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Two parts execute a fixed of p instrs driver do normal

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Unformatted text preview: to given device class P : privileged instruction (exception if mode not supervisor) Project Project #1 I instruction: yes, it is kludgey…. Two parts: “execute” a fixed # of P instrs ( ~ driver) do normal kernel bookkeeping Project Project #1 RR scheduling (fixed Q, ignore priorities) Lottery scheduling (priority ~ tickets) Don’t have to implement currencies , ticket exchange, inflation, inflation, unless you want to Project Project #1 Top: a separate Unix process that probes your OS tables to print system system state decide how top will get information from the kernel. Project Project #1: Suggestions Modular design C/C++ Synchronous, then asynchronous Make Make sure one of your team has strong C/C++ skills and Unix system programming esp. signals/timers, IPC Deadlock Deadlock vs. Starvation Starvation – there is a situation (maybe pathological) that an entity will have to wait for a resource for a long time, BUT eventually they get it Examples? Deadlock is different Deadlock Deadlock Deadlock is closely related to starvation. • Processes wait forever for each other to wake up and/or release resources. • Example: dinning philosophers . The difference between deadlock and starvation is subtle. • With starvation, there always exists a schedule that feeds the starving starving party. The situation may resolve itself…if you’re lucky. • Once deadlock occurs, it cannot be resolved by any possible future schedule. …though there may exist schedules that avoid deadlock. Dining Dining Philosophers • N processes share N resources • resource requests occur in pairs • random think times • hungry philosopher grabs a fork • ...and doesn’t let go • ...until the other fork is free • ...and the linguine is eaten will deadlock always occur? 4 A B D 3 1 C 2 while(true) { Think(); AcquireForks(); Eat(); ReleaseForks(); } Four Four Preconditions for Deadlock Four conditions must be present for deadlock to occur: 1. Non-preemptability. Resource ownership (e.g., by threads) is non-preemptable. Resources are never taken away from the holder. 2. 2. Exclusion. Some thread cannot acqu...
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