diff mercurial/util.py @ 33793:bbbbd3c30bfc

util: add base class for transactional context managers

We have at least three types with a close() and a release() method
where the close() method is supposed to be called on success and the
release() method is supposed to be called last, whether successful or
not. Two of them (transaction and dirstateguard) already have
identical implementations of __enter__ and __exit__. Let's extract a
base class for this, so we reuse the code and so the third type
(transactionmanager) can also be used as a context manager.

Differential Revision: https://phab.mercurial-scm.org/D392

--- a/mercurial/util.py	Mon Aug 14 16:26:36 2017 -0700
+++ b/mercurial/util.py	Fri Jul 28 22:42:10 2017 -0700
@@ -15,6 +15,7 @@
 
 from __future__ import absolute_import
 
+import abc
 import bz2
 import calendar
 import codecs
@@ -592,6 +593,31 @@
             for k, v in src:
                 self[k] = v
 
+class transactional(object):
+    """Base class for making a transactional type into a context manager."""
+    __metaclass__ = abc.ABCMeta
+
+    @abc.abstractmethod
+    def close(self):
+        """Successfully closes the transaction."""
+
+    @abc.abstractmethod
+    def release(self):
+        """Marks the end of the transaction.
+
+        If the transaction has not been closed, it will be aborted.
+        """
+
+    def __enter__(self):
+        return self
+
+    def __exit__(self, exc_type, exc_val, exc_tb):
+        try:
+            if exc_type is None:
+                self.close()
+        finally:
+            self.release()
+
 @contextlib.contextmanager
 def acceptintervention(tr=None):
     """A context manager that closes the transaction on InterventionRequired