plumpmath / pyos-coroutine

Python OS using Coroutines

Challenges

• Build a multitasking "operating system"
• Use nothing but pure python code
• No threads
• No subprocesses
• Use generators / coroutines

Motivations

• There has been a lot of recent interest in alternatives to threads (especially due to the GIL)
• Non-blocking and asynchronous I/O
• Example: servers capable of supporting thousands of simultaneous client connections
• A lot of work has focused on event-driven systems or the "Reactor Model" (e.g., Twisted)
• Coroutines are a whole different twist...

Step 1: Define Tasks

• pyos1.py

Step 2: The Scheduler

• pyos2.py

Step 3: Task Exit

• taskcrash.py
• pyos3.py

Step 4: System Calls

• pyos4.py

Step 5: Task Management

• pyos5.py
• pyos6.py (Task Waiting)

Interlude: An Echo Server Attempt

• echobad.py
• block IO is undesirable

I/O Waiting

• pyos7.py (Polling Task, Read/Write Syscalls)

Echo Server Example

• echogood.py

Trampolining

• When working with coroutines, you can't write subroutine functions that yield. (suspend)

• The yield statement can only be used to suspend a coroutine at the top-most level.

• There is a solution

  • it can only be done with the assistance of the task scheduler itself.
  • You have to strictly stick to yield statements
  • Involves a trick known as "trampolining"

• trampoline.py

• pyos8.py

• echoserver.py

• sockwrap.py

• echoserver2.py

Future topics

• Intertask communication
• Handling of blocking operations (e.g., accessing database)
• Coroutine multitasking and threads
• Error handling