1 files changed, 80 insertions, 0 deletions
diff --git a/coverage/multiproc.py b/coverage/multiproc.py
new file mode 100644
index 0000000..d0bdf00
--- /dev/null
+++ b/coverage/multiproc.py
@@ -0,0 +1,80 @@
+# Licensed under the Apache License: http://www.apache.org/licenses/LICENSE-2.0
+# For details: https://bitbucket.org/ned/coveragepy/src/default/NOTICE.txt
+
+"""Monkey-patching to make coverage.py work right in some cases."""
+
+import multiprocessing
+import multiprocessing.process
+import sys
+
+# An attribute that will be set on modules to indicate that they have been
+# 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.
+
+    This enables coverage measurement of processes started by multiprocessing.
+    This is wildly experimental!
+
+    """
+    if hasattr(multiprocessing, PATCHED_MARKER):
+        return
+
+    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
+        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)