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  1. #include <stdio.h>
  2. #include <pthread.h>
  3. #include <semaphore.h>
  4. #include <unistd.h>
  5. sem_t mutex, wrt;
  6. int readcount = 0;
  7. int data = 0;
  8. void* reader(void* arg)
  9. {
  10.     int id = *(int*)arg;
  11.     sem_wait(&mutex);
  12.     readcount++;
  13.     if(readcount == 1)
  14.         sem_wait(&wrt);
  15.     sem_post(&mutex);
  16.     printf("Reader %d reads data = %d\n", id, data);
  17.     sleep(1);
  18.     sem_wait(&mutex);
  19.     readcount--;
  20.     if(readcount == 0)
  21.         sem_post(&wrt);
  22.     sem_post(&mutex);
  23.     return NULL;
  24. }
  25. void* writer(void* arg)
  26. {
  27.     int id = *(int*)arg;
  28.     sem_wait(&wrt);
  29.     data++;
  30.     printf("Writer %d writes data = %d\n", id, data);
  31.     sleep(1);
  32.     sem_post(&wrt);
  33.     return NULL;
  34. }
  35. int main()
  36. {
  37.     pthread_t r[3], w[2];
  38.     int r_id[3] = {1,2,3};
  39.     int w_id[2] = {1,2};
  40.     sem_init(&mutex, 0, 1);
  41.     sem_init(&wrt, 0, 1);
  42.     for(int i = 0; i < 3; i++)
  43.         pthread_create(&r[i], NULL, reader, &r_id[i]);
  44.     for(int i = 0; i < 2; i++)
  45.         pthread_create(&w[i], NULL, writer, &w_id[i]);
  46.     for(int i = 0; i < 3; i++)
  47.         pthread_join(r[i], NULL);
  48.     for(int i = 0; i < 2; i++)
  49.         pthread_join(w[i], NULL);
  50.     sem_destroy(&mutex);
  51.     sem_destroy(&wrt);
  52.  
  53.     return 0;
  54. }
Success #stdin #stdout 0s 5284KB
comments (?)
stdin
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Standard input is empty
stdout
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Writer 2 writes data = 1
Writer 1 writes data = 2
Reader 3 reads data = 2
Reader 2 reads data = 2
Reader 1 reads data = 2
https://ideone.com/yZJlt2
language:
C (gcc 8.3)
created:
1 day ago
visibility:
public

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