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Published byMelissa Shaw Modified over 9 years ago
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Process Description and Control
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Process A program in execution OS Reponsibilities: –Creation/Termination –Scheduling processes –Suspension/resumption –Synchronization, Interprocess communication –Deadlock handling Needs –CPU time, memory, files, I/O devices, etc.
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Parallel Execution of processes Resource sharing Speed up Modular design of programs
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Process Description PCB--Process Control Block (a record containing following info): –Process state-new/ready/running/blocked/halted –Program Counter –CPU register values –Scheduling information –Memory management info –Accounting info –I/O status, other info
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Process State Diagram new terminated blocked running ready Scheduler chooses Time exceeded Needs to to I/O I/O done
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Process Creation In Unix, fork() system call fork() creates an almost identical copy of the process Child and parent if (fork()==0) {child_code} else {parent_code}
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Process termination When executing last instruction or killed by someone else Clean up Release resources held by the process Accounting info to be updated
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Process switch When to switch? –Clock interrupt –I/O interrupt –memory fault
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