System.IO.Compression.DeflateStream.AsyncOperationStarting C# (CSharp) Method

        private void AsyncOperationStarting()
        {
            if (Interlocked.CompareExchange(ref _activeAsyncOperation, 1, 0) != 0)
            {
                ThrowInvalidBeginCall();
            }
        }

            public async Task CopyFromSourceToDestinationAsync()
            {
                _deflateStream.AsyncOperationStarting();
                try
                {
                    // Flush any existing data in the inflater to the destination stream.
                    while (true)
                    {
                        int bytesRead = _deflateStream._inflater.Inflate(_arrayPoolBuffer, 0, _arrayPoolBuffer.Length);
                        if (bytesRead > 0)
                        {
                            await _destination.WriteAsync(new ReadOnlyMemory <byte>(_arrayPoolBuffer, 0, bytesRead), _cancellationToken).ConfigureAwait(false);
                        }
                        else
                        {
                            break;
                        }
                    }

                    // Now, use the source stream's CopyToAsync to push directly to our inflater via this helper stream
                    await _deflateStream._stream.CopyToAsync(this, _arrayPoolBuffer.Length, _cancellationToken).ConfigureAwait(false);
                }
                finally
                {
                    _deflateStream.AsyncOperationCompleting();

                    ArrayPool <byte> .Shared.Return(_arrayPoolBuffer);

                    _arrayPoolBuffer = null;
                }
            }