This document discusses processes and threads. It defines a process as a running program with a single flow of execution, while a thread is a flow of execution within a process. It describes how processes are created using fork and exec functions in Linux. It also discusses different types of processes like foreground, background, and daemon processes. Finally, it covers various inter-process communication (IPC) techniques like pipes, shared memory, message queues, semaphores, and signals that processes can use to communicate with each other.

1. 6 – Processes
and Threads
Borislav Varadinov
Marian Marinov
System
CEO of 1H Ltd.
Administrator
mm@1h.com
bobi [ at ] itp.bg

2. What is a Process?

3. What is a Process?
➢ Single process OS – Arduino
➢ Multy process OS – Any modern kernel

4. What is a Process?
MEMORY CPU I/O
APPLICATION

5. Multiple Processes?
MEMORY MEMORY CPU I/O
APPLICATION APPLICATION

6. Multiple Processes?
➢ Segmentation Fault
➢ Bus Error
➢ Access violation
SEGFAULT/SIGSEGV
➢ Since Linux 3.2
CROSS MEMORY ATTACH

7. What is a Thread?

8. What is a Thread?
MEMORY CPU I/O
Thread0 Thread1
Process

9. What is a Thread?

10. Creating a process
➢ FORK
➢ Copy the memory of the parent
➢ Inherit FD table
➢ Inherit credentials
➢ Inherit security
➢ EXEC
➢ Create new memory space
➢ Inherit FD table
➢ Inherit credentials

11. What is a Thread?

12. Creating a process
#include <stdio.h>
#include <unistd.h>
int main() {
int i;
pid_t p;
p = fork();
if (p == 0) {
for (i=0;i<=3;i++)
printf("I'm the child(%d)!n", p);
} else {
for (i=0;i<=3;i++)
printf("My child is %dn", p);
}
return 0;
}

13. Creating a process
hackman@terion:~$ ./f
My child is 3721
My child is 3721
My child is 3721
My child is 3721
I'm the child(0)!
I'm the child(0)!
I'm the child(0)!
I'm the child(0)!
hackman@terion:~$

14. Creating a process
#include <stdio.h>
#include <unistd.h>
int main() {
int i;
pid_t p;
p = fork();
if (p == 0) {
for (i=0;i<=3;i++)
printf("I'm the child(%d)!n", getpid());
} else {
for (i=0;i<=3;i++)
printf("My child is %dn", p);
}
printf("This is not good(%d)!n", getpid());
return 0;
}

15. Creating a process
hackman@terion:~$ ./f
My child is 3762
My child is 3762
My child is 3762
My child is 3762
This is not good(3761)!
I'm the child(3762)!
I'm the child(3762)!
I'm the child(3762)!
I'm the child(3762)!
This is not good(3762)!
hackman@terion:~$

16. Creating a process
EXEC functions
int execl(const char *path, const char *arg, ...);
int execlp(const char *file, const char *arg, ...);
int execle(const char *path, const char *arg,
..., char * const envp[]);
int execv(const char *path, char *const argv[]);
int execvp(const char *file, char *const argv[]);
int execvpe(const char *file, char *const argv[],
char *const envp[]);
Exec functions does not return

17. Creating a process
system() = exec('/bin/sh -c CMD')
Which means:
your process
- exec /bin/sh
- exec CMD

18. Types of processes
➢ Foreground
➢ Background
➢ Daemons
➢ co-relation with terminal

19. Foreground processes
➢ It has access to the terminal's
➢ STDIN –0
➢ STDOUT – 1
➢ STDERR – 2
➢ It is directly controlled by the user
➢ It is connected to the terminal (text or
graphic)

20. Background processes
➢ It has access only to the terminal's
➢ STDOUT – 1
➢ STDERR – 2
➢ It is NOT directly controlled by the user
➢ It is connected to the terminal (text or
graphic)

21. Daemon processes
➢ Its STDIN/OUT/ERR are redirected to files
➢ It is NOT directly controlled by the user
➢ It is NOT connected to the terminal (text or
graphic)

22. IPC
➢ FS PIPES
➢ Process PIPES
➢ Unix Domain Socket
➢ Shared Memory SHM (SysV/POSIX)
➢ Message Queues (SysV/POSIX)
➢ Semaphores (SysV/POSIX)
➢ Signals

23. IPC – process PIPEs
Proc 1
a = open(PIPE, “r”);
b = open(PIPE, “w”);
Proc 2
close(a); close(b);
a = open(PIPE, “w”);
b = open(PIPE, “r”);

24. IPC – Shared Memory
Proc 1 SHM
shmid = shmget(IPC_PRIVATE, ...);
mem = shmat(shmid, ...);
Proc 2
memset(mem, '0', 200);

25. IPC – Message Queues
Proc 1
Proc 2

26. IPC – Semaphores
Proc 1
Proc 2

27. IPC – Signals
Proc 1
Proc 2

28. Signals - Kill
Proc 1
Proc 2

29. Signals – Signal handlers
Proc 1
sig_handler
main()
init_some()
do_some()
log_some()

30. Signals – Signal handlers
Proc 1
sig_handler
main()
SIGHUP init_some()
0 - 255
do_some()
log_some()

31. Processes and Threads

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