1 files changed, 50 insertions, 20 deletions
diff --git a/coverage/monkey.py b/coverage/monkey.py
index c4ec68c6..e7517bf6 100644
--- a/coverage/monkey.py
+++ b/coverage/monkey.py
@@ -11,6 +11,36 @@ import sys
 # monkey-patched.
 PATCHED_MARKER = "_coverage$patched"
 
+if sys.version_info >= (3, 4):
+    klass = multiprocessing.process.BaseProcess
+else:
+    klass = multiprocessing.Process
+
+original_bootstrap = klass._bootstrap
+
+
+class ProcessWithCoverage(klass):
+    """A replacement for multiprocess.Process that starts coverage."""
+    def _bootstrap(self):
+        """Wrapper around _bootstrap to start coverage."""
+        from coverage import Coverage
+        cov = Coverage(data_suffix=True)
+        cov.start()
+        try:
+            return original_bootstrap(self)
+        finally:
+            cov.stop()
+            cov.save()
+
+
+class Stowaway(object):
+    """An object to pickle, so when it is unpickled, it can apply the monkey-patch."""
+    def __getstate__(self):
+        return {}
+
+    def __setstate__(self, state_unused):
+        patch_multiprocessing()
+
 
 def patch_multiprocessing():
     """Monkey-patch the multiprocessing module.
@@ -23,28 +53,28 @@ def patch_multiprocessing():
         return
 
     if sys.version_info >= (3, 4):
-        klass = multiprocessing.process.BaseProcess
-    else:
-        klass = multiprocessing.Process
-
-    original_bootstrap = klass._bootstrap
-
-    class ProcessWithCoverage(klass):
-        """A replacement for multiprocess.Process that starts coverage."""
-        def _bootstrap(self):
-            """Wrapper around _bootstrap to start coverage."""
-            from coverage import Coverage
-            cov = Coverage(data_suffix=True)
-            cov.start()
-            try:
-                return original_bootstrap(self)
-            finally:
-                cov.stop()
-                cov.save()
-
-    if sys.version_info >= (3, 4):
         klass._bootstrap = ProcessWithCoverage._bootstrap
     else:
         multiprocessing.Process = ProcessWithCoverage
 
+    # When spawning processes rather than forking them, we have no state in the
+    # new process.  We sneak in there with a Stowaway: we stuff one of our own
+    # objects into the data that gets pickled and sent to the sub-process. When
+    # the Stowaway is unpickled, it's __setstate__ method is called, which
+    # re-applies the monkey-patch.
+    # Windows only spawns, so this is needed to keep Windows working.
+    try:
+        from multiprocessing import spawn           # pylint: disable=no-name-in-module
+        original_get_preparation_data = spawn.get_preparation_data
+    except (ImportError, AttributeError):
+        pass
+    else:
+        def get_preparation_data_with_stowaway(name):
+            """Get the original preparation data, and also insert our stowaway."""
+            d = original_get_preparation_data(name)
+            d['stowaway'] = Stowaway()
+            return d
+
+        spawn.get_preparation_data = get_preparation_data_with_stowaway
+
     setattr(multiprocessing, PATCHED_MARKER, True)