Threading Issues (time)

• Understand these thread-related issues:

  • Event-based UI models as pseudo-threading
  • Interrupts vs threading
  • Events/interrupts vs polling
  • Non-repeatability of behaviour (correct and buggy)

• Things to watch:

  • Don't overdo threading: overhead will kill you
  • Chose appropriate lock granularity
  • Make sure you are right in theory and practice!

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EXAMPLE: Browsers used multiple TCP/IP connections to overcome 3xRTT (approx) setup latency; directory scanning algorithms can run many times faster even within one partition allowing better queueing of disk activity in OS.

Lock granularity: bigger locks and around code rather than data tend to easier to program and less error-prone but may reduce concurrency; finer-grained data-based locks may proved better if so. You usage patterns will determine this.

CHECKLIST:

• What is/are your main reason(s) for threading?

• Can you test results of your tinkering on your target system?

• Do you have multiple targets to optimise for some combination of?

Interrupts can be very expensive, eg for high-speed serial I/O; Sun uses combination of interrupts and polling for serial I/O. Strange effects on serial-connected clocks and NTP timekeeping, eg DHD Arcron code.

Interrupt code may be a special flavour of thread on some systems.