1. CGS 3763 Operating Systems Concepts Spring 2013
Dan C. Marinescu
Office: HEC 304
Office hours: M-Wd 11: :30 AM

2. Lecture 10 – Wednesday, January 30, 2013
Last time:
Answers to student questions
Interrupt processing
Kernel data structures for process management
Today:
Context switching
Kernel functions for process management
Creation and termination of processes
Inter-process communication
Shared memory
Message passing
Next time
Reading assignments
Chapters 3 and 4 of the textbook
Chapters 3 and 4 textbook slides
11/13/2018

3. Context switching
The storing and restoring the state (context) of a process so that execution can be resumed from the same point at a later time.
Enables multiple processes/threads to share a single CPU. 
11/13/2018

4. Process Control Block (PCB)

5. CPU Switch From Process to Process

6. Control data structure maintained by the kernel
To carry out its functions the kernel must maintain information about all objects in the system. For example:
Processes  Process Control Block (PCB)
Open files  File Control Block (FCB)
11/13/2018

7. Process Control Block (PCB)
The entry for a process contains the following information
Process state
Program counter
CPU registers
CPU scheduling information
Memory-management information
Accounting information
I/O status information

8. Process Control Block (PCB)

9. The state of a process
11/13/2018

10. Interrupt handlers are a component of the kernel
11/13/2018

11. 11/13/2018

12. 11/13/2018

13. Kernel functions for program execution
Process management
Scheduling and resource allocation
Interrupt handling
Error handling
11/13/2018

14. System calls for process control
Load
Execute
Create, terminate a process
Block a process, abort
Get process attributes/set process attributes
Allocate/deallocate memory for a process
11/13/2018

15. Process Scheduling Queues
Job queue – set of all processes in the system
Ready queue – set of all processes residing in main memory, ready and waiting to execute
Device queues – set of processes waiting for an I/O device
Processes migrate among the various queues

16. 11/13/2018

17. Process Creation
Parent process create children processes, which, in turn create other processes, forming a tree of processes
Generally, process identified and managed via a process identifier (pid)
Resource sharing
Parent and children share all resources
Children share subset of parent’s resources
Parent and child share no resources
Execution
Parent and children execute concurrently
Parent waits until children terminate

18. Process Creation (Cont’d)
Address space
Child duplicate of parent
Child has a program loaded into it
UNIX examples
fork system call creates new process
exec system call used after a fork to replace the process’ memory space with a new program

19. Process Creation

20. C Program Forking Separate Process
int main() {
pid_t pid;
/* fork another process */
pid = fork();
if (pid < 0) { /* error occurred */
fprintf(stderr, "Fork Failed");
exit(-1); }
else if (pid == 0) { /* child process */
execlp("/bin/ls", "ls", NULL);
else { /* parent process */
/* parent will wait for the child to complete */
wait (NULL);
printf ("Child Complete");
exit(0);

21. A tree of processes on a typical Solaris

22. Process Termination
Process executes last statement and asks the operating system to delete it (exit)
Output data from child to parent (via wait)
Process’ resources are deallocated by operating system
Parent may terminate execution of children processes (abort)
Child has exceeded allocated resources
Task assigned to child is no longer required
If parent is exiting
Some operating system do not allow child to continue if its parent terminates
All children terminated - cascading termination

23. Interprocess Communication
Processes within a system may be independent or cooperating
Cooperating process can affect or be affected by other processes, including sharing data
Reasons for cooperating processes:
Information sharing
Computation speedup
Modularity
Convenience
Cooperating processes need interprocess communication (IPC)
Two models of IPC
Shared memory
Message passing

24. Communications Models

25. Cooperating Processes
Independent process cannot affect or be affected by the execution of another process
Cooperating process can affect or be affected by the execution of another process
Advantages of process cooperation
Information sharing
Computation speed-up
Modularity
Convenience

26. Producer-Consumer Problem
Paradigm for cooperating processes, producer process produces information that is consumed by a consumer process
unbounded-buffer places no practical limit on the size of the buffer
bounded-buffer assumes that there is a fixed buffer size