private bool TryWrite(T item)
{
ReaderInteractor <T> blockedReader = null;
ReaderInteractor <bool> waitingReaders = null;
lock (SyncObj)
{
AssertInvariants();
// If we're done writing, nothing more to do.
if (_doneWriting != null)
{
return(false);
}
// Get the number of items in the channel currently.
int count = _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 (!_blockedReaders.IsEmpty)
{
ReaderInteractor <T> r = _blockedReaders.DequeueHead();
r.UnregisterCancellation(); // ensure that once we grab it, we own its completion
if (!r.Task.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.
_items.EnqueueTail(item);
waitingReaders = _waitingReaders;
if (waitingReaders == null)
{
return(true);
}
_waitingReaders = null;
}
}
else if (count < _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.
_items.EnqueueTail(item);
return(true);
}
else if (_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
{
// The channel is full, and we're in a dropping mode.
// Drop either the oldest or the newest and write the new item.
T droppedItem = _mode == BoundedChannelFullMode.DropNewest ?
_items.DequeueTail() :
_items.DequeueHead();
_items.EnqueueTail(item);
return(true);
}
}
// We either wrote the item already, or we're transfering it to the blocked reader we grabbed.
if (blockedReader != null)
{
// Transfer the written item to the blocked reader.
bool success = blockedReader.Success(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.
waitingReaders.Success(item: true);
}
return(true);
}
