//
// Tries to wakeup a waiting writer.
//
// NOTE: This method is called with the spinlock held
// and when the r/w lock is in the NonEntered state.
// If a waiter is woken, the method releases the spin lock
// and returns true; otherwise, the method returns false and
// with the spinlock held.
//
private bool TryWakeupWriter()
{
while (!wrQueue.IsEmpty)
{
WaitNode w = wrQueue.Dequeue();
if (w.TryLock())
{
//
// Become the waiter the next owner of the write lock,
// release the spinlock, unpark the waiter and return true.
//
writer = w.tid;
slock.Exit();
w.Unpark(StParkStatus.Success);
return(true);
}
}
//
// No writer can be released; so, return false with the
// spinlock held.
//
return(false);
}
//
// Writes the specified number of data items to the
// stream blocking queue, activating the specified cancellers.
//
public int Write(T[] buffer, int offset, int count, StCancelArgs cargs)
{
//
// If this is a zero length write, return immediately.
//
if (count == 0)
{
return(0);
}
//
// Initialize the local variables.
//
int remaining = count;
WaitNodeQueue <T> wl = new WaitNodeQueue <T>();
int toCopy;
//
// Acquire the queue's lock.
//
slock.Enter();
//
// If the queue's buffer is full, check if the current
// thread must wait.
//
if (available == length)
{
goto CheckForWait;
}
//
// If there are waiting readers (i.e., the buffer is empty),
// transfer data items transferring directly to the waiting
// readers' buffers.
//
if (!waitQueue.IsEmpty)
{
do
{
WaitNode <T> rdw = waitQueue.head;
//
// Compute the number of data items to transfer to the
// waiting reader's buffer and perform the transfer.
//
if ((toCopy = rdw.remaining) > remaining)
{
toCopy = remaining;
}
Array.Copy(buffer, offset, rdw.buffer, rdw.offset, toCopy);
rdw.remaining -= toCopy;
rdw.offset += toCopy;
remaining -= toCopy;
offset += toCopy;
//
// If the waiting reader completes its read operation,
// remove its wait node from the wait list and try to
// lock the associated parker.
//
if (rdw.remaining == 0)
{
waitQueue.Dequeue();
if (rdw.TryLock() && !rdw.UnparkInProgress(StParkStatus.Success))
{
wl.Add(rdw);
}
}
else
{
//
// The data items are not enough to satisfy the waiting
// reader that is at front of wait queue, so break the loop.
//
break;
}
} while (remaining != 0 && !waitQueue.IsEmpty);
}
//
// If we have still data items to write and there is free space
// in the queue's buffer, transfer the appropriate number of data
// items the queue's buffer.
//
if (remaining != 0 && available < length)
{
//
// Compute the number of data items that can be copied
// to the queue's buffer and perform the transfer.
//
if ((toCopy = remaining) > (length - available))
{
toCopy = length - available;
}
int t = tail;
int tillEnd;
if ((tillEnd = length - t) >= toCopy)
{
Array.Copy(buffer, offset, items, t, toCopy);
if ((t += toCopy) >= length)
{
t = 0;
}
}
else
{
int fromBegin = toCopy - tillEnd;
Array.Copy(buffer, offset, items, t, tillEnd);
Array.Copy(buffer, offset + tillEnd, items, 0, fromBegin);
t = fromBegin;
}
//
// Update counters and indexes.
//
tail = t;
available += toCopy;
remaining -= toCopy;
offset += toCopy;
}
CheckForWait:
//
// If there are still data items to write, the current thread must
// wait if a null timeout wasn't specified.
//
WaitNode <T> wn = null;
bool mustWait;
if (mustWait = (remaining != 0 && cargs.Timeout != 0))
{
waitQueue.Enqueue(wn = new WaitNode <T>(buffer, offset, remaining));
}
//
// Release the queue's lock and unpark the readers threads
// release above.
//
slock.Exit();
wl.UnparkAll();
//
// If the current thread doesn't need to wait, return the
// number of written data items.
//
if (!mustWait)
{
return(count - remaining);
}
//
// Park the current thread, activating the specified cancellers.
//
int ws = wn.Park(cargs);
//
// If the write was completed, return the number of written
// data items.
//
if (ws == StParkStatus.Success)
{
return(count);
}
//
// The write was cancelled due to timeout, alert or interrupt.
// If the wait node is still inserted in the wait queue, acquire
// the queue's lock and unlink it.
//
if (wn.next != wn)
{
slock.Enter();
waitQueue.Remove(wn);
slock.Exit();
}
//
// If at least a data item was written, ignore the cancellation
// and return the number of transferred data items.
//
int c;
if ((c = count - wn.remaining) != 0)
{
StCancelArgs.PostponeCancellation(ws);
return(c);
}
//
// No data items were written; so, report the failure appropriately.
//
StCancelArgs.ThrowIfException(ws);
return(0);
}
//
// Tries to wakeup a waiting upgrader and/or all the waiting readers.
//
private bool TryWakeupUpgraderAndReaders()
{
//
// Initialize the wakeup list and the released flag.
//
WaitNodeQueue wl = new WaitNodeQueue();
bool released = false;
//
// If the upgraders wait queue isn't empty, try to wakeup a
// waiting upgrader to enter the lock in upgradeable read mode.
//
if (!upQueue.IsEmpty)
{
do
{
WaitNode w = upQueue.Dequeue();
if (w.TryLock())
{
//
// Make the locked waiter as the current upgrader and
// add its wait node to the wake up list.
//
upgrader = w.tid;
wl.AddToWakeList(w);
released = true;
break;
}
} while (!upQueue.IsEmpty);
}
//
// Even when the r/w lock state changes to the upgrade read mode,
// all the waiting readers can enter the read lock.
//
while (!rdQueue.IsEmpty)
{
WaitNode w = rdQueue.Dequeue();
if (w.TryLock())
{
//
// Account for one more active reader, add the respective
// entry to the reader owners table and add the waiting reader
// to the wake up list.
//
readers++;
rdCounts.Add(w.tid);
wl.AddToWakeList(w);
released = true;
}
}
//
// If no thread was released, return false holding the
// spinlock; otherwise, release the spinlock, unpark all
// threads inserted in the wake up list and return true.
//
if (!released)
{
return(false);
}
slock.Exit();
wl.UnparkAll();
return(true);
}
