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18 Cards in this Set
- Front
- Back
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Process |
Program in execution Program = recipe (instructions) for making a cake Process = activity of making the cake |
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Creating a process in UNIX |
2 system calls: fork() exec() |
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fork() |
creates a duplicate of the calling process and both processes execute the next instruction |
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exec() |
uses executable as parameter calling process is overwritten by the process created to run this executable |
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What happens when you type "a.out" in the shell? |
Shell does a fork() The duplicate created by fork() does an exec() with the file a.out as a parameter |
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Batching |
Performing the activities one after another |
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multi-programming/time-sharing |
Time-multiplex the CPU among the processes |
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How do we implement time-sharing? |
Preempting the CPU from the currently executing process Give the CPU to another process that can potentially use the CPU |
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Context-switching |
Re-assigning of the CPU from one process to another. Is transparent to an application, do not want applications to be aware |
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When should OS perform context switching? |
When an application process cannot proceed Periodically |
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Implementing context-switch |
Save the "context" of the current process Restore the "context" of another process |
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Context |
The state of the process that is necessary for its execution |
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Address space |
Code Segment + Data Segment + Stack Segment + Heap Segment |
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Process Control Block (PCB) |
Data structure into which context is saved and restored from |
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Advantages of a "process" view |
Implement concurrency Insulate one activity from another |
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Drawbacks of a "process" view |
Heavy weight - higher scheduling (context switch) costs - Direct costs of switching address spaces - Indirect costs (e.g. cache flushes) State sharing |
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What are the overheads of process view? |
Switching code, data, stack and heap Saving and restoring registers Saving and restoring other state maintained by OS |
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pthread_create() pthread_exit() pthread_join() pthread_self() |
create a thread terminate a thread wait for a thread to exit returns thread id |
