Download Processes

LINUX System : Lecture 7
Process
Bong-Soo Sohn
Lecture notes acknowledgement : The design of UNIX Operating System
Process Management
2
What is Process?
• Definition
–
–
–
–
–
an instance of a running program (runnable program)
an execution environment of a program
scheduling entity
a control flow and address space
PCB (Process Control Block) : proc. table and U area
• Manipulation of Process
– create, destroy
– context
– state transition
• dispatch (context switch)
• sleep, wakeup
• swap
Process State Transition
user
running
syscall,
interrupt
fork
initial
(idle)
return from
syscall or
interrupt
kernel
running
swtch
swtch
ready
to run
swap
suspended
ready
zombie
exit
wait
sleep, lock
wakeup, unlock
asleep
swap
suspended
asleep
(Source : UNIX Internals)
Context
• context :
system context, address (memory) context, H/W context
proc table
file table
memory
segment tablepage table
fd
Registers (TSS)
eip
sp
U area
eax
eflag
….
s
cs
….
swap
disk
Context : system context
• System context
– proc. Table
•
•
•
•
•
•
•
identification: pid, process group id, …
family relation
state
sleep channel: sleep queue
scheduling information : p_cpu, p_pri, p_nice, ..
signal handling information
address (memory) information
– U area (swappable information)
•
•
•
•
•
•
stores hardware context when the process is not running currently
UID, GID
arguments, return values, and error status for system call
signal catch function
file descriptor
usage statistics
Context : address context
• fork example
int
char
glob = 6;
buf[] = “a write to stdout\n”;
int main(void)
{
int var;
pid_t pid;
var = 88;
write(STDOUT_FILENO, buf, sizeof(buf)-1);
printf(“before fork\n”);
if ((pid = fork()) == 0) {
glob++; var++;
} else
sleep(2);
}
/* child */
/* parent */
printf(“pid = %d, glob = %d, var = %d\n”, getpid(), glob, var);
exit (0);
(Source : Adv. programming in the UNIX Env., pgm 8.1)
 guess what can we get from this program?
Context : address context
• fork internal : compile results
gcc
test.c
header
text
0xffffffff
0xbfffffff
kernel
stack
…
movl %eax, [glob]
addl %eax, 1
movl [glob], %eax
...
glob, buf
data
bss
var, pid
stack
0x0
data
text
a.out
user’s perspective (virtual address)
Executable and Linking Format
Context : address context
• fork internal : before fork (after run a.out)
memory
proc T.
segment T.
text
var, pid
pid = 11
stack
glob, buf
data
cf) we assume that there is no paging mechanism in this figure.
Context : address context
• fork internal : after fork
proc T.
segment T.
pid = 11
memory glob, buf
data
text
var, pid
stack
proc T.
segment T.
glob, buf
pid = 12
data
stack
– address space : basic protection barrier
var, pid
Context : address context
• fork internal : with COW (Copy on Write) mechanism
after fork with COW
proc T.
memory
segment T.
pid = 11
after “glob++” operation
proc T.
text
segment T.
pid = 11
text
stack
proc T.
segment T.
stack
proc T.
pid = 12
data
data
segment T.
pid = 12
data
Context : address context
• execve internal
memory
proc T.
pid = 11
segment T.
data
text
a.out
stack
text
data
stack
12
header
text
data
bss
stack
Context : hardware context
• time sharing (multitasking)
Where am I ??
time quantum
process 1
process 2
process 3
13
…
Context : hardware context
• brief reminds the 80x86 architecture
ALU
IN
Control Unit
OUT
Registers
eip, eflags
eax, ebx, ecx, edx, esi, edi, …
cs, ds, ss, es, ...
cr0, cr1, cr2, cr3, GDTR, TR, ...
14
Context : hardware context
• context swtch
save
context
Proc T.
TSS
eip
sp
eflags
eax
CPU
Proc T.
cs
U area
15
restore
context
TSS
eip
sp
eflags
eax
cs
U area
Context : hardware context
• context swtch : pseudo-code in UNIX
…
/* need context swtch */
if (save_context())
{
/* pick another process to run from ready queue */
….
restore_context(new process)
/* The control does not arrive here, NEVER !!! */
}
/* resuming process executes from here !!! */
…...
(Source : The Design of the
UNIX OS)
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