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  1. // By Zachary Lilley, Username: lill0017 - Intro to Operating Systems 9/22/24 --Modified 10/25/24 For Programming Assignment #2
  2. #include <stdio.h> 
  3. #include <stdlib.h>
  4. #include <sys/ipc.h> 
  5. #include <sys/shm.h>
  6. #include <sys/wait.h>
  7. #include <unistd.h> 
  8. #include <semaphore.h> // Added Semaphore Library --10/25/24
  9. #include <fcntl.h>  // O_CREAT & O_EXCL --10/25
  10.  
  11.  
  12. // Declaring Semaphore Globally
  13. sem_t *sem;
  14.  
  15. void inc(int *total, int target, int process_id) {
  16.     for (int i = 0; i < target; i++) {
  17.         sem_wait(sem); // Enter critical section
  18.         (*total)++;
  19.         sem_post(sem); // Exit critical section
  20.     }
  21.     printf("From Process %d: counter = %d.\n", process_id, *total);
  22.     exit(0); // Exit after incrementing
  23. }
  24.  
  25. int main() {
  26.     int shmid;
  27.     int *total;
  28.     key_t key = IPC_PRIVATE;    // Only grants access to the 
  29.                                 // shared memory to parent proccess' children
  30.  
  31.     sem = sem_open("/zachs_sem", O_CREAT, 0666, 1); //Semaphore initialized with a value of 1
  32.     if (sem == SEM_FAILED) {
  33.         perror("semaphore failed");
  34.         exit(1);
  35.     }
  36.  
  37.     // Shared memory for total count
  38.     shmid = shmget(key, sizeof(int), IPC_CREAT | 0666); //IPC_CREAT makes the memory segment if it doesn't exist already 0666 gives read, write and execution permissions
  39.     if (shmid < 0) {  // Validate allocation
  40.         perror("shmget failed");
  41.         exit(1);
  42.     }
  43.  
  44.     // Attach total to the shared memory
  45.     total = (int *)shmat(shmid, NULL, 0); //cast to int 
  46.     if (total == (int *) -1) {
  47.         perror("shmat failed");
  48.         exit(1);
  49.     }
  50.  
  51.     *total = 0; // Initialize the shared variable once it's allocated
  52.  
  53.     // Fork 4 times
  54.     for (int i = 1; i <= 4; i = i + 1) {
  55.  
  56.         int pid = fork();
  57.  
  58.         if (pid == -1) {        //Handle fork error and close out semaphore --10/25/24
  59.         perror("fork failed");
  60.         sem_close(sem);
  61.         sem_unlink("/zachs_sem");
  62.         exit(1);
  63.         }
  64.  
  65.         // For each fork conduct an increment
  66.         if (pid == 0) {
  67.             // Set target values for each child process
  68.             int target = 0;
  69.             if (i == 1) target = 100000;
  70.             if (i == 2) target = 200000;
  71.             if (i == 3) target = 300000;
  72.             if (i == 4) target = 500000;
  73.             inc(total, target, getpid()); // Pass current PID to inc function
  74.         }
  75.     }
  76.  
  77.     // Parent processes wait for children
  78.     for (int i = 1; i <= 4; i++) {
  79.         int pid = wait(NULL);
  80.         printf("Child ID: %d exited.\n", pid);
  81.     }
  82.  
  83.     // Deallocate and release memory and the semaphore --10/25/24
  84.     shmdt(total);
  85.     shmctl(shmid, IPC_RMID, NULL);
  86.     sem_close(sem);
  87.     sem_unlink("/zachs_sem");
  88.  
  89.     printf("End of Simulation.\n");
  90.     return 0;
  91. }
  92.  
  93.  
Success #stdin #stdout 0.05s 5280KB
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stdin
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Standard input is empty
stdout
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From Process 1139444: counter = 704046.
From Process 1139443: counter = 770431.
From Process 1139445: counter = 1029487.
From Process 1139446: counter = 1100000.
Child ID: 1139444 exited.
Child ID: 1139443 exited.
Child ID: 1139445 exited.
Child ID: 1139446 exited.
End of Simulation.
https://ideone.com/9IkPM6
language:
C (gcc 8.3)
created:
5 days ago
visibility:
public

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