public ICancellableAsyncResult BeginOpenRead(AccessCondition accessCondition, BlobRequestOptions options, OperationContext operationContext, AsyncCallback callback, object state)
        {
            StorageAsyncResult<Stream> storageAsyncResult = new StorageAsyncResult<Stream>(callback, state);

            ICancellableAsyncResult result = this.BeginFetchAttributes(
                accessCondition,
                options,
                operationContext,
                ar =>
                {
                    try
                    {
                        this.EndFetchAttributes(ar);
                        storageAsyncResult.UpdateCompletedSynchronously(ar.CompletedSynchronously);
                        AccessCondition streamAccessCondition = AccessCondition.CloneConditionWithETag(accessCondition, this.Properties.ETag);
                        BlobRequestOptions modifiedOptions = BlobRequestOptions.ApplyDefaults(options, this.BlobType, this.ServiceClient, false);
                        storageAsyncResult.Result = new BlobReadStream(this, streamAccessCondition, modifiedOptions, operationContext);
                        storageAsyncResult.OnComplete();
                    }
                    catch (Exception e)
                    {
                        storageAsyncResult.OnComplete(e);
                    }
                },
                null /* state */);

            storageAsyncResult.CancelDelegate = result.Cancel;
            return storageAsyncResult;
        }

        public override IAsyncResult BeginRead(byte[] buffer, int offset, int count, AsyncCallback callback, object state)
        {
            CommonUtility.AssertNotNull("buffer", buffer);
            CommonUtility.AssertInBounds("offset", offset, 0, buffer.Length);
            CommonUtility.AssertInBounds("count", count, 0, buffer.Length - offset);

            StorageAsyncResult<int> result = new StorageAsyncResult<int>(callback, state);

            try
            {
                result.Result = this.Read(buffer, offset, count);
                result.OnComplete();
            }
            catch (Exception e)
            {
                result.OnComplete(e);
            }

            return result;
        }

 /// <summary>
 /// Dispatches an async read operation that either reads from the cache or makes a call to
 /// the server.
 /// </summary>
 /// <param name="storageAsyncResult">The reference to the pending asynchronous request to finish.</param>
 /// <param name="buffer">The buffer to read the data into.</param>
 /// <param name="offset">The byte offset in buffer at which to begin writing
 /// data read from the stream.</param>
 /// <param name="count">The maximum number of bytes to read.</param>
 private void DispatchReadAsync(StorageAsyncResult<int> storageAsyncResult, byte[] buffer, int offset, int count)
 {
     storageAsyncResult.OperationState = new ArraySegment<byte>(buffer, offset, count);
     
     try
     {
         this.internalBuffer.SetLength(0);
         this.blob.BeginDownloadRangeToStream(
             this.internalBuffer,
             this.currentOffset,
             this.GetReadSize(),
             this.accessCondition,
             this.options,
             this.operationContext,
             this.DownloadRangeToStreamCallback,
             storageAsyncResult);
     }
     catch (Exception e)
     {
         this.lastException = e;
         throw;
     }
 }

        internal ICancellableAsyncResult BeginUploadFromStreamHelper(Stream source, long? length, AccessCondition accessCondition, BlobRequestOptions options, OperationContext operationContext, AsyncCallback callback, object state)
        {
            CommonUtility.AssertNotNull("source", source);

            if (length.HasValue)
            {
                CommonUtility.AssertInBounds("length", length.Value, 1);

                if (source.CanSeek && length > source.Length - source.Position)
                {
                    throw new ArgumentOutOfRangeException("length", SR.StreamLengthShortError);
                }
            }

            this.attributes.AssertNoSnapshot();
            BlobRequestOptions modifiedOptions = BlobRequestOptions.ApplyDefaults(options, BlobType.BlockBlob, this.ServiceClient);

            ExecutionState<NullType> tempExecutionState = CommonUtility.CreateTemporaryExecutionState(modifiedOptions);
            StorageAsyncResult<NullType> storageAsyncResult = new StorageAsyncResult<NullType>(callback, state);

            bool lessThanSingleBlobThreshold = source.CanSeek &&
                (length ?? source.Length - source.Position) <= this.ServiceClient.SingleBlobUploadThresholdInBytes;
            if (this.ServiceClient.ParallelOperationThreadCount == 1 && lessThanSingleBlobThreshold)
            {
                if (modifiedOptions.StoreBlobContentMD5.Value)
                {
                    long startPosition = source.Position;
                    StreamDescriptor streamCopyState = new StreamDescriptor();
                    source.WriteToAsync(
                        Stream.Null,
                        length,
                        null /* maxLength */,
                        true,
                        tempExecutionState,
                        streamCopyState,
                        completedState =>
                        {
                            storageAsyncResult.UpdateCompletedSynchronously(completedState.CompletedSynchronously);

                            try
                            {
                                lock (storageAsyncResult.CancellationLockerObject)
                                {
                                    storageAsyncResult.CancelDelegate = null;
                                    if (completedState.ExceptionRef != null)
                                    {
                                        storageAsyncResult.OnComplete(completedState.ExceptionRef);
                                    }
                                    else
                                    {
                                        source.Position = startPosition;
                                        this.UploadFromStreamHandler(
                                            source,
                                            length,
                                            streamCopyState.Md5,
                                            accessCondition,
                                            operationContext,
                                            modifiedOptions,
                                            storageAsyncResult);
                                    }
                                }
                            }
                            catch (Exception e)
                            {
                                storageAsyncResult.OnComplete(e);
                            }
                        });

                    // We do not need to do this inside a lock, as storageAsyncResult is
                    // not returned to the user yet.
                    storageAsyncResult.CancelDelegate = tempExecutionState.Cancel;
                }
                else
                {
                    if (modifiedOptions.UseTransactionalMD5.Value)
                    {
                        throw new ArgumentException(SR.PutBlobNeedsStoreBlobContentMD5, "options");
                    }

                    this.UploadFromStreamHandler(
                        source,
                        length,
                        null /* contentMD5 */,
                        accessCondition,
                        operationContext,
                        modifiedOptions,
                        storageAsyncResult);
                }
            }
            else
            {
                ICancellableAsyncResult result = this.BeginOpenWrite(
                    accessCondition,
                    modifiedOptions,
                    operationContext,
                    ar =>
                    {
                        storageAsyncResult.UpdateCompletedSynchronously(ar.CompletedSynchronously);

                        lock (storageAsyncResult.CancellationLockerObject)
//.........这里部分代码省略.........

        public ICancellableAsyncResult BeginPutBlock(string blockId, Stream blockData, string contentMD5, AccessCondition accessCondition, BlobRequestOptions options, OperationContext operationContext, AsyncCallback callback, object state)
        {
            CommonUtility.AssertNotNull("blockData", blockData);

            BlobRequestOptions modifiedOptions = BlobRequestOptions.ApplyDefaults(options, BlobType.BlockBlob, this.ServiceClient);
            bool requiresContentMD5 = (contentMD5 == null) && modifiedOptions.UseTransactionalMD5.Value;
            operationContext = operationContext ?? new OperationContext();
            StorageAsyncResult<NullType> storageAsyncResult = new StorageAsyncResult<NullType>(callback, state);

            if (blockData.CanSeek && !requiresContentMD5)
            {
                this.PutBlockHandler(blockId, blockData, contentMD5, accessCondition, modifiedOptions, operationContext, storageAsyncResult);
            }
            else
            {
                ExecutionState<NullType> tempExecutionState = CommonUtility.CreateTemporaryExecutionState(modifiedOptions);
                storageAsyncResult.CancelDelegate = tempExecutionState.Cancel;

                Stream seekableStream;
                Stream writeToStream;
                if (blockData.CanSeek)
                {
                    seekableStream = blockData;
                    writeToStream = Stream.Null;
                }
                else
                {
                    seekableStream = new MultiBufferMemoryStream(this.ServiceClient.BufferManager);
                    writeToStream = seekableStream;
                }

                long startPosition = seekableStream.Position;
                StreamDescriptor streamCopyState = new StreamDescriptor();
                blockData.WriteToAsync(
                    writeToStream,
                    null /* copyLength */,
                    Constants.MaxBlockSize,
                    requiresContentMD5,
                    tempExecutionState,
                    streamCopyState,
                    completedState =>
                    {
                        storageAsyncResult.UpdateCompletedSynchronously(completedState.CompletedSynchronously);

                        if (completedState.ExceptionRef != null)
                        {
                            storageAsyncResult.OnComplete(completedState.ExceptionRef);
                        }
                        else
                        {
                            try
                            {
                                if (requiresContentMD5)
                                {
                                    contentMD5 = streamCopyState.Md5;
                                }

                                seekableStream.Position = startPosition;
                                this.PutBlockHandler(blockId, seekableStream, contentMD5, accessCondition, modifiedOptions, operationContext, storageAsyncResult);
                            }
                            catch (Exception e)
                            {
                                storageAsyncResult.OnComplete(e);
                            }
                        }
                    });
            }

            return storageAsyncResult;
        }

        public ICancellableAsyncResult BeginDeleteIfExists(DeleteSnapshotsOption deleteSnapshotsOption, AccessCondition accessCondition, BlobRequestOptions options, OperationContext operationContext, AsyncCallback callback, object state)
        {
            BlobRequestOptions modifiedOptions = BlobRequestOptions.ApplyDefaults(options, BlobType.BlockBlob, this.ServiceClient);
            operationContext = operationContext ?? new OperationContext();

            StorageAsyncResult<bool> storageAsyncResult = new StorageAsyncResult<bool>(callback, state)
            {
                RequestOptions = modifiedOptions,
                OperationContext = operationContext,
            };

            this.DeleteIfExistsHandler(deleteSnapshotsOption, accessCondition, modifiedOptions, operationContext, storageAsyncResult);
            return storageAsyncResult;
        }

        public ICancellableAsyncResult BeginDownloadRangeToByteArray(byte[] target, int index, long? blobOffset, long? length, AccessCondition accessCondition, BlobRequestOptions options, OperationContext operationContext, AsyncCallback callback, object state)
        {
            SyncMemoryStream stream = new SyncMemoryStream(target, index);
            StorageAsyncResult<int> storageAsyncResult = new StorageAsyncResult<int>(callback, state) { OperationState = stream };

            ICancellableAsyncResult result = this.BeginDownloadRangeToStream(
                stream,
                blobOffset,
                length,
                accessCondition,
                options,
                operationContext,
                this.DownloadRangeToByteArrayCallback,
                storageAsyncResult);

            storageAsyncResult.CancelDelegate = result.Cancel;
            return storageAsyncResult;
        }

        internal ICancellableAsyncResult BeginUploadFromStreamHelper(Stream source, long? length, AccessCondition accessCondition, BlobRequestOptions options, OperationContext operationContext, AsyncCallback callback, object state)
        {
            CommonUtility.AssertNotNull("source", source);

            if (!source.CanSeek)
            {
                throw new InvalidOperationException();
            }

            if (length.HasValue)
            {
                CommonUtility.AssertInBounds("length", (long)length, 1, source.Length - source.Position);
            }
            else
            {
                length = source.Length - source.Position;
            }

            if ((length % Constants.PageSize) != 0)
            {
                throw new ArgumentException(SR.InvalidPageSize, "source");
            }

            this.attributes.AssertNoSnapshot();
            BlobRequestOptions modifiedOptions = BlobRequestOptions.ApplyDefaults(options, BlobType.PageBlob, this.ServiceClient);

            ExecutionState<NullType> tempExecutionState = CommonUtility.CreateTemporaryExecutionState(modifiedOptions);
            StorageAsyncResult<NullType> storageAsyncResult = new StorageAsyncResult<NullType>(callback, state);

            ICancellableAsyncResult result = this.BeginOpenWrite(
                length,
                accessCondition,
                modifiedOptions,
                operationContext,
                ar =>
                {
                    storageAsyncResult.UpdateCompletedSynchronously(ar.CompletedSynchronously);

                    lock (storageAsyncResult.CancellationLockerObject)
                    {
                        storageAsyncResult.CancelDelegate = null;
                        try
                        {
                            CloudBlobStream blobStream = this.EndOpenWrite(ar);
                            storageAsyncResult.OperationState = blobStream;

                            source.WriteToAsync(
                                blobStream,
                                length,
                                null /* maxLength */,
                                false,
                                tempExecutionState,
                                null /* streamCopyState */,
                                completedState =>
                                {
                                    storageAsyncResult.UpdateCompletedSynchronously(completedState.CompletedSynchronously);
                                    if (completedState.ExceptionRef != null)
                                    {
                                        storageAsyncResult.OnComplete(completedState.ExceptionRef);
                                    }
                                    else
                                    {
                                        try
                                        {
                                            lock (storageAsyncResult.CancellationLockerObject)
                                            {
                                                storageAsyncResult.CancelDelegate = null;
                                                ICancellableAsyncResult commitResult = blobStream.BeginCommit(
                                                        CloudBlob.BlobOutputStreamCommitCallback,
                                                        storageAsyncResult);

                                                storageAsyncResult.CancelDelegate = commitResult.Cancel;
                                                if (storageAsyncResult.CancelRequested)
                                                {
                                                    storageAsyncResult.Cancel();
                                                }
                                            }
                                        }
                                        catch (Exception e)
                                        {
                                            storageAsyncResult.OnComplete(e);
                                        }
                                    }
                                });

                            storageAsyncResult.CancelDelegate = tempExecutionState.Cancel;
                            if (storageAsyncResult.CancelRequested)
                            {
                                storageAsyncResult.Cancel();
                            }
                        }
                        catch (Exception e)
                        {
                            storageAsyncResult.OnComplete(e);
                        }
                    }
                },
                null /* state */);

            // We do not need to do this inside a lock, as storageAsyncResult is
//.........这里部分代码省略.........

        public ICancellableAsyncResult BeginListBlobsSegmented(string prefix, bool useFlatBlobListing, BlobListingDetails blobListingDetails, int? maxResults, BlobContinuationToken currentToken, BlobRequestOptions options, OperationContext operationContext, AsyncCallback callback, object state)
        {
            string containerName;
            string listingPrefix;
            CloudBlobClient.ParseUserPrefix(prefix, out containerName, out listingPrefix);

            CloudBlobContainer container = this.GetContainerReference(containerName);
            StorageAsyncResult<BlobResultSegment> result = new StorageAsyncResult<BlobResultSegment>(callback, state);
            ICancellableAsyncResult asyncResult = container.BeginListBlobsSegmented(
                listingPrefix,
                useFlatBlobListing,
                blobListingDetails,
                maxResults,
                currentToken,
                options,
                operationContext,
                ar =>
                {
                    result.UpdateCompletedSynchronously(ar.CompletedSynchronously);

                    try
                    {
                        result.Result = container.EndListBlobsSegmented(ar);
                        result.OnComplete();
                    }
                    catch (Exception e)
                    {
                        result.OnComplete(e);
                    }
                },
                null /* state */);

            result.CancelDelegate = asyncResult.Cancel;
            return result;
        }

        /// <summary>
        /// Dispatches a write operation.
        /// </summary>
        /// <param name="asyncResult">The reference to the pending asynchronous request to finish.</param>
        private void DispatchWrite(StorageAsyncResult<NullType> asyncResult)
        {
            if (this.internalBuffer.Length == 0)
            {
                if (asyncResult != null)
                {
                    asyncResult.OnComplete(this.lastException);
                }

                return;
            }

            MultiBufferMemoryStream bufferToUpload = this.internalBuffer;
            this.internalBuffer = new MultiBufferMemoryStream(this.Blob.ServiceClient.BufferManager);
            bufferToUpload.Seek(0, SeekOrigin.Begin);

            string bufferMD5 = null;
            if (this.blockMD5 != null)
            {
                bufferMD5 = this.blockMD5.ComputeHash();
                this.blockMD5.Dispose();
                this.blockMD5 = new MD5Wrapper();
            }

            if (this.blockBlob != null)
            {
                string blockId = this.GetCurrentBlockId();
                this.blockList.Add(blockId);
                this.WriteBlock(bufferToUpload, blockId, bufferMD5, asyncResult);
            }
            else
            {
                if ((bufferToUpload.Length % Constants.PageSize) != 0)
                {
                    this.lastException = new IOException(SR.InvalidPageSize);
                    throw this.lastException;
                }

                long offset = this.currentPageOffset;
                this.currentPageOffset += bufferToUpload.Length;
                this.WritePages(bufferToUpload, offset, bufferMD5, asyncResult);
            }
        }

 public override ICancellableAsyncResult BeginCommit(AsyncCallback callback, object state)
 {
     StorageAsyncResult<NullType> storageAsyncResult = new StorageAsyncResult<NullType>(callback, state);
     ICancellableAsyncResult result = this.BeginFlush(this.CommitFlushCallback, storageAsyncResult);
     storageAsyncResult.CancelDelegate = result.Cancel;
     return storageAsyncResult;
 }

        private void CreateIfNotExistsHandler(BlobContainerPublicAccessType accessType, BlobRequestOptions options, OperationContext operationContext, StorageAsyncResult<bool> storageAsyncResult)
        {
            ICancellableAsyncResult savedExistsResult = this.BeginExists(
                true,
                options,
                operationContext,
                existsResult =>
                {
                    storageAsyncResult.UpdateCompletedSynchronously(existsResult.CompletedSynchronously);
                    lock (storageAsyncResult.CancellationLockerObject)
                    {
                        storageAsyncResult.CancelDelegate = null;
                        try
                        {
                            bool exists = this.EndExists(existsResult);
                            if (exists)
                            {
                                storageAsyncResult.Result = false;
                                storageAsyncResult.OnComplete();
                                return;
                            }

                            ICancellableAsyncResult savedCreateResult = this.BeginCreate(
                                accessType,
                                options,
                                operationContext,
                                createResult =>
                                {
                                    storageAsyncResult.UpdateCompletedSynchronously(createResult.CompletedSynchronously);
                                    storageAsyncResult.CancelDelegate = null;
                                    try
                                    {
                                        this.EndCreate(createResult);
                                        storageAsyncResult.Result = true;
                                        storageAsyncResult.OnComplete();
                                    }
                                    catch (StorageException e)
                                    {
                                        if (e.RequestInformation.HttpStatusCode == (int)HttpStatusCode.Conflict)
                                        {
                                            if ((e.RequestInformation.ExtendedErrorInformation == null) ||
                                                (e.RequestInformation.ExtendedErrorInformation.ErrorCode == BlobErrorCodeStrings.ContainerAlreadyExists))
                                            {
                                                storageAsyncResult.Result = false;
                                                storageAsyncResult.OnComplete();
                                            }
                                            else
                                            {
                                                storageAsyncResult.OnComplete(e);
                                            }
                                        }
                                        else
                                        {
                                            storageAsyncResult.OnComplete(e);
                                        }
                                    }
                                    catch (Exception e)
                                    {
                                        storageAsyncResult.OnComplete(e);
                                    }
                                },
                                null /* state */);

                            storageAsyncResult.CancelDelegate = savedCreateResult.Cancel;
                            if (storageAsyncResult.CancelRequested)
                            {
                                storageAsyncResult.Cancel();
                            }
                        }
                        catch (Exception e)
                        {
                            storageAsyncResult.OnComplete(e);
                        }
                    }
                },
                null /* state */);

            // We do not need to do this inside a lock, as storageAsyncResult is
            // not returned to the user yet.
            storageAsyncResult.CancelDelegate = savedExistsResult.Cancel;
        }

        public ICancellableAsyncResult BeginCreateIfNotExists(BlobContainerPublicAccessType accessType, BlobRequestOptions options, OperationContext operationContext, AsyncCallback callback, object state)
        {
            BlobRequestOptions modifiedOptions = BlobRequestOptions.ApplyDefaults(options, BlobType.Unspecified, this.ServiceClient);
            operationContext = operationContext ?? new OperationContext();

            StorageAsyncResult<bool> storageAsyncResult = new StorageAsyncResult<bool>(callback, state)
            {
                RequestOptions = modifiedOptions,
                OperationContext = operationContext,
            };

            this.CreateIfNotExistsHandler(accessType, modifiedOptions, operationContext, storageAsyncResult);
            return storageAsyncResult;
        }

        public virtual ICancellableAsyncResult BeginOpenWrite(bool createNew, AccessCondition accessCondition, BlobRequestOptions options, OperationContext operationContext, AsyncCallback callback, object state)
        {
            this.attributes.AssertNoSnapshot();
            BlobRequestOptions modifiedOptions = BlobRequestOptions.ApplyDefaults(options, this.BlobType, this.ServiceClient, false);

            StorageAsyncResult<CloudBlobStream> storageAsyncResult = new StorageAsyncResult<CloudBlobStream>(callback, state);
            ICancellableAsyncResult result;

#if !(WINDOWS_RT || ASPNET_K || PORTABLE)
            ICryptoTransform transform = null;
#endif

            if (createNew)
            {
#if !(WINDOWS_RT || ASPNET_K || PORTABLE)
                if (options != null && options.EncryptionPolicy != null)
                {
                    transform = options.EncryptionPolicy.CreateAndSetEncryptionContext(this.Metadata, false /* noPadding */);
                }
#endif
                result = this.BeginCreateOrReplace(
                    accessCondition,
                    options,
                    operationContext,
                    ar =>
                    {
                        storageAsyncResult.UpdateCompletedSynchronously(ar.CompletedSynchronously);

                        try
                        {
                            this.EndCreateOrReplace(ar);

                            if (accessCondition != null)
                            {
                                accessCondition = new AccessCondition() { LeaseId = accessCondition.LeaseId, IfAppendPositionEqual = accessCondition.IfAppendPositionEqual, IfMaxSizeLessThanOrEqual = accessCondition.IfMaxSizeLessThanOrEqual };
                            }

#if !(WINDOWS_RT || ASPNET_K || PORTABLE)
                            if (modifiedOptions.EncryptionPolicy != null)
                            {
                                storageAsyncResult.Result = new BlobEncryptedWriteStream(this, accessCondition, modifiedOptions, operationContext, transform);
                            }
                            else
#endif
                            {
                                storageAsyncResult.Result = new BlobWriteStream(this, accessCondition, modifiedOptions, operationContext);
                            }

                            storageAsyncResult.OnComplete();
                        }
                        catch (Exception e)
                        {
                            storageAsyncResult.OnComplete(e);
                        }
                    },
                    null /* state */);
            }
            else
            {
                if (modifiedOptions.StoreBlobContentMD5.Value)
                {
                    throw new ArgumentException(SR.MD5NotPossible);
                }

#if !(WINDOWS_RT || ASPNET_K || PORTABLE)
                if (modifiedOptions.EncryptionPolicy != null)
                {
                    throw new ArgumentException(SR.EncryptionNotSupportedForExistingBlobs);
                }
#endif
                // Although we don't need any properties from the service, we should make this call in order to honor the user specified conditional headers
                // while opening an existing stream and to get the append position for an existing blob if user didn't specify one.
                result = this.BeginFetchAttributes(
                    accessCondition,
                    options,
                    operationContext,
                    ar =>
                    {
                        storageAsyncResult.UpdateCompletedSynchronously(ar.CompletedSynchronously);

                        try
                        {
                            this.EndFetchAttributes(ar);

                            if (accessCondition != null)
                            {
                                accessCondition = new AccessCondition() { LeaseId = accessCondition.LeaseId, IfAppendPositionEqual = accessCondition.IfAppendPositionEqual };
                            }

                            storageAsyncResult.Result = new BlobWriteStream(this, accessCondition, modifiedOptions, operationContext);
                            storageAsyncResult.OnComplete();
                        }
                        catch (Exception e)
                        {
                            storageAsyncResult.OnComplete(e);
                        }
                    },
                    null /* state */);
            }

//.........这里部分代码省略.........

        /// <summary>
        /// Begins an asynchronous read operation.
        /// </summary>
        /// <param name="buffer">The buffer to read the data into.</param>
        /// <param name="offset">The byte offset in buffer at which to begin writing
        /// data read from the stream.</param>
        /// <param name="count">The maximum number of bytes to read.</param>
        /// <param name="callback">An optional asynchronous callback, to be called when the read is complete.</param>
        /// <param name="state">A user-provided object that distinguishes this particular asynchronous read request from other requests.</param>
        /// <returns>An <c>IAsyncResult</c> that represents the asynchronous read, which could still be pending.</returns>
        public override IAsyncResult BeginRead(byte[] buffer, int offset, int count, AsyncCallback callback, object state)
        {
            CommonUtility.AssertNotNull("buffer", buffer);
            CommonUtility.AssertInBounds("offset", offset, 0, buffer.Length);
            CommonUtility.AssertInBounds("count", count, 0, buffer.Length - offset);

            if (this.readPending)
            {
                throw new InvalidOperationException(SR.BlobStreamReadPending);
            }

            try
            {
                this.readPending = true;
                StorageAsyncResult<int> storageAsyncResult = new StorageAsyncResult<int>(callback, state);

                if (this.lastException != null)
                {
                    storageAsyncResult.OnComplete(this.lastException);
                    return storageAsyncResult;
                }

                if ((this.currentOffset == this.Length) || (count == 0))
                {
                    storageAsyncResult.Result = 0;
                    storageAsyncResult.OnComplete();
                    return storageAsyncResult;
                }

                int readCount = this.ConsumeBuffer(buffer, offset, count);
                if (readCount > 0)
                {
                    storageAsyncResult.Result = readCount;
                    storageAsyncResult.OnComplete();
                    return storageAsyncResult;
                }

                this.DispatchReadAsync(storageAsyncResult, buffer, offset, count);
                return storageAsyncResult;
            }
            catch (Exception)
            {
                this.readPending = false;
                throw;
            }
        }

        internal ICancellableAsyncResult BeginUploadFromStreamHelper(Stream source, long? length, AccessCondition accessCondition, BlobRequestOptions options, OperationContext operationContext, AsyncCallback callback, object state)
        {
            CommonUtility.AssertNotNull("source", source);

            if (length.HasValue)
            {
                CommonUtility.AssertInBounds("length", length.Value, 1);

                if (source.CanSeek && length > source.Length - source.Position)
                {
                    throw new ArgumentOutOfRangeException("length", SR.StreamLengthShortError);
                }
            }

            this.attributes.AssertNoSnapshot();
            BlobRequestOptions modifiedOptions = BlobRequestOptions.ApplyDefaults(options, BlobType.BlockBlob, this.ServiceClient);

            ExecutionState<NullType> tempExecutionState = CommonUtility.CreateTemporaryExecutionState(modifiedOptions);
            StorageAsyncResult<NullType> storageAsyncResult = new StorageAsyncResult<NullType>(callback, state);

            bool lessThanSingleBlobThreshold = CloudBlockBlob.IsLessThanSingleBlobThreshold(source, length, modifiedOptions, false);
            modifiedOptions.AssertPolicyIfRequired();
            
            if (modifiedOptions.ParallelOperationThreadCount.Value == 1 && lessThanSingleBlobThreshold)
            {
                // Because we may or may not want to calculate the MD5, and we may or may not want to encrypt, rather than have four branching code
                // paths, here we have an action that we will run, which continually gets added to, depending on which operations we need to do.
                // The confusing part is that we have to build it from the bottom up.

                string md5 = null;
                Stream sourceStream = source;
                Action actionToRun = null;

                Action uploadAction = () =>
                    {
                        if (md5 == null && modifiedOptions.UseTransactionalMD5.Value)
                        {
                            throw new ArgumentException(SR.PutBlobNeedsStoreBlobContentMD5, "options");
                        }

                        this.UploadFromStreamHandler(
                                            sourceStream,
                                            length,
                                            md5,
                                            accessCondition,
                                            operationContext,
                                            modifiedOptions,
                                            storageAsyncResult);

                    };
                actionToRun = uploadAction;

                if (modifiedOptions.StoreBlobContentMD5.Value)
                {
                    Action<Action> calculateMD5 = (continuation) =>
                    {
                        long startPosition = sourceStream.Position;
                        StreamDescriptor streamCopyState = new StreamDescriptor();
                        sourceStream.WriteToAsync(
                            Stream.Null,
                            length,
                            null /* maxLength */,
                            true,
                            tempExecutionState,
                            streamCopyState,
                            completedState =>
                            {
                                ContinueAsyncOperation(storageAsyncResult, completedState, () =>
                                    {
                                        if (completedState.ExceptionRef != null)
                                        {
                                            storageAsyncResult.OnComplete(completedState.ExceptionRef);
                                        }
                                        else
                                        {
                                            sourceStream.Position = startPosition;
                                            md5 = streamCopyState.Md5;
                                            continuation();
                                        }
                                    });
                            });

                        storageAsyncResult.CancelDelegate = tempExecutionState.Cancel;
                        if (storageAsyncResult.CancelRequested)
                        {
                            storageAsyncResult.Cancel();
                        }
                    };
                    Action oldActionToRun = actionToRun;
                    actionToRun = () => calculateMD5(oldActionToRun);
                }

                if (modifiedOptions.EncryptionPolicy != null)
                {
                    Action<Action> encryptStream = continuation =>
                        {
                            SyncMemoryStream syncMemoryStream = new SyncMemoryStream();
                            options.AssertPolicyIfRequired();

                            sourceStream = syncMemoryStream;
//.........这里部分代码省略.........

        public ICancellableAsyncResult BeginOpenWrite(long? size, AccessCondition accessCondition, BlobRequestOptions options, OperationContext operationContext, AsyncCallback callback, object state)
        {
            this.attributes.AssertNoSnapshot();
            bool createNew = size.HasValue;
            BlobRequestOptions modifiedOptions = BlobRequestOptions.ApplyDefaults(op