--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/env/lib/python3.7/site-packages/cwltool/mutation.py	Sat May 02 07:14:21 2020 -0400
@@ -0,0 +1,84 @@
+from __future__ import absolute_import
+
+from collections import namedtuple
+from typing import Any, Dict
+
+from typing_extensions import Text  # pylint: disable=unused-import
+# move to a regular typing import when Python 3.3-3.6 is no longer supported
+
+from .errors import WorkflowException
+
+
+MutationState = namedtuple("MutationTracker", ["generation", "readers", "stepname"])
+
+_generation = "http://commonwl.org/cwltool#generation"
+
+class MutationManager(object):
+    """Lock manager for checking correctness of in-place update of files.
+
+    Used to validate that in-place file updates happen sequentially, and that a
+    file which is registered for in-place update cannot be read or updated by
+    any other steps.
+
+    """
+
+    def __init__(self):  # type: () -> None
+        """Initialize."""
+        self.generations = {}  # type: Dict[Text, MutationState]
+
+    def register_reader(self, stepname, obj):
+        # type: (Text, Dict[Text, Any]) -> None
+        loc = obj["location"]
+        current = self.generations.get(loc, MutationState(0, [], ""))
+        obj_generation = obj.get(_generation, 0)
+
+        if obj_generation != current.generation:
+            raise WorkflowException(
+                "[job {}] wants to read {} from generation {} but current "
+                "generation is {}(last updated by {})".format(
+                    stepname, loc, obj_generation, current.generation, current.stepname))
+
+        current.readers.append(stepname)
+        self.generations[loc] = current
+
+    def release_reader(self, stepname, obj):
+        # type: (Text, Dict[Text, Any]) -> None
+        loc = obj["location"]
+        current = self.generations.get(loc, MutationState(0, [], ""))
+        obj_generation = obj.get(_generation, 0)
+
+        if obj_generation != current.generation:
+            raise WorkflowException(
+                "[job {}] wants to release reader on {} from generation {}"
+                " but current generation is {} (last updated by {})".format(
+                    stepname, loc, obj_generation, current.generation,
+                    current.stepname))
+
+        self.generations[loc].readers.remove(stepname)
+
+    def register_mutation(self, stepname, obj):
+        # type: (Text, Dict[Text, Any]) -> None
+        loc = obj["location"]
+        current = self.generations.get(loc, MutationState(0, [], ""))
+        obj_generation = obj.get(_generation, 0)
+
+        if len(current.readers) > 0:
+            raise WorkflowException(
+                "[job {}] wants to modify {} but has readers: {}".format(
+                    stepname, loc, current.readers))
+
+        if obj_generation != current.generation:
+            raise WorkflowException(
+                "[job {}] wants to modify {} from generation {} but current "
+                "generation is {} (last updated by {})".format(
+                    stepname, loc, obj_generation, current.generation, current.stepname))
+
+        self.generations[loc] = MutationState(current.generation+1, current.readers, stepname)
+
+    def set_generation(self, obj):  # type: (Dict[Text, Text]) -> None
+        loc = obj["location"]
+        current = self.generations.get(loc, MutationState(0, [], ""))
+        obj[_generation] = current.generation
+
+    def unset_generation(self, obj):  # type: (Dict[Text, Text]) -> None
+        obj.pop(_generation, None)