Log helpful error message if mmap fails.

CHANGELOG.md

@@ -28,6 +28,7 @@
       - fixed a bug that could result in inconsistent behaviour when collapsing instructions
       - fixed a bug that could result in crashes when leaving a ferry directly onto a motorway ramp
       - fixed a bug in the tile plugin that resulted in discovering invalid edges for connections
+      - improved error messages when missing files during traffic updates (#3114)
     - Debug Tiles
       - Added support for turn penalties
     - Internals

features/options/contract/invalid.feature

@@ -3,6 +3,14 @@ Feature: osrm-contract command line options: invalid options
 
     Background:
         Given the profile "testbot"
+        And the node map
+            """
+            a b
+            """
+        And the ways
+            | nodes |
+            | ab    |
+        And the data has been extracted
 
     Scenario: osrm-contract - Non-existing option
         When I try to run "osrm-contract --fly-me-to-the-moon"
@@ -10,3 +18,11 @@ Feature: osrm-contract command line options: invalid options
         And stderr should contain "option"
         And stderr should contain "fly-me-to-the-moon"
         And it should exit with an error
+
+    # This tests the error messages when you try to use --segment-speed-file,
+    # but osrm-extract has not been run with --generate-edge-lookup
+    Scenario: osrm-contract - Someone forgot --generate-edge-lookup on osrm-extract
+        When I try to run "osrm-contract --segment-speed-file /dev/null {processed_file}"
+        Then stderr should contain "Error while trying to mmap"
+        Then stderr should contain ".osrm.edge_penalties"
+        And it should exit with an error

src/contractor/contractor.cpp

@@ -521,10 +521,18 @@ EdgeID Contractor::LoadEdgeExpandedGraph(
         using boost::interprocess::mapped_region;
         using boost::interprocess::read_only;
 
+        try
+        {
             const file_mapping mapping{filename.c_str(), read_only};
             mapped_region region{mapping, read_only};
             region.advise(mapped_region::advice_sequential);
             return region;
+        }
+        catch (const std::exception &e)
+        {
+            util::Log(logERROR) << "Error while trying to mmap " + filename + ": " + e.what();
+            throw;
+        }
     };
 
     const auto edge_based_graph_region = mmap_file(edge_based_graph_filename);