Asynchronous I/O - Notification Types Summary

Event-Based Notification
Pros
- Only method that allows threads to wait until the operation completes
Cons
- Not useful in most other cases
- Potentially high latency on POSIX

Asynchronous Procedure Calls
Pros
- Calls only occur in the thread that requests the I/O
- Calls can be deferred until the thread is ready for them
- Most convenient method for single-threaded programs
Cons
- Must be polled for in the thread that requested the I/O
- Potentially high latency on POSIX

I/O Completion Ports
Pros
- Potentially fastest (highest throughput), most scalable method on multi-CPU systems, due to optimized thread pooling architecture
Cons
- Cumbersome to use, as often requires construction of a finite state machine
- Not particularly suitable for single-threaded programs
- Potentially high latency on POSIX

Unpredictable Callbacks
Pros
- Lowest latency method on POSIX
- Potentially fast on multi-CPU systems, if the OS does CPU load balancing of callbacks
Cons
- Calls may occur in any thread at any time
- Must be polled for in the thread that requested the I/O