//
// Adds an entry to the table for the specified thread.
//
internal void Add(int tid)
{
int hi = tid & HASH_TABLE_MASK;
ReaderCounter rc = table[hi].entry;
do
{
if (rc.count == 0)
{
rc.tid = tid;
rc.count = 1;
return;
}
} while ((rc = rc.next) != null);
rc = new ReaderCounter(tid, table[hi].entry);
table[hi].entry = rc;
}
//
// Looks up the entry belonging to the specified thread.
//
internal ReaderCounter Lookup(int tid)
{
ReaderCounter rc = table[tid & HASH_TABLE_MASK].entry;
if (rc.tid == tid && rc.count != 0)
{
return(rc);
}
while ((rc = rc.next) != null)
{
if (rc.tid == tid)
{
return((rc.count != 0) ? rc : null);
}
}
return(null);
}
//
// Constructors.
//
internal ReaderCounter(int id, ReaderCounter n) {
next = n;
tid = id;
count = 1;
}
//
// Adds an entry to the table for the specified thread.
//
internal void Add(int tid) {
int hi = tid & HASH_TABLE_MASK;
ReaderCounter rc = table[hi].entry;
do {
if (rc.count == 0) {
rc.tid = tid;
rc.count = 1;
return;
}
} while ((rc = rc.next) != null);
rc = new ReaderCounter(tid, table[hi].entry);
table[hi].entry = rc;
}
//
// Tries to enter the lock in upgrade read mode, activating
// the specified cancellers.
//
public bool TryEnterUpgradeableRead(StCancelArgs cargs)
{
int tid = Thread.CurrentThread.ManagedThreadId;
ReaderCounter rc = rdCounts.Lookup(tid);
if (!isReentrant)
{
if (tid == upgrader)
{
throw new StLockRecursionException("Recursive upgrade not allowed");
}
if (tid == writer)
{
throw new StLockRecursionException("Upgrade after write not allowed");
}
if (rc != null)
{
throw new StLockRecursionException("Upgrade after read not allowed");
}
}
else
{
//
// If the current thread is the current upgrader, increment the
// recursive acquisition counter and return.
//
if (tid == upgrader)
{
upCount++;
return(true);
}
//
// If the current thread is the current writer, it can also
// becomes the upgrader. If it is also a reader, it will be
// accounted as reader on the *upgraderIsReader* flag.
//
if (tid == writer)
{
upgrader = tid;
upCount = 1;
if (rc != null)
{
upgraderIsReader = true;
}
return(true);
}
if (rc != null)
{
throw new StLockRecursionException("Upgrade after read not allowed");
}
}
//
// Acquire the spinlock that protects the r/w lock shared state.
//
slock.Enter();
//
// If the lock isn't in write or upgrade read mode, the
// current thread becomes the current upgrader. Then, release
// the spinlock and return success.
//
if (writer == UNOWNED && upgrader == UNOWNED)
{
upgrader = tid;
slock.Exit();
upgraderIsReader = false;
upCount = 1;
return(true);
}
//
// The upgrade read lock can't be acquired immediately.
// So, if a null timeout was specified, return failure.
//
if (cargs.Timeout == 0)
{
slock.Exit();
return(false);
}
//
// Create a wait node and insert it in the upgrader's queue.
//
int sc = (upQueue.IsEmpty && wrQueue.IsEmpty) ? spinCount : 0;
WaitNode wn;
upQueue.Enqueue(wn = new WaitNode(tid));
//
// Release the spinlock and park the current thread activating
// the specified cancellers and spinning, if appropriate.
//
slock.Exit();
int ws = wn.Park(sc, cargs);
//
// If we acquired the upgrade lock, initialize the recursive
// acquisition count and the *upgraderIsReader flag and return
// success.
//
if (ws == StParkStatus.Success)
{
upCount = 1;
upgraderIsReader = false;
return(true);
}
//
// The acquire attemptwas cancelled. So, ensure that the
// wait node is unlinked from the wait queue and report
// the failure appropriately.
//
if (wn.next != wn)
{
slock.Enter();
upQueue.Remove(wn);
slock.Exit();
}
StCancelArgs.ThrowIfException(ws);
return(false);
}
//
// Exits the read lock.
//
public void ExitRead()
{
int tid = Thread.CurrentThread.ManagedThreadId;
ReaderCounter rc = rdCounts.Lookup(tid);
if (rc == null)
{
throw new StSynchronizationLockException("Mismatched read");
}
//
// If this is a recursive exit of the read lock, decrement
// the recursive acquisition count and return.
//
if (--rc.count > 0)
{
return;
}
//
// The read lock was exited by the current thread. So, if the current
// thread is also the upgrader clear the *upgraderIsReader* flag
// and return, because no other waiter thread can be released.
//
if (tid == upgrader)
{
upgraderIsReader = false;
return;
}
//
// Acquire the spinlock that protecteds the r/u/w lock shared state.
// Then, decrement the number of active readers; if this is not the
// unique lock reader, release the spin lock and return.
//
slock.Enter();
if (--readers > 0)
{
slock.Exit();
return;
}
//
// Here, we know that the r/u/w lock doesn't have readers.
// First, check the current upgarder is waiting to enter the write lock,
// and, if so, try to release it.
//
WaitNode w;
if ((w = upgToWrWaiter) != null)
{
upgToWrWaiter = null;
if (w.TryLock())
{
writer = w.tid;
slock.Exit();
w.Unpark(StParkStatus.Success);
return;
}
}
//
// If the r/w lock isn't in the upgrade read mode nor in write
// mode, try to wake up a waiting writer; failing that, try to
// wake up a waiting upgrader and/or all waiting readers.
//
if (!(upgrader == UNOWNED && writer == UNOWNED &&
(TryWakeupWriter() || TryWakeupUpgraderAndReaders())))
{
slock.Exit();
}
}
//
// Constructors.
//
internal ReaderCounter(int id, ReaderCounter n)
{
next = n;
tid = id;
count = 1;
}
//
// Tries to enter the read lock, activating the
// specified cancellers.
//
public bool TryEnterRead(StCancelArgs cargs)
{
int tid = Thread.CurrentThread.ManagedThreadId;
ReaderCounter rc = rdCounts.Lookup(tid);
if (!isReentrant)
{
if (tid == writer)
{
throw new StLockRecursionException("Read after write not allowed");
}
if (rc != null)
{
throw new StLockRecursionException("Recursive read not allowed");
}
}
else
{
//
// If this is a recursive enter, increment the recursive
// acquisition counter and return.
//
if (rc != null)
{
rc.count++;
return(true);
}
}
//
// Acquire the spinlock that protected the r/u/w lock shared state.
//
slock.Enter();
//
// If the current thread is the upgrader, it can also enter
// the read lock. So, add an entry to the readers table,
// release the spinlock and return success.
//
if (tid == upgrader)
{
rdCounts.Add(tid);
slock.Exit();
upgraderIsReader = true;
return(true);
}
//
// The read lock can be entered, if the r/w lock isn't in write
// mode and no thread is waiting to enter the writer mode.
// If these conditions are met, increment the number of lock
// readers, add an entry to the readers table, release the
// spinlock and return success.
//
if (writer == UNOWNED && wrQueue.IsEmpty && upgToWrWaiter == null)
{
readers++;
rdCounts.Add(tid);
slock.Exit();
return(true);
}
//
// If the r/w lock is reentrant and the current thread is the
// current writer, it can also to become a reader. So, increment
// the number of lock readers, add an entry to the readers table,
// release the spinlock and return success.
//
if (isReentrant && tid == writer)
{
readers++;
rdCounts.Add(tid);
slock.Exit();
return(true);
}
//
// The current thread can't enter the read lock immediately.
// So, if a null timeout was specified, release the spinlock
// and return failure.
//
if (cargs.Timeout == 0)
{
slock.Exit();
return(false);
}
//
// Create a wait node and insert it in the readers queue.
// Compute also the amount of spinning.
//
int sc = rdQueue.IsEmpty ? spinCount : 0;
WaitNode wn;
rdQueue.Enqueue(wn = new WaitNode(tid));
//
// Release the spinlock and park the current thread, activating
// the specified cancellers and spinning if appropriate.
//
slock.Exit();
int ws = wn.Park(sc, cargs);
//
// If we entered the read lock, return success.
//
if (ws == StParkStatus.Success)
{
return(true);
}
//
// The enter attempt was cancelled. So, ensure that the wait node
// is unlinked from the queue and report the failure appropriately.
//
if (wn.next != wn)
{
slock.Enter();
rdQueue.Remove(wn);
slock.Exit();
}
StCancelArgs.ThrowIfException(ws);
return(false);
}
