Cook Computing

Channel9 Video on Singularity

Last night I watched the second Channel9 video on Singularity. Some notes I made while watching:

• Dependability is the main goal - not performance.
• Managed code right down to the lowest level of the OS stack.
• Device drivers in managed code.
• 12 people working fulltime - about 20 other contributors.
• OS not JIT'ed - obvious bootstrap problem.
• 2% of files assembly code, 3% C++, 18% unsafe C#.
• 18% of files contain unsafe C# - but only parts of each file - better than mix of C# and C++ because no interop problems and easier to encapsulate unsafe code.
• Plans for verification of more unsafe code in future - for example array bounds checking.
• Apps must be 100% verified managed code.
• Status - kernel up and running - file system - network stack - web server (based on Cassini).
• Running modified SPECWeb tests - latency better than Windows - throughput worse due to poor performance of current filesystem.
• Processes are "closed" - cannot load code dynamically or do codegen - allows better program analysis - for example convert virtual calls into static calls.
• Processess communicate with other processes via "channels" - no shared memory so that process state is completely independent - if one process fails does not require other to be shut down.
• Channels are defined via contract - format of message and legal sequence of messages (state machine so buffers required for a channel can be determined at compile time).
• Implementation of channels is opaque to processes and once message has been sent the sending process loses ownership and cannot modify message (guaranteed by compiler).
• A channel is not a process - has own memory but not code.
• Why have threads in process and associated synchronization problems - support multiple async channels - also better code structure when using threads as opposed to event handling.
• Other threading mechanisms being explored - for example "transactional memory" - traditional transactional guarantees when accessing data structure in memory (atomic, rollbacks, etc).

Towards the end of the video they drew an outline of the Singularity architecture on a whiteboard. It looked something like this: The diagram is taken from An Overview of the Singularity Project. This document covers the topics in the video in much more detail and is well worth reading for a glimpse of the type of OS we might be using in the future.