1. CMP320 Operating Systems Lecture 07, 08 Operating System Concepts
October
Arif Butt
Note: Some slides and/or pictures are adapted from Lecture slides / Books of
Dr Mansoor Sarwar.
Dr Kubiatowicz.
Dr P. Bhat.
Dr Hank Levy.
Dr Indranil Gupta.
Text Book - OS Concepts by Silberschatz, Galvin, and Gagne.
Ref Books
Operating Systems Design and Implementation by Tanenbaum.
Operating Systems by William Stalling.
Operating Systems by Colin Ritchie.

2. Today’s Agenda Review of previous lecture Cooperating Processes
Producer Consumer Problem
IPC
Message Passing System
Direct Communication
Indirect Communication
Shared Memory System
Using pipes and FIFOS on the shell
Using pipe() system call in UNIX programs
Using mknod() system call in UNIX programs
Using shmget() system call in UNIX programs
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3. Cooperating Processes
Independent process is a process that cannot affect or cannot be affected by the execution of another process. A process that does not share data with another process is independent
Cooperating process is a process that can affect or can be affected by the execution of another process. A process that share data with other process is a cooperating process
Advantages of Cooperating processes:
Information sharing
Computation speed up
Modularity
Convenience
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4. Inter Process Communication
IPC is a mechanism for processes to communicate and to synchronize their actions. There are two fundamental models of IPC:
Shared Memory – A region of memory that is shared by cooperating processes is established. Processes can then exchange information by reading and writing data to the shared region
Messaging system – Communication takes place by means of messages exchanged between the cooperating processes. Processes communicate with each other without resorting to shared variables. (pipes, FIFO, sockets, message queues, semaphores, signals)
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5. Inter Process Communication
Read Comparisons on book page 96
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6. Producer-Consumer Problem
Empty Pool
Producer
Consumer
Full Pool
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7. Producer-Consumer Problem (cont…)
A producer process produces information that is consumed by a consumer process
To allow producer and consumer run concurrently we must have a buffer that can be filled by the producer and emptied by the consumer. Buffer can be bounded or unbounded
Unbounded Buffer
Places no practical limit on the size of the buffer
The consumer may have to wait for new items (if the buffer is empty), but the producer can always produce new items
Bounded Buffer
Assumes a fixed size buffer
The consumer must wait if the buffer is empty, and the producer must wait if the buffer is full
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8. Solution 1-Bounded Buffer Problem
#define BUFFER_SIZE 5
typedef struct{ ---- } item;
item buffer[BUFFER_SIZE];
int in = 0; //points to location where next item will be placed, will be used by producer process
int out = 0; //points to location from where item is to be consumed, will be used by consumer process
Producer Process
item nextProduced;
while(1) {
nextProduced = getItem();
while(((in + 1)%BUFFER_SIZE) == out)
; //do nothing
buffer[in] = nextProduced;
in = (in + 1) % BUFFER_SIZE; }
Consumer Process
item nextConsumed;
while(1) {
while(in == out)
; //do nothing
nextConsumed = buffer[out];
out = (out + 1) % BUFFER_SIZE; }
What is the problem with this solution?
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9. Solution 2 - Bounded Buffer Problem
#define BUFFER_SIZE 5
typedef struct{ ---- } item;
item buffer[BUFFER_SIZE];
int in = 0; //points to location where next item will be placed, will be used by producer process
int out = 0; //points to location from where item is to be consumed, will be used by consumer process
int ctr = 0;
Can you do it without
using the ctr variable?
Producer Process
item nextProduced;
while(1) {
nextProduced = getItem();
while(ctr == BUFFER_SIZE)
; //do nothing
buffer[in] = nextProduced;
in = (in + 1) % BUFFER_SIZE;
ctr++; }
Consumer Process
item nextConsumed;
while(1) {
while(ctr == 0)
; //do nothing
nextConsumed = buffer[out];
out = (out + 1) % BUFFER_SIZE;
ctr--; }
Instead using the ctr variable. Initialize the entire buffer with -1. While consuming an item remember to place a -1 where out is pointing to.
While(in == out && buff[in] != -1) // means the buffer is full, so a producer cannot produce
While(in == out && buff[in] == -1) // means the buffer is empty, so a consumer cannot consume
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10. Messaging System
Message passing provides a mechanism to allow processes to communicate and to synchronize their actions without sharing the same address space
It is particularly useful in a distributed environment, where the communicating processes may reside on different computers connected by a network
For example; a chat program used on the www
Message Passing is one solution to the communication requirement. The added bonus is: It works with shared memory and with distributed systems
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11. Messaging System (cont…)
A message passing facility provides at least two operations:
send(message) – message size fixed or variable
receive(message)
If P and Q wish to communicate, they need to:
establish a communication link between them
exchange messages via send/receive
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12. Messaging System (cont…)
Direct Communication
Processes must name each other explicitly:
send (P, message) – send a message to process P
receive(Q, message) – receive a message from process Q
Send primitive includes a specific identifier of the destination process
Receive primitive could know ahead of time which process a message is expected
Receive primitive could use source parameter to return a value when the receive operation has been performed
Example is a letter mailed via Pakistan Postal Service
Properties of communication link in Direct Comm.:
A Link is established automatically
A link is associated with exactly one pair of communicating processes
Between each pair there exists exactly one link
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13. Messaging System (cont…)
Indirect Communication
Messages are directed and received from mailboxes (also referred to as ports)
Each mailbox has a unique id
Processes can communicate only if they share a mailbox
We can think of a mailbox as an abstract object into which a message can be placed in or removed from
Properties of communication link in Indirect Comm.:
Link established only if processes share a common mailbox.
A link may be associated with many processes
Each pair of processes may share several communication links
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14. Messaging System (cont…)
Indirect Communication (cont…)
Operations
create a new mailbox.
send and receive messages through mailbox.
destroy a mailbox.
Primitives are defined as:
send(A, message) – send a message to mailbox A
receive(A, message) – receive a message from mailbox A
Mailbox Sharing
P1, P2, and P3 share mailbox A
P1, sends; P2 and P3 receive
Who gets the message?
Solutions
Allow a link to be associated with at most two processes.
Allow only one process at a time to execute a receive operation.
Allow the system to select arbitrarily the receiver. Sender is notified who the receiver was.
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15. Indirect Process Communication (…)
Animated Slide – each item below is magnified for instructor to address separately
1) A one-to-one relationship
allows a private communications link to be set up between two processes.
This insulates their interaction from erroneous interference from other processes.
2) A many-to-one relationship is useful for client/server interaction;
one process provides service to a number of other processes.
In this case, the mailbox is often referred to as a port.
3) A one-to-many relationship allows for one sender and multiple receivers;
it is useful for applications where a message or some information is to be broadcast to a set of processes.
4) A many-to-many relationship
allows multiple server processes to provide concurrent service to multiple clients.
The association of processes to mailboxes can be either static or dynamic.
Ports are often statically associated with a particular process; that is, the port is created and assigned to the process permanently.
Similarly, a one-to-one relationship is typically defined statically and permanently. When there are many senders, the association of a sender to a mailbox may occur dynamically. Primitives such as connect and disconnect may be used for this purpose
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16. General Message Format
The format of the message depends on the objectives of the messaging facility and whether the facility runs on a single computer or on a distributed system.
This is a typical message format for operating systems that support variable-length messages.
The message is divided into two parts:
a header, which contains information about the message.
The header may contain an identification of the source and intended destination of the message, a length field, and a type field to discriminate among various types of messages.
additional control information, e.g. pointer field so a linked list of messages can be created; a sequence number, to keep track of the number and order of messages passed between source and destination; and a priority field.
a body, which contains the actual contents of the message.
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17. Messaging System (cont…)
Synchronization
Message passing may be either blocking or non-blocking
Blocking is considered synchronous
Blocking send. The sending process is blocked until the message is received by the receiving process or by the mailbox. (Producer process blocks when the buffer is full)
Blocking receive. The receiver blocks until a message is available. (Consumer process blocks when the buffer is empty)
Non-blocking is considered asynchronous
Non-blocking send. The sending process sends the message and resumes operation
Non-blocking receive. The receiver receives either a valid message or a null
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18. Messaging System (cont…)
Buffering
Whether communication is direct or indirect, messages exchanged by communicating processes reside in a temporary queue. Such queues can be implemented in three ways:
Zero Capacity. The queue has a length of zero. Thus the link cannot have any messages waiting in it. The sender must block until the recipient receives the message
Bounded Capacity. The queue has finite length n. Sender must wait if link is full
Unbounded Capacity. The queue is of infinite length. So any number of messages can wait in it. Thus the sender never blocks
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19. UNIX / LINUX IPC Tools
Pipes are used for communication between related processes (parent-child-sibling) on the same UNIX system. P1 P2
Pipe
UNIX/Linux System
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20. UNIX / LINUX IPC Tools
Named pipes (FIFO) are used for communication between related or unrelated processes on the same UNIX system. P1 P2 p1 p2
FIFO
UNIX/Linux System
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21. UNIX / LINUX IPC Tools
Sockets are used for communication between related or unrelated processes on the same or different UNIX systems. P1 P2
Network Connection
Socket
Socket
Computer 1
Computer 2
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22. USING PIPES IN CMD LINE & PROGRAMMING
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23. Cmd Line use of Pipes cmd1 | cmd2 | cmd3 | … | cmdN
The UNIX system allows stdout of a command to be connected to stdin of another command using the pipe operator |.
cmd1 | cmd2 | cmd3 | … | cmdN
Stdout of cmd1 is connected to stdin of cmd2, stdout of cmd2 is connected to stdin of cmd3, … and stdout of cmdN-1 is connected to stdin of cmdN.
Collaboration allows faults to propagate…
cmd1
pipe
cmd2
pipe
pipe
cmdN
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24. Cmd Line Use of Pipes
Example 1. Write a command that displays the contents of /etc/ directory, one page at a time.
$ ls –l /etc/ 1> temp
$ less 0< temp
This will display the contents of file temp on screen one page at a time. After this we need to remove the temp file as well.
$ rm temp
So we needed three commands to accomplish the task, and the command sequence is also extremely slow because file read and write operations are involved.
Collaboration allows faults to propagate…
Lets use the pipe symbol
$ ls –l /etc/ | less
The net effect of this command is the same. It does not use a disk to connect standard output of ls –l to standard input of less because pipe is implemented in the main memory.
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25. Cmd Line Use of Pipes (cont…)
Example 2. Write a command that will sort the contents of file students.txt and displays those contents on screen after removing duplication if any.
$ sort 0< students.txt 1> stds_sorted
$ uniq stds_sorted
$ rm stds_sorted
Collaboration allows faults to propagate…
Lets use the pipe symbol
$ sort students.txt | uniq
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26. Cmd Line Use of Pipes (cont…)
Pipes and redirection operators alone cannot be used to redirect stdout of a command to a file as well as another command in a single command
tee command copies stdin to stdout and at the same time copies it to one or more files
$ tee tout1.txt tout2.txt
tee command is used to redirect the stdout of a command to one or more files, as well as to another command
cmd1 | tee file1 … fileN | cmd2
Stdout of cmd1 is connected to stdin of tee, and tee sends its input to files file1, … fileN and as stdin of cmd2
$ who | tee who.txt
Sarwar page = 320
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27. System Call - pipe() int pipe(int pipefd[2]); Call Fails when:
pipefd[0] and pipefd[1] are read and write descriptors respectively.
Will return -1 on failure
Bounded buffer, maximum data written is PIPE_BUF <linux/param.h>, 4096 bytes
Call Fails when:
Opening a pipe is equivalent to opening two files, so at least two slots need to be empty in the PPFDT, otherwise, the call will fail.
Buffer space not available in the kernel.
File table is full.
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28. System Call - pipe() fork P2 P1 pipe parent child
Child Process will send a string to Parent Process
and Parent Process will print that on screen.
fork P2 P1
parent
child
Child writes in the pipe. It blocks if the pipe is full.
Parent read from the pipe. It blocks if the pipe is empty.
pipe
Read end
Write end
Process P1 will create a pipe (having two ends, a read end and a write end).
Then the Parent Process P1 will create a child process P2.
There are two descriptors associated with the pipe. The writer process (child) will use the write descriptor of the pipe. The reader process (parent) will use the read descriptor of the pipe.
The child process will write data onto the pipe and the parent process will read that data at the read end and will display it on the screen.
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29. Sample Program using pipe()
/* pipe1.c (Parent creates pipe, forks a child, child writes into pipe, and parent reads from pipe).*/
#include <stdio.h> #include <stdlib.h>
#include <string.h> #include <sys/types.h>
#include <sys/wait.h>
int main(){
int pipefd[2], cpid, n, rc, nr;
char *msg = "Hello, world!\n“;
char * buf[1024];
rc = pipe(pipefd); //create a pipe
if (rc == -1) {//if pipe call fails
printf(“\n Pipe failed");
exit(1);}
cpid = fork(); //if pipe call is successful we create a child
if (cpid == -1) {
printf(“\n Fork failed"); //if fork fails
exit(1); }
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30. Sample Program using pipe() (cont…)
if (cpid == 0) { // Child’s Code (child is the writer process)
write(pipefd[1], msg, strlen(msg));
exit(0); }
else { // Parent’s Code (parent is the reader process)
n = strlen(msg);
nr = read(pipefd[0], buf, n);
rc = write(1, buf, nr);//use write sc to display the data //read from the pipe on the screen
printf("Good work child!\n");
return(0);
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31. USING FIFOS IN CMD LINE & PROGRAMMING
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32. Named Pipes / FIFOs
First In First Out are special file types in UNIX used for communication between related or unrelated processes on a computer.
Processes communicating with pipes must be related to each other through a common ancestor process that you execute, processes communicating with FIFOs do not have to have this kind of relationship. They can be independently executed programs on a system.
A pipe is a main memory buffer and has no name, while FIFO is created on disk and has a name like a file name.
So like files and unlike a pipe, a FIFO has to be created and opened before using it for communication.
We can use mkfifo command to create a FIFO file in a shell session. We can use mknod() system call or mkfifo() library call to create a FIFO in a process.
UNIX system calls read(), write(), close(), etc. can be used with FIFOs.
Major differences between pipes and FIFOs
pipe is an in-memory buffer, while FIFOs are mostly created on disk.
After creating a pipe, you don’t need to explicitly open it before using it.
After creating a FIFO, you need to open it and you need to tell the system whether you are opening it for reading or writing or both. After you are done you need to close them. (Just as you do I/O with files)
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33. Named Pipes / FIFOs Two common uses of FIFOs are:
Used by shell commands to pass data from one shell pipeline to another, without creating temporary files
In client server applications, FIFOs are used to pass data between a server process and client processes
Collaboration allows faults to propagate…
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34. Cmd Line Use of FIFOs
Example. Write a command that will count the number of lines in the man page of ls.
$ man ls | wc –l
239 $
Example. Write a command that will count only the number of lines containing string “ls” in the man page of ls.
Collaboration allows faults to propagate…
$ man ls | grep ls | wc –l 9 $
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35. Cmd Line Use of FIFOs (cont…)
$ mkfifo fifo1
$ prog3 0< fifo1 &
$ prog1 0< infile | tee fifo1 | prog2
First line will create an empty FIFO named fifo1.
In second line, prog3 is trying to read its input from fifo1. Since fifo1 is empty therefore prog3 will block at the read operation. More so the & shows that it will run in the back ground.
In third line, prog1 will read its input from infile and send its o/p to tee utility and tee will do two things:
Write the o/p to fifo1 as well as to the stdout which will be sent to prog3
Through the pipe will give the o/p to prog2
$ mkfifo fifo1
man ls 1> ls.dat
$ cat 0< fifo1 | grep ls | wc –l &
[1] 21108
$ sort 0< ls.dat | tee fifo1 | wc –l 9
239
wc -l
grep
fifo1
Pipe
The no 31 is the count of lines in ls.dat containing the string ls, while 239 is the total count of lines in ls.dat
sort
tee
infile
Pipe
wc -l
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36. Client Server Comm with FIFOs
Server will open a well known FIFO, which it will use
to read the request of client.
Each client will open a client FIFO and send its name to the server process,
so now the server knows via which client FIFO it can send reply to a particular client
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37. System Call - mknod() Call Fails when: #include <sys/types.h>
#include <sys/stat.h>
int mknod(const char * pathname, mode_t mode, dev_t dev);
mode should be permission mode ORed with S_IFIFO flag.
dev is set to 0 for a FIFO, i.e. we are not making a device file.
Call Fails when:
File with the given name already exists
Pathname too long
A component in the pathname not searchable or non existent
Destination directory is read only
Not enough memory space available
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38. Library Call - mkfifo()
#include <sys/types.h>
#include <sys/stat.h>
int mkfifo(const char * pathname, mode_t mode);
mode sets permission on FIFO
Calls mknod()
Call Fails when:
File with the given name already exists
Pathname too long
A component in the pathname not searchable or non existent
Destination directory is read only
Not enough memory space available
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39. Example - FIFO FIFO1 FIFO2 Display Screen Server Client Reading
Writing
FIFO1
Server
Client
FIFO2
Writing
Reading
Server
Create FIFO1 and FIFO2
Open FIFO1 for reading.
Open FIFO2 for writing.
Make a blocking read() system call on FIFO1
Once the client writes in FIFO1 (sent msg to server), the server will display that msg on screen.
Then server will send a msg to client “Hello Class”.
CLIENT
Open FIFO1 for writing.
Open FIFO2 for reading.
Write “Hello World” msg in FIFO1 (this will make server come out of the blocked read() system call)
Client will read from FIFO2
Once client will receive the msg sent by server from FIFO2 and will display that msg on screen.
Display Screen
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40. Client - Server Code //myheader.h #include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/errno.h>
 #define FIFO1 "/tmp/fifo1"
#define FIFO2 "/tmp/fifo2"
#define PERMS
#define MESSAGE "Hello, world!\n"
#define MESSAGE "Hello, class!\n“
extern int errno;
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41. Server Code - 1 #include “myheader.h” main(){ char buff[1024];
int readfd, writefd, n, size;
/*create fifo1 using mknod system call*/
if (mknod (FIFO1, S_IFIFO | PERMS, 0) < 0) {
perror ("mknod FIFO1");
exit (1); }
/*create fifo2 using mkfifo library call. if mkfifo() fails in creating FIFO2, before exiting we must remove FIFO1 from file system*/
if (mkfifo(FIFO2, PERMS) < 0) {
unlink (FIFO1);
perror("mknod FIFO2");
Create two FIFOs
Open FIFO1 for reading and FIFO2 for writing.
Block at reading until some client writes in FIFO1.
Read the data and display it on stdout.
Write message2 to FIFO2
Close both FIFOs
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42. Server Code - 2
if ((readfd = open(FIFO1, 0)) < 0) {//open FIFO1 for reading
perror ("open FIFO1");
exit (1); }
if ((writefd = open(FIFO2, 1)) < 0){//open FIFO2 for writing
perror ("open FIFO2");
size = strlen(MESSAGE1) + 1;
/*if client has yet not run, the server process will block on following read. As soon as some client executes and writes some msg in FIFO1, the server process will automatically unblock.*/
if ((n = read(readfd, buff, size)) < 0) {
perror ("server read"); exit (1);
if (write (1, buff, n) < n) {//write on screen
perror("server write1"); exit (1);
size = strlen(MESSAGE2) + 1;
if(write(writefd,MESSAGE2,size) != size){//write on FIFO2
perror ("server write2"); exit (1);
close (readfd); close (writefd);
Create two FIFOs
Open FIFO1 for reading and FIFO2 for writing.
Block at reading until some client writes in FIFO1.
Read the data and display it on stdout.
Write message2 to FIFO2
Close both FIFOs
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43. Client Code - 1 #include “myheader.h” main() { char buff[BUFSIZ];
int readfd, writefd, n, size;
 // open FIFO1 for writing
if ((writefd = open(FIFO1, 1)) < 0) {
perror ("client open FIFO1"); exit (1); }
 // open FIFO2 for reading
if ((readfd = open(FIFO2, 0)) < 0) {
perror ("client open FIFO2"); exit (1);
size = strlen(MESSAGE1) + 1;
 // write message in FIFO1
if (write(writefd, MESSAGE1, size) != size) {
perror ("client write1"); exit (1);
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44. Client Code - 2 if ((n = read(readfd, buff, size)) < 0) {
/*if server has yet not run, the client process will block on following read. As soon as the server writes some msg in FIFO2, the client process will automatically unblock.*/
if ((n = read(readfd, buff, size)) < 0) {
perror ("client read"); exit (1); }
else
if (write(1, buff, n) != n) {
perror ("client write2"); exit (1);
close(readfd); close(writefd);
/* Remove FIFOs now that we are done using them */
if (unlink (FIFO1) < 0) {
perror("client unlink FIFO1"); exit (1);
if (unlink (FIFO2) < 0) {
perror("client unlink FIFO2"); exit (1);
exit (0);
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45. FIFO-Running the Code
Use any editor to type your program and then to compile use gcc compiler:
$ gcc server.c –o server
$ gcc client.c –o client
$ server &
[1]
$ client
Hello, World!
Hello, Class! $
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46. Shared Memory
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47. Shared Memory System
Shared memory allows two or more processes to share a given region of memory.
This is the fastest form of IPC because the data does not need to be copied between the client and server.
The only trick in using shared memory is synchronizing access to a given region among multiple processes.
If the server is placing data into a shared memory region, the client shouldn't try to access the data until the sever is done.
Often semaphores are used to synchronize shared memory access. We can use record locking as well.
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48. Shared Memory System (cont…)
Data 2
Code
Data
Heap
Stack
Shared
Code
Data
Heap
Stack
Shared
Stack 1
Heap 1
Code 1
Stack 2
Data 1
Prog 2
Logical
Address
Space 2
Prog 1
Logical
Address
Space 1
Heap 2
Code 2
Shared
In shared memory we declare a given section in the memory as one that will be used simultaneously by several processes.
Typically a shared memory region resides in the address space of the process creating the shared memory segment.
Other processes that wish to communicate using this shared memory segment must attach it to their address space.
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49. int segment_id = shmget(IPC_PRIVATE, 4096, S_IRUSR | S_IWUSR);
System Call shmget()
A process must first create a shared memory segment using shmget() system call (SHared Memory GET).
On success, shmget() returns a shared memory identifier that is used in subsequent shared memory functions.
On failure, it returns -1.
int segment_id = shmget(IPC_PRIVATE, 4096, S_IRUSR | S_IWUSR);
#include <sys/types.h> #include <sys/ipc.h> #include <sys/shm.h> int shmget(key_t key, int size, int flag); There is a special key value, IPC_PRIVATE, that creates shared memory private to the process. The second parameter, size, specifies the amount of memory required in bytes. The third parameter, flag consists of nine permission flags. Normally it is IPC_CREAT | 0666
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50. char * shared_memory = (char*) shmat(segment_id, NULL, 0);
System Call shmat()
Processes that wish to access a shared memory segment must attach it to their address space using the shmat() system call. (SHared Memory ATach)
On success, shmat() returns a pointer to the first byte of shared memory.
On failure, it returns -1.
char * shared_memory = (char*) shmat(segment_id, NULL, 0);
void* shmat(int shmid, const void *shmaddr, int flag); First parameter, shm_id, is the shared memory identifier returned from shmget. Second parameter is a pointer location in memory indicating where the shared memory will be attached. NULL pointer allows the system to choose the address at which the memory appears. Third parameter identifies the mode, a 0 means read-write.
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51. shmdt(shared_memory);
System Call shdt()
When a process no longer requires access to the shared memory segment, it detaches the segment form its address space.
This does not remove the identifier and its associated data structure from the system. The identifier remains in existence until some process specifically removes it by calling shmctl() with a command of IPC_RMID.
To detach a region of shared memory, the process can pass the pointer of the shared memory region to the shmdt() system call. (SHared Memory DeTach)
shmdt(shared_memory);
int shmdt(void * addr);
The addr argument is the value that was returned by a previous call to shmat.
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52. shmctl(segment_id, IPC_RMID, NULL);
System Call shctl()
Shared memory segment can be removed from the system with the shmctl() system call. (SHared Memory ConTroL)
Returns 0 if OK, -1 on error.
shmctl(segment_id, IPC_RMID, NULL);
void* shmctl(int shmid, int cmd, struct shmid_ds * buf); First parameter, shmid, is the shared memory identifier returned from shmget(). Second parameter can take five different values. IPC_RMID removes the shared memory segment set from the system. Third parameter is normally a NULL.
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53. Sample Program-Shared Memory
/* Program creates a shared memory area, attaches it to its address space, writes a string in it. Reads and print the contents of shared memory. Detach and finally remove shared memory segment.*/
#include <stdio.h>
#include <sys/shm.h>
#include <sys/ipc.h>
#include <sys/stat.h>
int main(){
const int size = 4096;
int segment_id = shmget(IPC_PRIVATE, size, IPC_CREAT | 0666);
char * shared_memory = (char*) shmat(segment_id, NULL, 0);
sprintf(shared_memory, “Hello World”);
printf(“%s\n”,shared_memory);
shmdt(shared_memory);
shmctl(segment_id, IPC_RMID, NULL);
return 0;}
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54. SUMMARY
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55. We’re done for now, but Todo’s for you after this lecture…
Go through the slides and Book Sections: 3.1 to 3.4, 3.51
Solution 2 to the bounded buffer problem is using an additional variable ctr. Suggest another solution that do not use any additional variable (do not mention the one discussed in class).
Write down the programs discussed in class in vim editor and execute them. Make variations in the programs and understand the underlying details.
If you have problems visit me in counseling hours
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CMP320 PUCIT Arif Butt