stuff

Examples/pthreads/pthreads_race.c

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+/*
+ * pthreads_race.c - Shows a "race condition" when multiple threads
+ *                   try to race to modify a global value
+ *                   Due to unpredictable behavior in context switching
+ *                   the value of global_value does not result in what is
+ *                   expected
+ */
+
+#include <pthread.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+int global_value = 0;
+
+void* thread_routine()
+{
+    for(int i = 0; i < 100000000; i++) {
+        global_value++;
+    }
+    return NULL;
+}
+
+int main()
+{
+    // Create 5 threads
+    pthread_t thr_id[5];
+    for(int i = 0; i < 5; i++) {
+        if(pthread_create(&thr_id[i], NULL, thread_routine, NULL) == -1) {
+            printf("COULD NOT CREATE A THREAD\n");
+            exit(EXIT_FAILURE);
+        }
+    }
+
+    // Wait for all threads to finish
+    for(int i = 0; i < 5; i++) {
+        pthread_join(thr_id[i], NULL);
+    }
+
+    // Print out final value of global value
+    // 5 threads * 100000000 iterations - expected value is 500000000
+    printf("PARENT READS GLOBAL: %d\n", global_value);
+
+    // Return success
+    return 0;
+}