Don't throw exceptions when logging

When NMSLIB is logging to the python logger, there can occasionally be exceptions
be thrown on system exit (https://github.com/nmslib/nmslib/issues/327).

Fix by trapping these exceptions since making a log call shouldn't throw an exception.

python_bindings/nmslib.cc

@@ -388,23 +388,32 @@ class PythonLogger
            int line,
            const char * function,
            const std::string & message) {
-    AcquireGIL l;
-    switch(severity) {
-      case LIB_DEBUG:
-        inner.attr("debug")(message);
-        break;
-      case LIB_INFO:
-        inner.attr("info")(message);
-        break;
-      case LIB_WARNING:
-        inner.attr("warning")(message);
-        break;
-      case LIB_ERROR:
-        inner.attr("error")(message);
-        break;
-      case LIB_FATAL:
-        inner.attr("critical")(message);
-        break;
+    // In cases when the interpreter was shutting down, attempting to log in python
+    // could throw an exception (https://github.com/nmslib/nmslib/issues/327).
+    // Logging shouldn't cause exceptions, so catch it and dump to stderr instead.
+    try {
+      AcquireGIL l;
+      switch(severity) {
+        case LIB_DEBUG:
+          inner.attr("debug")(message);
+          break;
+        case LIB_INFO:
+          inner.attr("info")(message);
+          break;
+        case LIB_WARNING:
+          inner.attr("warning")(message);
+          break;
+        case LIB_ERROR:
+          inner.attr("error")(message);
+          break;
+        case LIB_FATAL:
+          inner.attr("critical")(message);
+          break;
+      }
+    } catch (const std::exception & e) {
+      std::cerr << "Failed to log '" << message << "'. Exception:" << e.what() << std::endl;
+    } catch (...) {
+      std::cerr << "Failed to log '" << message << "'" << std::endl;
     }
   }
 };

python_bindings/tests/bindings_test.py

@@ -169,5 +169,11 @@ def testSparse(self):
         self.assertEqual(index[3], [(3, 1.0)])
 
 
+class GlobalTestCase(unittest.TestCase):
+    def testGlobal(self):
+        # this is a one line reproduction of https://github.com/nmslib/nmslib/issues/327
+        GlobalTestCase.index = nmslib.init()
+
+
 if __name__ == "__main__":
     unittest.main()