public override bool TryWrite(T item)
{
AsyncOperation <T>? blockedReader = null;
AsyncOperation <bool>?waitingReadersTail = null;
BoundedChannel <T> parent = _parent;
lock (parent.SyncObj)
{
parent.AssertInvariants();
// If we're done writing, nothing more to do.
if (parent._doneWriting != null)
{
return(false);
}
// Get the number of items in the channel currently.
int count = parent._items.Count;
if (count == 0)
{
// There are no items in the channel, which means we may have blocked/waiting readers.
// If there are any blocked readers, find one that's not canceled
// and store it to complete outside of the lock, in case it has
// continuations that'll run synchronously
while (!parent._blockedReaders.IsEmpty)
{
AsyncOperation <T> r = parent._blockedReaders.DequeueHead();
r.UnregisterCancellation(); // ensure that once we grab it, we own its completion
if (!r.IsCompleted)
{
blockedReader = r;
break;
}
}
if (blockedReader == null)
{
// If there wasn't a blocked reader, then store the item. If no one's waiting
// to be notified about a 0-to-1 transition, we're done.
parent._items.EnqueueTail(item);
waitingReadersTail = parent._waitingReadersTail;
if (waitingReadersTail == null)
{
return(true);
}
parent._waitingReadersTail = null;
}
}
else if (count < parent._bufferedCapacity)
{
// There's room in the channel. Since we're not transitioning from 0-to-1 and
// since there's room, we can simply store the item and exit without having to
// worry about blocked/waiting readers.
parent._items.EnqueueTail(item);
return(true);
}
else if (parent._mode == BoundedChannelFullMode.Wait)
{
// The channel is full and we're in a wait mode.
// Simply exit and let the caller know we didn't write the data.
return(false);
}
else if (parent._mode == BoundedChannelFullMode.DropWrite)
{
// The channel is full. Just ignore the item being added
// but say we added it.
return(true);
}
else
{
// The channel is full, and we're in a dropping mode.
// Drop either the oldest or the newest and write the new item.
if (parent._mode == BoundedChannelFullMode.DropNewest)
{
parent._items.DequeueTail();
}
else
{
parent._items.DequeueHead();
}
parent._items.EnqueueTail(item);
return(true);
}
}
// We either wrote the item already, or we're transferring it to the blocked reader we grabbed.
if (blockedReader != null)
{
Debug.Assert(waitingReadersTail == null, "Shouldn't have any waiters to wake up");
// Transfer the written item to the blocked reader.
bool success = blockedReader.TrySetResult(item);
Debug.Assert(success, "We should always be able to complete the reader.");
}
else
{
// We stored an item bringing the count up from 0 to 1. Alert
// any waiting readers that there may be something for them to consume.
// Since we're no longer holding the lock, it's possible we'll end up
// waking readers that have since come in.
ChannelUtilities.WakeUpWaiters(ref waitingReadersTail, result: true);
}
return(true);
}
internal BoundedChannelWriter(BoundedChannel <T> parent)
{
_parent = parent;
_writerSingleton = new VoidAsyncOperationWithData <T>(runContinuationsAsynchronously: true, pooled: true);
_waiterSingleton = new AsyncOperation <bool>(runContinuationsAsynchronously: true, pooled: true);
}