Assignment 4 Cooperating processes

Assignment 4 (10 points)


Cooperating processes need to communicate between them. Another way Linux supports interprocess communication is shared memory. A System V shared memory segment can be created and controlled using system calls shmget, shmctl, shmat, shmdt, and a C library function memcpy. Please consult the man pages of these system calls for details. This assignment is designed to illustrate a critical problem with processes executing concurrently that try to access shared data.
For this assignment you need to copy the following two C++ programs (named shmp1.cpp and shmc1.cpp with a header file registration.h) into your Linux directory, compile them into shmp1, and shmc1, respectively. Then run shmp1 and observe what happens. Run shmp1 at least 5 times and observe and report the results.

The program must run successfully on a Linux machine in the CECS Lab.

Do the following for this assignment:
1. Compile shmp1.cpp and shmc1.cpp into shmp1 and shmc1, respectively, and run shmp1. Try to understand what the programs do
2. Annotate the programs with adequate amount of comments throughout the program to explain what the program does. System calls require especially detailed comments.
3. Run shmp1 at least 5 times and observe the results. Explain the problems you have observed in these runs on the cover page.
4. Submit on BeachBoard the annotated shmp1.cpp and shmc1.cpp, with a cover page that provides your name, your student ID, course # and section, assignment #, due date, submission date, a clear program description, and any problem you observe. Format of the cover page should follow the cover page template on BeachBoard.
5. The programs must be properly formatted and adequately commented to enhance readability and understanding.
6. Demonstrate your program on a Linux machine in the Lab and explain details of the program logic and execution results. Bring a hardcopy of the cover page for the demo.


 
/* Header file to be used with
* shmp1.c and shmc1.c
*/

struct CLASS {
char class_number[6];
char date[7];
char title[50];
int seats_left;
};
 
/* shmp1.cpp */

#include "registration.h"
#include <sys/types.h
#include <sys/ipc.h
#include <sys/shm.h
#include <sys/wait.h
#include <unistd.h
#include <stdlib.h
#include <iostream
#include <stdio.h
#include <memory.h

using namespace std;

CLASS myclass = { "1001", "120119", "Operating Systems", 15 };

#define NCHILD 3

int shm_init( void * );
void wait_and_wrap_up( int [], void *, int );
void rpterror( char *, char * );

main(int argc, char *argv[])
{
int child[NCHILD], i, shmid;
void *shm_ptr;
char ascshmid[10], pname[14];

shmid = shm_init(shm_ptr);
sprintf (ascshmid, "%d", shmid);

for (i = 0; i < NCHILD; i++) {
child[i] = fork();
switch (child[i]) {
case -1:
rpterror ("fork failure", pname);
exit(1);
case 0:
sprintf (pname, "shmc%d", i+1);
execl("shmc1", pname, ascshmid, (char *)0);
perror ("execl failed");
exit (2);
}
}
wait_and_wrap_up (child, shm_ptr, shmid);}

int shm_init(void *shm_ptr)
{
int shmid;

shmid = shmget(ftok(".",'u'), sizeof(CLASS), 0600 | IPC_CREAT);
if (shmid == -1) {
perror ("shmget failed");
exit(3);
}
shm_ptr = shmat(shmid, (void * ) 0, 0);
if (shm_ptr == (void *) -1) {
perror ("shmat failed");
exit(4);
}
memcpy (shm_ptr, (void *) &myclass, sizeof(CLASS) );
return (shmid);
}

void wait_and_wrap_up(int child[], void *shm_ptr, int shmid)
{
int wait_rtn, w, ch_active = NCHILD;

while (ch_active 0) {
wait_rtn = wait( (int *)0 );
for (w = 0; w < NCHILD; w++)
if (child[w] == wait_rtn) {
ch_active--;
break;
}
}
cout << "Parent removing shm" << endl;
shmdt (shm_ptr);
shmctl (shmid, IPC_RMID, (struct shmid_ds *) 0);
exit (0);
}

void rpterror(char *string, char *pname)
{
char errline[50];

sprintf (errline, "%s %s", string, pname);
perror (errline);
}
 
/* shmc1.cpp */

#include "registration.h"
#include <sys/types.h
#include <sys/ipc.h
#include <sys/shm.h
#include <sys/wait.h
#include <unistd.h
#include <stdlib.h
#include <iostream
#include <stdio.h
#include <memory.h

using namespace std;

CLASS *class_ptr;
void *memptr;
char *pname;
int shmid, ret;
void rpterror(char *), srand(), perror(), sleep();
void sell_seats();

main(int argc, char* argv[])
{
if (argc < 2) {
fprintf (stderr, "Usage:, %s shmid\n", argv[0]);
exit(1);
}

pname = argv[0];
sscanf (argv[1], "%d", &shmid);
memptr = shmat (shmid, (void *)0, 0);
if (memptr == (char *)-1 ) {
rpterror ("shmat failed");
exit(2);
}

class_ptr = (struct CLASS *)memptr;

sell_seats();

ret = shmdt(memptr);
exit(0);
}

void sell_seats()
{
int all_out = 0;

srand ( (unsigned) getpid() );
while ( !all_out) { /* loop to sell all seats */
if (class_ptr-seats_left 0) {
sleep ( (unsigned)rand()%5 + 1);
class_ptr-seats_left--;
sleep ( (unsigned)rand()%5 + 1);
cout << pname << " SOLD SEAT -- "
<< class_ptr-seats_left << " left" << endl;
}
else {
all_out++;
cout << pname << " sees no seats left" << endl;
}
sleep ( (unsigned)rand()%10 + 1);
}
}

void rpterror(char* string)
{
char errline[50];

sprintf (errline, "%s %s", string, pname);
perror (errline);
}