Calls to Read(), ReadByte(), Write() and WriteByte() will only block if there are insufficient bytes available in the buffer. This may occur on the first call immediately after instantiation (when in reading Mode), immediately after switching from writing to reading mode, when trying to write more data than can fit in the buffer, or in general when the stream is being read or written faster than its underlying source or sink permits (e.g. FileStreams for files on local fixed disks are limited by disk transfer rate). To avoid blocking, use Available to get the number of bytes that can be written or read (depending on the mode) without blocking.

AsyncStreams operate by invoking the underlying stream's Read() and Write() methods on a dedicated background thread. If the underlying stream throws an exception during this background I/O, the background thread will stop and a AsynchronousBaseStreamException will be thrown the next time the Position or Mode properties are set or any method is invoked. Similarly, a SynchronousBaseStreamException exception will be immediately thrown if an unanticipated exception is thrown by the underlying stream during a method call or property assignment. In both cases, the original exception will be available via the Asynchronous/SynchronousBaseStreamException's InnerException property.

After an AsynchronousBaseStreamException is thrown, the asynchronous exception will be "forgotten" by the AsyncStream and the next time a method is called or Mode or Position is set the background thread will resume; you may also call ClearAsynchronousException() to forget an asynchronous exception and resume background I/O immediately.

Note: Do not use an AsyncStream to wrap a stream whose Read() or Write() methods may never return (e.g. a NetworkStream with infinite ReadTimeout or WriteTimeout) as this can potentially allow certain AsyncStream methods to also never return or prevent the AsyncStream object from being disposed properly.