coverage: cache parsed C files to avoid parsing them again

Cython/Coverage.py

@@ -37,10 +37,12 @@ def _find_dep_file_path(main_file, file_path):
 
 
 class Plugin(CoveragePlugin):
-    # map from traced file paths to corresponding C files
-    _c_files_map = None
     # map from traced file paths to absolute file paths
     _file_path_map = None
+    # map from traced file paths to corresponding C files
+    _c_files_map = None
+    # map from parsed C files to their content
+    _parsed_c_files = None
 
     def sys_info(self):
         return [('Cython version', __version__)]
@@ -155,6 +157,11 @@ class Plugin(CoveragePlugin):
         Each executable line starts with a comment header that states source file
         and line number, as well as the surrounding range of source code lines.
         """
+        if self._parsed_c_files is None:
+            self._parsed_c_files = {}
+        if c_file in self._parsed_c_files:
+            code_lines = self._parsed_c_files[c_file]
+        else:
             match_source_path_line = re.compile(r' */[*] +"(.*)":([0-9]+)$').match
             match_current_code_line = re.compile(r' *[*] (.*) # <<<<<<+$').match
             match_comment_end = re.compile(r' *[*]/$').match
@@ -188,15 +195,17 @@ class Plugin(CoveragePlugin):
                             # unexpected comment format - false positive?
                             break
 
+            self._parsed_c_files[c_file] = code_lines
+
         if self._c_files_map is None:
             self._c_files_map = {}
 
-        for filename in filenames:
+        for filename, code in code_lines.iteritems():
             abs_path = _find_dep_file_path(c_file, filename)
-            self._c_files_map[abs_path] = (c_file, filename, code_lines[filename])
+            self._c_files_map[abs_path] = (c_file, filename, code)
 
         if sourcefile not in self._c_files_map:
-            return (None,) * 2  # shouldn't happen ...
+            return (None,) * 2  # e.g. shared library file
         return self._c_files_map[sourcefile][1:]