[examples] Add ashell example and a tag to detect that a process shou…

…ld run only once

examples/Raw/Shell.hpp

@@ -0,0 +1,58 @@
+#pragma once
+
+/* SPDX-License-Identifier: GPL-3.0-or-later */
+
+#include <functional>
+#include <string>
+#include <thread>
+namespace examples
+{
+struct Shell
+{
+  static consteval auto name() { return "Shell command"; }
+  static consteval auto c_name() { return "avnd_shell"; }
+  static consteval auto category() { return "Script"; }
+  static consteval auto uuid() { return "7e4ae744-1825-4f1c-9fc9-675e41f316bc"; }
+
+  // This tag is an indication that the operator() should only called on
+  // the first tick, not on every tick
+  enum
+  {
+    single_exec
+  };
+
+  struct
+  {
+    struct
+    {
+      static constexpr auto name() { return "Script"; }
+      static constexpr auto language() { return "shell"; }
+      enum widget
+      {
+        textedit
+      };
+
+      struct range
+      {
+        const std::string_view init = "#!/bin/bash\n";
+      };
+      std::string value;
+    } command;
+  } inputs;
+
+  struct
+  {
+  } outputs;
+
+  void operator()() { worker.request(std::move(inputs.command.value)); }
+
+  struct worker
+  {
+    std::function<void(std::string)> request;
+    static void work(std::string&& s)
+    {
+      std::thread{[code = std::move(s)] { ::system(code.c_str()); }}.detach();
+    }
+  } worker;
+};
+}

include/avnd/binding/ossia/data_node.hpp

@@ -1,5 +1,7 @@
 #pragma once
 #include <avnd/binding/ossia/node.hpp>
+#include <avnd/concepts/temporality.hpp>
+
 namespace oscr
 {
 
@@ -10,11 +12,21 @@ class safe_node<T> : public safe_node_base<T, safe_node<T>>
 public:
   using safe_node_base<T, safe_node<T>>::safe_node_base;
 
+  bool exec_once{};
+
   constexpr bool scan_audio_input_channels() { return false; }
 
   OSSIA_MAXIMUM_INLINE
   void run(const ossia::token_request& tk, ossia::exec_state_facade st) noexcept override
   {
+    if constexpr(avnd::tag_single_exec<T>)
+    {
+      if(std::exchange(exec_once, true))
+      {
+        return;
+      }
+    }
+
     auto [start, frames] = st.timings(tk);
 
     if(!this->prepare_run(tk, start, frames))

include/avnd/concepts/temporality.hpp

@@ -0,0 +1,18 @@
+#pragma once
+
+/* SPDX-License-Identifier: GPL-3.0-or-later OR BSL-1.0 OR CC0-1.0 OR CC-PDCC OR 0BSD */
+
+#include <avnd/common/concepts_polyfill.hpp>
+#include <avnd/common/enums.hpp>
+#include <avnd/concepts/generic.hpp>
+
+namespace avnd
+{
+/**
+ * @brief single_exec tag: the 'process' method should only be called once 
+ * per execution.
+ * 
+ * Example: in ossia, this means that the processor can be assigned to a state.
+ */
+AVND_DEFINE_TAG(single_exec)
+}