very, very simple WP with midi CC out

include/libremidi/detail/semaphore.hpp

@@ -0,0 +1,24 @@
+#pragma once
+
+#include <chrono>
+#include <semaphore>
+
+struct semaphore_pair_lock
+{
+  std::binary_semaphore sem_cleanup{0};
+  std::binary_semaphore sem_needpost{0};
+  void prepare_release_client()
+  {
+    using namespace std::literals;
+
+    // FIXME if jack is not running we can skip this
+    this->sem_needpost.release();
+    this->sem_cleanup.try_acquire_for(1s);
+  }
+
+  void check_client_released()
+  {
+    if (!this->sem_needpost.try_acquire())
+      this->sem_cleanup.release();
+  }
+};