System.IO.BufferedStream.ReadAsync C# (CSharp) Méthode

        public override Task<int> ReadAsync(byte[] buffer, int offset, int count, CancellationToken cancellationToken)
        {

            if (buffer == null)
                throw new ArgumentNullException(nameof(buffer), SR.ArgumentNull_Buffer);
            if (offset < 0)
                throw new ArgumentOutOfRangeException(nameof(offset), SR.ArgumentOutOfRange_NeedNonNegNum);
            if (count < 0)
                throw new ArgumentOutOfRangeException(nameof(count), SR.ArgumentOutOfRange_NeedNonNegNum);
            if (buffer.Length - offset < count)
                throw new ArgumentException(SR.Argument_InvalidOffLen);

            // Fast path check for cancellation already requested
            if (cancellationToken.IsCancellationRequested)
                return Task.FromCanceled<int>(cancellationToken);

            EnsureNotClosed();
            EnsureCanRead();

            int bytesFromBuffer = 0;
            // Try to satisfy the request from the buffer synchronously. But still need a sem-lock in case that another
            // Async IO Task accesses the buffer concurrently. If we fail to acquire the lock without waiting, make this 
            // an Async operation.
            SemaphoreSlim sem = LazyEnsureAsyncActiveSemaphoreInitialized();
            Task semaphoreLockTask = sem.WaitAsync();
            if (semaphoreLockTask.Status == TaskStatus.RanToCompletion)
            {

                bool completeSynchronously = true;
                try
                {
                    Exception error;
                    bytesFromBuffer = ReadFromBuffer(buffer, offset, count, out error);

                    // If we satisfied enough data from the buffer, we can complete synchronously.
                    // Reading again for more data may cause us to block if we're using a device with no clear end of file,
                    // such as a serial port or pipe. If we blocked here and this code was used with redirected pipes for a
                    // process's standard output, this can lead to deadlocks involving two processes.              
                    // BUT - this is a breaking change. 
                    // So: If we could not read all bytes the user asked for from the buffer, we will try once from the underlying
                    // stream thus ensuring the same blocking behaviour as if the underlying stream was not wrapped in this BufferedStream.
                    completeSynchronously = (bytesFromBuffer == count || error != null);

                    if (completeSynchronously)
                    {

                        return (error == null)
                                    ? LastSyncCompletedReadTask(bytesFromBuffer)
                                    : Task.FromException<int>(error);
                    }
                }
                finally
                {
                    if (completeSynchronously)  // if this is FALSE, we will be entering ReadFromUnderlyingStreamAsync and releasing there.
                        sem.Release();
                }
            }

            // Delegate to the async implementation.
            return ReadFromUnderlyingStreamAsync(buffer, offset + bytesFromBuffer, count - bytesFromBuffer, cancellationToken,
                                                 bytesFromBuffer, semaphoreLockTask);
        }

        /// <summary>
        /// Writes the content of the ResponseStream a file indicated by the filePath argument.
        /// </summary>
        /// <param name="filePath">The location where to write the ResponseStream</param>
        /// <param name="append">Whether or not to append to the file if it exists</param>
        /// <param name="cancellationToken">Cancellation token which can be used to cancel this operation.</param>
        public async Task WriteResponseStreamToFileAsync(string filePath, bool append, CancellationToken cancellationToken)
        {
            // Make sure the directory exists to write too.
            FileInfo fi = new FileInfo(filePath);
            Directory.CreateDirectory(fi.DirectoryName);
                        
            Stream downloadStream;
            if (append && File.Exists(filePath))
                downloadStream = new FileStream(filePath, FileMode.Append, FileAccess.Write, FileShare.Read,S3Constants.DefaultBufferSize);
            else
                downloadStream = new FileStream(filePath, FileMode.Create, FileAccess.ReadWrite, FileShare.Read, S3Constants.DefaultBufferSize);

            try
            {
                long current = 0;
                BufferedStream bufferedStream = new BufferedStream(this.ResponseStream);
                byte[] buffer = new byte[S3Constants.DefaultBufferSize];
                int bytesRead = 0;
                long totalIncrementTransferred = 0;
                while ((bytesRead = await bufferedStream.ReadAsync(buffer, 0, buffer.Length)
                    .ConfigureAwait(continueOnCapturedContext:false)) > 0)
                {
                    cancellationToken.ThrowIfCancellationRequested();

                    await downloadStream.WriteAsync(buffer, 0, bytesRead)
                        .ConfigureAwait(continueOnCapturedContext: false);
                    current += bytesRead;
                    totalIncrementTransferred += bytesRead;

                    if (totalIncrementTransferred >= AWSSDKUtils.DefaultProgressUpdateInterval ||
                        current == this.ContentLength)
                    {
                        this.OnRaiseProgressEvent(filePath, totalIncrementTransferred, current, this.ContentLength);
                        totalIncrementTransferred = 0;
                    }
                }

                ValidateWrittenStreamSize(current);
            }
            finally
            {
                downloadStream.Close();
            }
        }