Process Description and Control

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.

Parallel Execution of processes Resource sharing Speed up Modular design of programs

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

Process State Diagram new terminated blocked running ready Scheduler chooses Time exceeded Needs to to I/O I/O done

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}

Process termination When executing last instruction or killed by someone else Clean up Release resources held by the process Accounting info to be updated

Process switch When to switch? –Clock interrupt –I/O interrupt –memory fault