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Lectures
Lecture 09 Template
09 - Processes (2)
Outline
Process Creation
Process State
Process State Transitions
Announcements
Reading: MOS 2.1
Process Creation
System initialization (init)
UNIX
UNIX fork
UNIX exec
Windows CreateProcess
PollEv
PollEv
From existing process (syscall)
Windows
1
1 2 3 5 1 3 2 3 4
2 3 1 2 3 5 1 3 4
1 2 2 3 5 3 1 4 3
all of them
2
3
4
Program logic
User interaction
Duplicate the current process (fork)
Duplicate current process with
returns in both processes (twice):
Both processes continue executing from after the
fork syscall instruction.
Each has a different PID number.
Creating a clone:
Different behaviors:
Parent and children processes form a process tree
If process exits before its children, children
are adopted by a system process like init
Different PIDs
parent: fork returns child's PID
including global variables
PC, SP, registers all separate
child: fork returns 0
Separate copies of address space/memory
Separate CPU execution context
wipes the current address space and loads
the new program
Executing in CPU
child begins execution from the new program's
main function (or entry point)
shared program text (read-only)
shared memory with copy-on-write
Ready to execute, waiting for CPU
Waiting for event (I/O)
Parent process:
Child process returns with 0
Parent process returns with child's PID
calls
created by
Child process:
Scheduled batch job (mainframe)
Load another program (exec)
Create a new process and immediately
load target program (CreateProcess)
When are processes created?
How are processes created?
2 main approaches:
Process State
Late penalties will be applied on canvas.
PollEverywhere today: pollev.com/rtsang1
1)
1)
1)
2)
2)
A)
A)
B)
C)
D)
B)
C)
D)
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
Running
blocked -> running:
ready -> blocked:
no event + unfair
not running, can't syscall
-
-
-
Ready
Blocked/
Waiting
-
2)
fork()
fork()
fork()
fork()
parent
output:
pid 100: hello
pid 100: world
pid 101: world
output:
child
Linux:
Windows:
Parent and Child have:
Loads another program in current process
Represents what a process is currently doing.
3 basic states (OS-dependent)
There are caveats about how system resources
behave when forked in some UNIX versions:
Consider the following program:
What does this program do?
CreateProcess runs new program from the start.
How many processes will executing this program
create?
Which of the following is a possible output of this
program?
or
Process Explorer
Example output (partial):
ps -elf --forest
pslist.exe -t
PID PPID CMD
1 0 /sbin/init
1516 1 \_ /usr/lib/systemd/systemd --user
2503 1516 \_ /usr/libexec/gnome-terminal-server
2528 2503 \_ bash
2533 2528 \_ ps -elf --forest
root
[kthreadd]
init
systemd
logind
networkd
parent
context
parent
parent resumes
child
context
child
context
memory
memory
memory
registers
registers
registers
demo2
demo2
xcalc
fork
exec
pid = fork()
exec()
exit()
wait()
Running
Blocked
Ready
child
(pid == 0)
parent
(pid > 0)
0
1
2
infinite
A)
B)
C)
D)
How many processes in the running state can there
be simultaneously on a single-CPU system?
Missing transitions:
Many processes live in blocked, waiting for input.
waiting
for event
switched by
scheduler
event
occurs
selected by
scheduler
based on MOS Figure 2-2