Adds synchronous option to avoid I/O issues in batch builds

cppwinrt/main.cpp

@@ -38,6 +38,7 @@ namespace cppwinrt
         { "brackets", 0, 0 }, // Use angle brackets for #includes (defaults to quotes)
         { "fastabi", 0, 0 }, // Enable support for the Fast ABI
         { "ignore_velocity", 0, 0 }, // Ignore feature staging metadata and always include implementations
+        { "synchronous", 0, 0 }, // Instructs cppwinrt to run on a single thread to avoid file system issues in batch builds
     };
 
     static void print_usage(writer& w)
@@ -290,6 +291,7 @@ Where <spec> is one or more of:
 
             w.flush_to_console();
             task_group group;
+            group.synchronous(args.exists("synchronous"));
             writer ixx;
             write_preamble(ixx);
             ixx.write("module;\n");

cppwinrt/task_group.h

@@ -17,14 +17,22 @@ namespace cppwinrt
             }
         }
 
+        void synchronous(bool synchronous) noexcept
+        {
+            m_synchronous = synchronous;
+        }
+
         template <typename T>
         void add(T&& callback)
         {
-#if defined(_DEBUG)
-            callback();
-#else
-            m_tasks.push_back(std::async(std::forward<T>(callback)));
-#endif
+            if (m_synchronous)
+            {
+                callback();
+            }
+            else
+            {
+                m_tasks.push_back(std::async(std::forward<T>(callback)));
+            }
         }
 
         void get()
@@ -45,5 +53,6 @@ namespace cppwinrt
     private:
 
         std::vector<std::future<void>> m_tasks;
+        bool m_synchronous{};
     };
 }