processes
OUTLINE
Process Concept
Process Scheduling
Operations on Processes
Inter-process Communication
Examples of IPC Systems
Communication in Client-Server Systems
Process creation
Aprocess may create several processes during the execution.
Creating process is called a parent and a created process is called a
child.
Parent process create children process, which, in turn create other
processes, forming a tree of processes
Generally, process identified and managed via a process identifier (pid)
11.
Process creation: fork()
Creates a child process.
Child process contains exact copy of the memory space of the parent
process.
Child process contains the same text/code section but executes
independently
12.
Exec()
Exec isa collection of function e.g., execlp(), ececve(), execl(), are use to
execute any program/script.
Typically exec used after a fork() by child process to replace the memory
space with a new program.
PID does not change but the data, heap, and stack of the child are
replace by new program
13.
Process creation (cont..)
Fork( ) system call creates new process
Exec( ) system call used after fork to replace the process memory space
with a new program.
14.
Process Termination
Processexecutes last statement and asks the operating system to delete it
(exit)
Process resources are deallocated by operating system
Parent may terminate execution of children processes (abort).
Task assigned to child is no longer required
If parent is exiting
o Some operating system do not allow to continue if its parent
terminates
o All children terminated – cascading termination.
16
Execution Trace: fork()with execlp()
RAM
CPU
Kernel
stack
data
text
….
n=fork();
If (n == 0)
…exec()
else if (n>0)
...
PC
PCB-Parent
Process-Parent
x pid
PC
n
sys_fork()
{….}
PC
y pid
PCB-Child
text
Process-Child
n
stack
data
….
n=fork();
If (n == 0)
…exec()
else if (n>0)
...
y 0
sys_execve()
{….}
new code
