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/******************************************************************************** * The following functions manage InterProcess Communication ********************************************************************************/#include "ipc.h"#include "image.h"#include <stdlib.h>#include <sys/ipc.h>#include <sys/sem.h>#include <sys/shm.h>#include <sys/msg.h>#define SERVER_MESSAGE_ID   1#define CLIENT_MESSAGE_ID   2struct mymsgbuf{  long mtype;  int width;  int height;  };void *manageJPEGUpdates (void *arg){  key_t key;  int sem_id, msq_id, shm_id;  int width, height;  char *shmsegptr;  int length;  struct mymsgbuf msg;      // Initialize IPC  key = create_key();    sem_id = init_semaphore( key );  msq_id = init_message_queue( key, &width, &height );  shm_id = init_shared_memory( key, width, height, shmsegptr );  length = sizeof(struct mymsgbuf) - sizeof(long);    // Listen for update messages  while (1)  {    // Get message    if (msgrcv(msq_id, &msg, length, SERVER_MESSAGE_ID, 0) == -1)    {      perror("manageJPEGUpdates: msgrcv() failed");    }        czsImgClr img;    img.w = width;    img.h = height;        img.data = shmsegptr;        czfWriteImgPPM(img, "test.ppm");        // Update JPEG    createJPEG ((imageJPEG *) arg, sem_id, shmsegptr, width, height);  }}key_t create_key (){  key_t key;    if ((key = ftok( "/myApp", 'c' )) == -1)  {    perror("create_key: ftok() failed");    return (-1);  }  else  {    return (key);  }}// Initialize semaphore setint init_semaphore(key_t key){  int sem_id;  if ((sem_id = semget(key, 1, 0666)) == -1)  {    perror("init_semaphore: semget() failed");    return (-1);  }    return (sem_id);}// Lock semaphore (BLOCKING !)void semaphore_lock (int sem_id){  struct sembuf sem_lock = {0, -1, 0};  if (semop(sem_id, &sem_lock, 1) == -1)  {    perror("semaphore_lock: semop() failed");  }}// Unlock semaphorevoid semaphore_unlock (int sem_id){  struct sembuf sem_unlock = {0, 1, 0};  if (semop(sem_id, &sem_unlock, 1) == -1)  {    perror("semaphore_unlock: semop() failed");  }}// Initialize  message queueint init_message_queue( key_t key, int *width, int *height ){  int msq_id, length;  struct mymsgbuf msg, ack;    /* Open the message queue */  if ((msq_id = msgget(key, 0666)) == -1)  {    perror("init_message_queue: msgget() failed");    return (-1);  }    ack.mtype = CLIENT_MESSAGE_ID;  length = sizeof(struct mymsgbuf) - sizeof(long);    /* Receive initial width and height */  if (msgrcv(msq_id, &msg, length, SERVER_MESSAGE_ID, 0) == -1)  {    perror("init_message_queue: msgrcv() failed");    return (-1);  }    *width = ack.width = msg.width;  *height = ack.height = msg.height;    /* Acknowledge this width and height to the server */  if (msgsnd(msq_id, &ack, length, 0) == -1)  {    perror("init_message_queue: msgrcv() failed");    return (-1);  }    return (msq_id);}// Initialize shared memory segmentint init_shared_memory(key_t key, int width, int height, char *shmsegptr){  int shm_id;    if ((shm_id = shmget(key, width * height * 3, 0666)) == -1)  {    perror("init_shared_memory(): shmget failed");    return (-1);  }    if ((shmsegptr = (char *) shmat(shm_id, 0, 0 )) == (char *) -1)  {    perror("init_shared_memory(): shmat failed");    return (-1);  }    printf("\n\n%d\n\n", *shmsegptr);  return (shm_id);}