From b5da31498d3f606be55d9387e075b8df6366f859 Mon Sep 17 00:00:00 2001
From: Dennis Klein <d.klein@gsi.de>
Date: Fri, 19 Jul 2019 19:48:47 +0200
Subject: [PATCH] Tools: Add InstanceLimiter utility

---
 fairmq/CMakeLists.txt        |  1 +
 fairmq/Tools.h               |  1 +
 fairmq/tools/InstanceLimit.h | 53 ++++++++++++++++++++++++++++++++++++
 3 files changed, 55 insertions(+)
 create mode 100644 fairmq/tools/InstanceLimit.h

diff --git a/fairmq/CMakeLists.txt b/fairmq/CMakeLists.txt
index 0d41cef2..26a2f860 100644
--- a/fairmq/CMakeLists.txt
+++ b/fairmq/CMakeLists.txt
@@ -35,6 +35,7 @@ if(BUILD_FAIRMQ OR BUILD_SDK)
 
   set(TOOLS_PUBLIC_HEADER_FILES
     tools/CppSTL.h
+    tools/InstanceLimit.h
     tools/Network.h
     tools/Process.h
     tools/RateLimit.h
diff --git a/fairmq/Tools.h b/fairmq/Tools.h
index f0057eb7..3ec4aff9 100644
--- a/fairmq/Tools.h
+++ b/fairmq/Tools.h
@@ -11,6 +11,7 @@
 
 // IWYU pragma: begin_exports
 #include <fairmq/tools/CppSTL.h>
+#include <fairmq/tools/InstanceLimit.h>
 #include <fairmq/tools/Network.h>
 #include <fairmq/tools/Process.h>
 #include <fairmq/tools/RateLimit.h>
diff --git a/fairmq/tools/InstanceLimit.h b/fairmq/tools/InstanceLimit.h
new file mode 100644
index 00000000..ffa1ec43
--- /dev/null
+++ b/fairmq/tools/InstanceLimit.h
@@ -0,0 +1,53 @@
+/********************************************************************************
+ *    Copyright (C) 2019 GSI Helmholtzzentrum fuer Schwerionenforschung GmbH    *
+ *                                                                              *
+ *              This software is distributed under the terms of the             *
+ *              GNU Lesser General Public Licence (LGPL) version 3,             *
+ *                  copied verbatim in the file "LICENSE"                       *
+ ********************************************************************************/
+
+#ifndef FAIR_MQ_TOOLS_INSTANCELIMIT_H
+#define FAIR_MQ_TOOLS_INSTANCELIMIT_H
+
+#include "Strings.h"
+
+namespace fair {
+namespace mq {
+namespace tools {
+
+template<typename Tag, int Max>
+struct InstanceLimiter
+{
+    InstanceLimiter() { Increment(); }
+    ~InstanceLimiter() { Decrement(); }
+    auto GetCount() -> int { return fCount; }
+
+  private:
+    auto Increment() -> void
+    {
+        if (fCount < Max) {
+            ++fCount;
+        } else {
+            throw std::runtime_error(
+                ToString("More than ", Max, " instances of ", Tag(), " in parallel not supported"));
+        }
+    }
+
+    auto Decrement() -> void
+    {
+        if (fCount > 0) {
+            --fCount;
+        }
+    }
+
+    static int fCount;
+};
+
+template<typename Tag, int Max>
+int InstanceLimiter<Tag, Max>::fCount(0);
+
+} /* namespace tools */
+} /* namespace mq */
+} /* namespace fair */
+
+#endif /* FAIR_MQ_TOOLS_INSTANCELIMIT_H */