supersize: Parse build.ninja concurrently

tools/binary_size/libsupersize/helpers.py

Index: tools/binary_size/libsupersize/helpers.py
diff --git a/tools/binary_size/libsupersize/helpers.py b/tools/binary_size/libsupersize/helpers.py
index bddcd76479f26e71ea8ea3bcd867eb72bcca4b9d..4379f82dbbe2fea7796d4bfc79538c211b99e957 100644
--- a/tools/binary_size/libsupersize/helpers.py
+++ b/tools/binary_size/libsupersize/helpers.py
@@ -4,8 +4,40 @@
 
 """Utility methods."""
 
+import atexit
+import multiprocessing
 import os
+import threading
 
 
 SRC_ROOT = os.path.dirname(
     os.path.dirname(os.path.dirname(os.path.dirname(__file__))))
+
+
+def MakeProcessPool(*args):
+  """Wrapper for multiprocessing.Pool, with fix to terminate on exit."""
+  ret = multiprocessing.Pool(*args)
+  def close_pool():
+    ret.terminate()
+
+  def on_exit():
+    thread = threading.Thread(target=close_pool)
+    thread.daemon = True
+    thread.start()
+
+  # Without calling terminate() on a separate thread, the call can block
+  # forever.
+  atexit.register(on_exit)
+  return ret
+
+
+def ForkAndCall(func, *args, **kwargs):
+  """Uses multiprocessing to run the given function in a fork'ed process.
+
+  Returns:
+    A Result object (call .get() to get the return value)
+  """
+  pool_of_one = MakeProcessPool(1)
+  result = pool_of_one.apply_async(func, args=args, kwds=kwargs)
+  pool_of_one.close()
+  return result