stuff

Examples/pthreads/pthreads4.c

@@ -0,0 +1,72 @@
+/*
+ * pthreads4.c - Shows how to pass parameter values to thread routines
+ *               The threads dereference the pointer passed to the
+ *               thread routine to demonstrate that memory is shared
+ *               between all threads
+ */
+
+#include <pthread.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+// Function to check if a number is prime
+//   Returns 1 if prime, 0 if not prime
+int is_prime(int v)
+{
+    for(int i = 2; i < v; i++) {
+        if(v % i == 0) {
+            return 0;
+        }
+    }
+    return 1;
+}
+
+// Thread routine
+//    calls is_prime to check if the input argument is prime
+//    Modifies the input parameter by dereferencing the pointer
+//
+// NOTE: that parameters and return value are pointers
+void* thread_routine(void* args)
+{
+    int* val = (int*)args;
+    if(is_prime(*val)) {
+        printf("THREAD %lu FOUND that %d is prime\n", pthread_self(), *val);
+        *val = 1;
+    } else {
+        printf("THREAD %lu FOUND that %d is not prime\n", pthread_self(), *val);
+        *val = 0;
+    }
+    return NULL;
+}
+
+int main()
+{
+    int val1 = 2;
+    int val2 = 100;
+
+    // Print out the values before creating threads
+    printf("Parent val1=%d val2=%d\n", val1, val2);
+
+    // Create 2 threads
+    pthread_t thr1;
+    pthread_t thr2;
+    if(pthread_create(&thr1, NULL, thread_routine, (void*)&val1) == -1) {
+        printf("COULD NOT CREATE A THREAD\n");
+        exit(EXIT_FAILURE);
+    }
+    if(pthread_create(&thr2, NULL, thread_routine, (void*)&val2) == -1) {
+        printf("COULD NOT CREATE A THREAD\n");
+        exit(EXIT_FAILURE);
+    }
+
+    // Wait for the threads to finish
+    pthread_join(thr1, NULL);
+    pthread_join(thr2, NULL);
+
+    // Print out the final values
+    printf("Parent val1=%d val2=%d\n", val1, val2);
+
+    // Return success
+    return 0;
+}