examples/: Add test program mutex.cpp

rt/examples/mutex.cpp

+#include <typon/typon.hpp>
+#include <typon/logger.hpp>
+
+
+using namespace typon;
+
+Mutex mutex;
+
+int N = 30;
+
+int fibo(int n) {
+  if (n < 2)
+    return n;
+  return fibo(n - 1) + fibo(n - 2);
+}
+
+Task<void> with_lock(int id)
+{
+  {
+    LOG("with_lock(%d), locking", id);
+    auto lock = mutex.lock();
+    co_await lock;
+    LOG("with_lock(%d), acquired", id);
+    int n = fibo(N);
+    LOG("with_lock(%d), fibo(%d) = %d", id, N, n);
+  }
+  LOG("with_lock(%d), released", id);
+}
+
+Join<void> parallel() {
+  for (int id = 0; id < 10; id++) {
+    co_await fork(with_lock(id));
+  }
+}
+
+Root root() {
+  co_await parallel();
+}
+
+int main() {
+  root().call();
+  puts("done");
+  return 0;
+}