/// <summary>
/// <see cref="IDevice.ReadAsync(int, ulong, IntPtr, uint, IOCompletionCallback, IAsyncResult)">Inherited</see>
/// </summary>
public override unsafe void ReadAsync(int segmentId, ulong sourceAddress, IntPtr destinationAddress, uint readLength, IOCompletionCallback callback, IAsyncResult asyncResult)
{
// It is up to the allocator to make sure no reads are issued to segments before they are written
if (!blobs.TryGetValue(segmentId, out BlobEntry blobEntry))
{
throw new InvalidOperationException("Attempting to read non-existent segments");
}
// Even though Azure Page Blob does not make use of Overlapped, we populate one to conform to the callback API
Overlapped ov = new Overlapped(0, 0, IntPtr.Zero, asyncResult);
NativeOverlapped *ovNative = ov.UnsafePack(callback, IntPtr.Zero);
UnmanagedMemoryStream stream = new UnmanagedMemoryStream((byte *)destinationAddress, readLength, readLength, FileAccess.Write);
CloudPageBlob pageBlob = blobEntry.GetPageBlob();
pageBlob.BeginDownloadRangeToStream(stream, (Int64)sourceAddress, readLength, ar => {
try
{
pageBlob.EndDownloadRangeToStream(ar);
}
// I don't think I can be more specific in catch here because no documentation on exception behavior is provided
catch (Exception e)
{
Trace.TraceError(e.Message);
// Is there any documentation on the meaning of error codes here? The handler suggests that any non-zero value is an error
// but does not distinguish between them.
callback(2, readLength, ovNative);
}
callback(0, readLength, ovNative);
}, asyncResult);
}