private void FlushWriteBufferForWriteByte()
{
_asyncState?.Wait();
try { FlushWriteBuffer(); }
finally { _asyncState?.Release(); }
}
/// <summary>
/// Asynchronously reads a sequence of bytes from the current stream and advances
/// the position within the stream by the number of bytes read.
/// </summary>
/// <param name="destination">The buffer to write the data into.</param>
/// <param name="cancellationToken">The token to monitor for cancellation requests.</param>
/// <param name="synchronousResult">If the operation completes synchronously, the number of bytes read.</param>
/// <returns>A task that represents the asynchronous read operation.</returns>
private Task <int> ReadAsyncInternal(Memory <byte> destination, CancellationToken cancellationToken, out int synchronousResult)
{
Debug.Assert(_useAsyncIO);
if (!CanRead) // match Windows behavior; this gets thrown synchronously
{
throw Error.GetReadNotSupported();
}
// Serialize operations using the semaphore.
Task waitTask = _asyncState.WaitAsync();
// If we got ownership immediately, and if there's enough data in our buffer
// to satisfy the full request of the caller, hand back the buffered data.
// While it would be a legal implementation of the Read contract, we don't
// hand back here less than the amount requested so as to match the behavior
// in ReadCore that will make a native call to try to fulfill the remainder
// of the request.
if (waitTask.Status == TaskStatus.RanToCompletion)
{
int numBytesAvailable = _readLength - _readPos;
if (numBytesAvailable >= destination.Length)
{
try
{
PrepareForReading();
new Span <byte>(GetBuffer(), _readPos, destination.Length).CopyTo(destination.Span);
_readPos += destination.Length;
synchronousResult = destination.Length;
return(null);
}
catch (Exception exc)
{
synchronousResult = 0;
return(Task.FromException <int>(exc));
}
finally
{
_asyncState.Release();
}
}
}
// Otherwise, issue the whole request asynchronously.
synchronousResult = 0;
_asyncState.Memory = destination;
return(waitTask.ContinueWith((t, s) =>
{
// The options available on Unix for writing asynchronously to an arbitrary file
// handle typically amount to just using another thread to do the synchronous write,
// which is exactly what this implementation does. This does mean there are subtle
// differences in certain FileStream behaviors between Windows and Unix when multiple
// asynchronous operations are issued against the stream to execute concurrently; on
// Unix the operations will be serialized due to the usage of a semaphore, but the
// position /length information won't be updated until after the write has completed,
// whereas on Windows it may happen before the write has completed.
Debug.Assert(t.Status == TaskStatus.RanToCompletion);
var thisRef = (FileStream)s;
try
{
Memory <byte> memory = thisRef._asyncState.Memory;
thisRef._asyncState.Memory = default(Memory <byte>);
return thisRef.ReadSpan(memory.Span);
}
finally { thisRef._asyncState.Release(); }
}, this, CancellationToken.None, TaskContinuationOptions.DenyChildAttach, TaskScheduler.Default));
}
