Merge pull request #3 from PrathamKumar125/PrathamKumar125-patch-4

Create Dining_Philosophers_Problem.c

Author: PrathamKumar125

Diff for: code/operating_system/src/concurrency/dining_philosophers/Dining_Philosophers_Problem.c

@@ -0,0 +1,99 @@
+#include <stdio.h>
+#include <semaphore.h>
+#include <pthread.h>
+ 
+#define N 5
+#define THINKING 2
+#define HUNGRY 1
+#define EATING 0
+#define LEFT (phnum + 4)%N
+#define RIGHT (phnum + 1)%N
+ 
+int state[N];
+int phil[N] = {0, 1, 2, 3, 4};
+
+sem_t mutex;
+sem_t S[N];
+ 
+void test(int phnum)
+{
+    if (state[phnum] == HUNGRY && state[LEFT] != EATING && state[RIGHT] != EATING)
+    {
+        //state that eating
+        state[phnum] = EATING;
+        sleep(2);
+        printf("Philosopher %d takes fork %d and %d\n", phnum + 1, LEFT + 1, phnum + 1);
+        printf("Philosopher %d is Eating\n", phnum + 1);
+
+        //sem_post(&S[phnum]) has no effect during takefork
+        //used to wake up hungry philosophers during putfork
+        sem_post(&S[phnum]);
+    }
+}
+
+//take up chopsticks 
+void take_fork(int phnum)
+{
+    //access critical section
+    sem_wait(&mutex);
+    //state that hungry
+    state[phnum] = HUNGRY;
+    printf("Philosopher %d is Hungry\n", phnum + 1);
+
+    //eat if neighbours are not eating
+    test(phnum);
+    //leave critical section
+    sem_post(&mutex);
+
+    //if unable to eat wait to be signalled
+    sem_wait(&S[phnum]);
+    sleep(1);
+}
+ 
+
+//put down chopsticks
+void put_fork(int phnum)
+{
+    //access critical section
+    sem_wait(&mutex); 
+    // state that thinking
+    state[phnum] = THINKING;
+    printf("Philosopher %d putting", phnum + 1);
+	printf(" fork %d and %d down\n", LEFT + 1, phnum + 1);
+    printf("Philosopher %d is thinking\n", phnum + 1);
+    test(LEFT);
+    test(RIGHT);
+    //leave critical section
+    sem_post(&mutex);
+}
+
+void *philospher(void *num)
+{
+    while(1)
+    {
+        int *i = num;
+        sleep(1);
+        take_fork(*i);
+        sleep(0);
+        put_fork(*i);
+    }
+}
+ 
+int main()
+{
+    int i;
+    pthread_t thread_id[N];
+    // initialize the semaphores
+    sem_init(&mutex, 0, 1);
+    for(i = 0; i < N; i++)
+        sem_init(&S[i], 0, 0);
+    for(i = 0; i < N; i++)
+    {
+        // create philosopher processes
+        pthread_create(&thread_id[i], NULL, philospher, &phil[i]);
+        printf("Philosopher %d is thinking\n", i + 1);
+    }
+    for(i = 0; i < N; i++)
+        pthread_join(thread_id[i], NULL);
+    return 0;
+}