Disabled external gits

cs453-ca/CS453-2021-project/sync-examples/election4.c

@@ -0,0 +1,48 @@
+#include <pthread.h>
+#include <inttypes.h>
+#include <assert.h>
+#include <stdio.h>
+#include <stdatomic.h>
+
+#define RUNS (4096 * 256)
+#define THREADS 4
+
+static atomic_int leader[RUNS] = { 0 };
+static atomic_int nb_leaders[RUNS] = { 0 }; // used to check correctness
+
+void* elect(void* _tid) {
+  intptr_t tid = (intptr_t) _tid;
+  for (int r = 0; r < RUNS; r++) {
+    int expected = 0;
+    if (atomic_compare_exchange_strong(&leader[r], &expected, tid)) {
+      atomic_fetch_add(&nb_leaders[r], 1); // used to check correctness
+    }
+    // **Correct**, we use the Compare and Swap operation to atomically check if
+    // a leader has already been elected and if not, we impose ourselves. :)
+  }
+}
+
+int main() {
+  pthread_t handlers[THREADS];
+
+  for (intptr_t i = 0; i < THREADS; i++) {
+    int res = pthread_create(&handlers[i], NULL, elect, (void*)(i + 1));
+    assert(!res);
+  }
+
+  for (int i = 0; i < THREADS; i++) {
+    int res = pthread_join(handlers[i], NULL);
+    assert(!res);
+  }
+
+  int r = 0;
+  for (; r < RUNS; r++) {
+    if (nb_leaders[r] != 1) {
+      printf("Leader election for round %d failed.\n", r);
+      break;
+    }
+  }
+  if (r == RUNS) {
+    printf("Looks correct to me! :)\n");
+  }
+}