Merge "Do not use multiprocessing.Pool when --processes=1."

am: 948ebf5510

Change-Id: Ia305f1c26706069d8e048340eac9037782f895b7

tools/warn.py

@@ -2096,6 +2096,7 @@ def classify_warnings(lines):
 def parallel_classify_warnings(warning_lines):
   """Classify all warning lines with num_cpu parallel processes."""
   num_cpu = args.processes
+  if num_cpu > 1:
     groups = [[] for x in range(num_cpu)]
     i = 0
     for x in warning_lines:
@@ -2103,6 +2104,9 @@ def parallel_classify_warnings(warning_lines):
       i = (i + 1) % num_cpu
     pool = multiprocessing.Pool(num_cpu)
     group_results = pool.map(classify_warnings, groups)
+  else:
+    group_results = [classify_warnings(warning_lines)]
+
   for result in group_results:
     for line, pattern_idx, project_idx in result:
       pattern = warn_patterns[pattern_idx]