent).
int myLock;
//The variables controlling spinning behaviior of Mylock(which is a spin-lock)
const int LockSpinCycles = 20;
const int LockSpinCount = 10;
const int LockSleep0Count = 5;
// These variables allow use to avoid Setting events (which is expensive) if we don't have to.
uint numWriteWaiters; // maximum number of threads that can be doing a WaitOne on the writeEvent
uint numReadWaiters; // maximum number of threads that can be doing a WaitOne on the readEvent
uint numWriteUpgradeWaiters; // maximum number of threads that can be doing a WaitOne on the upgradeEvent (at most 1).
uint numUpgradeWaiters;
//Variable used for quick check when there are no waiters.
bool fNoWaiters;
int upgradeLockOwnerId;
int writeLockOwnerId;
// conditions we wait on.
EventWaitHandle writeEvent; // threads waiting to aquire a write lock go here.
EventWaitHandle readEvent; // threads waiting to aquire a read lock go here (will be released in bulk)
EventWaitHandle upgradeEvent; // thread waiting to acquire the upgrade lock
EventWaitHandle waitUpgradeEvent; // thread waiting to upgrade from the upgrade lock to a write lock go here (at most one)
ReaderWriterCount[] rwc;
bool fUpgradeThreadHoldingRead;
//Per thread Hash;
private const int hashTableSize = 0xff;
private const int MaxSpinCount = 20;
//The uint, that contains info like if the writer lock is held, num of
//readers etc.
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 it's 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()
{
rwc = new ReaderWriterCount[hashTableSize+1];
upgradeLockOwnerId = -1;
writeLockOwnerId = -1;
}
public ReaderWriterLockSlim()
: this(LockRecursionPolicy.NoRecursion)
{
}
public ReaderWriterLockSlim(LockRecursionPolicy recursionPolicy)
{
if (recursionPolicy == LockRecursionPolicy.SupportsRecursion)
{
fIsReentrant = true;
}
InitializeThreadCounts();
}
private static bool IsRWEntryEmpty(ReaderWriterCount rwc)
{
if (rwc.threadid == -1)
return true;
else if (rwc.readercount == 0 && rwc.rc == null)
return true;
else if (rwc.readercount == 0 && rwc.rc.writercount == 0 && rwc.rc.upgradecount == 0)
return true;
else
return false;
}
private static bool IsRwHashEntryChanged(ReaderWriterCount lrwc, int id)
{
return lrwc.threadid != id;
}
///
/// This routine retrieves/sets the per-thread counts needed to enforce the
/// various rules related to acquiring the lock. It's a simple hash table,
/// where the first entry is pre-allocated for optimizing the common case.
/// After the first element has been allocated, duplicates are kept of in
/// linked-list. The entries are never freed, and the max size of the
/// table would be bounded by the max number of threads that held the lock
/// simultaneously.
///
/// 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.
///
private ReaderWriterCount GetThreadRWCount(int id, bool DontAllocate)
{
int hash = id & hashTableSize;
ReaderWriterCount firstfound = null;
#if DEBUG
Debug.Assert(MyLockHeld);
#endif
if (null == rwc[hash])
{
if (DontAllocate)
return null;
else
rwc[hash] = new ReaderWriterCount(fIsReentrant);
}
if (rwc[hash].threadid == id)
{
return rwc[hash];
}
if (IsRWEntryEmpty(rwc[hash]) && !DontAllocate)
{
//No more entries in chain, so no more searching required.
if (rwc[hash].next == null)
{
rwc[hash].threadid = id;
return rwc[hash];
}
else
firstfound = rwc[hash];
}
//SlowPath
ReaderWriterCount temp = rwc[hash].next;
while (temp != null)
{
if (temp.threadid == id)
{
return temp;
}
if (firstfound == null)
{
if (IsRWEntryEmpty(temp))
firstfound = temp;
}
temp = temp.next;
}
if (DontAllocate)
return null;
if (firstfound == null)
{
temp = new ReaderWriterCount(fIsReentrant);
temp.threadid = id;
temp.next = rwc[hash].next;
rwc[hash].next = temp;
return temp;
}
else
{
firstfound.threadid = id;
return firstfound;
}
}
public void EnterReadLock()
{
TryEnterReadLock(-1);
}
public bool TryEnterReadLock(TimeSpan timeout)
{
long ltm = (long)timeout.TotalMilliseconds;
if (ltm < -1 || ltm > (long) Int32.MaxValue)
throw new ArgumentOutOfRangeException("timeout");
int tm = (int)timeout.TotalMilliseconds;
return TryEnterReadLock(tm);
}
public bool TryEnterReadLock(int millisecondsTimeout)
{
Thread.BeginCriticalRegion();
bool result = false;
try
{
result = TryEnterReadLockCore(millisecondsTimeout);
}
finally
{
if (!result)
Thread.EndCriticalRegion();
}
return result;
}
private bool TryEnterReadLockCore(int millisecondsTimeout)
{
if (millisecondsTimeout < -1)
throw new ArgumentOutOfRangeException("millisecondsTimeout");
if(fDisposed)
throw new ObjectDisposedException(null);
ReaderWriterCount lrwc = null;
int id = Thread.CurrentThread.ManagedThreadId;
if (!fIsReentrant)
{
if (id == writeLockOwnerId)
{
//Check for AW->AR
throw new LockRecursionException(SR.GetString(SR.LockRecursionException_ReadAfterWriteNotAllowed));
}
EnterMyLock();
lrwc = GetThreadRWCount(id, 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 struucture).
if (lrwc.readercount > 0)
{
ExitMyLock();
throw new LockRecursionException(SR.GetString(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(id, 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 (millisecondsTimeout == 0)
return false;
spincount++;
SpinWait(spincount);
EnterMyLock();
//The per-thread structure may have been recycled as the lock is released, load again.
if(IsRwHashEntryChanged(lrwc, id))
lrwc = GetThreadRWCount(id, 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, id))
lrwc = GetThreadRWCount(id, false);
continue; // since we left the lock, start over.
}
retVal = WaitOnEvent(readEvent, ref numReadWaiters, millisecondsTimeout);
if (!retVal)
{
return false;
}
if (IsRwHashEntryChanged(lrwc, id))
lrwc = GetThreadRWCount(id, false);
}
ExitMyLock();
return retVal;
}
public void EnterWriteLock()
{
TryEnterWriteLock(-1);
}
public bool TryEnterWriteLock(TimeSpan timeout)
{
long ltm = (long)timeout.TotalMilliseconds;
if (ltm < -1 || ltm > (long) Int32.MaxValue)
throw new ArgumentOutOfRangeException("timeout");
int tm = (int)timeout.TotalMilliseconds;
return TryEnterWriteLock(tm);
}
public bool TryEnterWriteLock(int millisecondsTimeout)
{
Thread.BeginCriticalRegion();
bool result = false;
try
{
result = TryEnterWriteLockCore(millisecondsTimeout);
}
finally
{
if (!result)
Thread.EndCriticalRegion();
}
return result;
}
private bool TryEnterWriteLockCore(int millisecondsTimeout)
{
if (millisecondsTimeout < -1)
throw new ArgumentOutOfRangeException("millisecondsTimeout");
if(fDisposed)
throw new ObjectDisposedException(null);
int id = Thread.CurrentThread.ManagedThreadId;
ReaderWriterCount lrwc;
bool upgradingToWrite = false;
if (!fIsReentrant)
{
if (id == writeLockOwnerId)
{
//Check for AW->AW
throw new LockRecursionException(SR.GetString(SR.LockRecursionException_RecursiveWriteNotAllowed));
}
else if (id == upgradeLockOwnerId)
{
//AU->AW case is allowed once.
upgradingToWrite = true;
}
EnterMyLock();
lrwc = GetThreadRWCount(id, true);
//Can't acquire write lock with reader lock held.
if (lrwc != null && lrwc.readercount > 0)
{
ExitMyLock();
throw new LockRecursionException(SR.GetString(SR.LockRecursionException_WriteAfterReadNotAllowed));
}
}
else
{
EnterMyLock();
lrwc = GetThreadRWCount(id, false);
if (id == writeLockOwnerId)
{
lrwc.rc.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.GetString(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, id))
lrwc = GetThreadRWCount(id, 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 (millisecondsTimeout == 0)
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, millisecondsTimeout);
//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, millisecondsTimeout);
//The lock is not held in case of failure.
if (!retVal)
return false;
}
}
Debug.Assert((owners & WRITER_HELD) > 0);
if (fIsReentrant)
{
if (IsRwHashEntryChanged(lrwc, id))
lrwc = GetThreadRWCount(id, false);
lrwc.rc.writercount++;
}
ExitMyLock();
writeLockOwnerId = id;
return true;
}
public void EnterUpgradeableReadLock()
{
TryEnterUpgradeableReadLock(-1);
}
public bool TryEnterUpgradeableReadLock(TimeSpan timeout)
{
long ltm = (long)timeout.TotalMilliseconds;
if (ltm < -1 || ltm > (long) Int32.MaxValue)
throw new ArgumentOutOfRangeException("timeout");
int tm = (int)timeout.TotalMilliseconds;
return TryEnterUpgradeableReadLock(tm);
}
public bool TryEnterUpgradeableReadLock(int millisecondsTimeout)
{
Thread.BeginCriticalRegion();
bool result = false;
try
{
result = TryEnterUpgradeableReadLockCore(millisecondsTimeout);
}
finally
{
if (!result)
Thread.EndCriticalRegion();
}
return result;
}
private bool TryEnterUpgradeableReadLockCore(int millisecondsTimeout)
{
if (millisecondsTimeout < -1)
throw new ArgumentOutOfRangeException("millisecondsTimeout");
if(fDisposed)
throw new ObjectDisposedException(null);
int id = Thread.CurrentThread.ManagedThreadId;
ReaderWriterCount lrwc;
if (!fIsReentrant)
{
if (id == upgradeLockOwnerId)
{
//Check for AU->AU
throw new LockRecursionException(SR.GetString(SR.LockRecursionException_RecursiveUpgradeNotAllowed));
}
else if (id == writeLockOwnerId)
{
//Check for AU->AW
throw new LockRecursionException(SR.GetString(SR.LockRecursionException_UpgradeAfterWriteNotAllowed));
}
EnterMyLock();
lrwc = GetThreadRWCount(id, true);
//Can't acquire upgrade lock with reader lock held.
if (lrwc != null && lrwc.readercount > 0)
{
ExitMyLock();
throw new LockRecursionException(SR.GetString(SR.LockRecursionException_UpgradeAfterReadNotAllowed));
}
}
else
{
EnterMyLock();
lrwc = GetThreadRWCount(id, false);
if (id == upgradeLockOwnerId)
{
lrwc.rc.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.rc.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.GetString(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 (millisecondsTimeout == 0)
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, millisecondsTimeout);
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, id))
lrwc = GetThreadRWCount(id, false);
lrwc.rc.upgradecount++;
}
ExitMyLock();
return true;
}
public void ExitReadLock()
{
int id = Thread.CurrentThread.ManagedThreadId;
ReaderWriterCount lrwc = null;
EnterMyLock();
lrwc = GetThreadRWCount(id, true);
if (!fIsReentrant)
{
if (lrwc == null)
{
//You have to be holding the read lock to make this call.
ExitMyLock();
throw new SynchronizationLockException(SR.GetString(SR.SynchronizationLockException_MisMatchedRead));
}
}
else
{
if (lrwc == null || lrwc.readercount < 1)
{
ExitMyLock();
throw new SynchronizationLockException(SR.GetString(SR.SynchronizationLockException_MisMatchedRead));
}
if (lrwc.readercount > 1)
{
lrwc.readercount--;
ExitMyLock();
Thread.EndCriticalRegion();
return;
}
if (id == upgradeLockOwnerId)
{
fUpgradeThreadHoldingRead = false;
}
}
Debug.Assert(owners > 0, "ReleasingReaderLock: releasing lock and no read lock taken");
--owners;
Debug.Assert(lrwc.readercount == 1);
lrwc.readercount--;
ExitAndWakeUpAppropriateWaiters();
Thread.EndCriticalRegion();
}
public void ExitWriteLock()
{
int id = Thread.CurrentThread.ManagedThreadId;
ReaderWriterCount lrwc;
if (!fIsReentrant)
{
if (id != writeLockOwnerId)
{
//You have to be holding the write lock to make this call.
throw new SynchronizationLockException(SR.GetString(SR.SynchronizationLockException_MisMatchedWrite));
}
EnterMyLock();
}
else
{
EnterMyLock();
lrwc = GetThreadRWCount(id, false);
if (lrwc == null)
{
ExitMyLock();
throw new SynchronizationLockException(SR.GetString(SR.SynchronizationLockException_MisMatchedWrite));
}
RecursiveCounts rc = lrwc.rc;
if (rc.writercount < 1)
{
ExitMyLock();
throw new SynchronizationLockException(SR.GetString(SR.SynchronizationLockException_MisMatchedWrite));
}
rc.writercount--;
if (rc.writercount > 0)
{
ExitMyLock();
Thread.EndCriticalRegion();
return;
}
}
Debug.Assert((owners & WRITER_HELD) > 0, "Calling ReleaseWriterLock when no write lock is held");
ClearWriterAcquired();
writeLockOwnerId = -1;
ExitAndWakeUpAppropriateWaiters();
Thread.EndCriticalRegion();
}
public void ExitUpgradeableReadLock()
{
int id = Thread.CurrentThread.ManagedThreadId;
ReaderWriterCount lrwc;
if (!fIsReentrant)
{
if (id != upgradeLockOwnerId)
{
//You have to be holding the upgrade lock to make this call.
throw new SynchronizationLockException(SR.GetString(SR.SynchronizationLockException_MisMatchedUpgrade));
}
EnterMyLock();
}
else
{
EnterMyLock();
lrwc = GetThreadRWCount(id, true);
if (lrwc == null)
{
ExitMyLock();
throw new SynchronizationLockException(SR.GetString(SR.SynchronizationLockException_MisMatchedUpgrade));
}
RecursiveCounts rc = lrwc.rc;
if (rc.upgradecount < 1)
{
ExitMyLock();
throw new SynchronizationLockException(SR.GetString(SR.SynchronizationLockException_MisMatchedUpgrade));
}
rc.upgradecount--;
if (rc.upgradecount > 0)
{
ExitMyLock();
Thread.EndCriticalRegion();
return;
}
fUpgradeThreadHoldingRead = false;
}
owners--;
upgradeLockOwnerId = -1;
ExitAndWakeUpAppropriateWaiters();
Thread.EndCriticalRegion();
}
///
/// 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'
///
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.Close();
}
///
/// Waits on 'waitEvent' with a timeout of 'millisceondsTimeout.
/// Before the wait 'numWaiters' is incremented and is restored before leaving this routine.
///
private bool WaitOnEvent(EventWaitHandle waitEvent, ref uint numWaiters, int millisecondsTimeout)
{
#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(millisecondsTimeout, false);
}
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 aboutto throw for some reason. Exit myLock.
ExitMyLock();
}
return waitSuccessful;
}
///
/// Determines the appropriate events to set, leaves the locks, and sets the events.
///
private void ExitAndWakeUpAppropriateWaiters()
{
#if DEBUG
Debug.Assert(MyLockHeld);
#endif
if (fNoWaiters)
{
ExitMyLock();
return;
}
ExitAndWakeUpAppropriateWaitersPreferringWriters();
}
private void ExitAndWakeUpAppropriateWaitersPreferringWriters()
{
bool setUpgradeEvent = false;
bool setReadEvent = false;
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 droppping 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 if (readercount >= 0)
{
if (numReadWaiters != 0 || numUpgradeWaiters != 0)
{
if (numReadWaiters != 0)
setReadEvent = true;
if (numUpgradeWaiters != 0 && upgradeLockOwnerId == -1)
{
setUpgradeEvent = true;
}
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.
}
else
ExitMyLock();
}
else
ExitMyLock();
}
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;
}
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)
{
Thread.SpinWait(LockSpinCycles * (i + 1)); // Wait a few dozen instructions to let another processor release lock.
}
else if (i < (LockSpinCount + LockSleep0Count))
{
Thread.Sleep(0); // Give up my quantum.
}
else
{
Thread.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");
myLock = 0;
}
#if DEBUG
private bool MyLockHeld { get { return myLock != 0; } }
#endif
private static void SpinWait(int SpinCount)
{
//Exponential backoff
if ((SpinCount < 5) && (Environment.ProcessorCount > 1))
{
Thread.SpinWait(LockSpinCycles * SpinCount);
}
else if (SpinCount < MaxSpinCount - 3)
{
Thread.Sleep(0);
}
else
{
Thread.Sleep(1);
}
}
public void Dispose()
{
Dispose(true);
}
private void Dispose(bool disposing)
{
if(disposing)
{
if(fDisposed)
throw new ObjectDisposedException(null);
if(WaitingReadCount>0 || WaitingUpgradeCount > 0 || WaitingWriteCount > 0)
throw new SynchronizationLockException(SR.GetString(SR.SynchronizationLockException_IncorrectDispose));
if(IsReadLockHeld || IsUpgradeableReadLockHeld || IsWriteLockHeld)
throw new SynchronizationLockException(SR.GetString(SR.SynchronizationLockException_IncorrectDispose));
if (writeEvent != null)
{
writeEvent.Close();
writeEvent = null;
}
if (readEvent != null)
{
readEvent.Close();
readEvent = null;
}
if (upgradeEvent != null)
{
upgradeEvent.Close();
upgradeEvent = null;
}
if (waitUpgradeEvent != null)
{
waitUpgradeEvent.Close();
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
{
ReaderWriterCount lrwc;
int id = Thread.CurrentThread.ManagedThreadId;
int count = 0;
Thread.BeginCriticalRegion();
EnterMyLock();
lrwc = GetThreadRWCount(id, true);
if(lrwc != null)
count = lrwc.readercount;
ExitMyLock();
Thread.EndCriticalRegion();
return count;
}
}
public int RecursiveUpgradeCount
{
get
{
int id = Thread.CurrentThread.ManagedThreadId;
if (fIsReentrant)
{
ReaderWriterCount lrwc;
int count = 0;
Thread.BeginCriticalRegion();
EnterMyLock();
lrwc = GetThreadRWCount(id, true);
if(lrwc != null)
count = lrwc.rc.upgradecount;
ExitMyLock();
Thread.EndCriticalRegion();
return count;
}
else
{
if (id == upgradeLockOwnerId)
return 1;
else
return 0;
}
}
}
public int RecursiveWriteCount
{
get
{
int id = Thread.CurrentThread.ManagedThreadId;
int count = 0;
if (fIsReentrant)
{
ReaderWriterCount lrwc;
Thread.BeginCriticalRegion();
EnterMyLock();
lrwc = GetThreadRWCount(id, true);
if(lrwc != null)
count = lrwc.rc.writercount;
ExitMyLock();
Thread.EndCriticalRegion();
return count;
}
else
{
if (id == 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;
}
}
}
}
// File provided for Reference Use Only by Microsoft Corporation (c) 2007.
// Copyright (c) Microsoft Corporation. All rights reserved.
// optimize
using System; // for Basic system types
using System.IO; // for File, Path
using System.Diagnostics; // for TraceInformation ...
using System.Threading;
using System.Security.Permissions;
namespace System.Threading
{
public enum LockRecursionPolicy
{
NoRecursion = 0,
SupportsRecursion = 1,
}
internal class RecursiveCounts
{
public int writercount;
public int upgradecount;
}
//Ideally ReadCount should be part of recursivecount too.
//However,to avoid an extra lookup in the common case (readers only)
//we maintain the readercount in the common per-thread structure.
internal class ReaderWriterCount
{
public int threadid;
public int readercount;
public ReaderWriterCount next;
public RecursiveCounts rc;
public ReaderWriterCount(bool fIsReentrant)
{
threadid = -1;
if (fIsReentrant)
rc = new RecursiveCounts();
}
}
///
/// 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).
///
[HostProtection(SecurityAction.LinkDemand, Synchronization=true, ExternalThreading=true)]
[System.Security.Permissions.HostProtection(MayLeakOnAbort = true)]
public class ReaderWriterLockSlim : IDisposable
{
//Specifying if locked can be reacquired recursively.
bool fIsReentrant;
// Lock specifiation for myLock: This lock protects exactly the local fields associted
// instance of ReaderWriterLockSlim. It does NOT protect the memory associted with the
// the events that hang off this lock (eg writeEvent, readEvent upgradeEvent).
int myLock;
//The variables controlling spinning behaviior of Mylock(which is a spin-lock)
const int LockSpinCycles = 20;
const int LockSpinCount = 10;
const int LockSleep0Count = 5;
// These variables allow use to avoid Setting events (which is expensive) if we don't have to.
uint numWriteWaiters; // maximum number of threads that can be doing a WaitOne on the writeEvent
uint numReadWaiters; // maximum number of threads that can be doing a WaitOne on the readEvent
uint numWriteUpgradeWaiters; // maximum number of threads that can be doing a WaitOne on the upgradeEvent (at most 1).
uint numUpgradeWaiters;
//Variable used for quick check when there are no waiters.
bool fNoWaiters;
int upgradeLockOwnerId;
int writeLockOwnerId;
// conditions we wait on.
EventWaitHandle writeEvent; // threads waiting to aquire a write lock go here.
EventWaitHandle readEvent; // threads waiting to aquire a read lock go here (will be released in bulk)
EventWaitHandle upgradeEvent; // thread waiting to acquire the upgrade lock
EventWaitHandle waitUpgradeEvent; // thread waiting to upgrade from the upgrade lock to a write lock go here (at most one)
ReaderWriterCount[] rwc;
bool fUpgradeThreadHoldingRead;
//Per thread Hash;
private const int hashTableSize = 0xff;
private const int MaxSpinCount = 20;
//The uint, that contains info like if the writer lock is held, num of
//readers etc.
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 it's 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()
{
rwc = new ReaderWriterCount[hashTableSize+1];
upgradeLockOwnerId = -1;
writeLockOwnerId = -1;
}
public ReaderWriterLockSlim()
: this(LockRecursionPolicy.NoRecursion)
{
}
public ReaderWriterLockSlim(LockRecursionPolicy recursionPolicy)
{
if (recursionPolicy == LockRecursionPolicy.SupportsRecursion)
{
fIsReentrant = true;
}
InitializeThreadCounts();
}
private static bool IsRWEntryEmpty(ReaderWriterCount rwc)
{
if (rwc.threadid == -1)
return true;
else if (rwc.readercount == 0 && rwc.rc == null)
return true;
else if (rwc.readercount == 0 && rwc.rc.writercount == 0 && rwc.rc.upgradecount == 0)
return true;
else
return false;
}
private static bool IsRwHashEntryChanged(ReaderWriterCount lrwc, int id)
{
return lrwc.threadid != id;
}
///
/// This routine retrieves/sets the per-thread counts needed to enforce the
/// various rules related to acquiring the lock. It's a simple hash table,
/// where the first entry is pre-allocated for optimizing the common case.
/// After the first element has been allocated, duplicates are kept of in
/// linked-list. The entries are never freed, and the max size of the
/// table would be bounded by the max number of threads that held the lock
/// simultaneously.
///
/// 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.
///
private ReaderWriterCount GetThreadRWCount(int id, bool DontAllocate)
{
int hash = id & hashTableSize;
ReaderWriterCount firstfound = null;
#if DEBUG
Debug.Assert(MyLockHeld);
#endif
if (null == rwc[hash])
{
if (DontAllocate)
return null;
else
rwc[hash] = new ReaderWriterCount(fIsReentrant);
}
if (rwc[hash].threadid == id)
{
return rwc[hash];
}
if (IsRWEntryEmpty(rwc[hash]) && !DontAllocate)
{
//No more entries in chain, so no more searching required.
if (rwc[hash].next == null)
{
rwc[hash].threadid = id;
return rwc[hash];
}
else
firstfound = rwc[hash];
}
//SlowPath
ReaderWriterCount temp = rwc[hash].next;
while (temp != null)
{
if (temp.threadid == id)
{
return temp;
}
if (firstfound == null)
{
if (IsRWEntryEmpty(temp))
firstfound = temp;
}
temp = temp.next;
}
if (DontAllocate)
return null;
if (firstfound == null)
{
temp = new ReaderWriterCount(fIsReentrant);
temp.threadid = id;
temp.next = rwc[hash].next;
rwc[hash].next = temp;
return temp;
}
else
{
firstfound.threadid = id;
return firstfound;
}
}
public void EnterReadLock()
{
TryEnterReadLock(-1);
}
public bool TryEnterReadLock(TimeSpan timeout)
{
long ltm = (long)timeout.TotalMilliseconds;
if (ltm < -1 || ltm > (long) Int32.MaxValue)
throw new ArgumentOutOfRangeException("timeout");
int tm = (int)timeout.TotalMilliseconds;
return TryEnterReadLock(tm);
}
public bool TryEnterReadLock(int millisecondsTimeout)
{
Thread.BeginCriticalRegion();
bool result = false;
try
{
result = TryEnterReadLockCore(millisecondsTimeout);
}
finally
{
if (!result)
Thread.EndCriticalRegion();
}
return result;
}
private bool TryEnterReadLockCore(int millisecondsTimeout)
{
if (millisecondsTimeout < -1)
throw new ArgumentOutOfRangeException("millisecondsTimeout");
if(fDisposed)
throw new ObjectDisposedException(null);
ReaderWriterCount lrwc = null;
int id = Thread.CurrentThread.ManagedThreadId;
if (!fIsReentrant)
{
if (id == writeLockOwnerId)
{
//Check for AW->AR
throw new LockRecursionException(SR.GetString(SR.LockRecursionException_ReadAfterWriteNotAllowed));
}
EnterMyLock();
lrwc = GetThreadRWCount(id, 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 struucture).
if (lrwc.readercount > 0)
{
ExitMyLock();
throw new LockRecursionException(SR.GetString(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(id, 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 (millisecondsTimeout == 0)
return false;
spincount++;
SpinWait(spincount);
EnterMyLock();
//The per-thread structure may have been recycled as the lock is released, load again.
if(IsRwHashEntryChanged(lrwc, id))
lrwc = GetThreadRWCount(id, 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, id))
lrwc = GetThreadRWCount(id, false);
continue; // since we left the lock, start over.
}
retVal = WaitOnEvent(readEvent, ref numReadWaiters, millisecondsTimeout);
if (!retVal)
{
return false;
}
if (IsRwHashEntryChanged(lrwc, id))
lrwc = GetThreadRWCount(id, false);
}
ExitMyLock();
return retVal;
}
public void EnterWriteLock()
{
TryEnterWriteLock(-1);
}
public bool TryEnterWriteLock(TimeSpan timeout)
{
long ltm = (long)timeout.TotalMilliseconds;
if (ltm < -1 || ltm > (long) Int32.MaxValue)
throw new ArgumentOutOfRangeException("timeout");
int tm = (int)timeout.TotalMilliseconds;
return TryEnterWriteLock(tm);
}
public bool TryEnterWriteLock(int millisecondsTimeout)
{
Thread.BeginCriticalRegion();
bool result = false;
try
{
result = TryEnterWriteLockCore(millisecondsTimeout);
}
finally
{
if (!result)
Thread.EndCriticalRegion();
}
return result;
}
private bool TryEnterWriteLockCore(int millisecondsTimeout)
{
if (millisecondsTimeout < -1)
throw new ArgumentOutOfRangeException("millisecondsTimeout");
if(fDisposed)
throw new ObjectDisposedException(null);
int id = Thread.CurrentThread.ManagedThreadId;
ReaderWriterCount lrwc;
bool upgradingToWrite = false;
if (!fIsReentrant)
{
if (id == writeLockOwnerId)
{
//Check for AW->AW
throw new LockRecursionException(SR.GetString(SR.LockRecursionException_RecursiveWriteNotAllowed));
}
else if (id == upgradeLockOwnerId)
{
//AU->AW case is allowed once.
upgradingToWrite = true;
}
EnterMyLock();
lrwc = GetThreadRWCount(id, true);
//Can't acquire write lock with reader lock held.
if (lrwc != null && lrwc.readercount > 0)
{
ExitMyLock();
throw new LockRecursionException(SR.GetString(SR.LockRecursionException_WriteAfterReadNotAllowed));
}
}
else
{
EnterMyLock();
lrwc = GetThreadRWCount(id, false);
if (id == writeLockOwnerId)
{
lrwc.rc.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.GetString(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, id))
lrwc = GetThreadRWCount(id, 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 (millisecondsTimeout == 0)
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, millisecondsTimeout);
//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, millisecondsTimeout);
//The lock is not held in case of failure.
if (!retVal)
return false;
}
}
Debug.Assert((owners & WRITER_HELD) > 0);
if (fIsReentrant)
{
if (IsRwHashEntryChanged(lrwc, id))
lrwc = GetThreadRWCount(id, false);
lrwc.rc.writercount++;
}
ExitMyLock();
writeLockOwnerId = id;
return true;
}
public void EnterUpgradeableReadLock()
{
TryEnterUpgradeableReadLock(-1);
}
public bool TryEnterUpgradeableReadLock(TimeSpan timeout)
{
long ltm = (long)timeout.TotalMilliseconds;
if (ltm < -1 || ltm > (long) Int32.MaxValue)
throw new ArgumentOutOfRangeException("timeout");
int tm = (int)timeout.TotalMilliseconds;
return TryEnterUpgradeableReadLock(tm);
}
public bool TryEnterUpgradeableReadLock(int millisecondsTimeout)
{
Thread.BeginCriticalRegion();
bool result = false;
try
{
result = TryEnterUpgradeableReadLockCore(millisecondsTimeout);
}
finally
{
if (!result)
Thread.EndCriticalRegion();
}
return result;
}
private bool TryEnterUpgradeableReadLockCore(int millisecondsTimeout)
{
if (millisecondsTimeout < -1)
throw new ArgumentOutOfRangeException("millisecondsTimeout");
if(fDisposed)
throw new ObjectDisposedException(null);
int id = Thread.CurrentThread.ManagedThreadId;
ReaderWriterCount lrwc;
if (!fIsReentrant)
{
if (id == upgradeLockOwnerId)
{
//Check for AU->AU
throw new LockRecursionException(SR.GetString(SR.LockRecursionException_RecursiveUpgradeNotAllowed));
}
else if (id == writeLockOwnerId)
{
//Check for AU->AW
throw new LockRecursionException(SR.GetString(SR.LockRecursionException_UpgradeAfterWriteNotAllowed));
}
EnterMyLock();
lrwc = GetThreadRWCount(id, true);
//Can't acquire upgrade lock with reader lock held.
if (lrwc != null && lrwc.readercount > 0)
{
ExitMyLock();
throw new LockRecursionException(SR.GetString(SR.LockRecursionException_UpgradeAfterReadNotAllowed));
}
}
else
{
EnterMyLock();
lrwc = GetThreadRWCount(id, false);
if (id == upgradeLockOwnerId)
{
lrwc.rc.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.rc.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.GetString(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 (millisecondsTimeout == 0)
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, millisecondsTimeout);
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, id))
lrwc = GetThreadRWCount(id, false);
lrwc.rc.upgradecount++;
}
ExitMyLock();
return true;
}
public void ExitReadLock()
{
int id = Thread.CurrentThread.ManagedThreadId;
ReaderWriterCount lrwc = null;
EnterMyLock();
lrwc = GetThreadRWCount(id, true);
if (!fIsReentrant)
{
if (lrwc == null)
{
//You have to be holding the read lock to make this call.
ExitMyLock();
throw new SynchronizationLockException(SR.GetString(SR.SynchronizationLockException_MisMatchedRead));
}
}
else
{
if (lrwc == null || lrwc.readercount < 1)
{
ExitMyLock();
throw new SynchronizationLockException(SR.GetString(SR.SynchronizationLockException_MisMatchedRead));
}
if (lrwc.readercount > 1)
{
lrwc.readercount--;
ExitMyLock();
Thread.EndCriticalRegion();
return;
}
if (id == upgradeLockOwnerId)
{
fUpgradeThreadHoldingRead = false;
}
}
Debug.Assert(owners > 0, "ReleasingReaderLock: releasing lock and no read lock taken");
--owners;
Debug.Assert(lrwc.readercount == 1);
lrwc.readercount--;
ExitAndWakeUpAppropriateWaiters();
Thread.EndCriticalRegion();
}
public void ExitWriteLock()
{
int id = Thread.CurrentThread.ManagedThreadId;
ReaderWriterCount lrwc;
if (!fIsReentrant)
{
if (id != writeLockOwnerId)
{
//You have to be holding the write lock to make this call.
throw new SynchronizationLockException(SR.GetString(SR.SynchronizationLockException_MisMatchedWrite));
}
EnterMyLock();
}
else
{
EnterMyLock();
lrwc = GetThreadRWCount(id, false);
if (lrwc == null)
{
ExitMyLock();
throw new SynchronizationLockException(SR.GetString(SR.SynchronizationLockException_MisMatchedWrite));
}
RecursiveCounts rc = lrwc.rc;
if (rc.writercount < 1)
{
ExitMyLock();
throw new SynchronizationLockException(SR.GetString(SR.SynchronizationLockException_MisMatchedWrite));
}
rc.writercount--;
if (rc.writercount > 0)
{
ExitMyLock();
Thread.EndCriticalRegion();
return;
}
}
Debug.Assert((owners & WRITER_HELD) > 0, "Calling ReleaseWriterLock when no write lock is held");
ClearWriterAcquired();
writeLockOwnerId = -1;
ExitAndWakeUpAppropriateWaiters();
Thread.EndCriticalRegion();
}
public void ExitUpgradeableReadLock()
{
int id = Thread.CurrentThread.ManagedThreadId;
ReaderWriterCount lrwc;
if (!fIsReentrant)
{
if (id != upgradeLockOwnerId)
{
//You have to be holding the upgrade lock to make this call.
throw new SynchronizationLockException(SR.GetString(SR.SynchronizationLockException_MisMatchedUpgrade));
}
EnterMyLock();
}
else
{
EnterMyLock();
lrwc = GetThreadRWCount(id, true);
if (lrwc == null)
{
ExitMyLock();
throw new SynchronizationLockException(SR.GetString(SR.SynchronizationLockException_MisMatchedUpgrade));
}
RecursiveCounts rc = lrwc.rc;
if (rc.upgradecount < 1)
{
ExitMyLock();
throw new SynchronizationLockException(SR.GetString(SR.SynchronizationLockException_MisMatchedUpgrade));
}
rc.upgradecount--;
if (rc.upgradecount > 0)
{
ExitMyLock();
Thread.EndCriticalRegion();
return;
}
fUpgradeThreadHoldingRead = false;
}
owners--;
upgradeLockOwnerId = -1;
ExitAndWakeUpAppropriateWaiters();
Thread.EndCriticalRegion();
}
///
/// 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'
///
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.Close();
}
///
/// Waits on 'waitEvent' with a timeout of 'millisceondsTimeout.
/// Before the wait 'numWaiters' is incremented and is restored before leaving this routine.
///
private bool WaitOnEvent(EventWaitHandle waitEvent, ref uint numWaiters, int millisecondsTimeout)
{
#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(millisecondsTimeout, false);
}
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 aboutto throw for some reason. Exit myLock.
ExitMyLock();
}
return waitSuccessful;
}
///
/// Determines the appropriate events to set, leaves the locks, and sets the events.
///
private void ExitAndWakeUpAppropriateWaiters()
{
#if DEBUG
Debug.Assert(MyLockHeld);
#endif
if (fNoWaiters)
{
ExitMyLock();
return;
}
ExitAndWakeUpAppropriateWaitersPreferringWriters();
}
private void ExitAndWakeUpAppropriateWaitersPreferringWriters()
{
bool setUpgradeEvent = false;
bool setReadEvent = false;
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 droppping 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 if (readercount >= 0)
{
if (numReadWaiters != 0 || numUpgradeWaiters != 0)
{
if (numReadWaiters != 0)
setReadEvent = true;
if (numUpgradeWaiters != 0 && upgradeLockOwnerId == -1)
{
setUpgradeEvent = true;
}
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.
}
else
ExitMyLock();
}
else
ExitMyLock();
}
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;
}
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)
{
Thread.SpinWait(LockSpinCycles * (i + 1)); // Wait a few dozen instructions to let another processor release lock.
}
else if (i < (LockSpinCount + LockSleep0Count))
{
Thread.Sleep(0); // Give up my quantum.
}
else
{
Thread.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");
myLock = 0;
}
#if DEBUG
private bool MyLockHeld { get { return myLock != 0; } }
#endif
private static void SpinWait(int SpinCount)
{
//Exponential backoff
if ((SpinCount < 5) && (Environment.ProcessorCount > 1))
{
Thread.SpinWait(LockSpinCycles * SpinCount);
}
else if (SpinCount < MaxSpinCount - 3)
{
Thread.Sleep(0);
}
else
{
Thread.Sleep(1);
}
}
public void Dispose()
{
Dispose(true);
}
private void Dispose(bool disposing)
{
if(disposing)
{
if(fDisposed)
throw new ObjectDisposedException(null);
if(WaitingReadCount>0 || WaitingUpgradeCount > 0 || WaitingWriteCount > 0)
throw new SynchronizationLockException(SR.GetString(SR.SynchronizationLockException_IncorrectDispose));
if(IsReadLockHeld || IsUpgradeableReadLockHeld || IsWriteLockHeld)
throw new SynchronizationLockException(SR.GetString(SR.SynchronizationLockException_IncorrectDispose));
if (writeEvent != null)
{
writeEvent.Close();
writeEvent = null;
}
if (readEvent != null)
{
readEvent.Close();
readEvent = null;
}
if (upgradeEvent != null)
{
upgradeEvent.Close();
upgradeEvent = null;
}
if (waitUpgradeEvent != null)
{
waitUpgradeEvent.Close();
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
{
ReaderWriterCount lrwc;
int id = Thread.CurrentThread.ManagedThreadId;
int count = 0;
Thread.BeginCriticalRegion();
EnterMyLock();
lrwc = GetThreadRWCount(id, true);
if(lrwc != null)
count = lrwc.readercount;
ExitMyLock();
Thread.EndCriticalRegion();
return count;
}
}
public int RecursiveUpgradeCount
{
get
{
int id = Thread.CurrentThread.ManagedThreadId;
if (fIsReentrant)
{
ReaderWriterCount lrwc;
int count = 0;
Thread.BeginCriticalRegion();
EnterMyLock();
lrwc = GetThreadRWCount(id, true);
if(lrwc != null)
count = lrwc.rc.upgradecount;
ExitMyLock();
Thread.EndCriticalRegion();
return count;
}
else
{
if (id == upgradeLockOwnerId)
return 1;
else
return 0;
}
}
}
public int RecursiveWriteCount
{
get
{
int id = Thread.CurrentThread.ManagedThreadId;
int count = 0;
if (fIsReentrant)
{
ReaderWriterCount lrwc;
Thread.BeginCriticalRegion();
EnterMyLock();
lrwc = GetThreadRWCount(id, true);
if(lrwc != null)
count = lrwc.rc.writercount;
ExitMyLock();
Thread.EndCriticalRegion();
return count;
}
else
{
if (id == 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;
}
}
}
}
// File provided for Reference Use Only by Microsoft Corporation (c) 2007.
// Copyright (c) Microsoft Corporation. All rights reserved.
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