Add graph references

references/igraph-1.0.1/etc/cmake/tls.cmake

@@ -0,0 +1,25 @@
+tristate(IGRAPH_ENABLE_TLS "Enable thread-local storage for igraph global variables" AUTO)
+
+include(CheckTLSSupport)
+check_tls_support(TLS_KEYWORD)
+
+if(IGRAPH_ENABLE_TLS STREQUAL "AUTO")
+  if(TLS_KEYWORD)
+    set(IGRAPH_ENABLE_TLS ON)
+  else()
+    set(IGRAPH_ENABLE_TLS OFF)
+  endif()
+endif()
+
+if(IGRAPH_ENABLE_TLS)
+  if(NOT TLS_KEYWORD)
+    message(FATAL_ERROR "Thread-local storage not supported on this compiler")
+  endif()
+
+  # TODO: we should probably set this only if we are building igraph with
+  # internal-everything
+  set(IGRAPH_THREAD_SAFE YES)
+else()
+  set(TLS_KEYWORD "")
+  set(IGRAPH_THREAD_SAFE NO)
+endif()