g memory Serializability a group of operations transaction which may be interleaved with operations of another group transaction each operating on a shared resource eg a database Linearizability Herlihy Wing a group of operations transaction not inte ID: 53835
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CS 5204 Operating Systems Concurrent Processing How can concurrent processing activity be structured on a single processor?How can application-level information and system-level information be combined to provide efficient scheduling of processing activities? CS 5204 Operating Systems Support for concurrent and parallel programmingconform to application semanticsrespect priorities of applicationsno unnecessary blockingfast context switchhigh processor utilization concurrent relative importance CS 5204 Operating Systems Lightweight(User-level) Threads . . .kernel fast context switch time (within an order of magnitude ofprocedure call time)system scheduler unaware of user thread priorities CS 5204 Operating Systems Application has knowledge of the userknowledge of or influence over critiKernel has inadequate knowledge of optimal scheduling decisions A general system design problem: communicating information and control across layer boundaries while abstraction, and virtualization. CS 5204 Operating Systems Communication via UpcallsThe kernel-level scheduler activation mechanism communicates with the user-level thread library by a set of upcalls: Add this processor (processor #)Processor has been preempted (preempted activation #, machine state)Scheduler activation has unblocked (unblocked activation #, machine state)The thread library must maintain the association between a threads identity and threads scheduler activation number. CS 5204 Operating Systems Avoiding Effects of Blocking user 3: new Kernel threads Scheduler Activations 1: system call2: block124: upcall 5: start CS 5204 Operating Systems FastThreadsonTopaz ThreadsFastThreadsonTopaz ThreadsUltrix process Signal-Wait