Lecture 10: Processes II-A Process States Process vs. Thread Background/Foreground

Process States We’ve mentioned these before: –Running –Idle/Sleeping –Waiting for I/O –Zombie Now a new one: –Swapped Out

“Swapped Out” State We only have so much CPU power –Can’t run everything at the same time The processes must share How do we decide who gets processor time? –Does this question sound familiar?

“Swapped Out” State We only have so much CPU power –Can’t run everything at the same time The processes must share How do we decide who gets processor time? –Does this question sound familiar? –Similar to memory management!

Process Priority Linux –“Niceness” level –-20 (greedy) to +20 (charitable) Windows –IDLE_PRIORITY_CLASS –BELOW_NORMAL_PRIORITY_CLASS –NORMAL_PRIORITY_CLASS –ABOVE_NORMAL_PRIORITY_CLASS –HIGH_PRIORITY_CLASS –REALTIME_PRIORITY_CLASS

Process Priority Setting high priorities can be bad Why?

Process Priority Setting high priorities can be bad Why? –Other processes get neglected –Those other processes may be system processes –Neglected system processes can degrade performance of your process

Process Management On modern computers, we want to run tasks “simultaneously”… –…by interweaving Single CPU Appears simultaneous to us –…in parallel Multiple CPUs Truly simultaneous! For upcoming slides, we’re interweaving

Process Created out of a program Communicates with peers via interprocess communication –Low level: pipes, shared memory, etc –High level: MPI, ZeroMQ, etc Lasts for “length of program”

Thread Created out of ________ Communicates with peers –? Lasts for _________

Thread Created out of a process Communicates with peers –? Lasts for _________

Thread Created out of a process Communicates with peers –Shared memory space* Lasts for ________ * Not generally referred to as “shared memory”

Thread Created out of a process Communicates with peers –Shared memory space* Lasts for length of code segment * Not generally referred to as “shared memory”

Process Management We want to run multiple processes simultaneously –Let’s restrict ourselves to single terminal So far, we can… –…suspend a process –…resume a process What else can I do? –Change background/foreground

Background/Foreground A terminal can run many jobs* –“Infinite” in the background –One in the foreground By default, the job launches in the foreground How do we get stuff in the background? * A “job” is a command we ran

Background/Foreground At process launch –Use the ampersand –find / -name “*.txt &” While process is running –ctrl+z to suspend –bg %n n is the job number Use jobs command to discover job #s bg executes/resumes job… –…but in background

Background/Foreground BG jobs –What happens to stdout/stderr? –What happens to stdin?

Background/Foreground BG jobs –What happens to stdout/stderr? Still goes to specified place Output can get mixed with BGs and FG –What happens to stdin?

Background/Foreground BG jobs –What happens to stdout/stderr? Still goes to specified place Output can get mixed with BGs and FG –What happens to stdin? It doesn’t have access to it –How do we return stdin access to job?

Background/Foreground BG jobs –What happens to stdout/stderr? Still goes to specified place Output can get mixed with BGs and FG –What happens to stdin? It doesn’t have access to it –How do we return stdin access to job? Return it to foreground fg %n