Transcript ppt

CS533 Concepts of Operating Systems
Class 3
Monitors
Questions
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Which concurrent programming problems do
monitors address?
Are monitors useful as a programming convention,
i.e., without compiler support?
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What is the convention?
With compiler support for monitors, what are the
important tasks of the compiler?
Why does encapsulation help with synchronization?
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Questions
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Do monitors solve the deadlock problem?
How might the queuing discipline for waiting
processes avoid starvation?
Why do we need condition variables instead of a
single waiting queue per monitor?
Does a condition variable have a value (such as
true/false)?
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Questions
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What are the implications of allowing monitor calls
to make calls to different monitors?
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Should the monitor lock be released before such a call?
Which kinds of monitor procedures do not need to
acquire/release the monitor lock, and why?
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Questions
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How does non-preemptive scheduling solve
concurrency problems?
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What problem does it have on multiprocessors?
What problem does I/O present?
Why are page faults a problem for this approach?
How can mutual exclusion in a monitor be enforced?
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… on uniprocessors and multiprocessors?
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Questions
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Mesa operates in an environment that doesn’t use
hardware protection
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How does this affect the cost of monitor operations?
How is processes creation in Mesa similar to thread
creation in Pthreads?
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Why join?
Why detatch?
Why might you still use p after calling Detach[p]?
What dangling reference problems can arise with process
pointers?
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Questions
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How is handling exceptions in root procedures of
Mesa processes more complicated than in normal
Mesa procedures?
What issues arise when an exception is generated
within a monitor procedure?
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What does UNWIND do in Mesa?
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Questions
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What is the difference between Hoare’s semantics
for wait/signal and Mesa’s wait/notify?
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What invariants can be assumed in each case?
What implications does this have for code surrounding a
wait call?
What is the advantage of Hoare’s semantics for
wait/signal vs Mesa’s wait/notify?
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Why do Hoare semantics require more context switches?
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Questions
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What are the advantages of Mesa’s wait/notify
semantics?
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In what way does it enable the use of timeouts?
In what way does it encourage the use of broadcast?
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Questions
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How might you use monitors for I/O
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Can interrupts be treated as signals?
What if no process was waiting?
How can devices make monitor calls?
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If a device can’t wait on the monitor lock, how can it update
monitor state?
What is a naked notify, and who is waiting on it?
Why is a wakeup-waiting switch needed with naked notifies?
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Questions
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Why implement process creation as a monitor?
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How is fork implemented?
How are join and end implemented?
Why is fork/join so expensive compared to other
operations?
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Reminder
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Please mail me your slides to put on the web page
The next paper is work in progress, presented by me
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