I’m trying to implement a functional version of the classic reader-writer problem in IPC which doesn’t cause starvation. You can find the full article here

To me my implementation seems correct, but I prefer asking people who knows more stuff than me. What do you think, is it correct? (list is a shared memory i didnt post the full code because here is the sauce)

Here’s the code

#include <stdio.h> #include <stdlib.h> #include <unistd.h> #include <errno.h> #include <time.h> #include <string.h> #include <sys/types.h> #include <sys/stat.h> #include <sys/wait.h> #include <sys/ipc.h> #include <sys/sem.h> #include <sys/shm.h> #include <sys/msg.h> #include <semaphore.h> #include <fcntl.h>  #define TEST_ERROR    if (errno) {fprintf(stderr,           \                       "%s:%d: PID=%5d: Error %d (%s)\n", \                       __FILE__,         \                       __LINE__,         \                       getpid(),         \                       errno,            \                       strerror(errno));}  //third read-writer problem int readers, writers;  int main() {      struct sembuf sops_mutex, sops_resource;     int sem_mutex, sem_resource, shm_id, *list, i, j, status;     pid_t child_pid;      shm_id = shmget(IPC_PRIVATE, sizeof(list), 0666 | IPC_CREAT | IPC_EXCL);      TEST_ERROR;      list = shmat(shm_id, NULL, 0);     TEST_ERROR;       sem_mutex = semget((key_t)getpid(), 1, 0600 | IPC_CREAT | IPC_EXCL);     TEST_ERROR;      sem_resource = semget((key_t)getpid()+1, 1, 0600 | IPC_CREAT | IPC_EXCL);      TEST_ERROR;      semctl(sem_mutex, 0, SETVAL, 1);          //signal(mutex)                    semctl(sem_resource, 0, SETVAL, 1);       //signal(mutex)                       //i%2==0 reader else writer     for(i=0; i<20; i++) {         switch(fork()) {             case 0:               switch(i%2) {                 case 0://reader                      while(semctl(sem_mutex, 0, GETVAL) != 1); //wait(mutex)                      if(writers > 0 || readers == 0) {                         semctl(sem_mutex, 0, SETVAL, 1);          //signal(mutex)                                        while(semctl(sem_resource, 0, GETVAL) != 1); //wait(mutex)                         while(semctl(sem_mutex, 0, GETVAL) != 1); //wait(mutex)                     }                      readers++;                     semctl(sem_mutex, 0, SETVAL, 1);          //signal(mutex)                                     for(j = 0; j<20; j++) { //reading                         if(j%2!=0)                             printf("%d %d ", getpid(), list[j]);                     }printf("\n");                      while(semctl(sem_mutex, 0, GETVAL) != 1); //wait(mutex)                     readers--;                     if(readers==0)                         semctl(sem_resource, 0, SETVAL, 1);       //signal(resource)                                     semctl(sem_mutex, 0, SETVAL, 1);          //signal(mutex)                                      break;                  default://writer                      while(semctl(sem_mutex, 0, GETVAL) != 1); //wait(mutex)                     writers++;                                //writers <- +1                     semctl(sem_mutex, 0, SETVAL, 1);          //signal(mutex)                                    while(semctl(sem_resource, 0, GETVAL) != 1); //wait(resource)                      list[i] = i; //writing                      while(semctl(sem_mutex, 0, GETVAL) != 1); //wait(mutex)                     writers--;                                       semctl(sem_mutex, 0, SETVAL, 1);          //signal(mutex)                                    semctl(sem_resource, 0, SETVAL, 1);       //signal(resource)                                      break;              }              shmdt(list);             TEST_ERROR;                        exit(0);             break;              default:                 break;          }      }      while (shmctl(shm_id, IPC_RMID, NULL)) {         TEST_ERROR;     }      while((child_pid = wait(&status)) != -1) {         printf("PARENT: %d, CHILD_TERMINATED: %d STATUS: %d \n", getpid(), child_pid, WEXITSTATUS(status));          }         semctl(sem_resource, 0, IPC_RMID);     semctl(sem_mutex, 0, IPC_RMID);   } 

This is the wait-signal portion

And this is the code of interest