treemanifest: subclass remotetreedatastore from generatingdatastore

Summary:
Introducing class generatingdatastore to represent all stores like
remotetreedatastore which generate the trees when they are not found in the
shared store, add them to the shared store, and thereafter, repeat the original
operation on the shared store expecting it to succeed.

Reviewed By: ryanmce

Differential Revision: D6867898

fbshipit-source-id: 59af9d4833e402b36c35b6247d319888d19bef66

hgext/treemanifest/__init__.py

@@ -83,6 +83,7 @@ when the maximum size is hit.
 """
 from __future__ import absolute_import
 
+import abc
 import hashlib
 import os
 import random
@@ -1676,7 +1677,13 @@ def generatepackstream(repo, rootdir, mfnodes, basemfnodes, directories):
 
     yield wirepack.closepart()
 
-class remotetreestore(object):
+class generatingdatastore(object):
+    """Abstract base class representing stores which generate trees on the
+    fly and write them to the shared store. Thereafter, the stores replay the
+    lookup operation on the shared store expecting it to succeed."""
+    # Make this an abstract class, so it cannot be instantiated on its own.
+    __metaclass__ = abc.ABCMeta
+
     def __init__(self, repo):
         self._repo = repo
         self._shareddata = None
@@ -1685,6 +1692,39 @@ class remotetreestore(object):
         self._shareddata = shareddata
         self._sharedhistory = sharedhistory
 
+    @abc.abstractmethod
+    def _generatetrees(self, name, node):
+        pass
+
+    def get(self, name, node):
+        self._generatetrees(name, node)
+        return self._shareddata.get(name, node)
+
+    def getdeltachain(self, name, node):
+        self._generatetrees(name, node)
+        return self._shareddata.getdeltachain(name, node)
+
+    def add(self, name, node, data):
+        raise RuntimeError("cannot add to a generating store")
+
+    def getmissing(self, keys):
+        return keys
+
+    def markledger(self, ledger, options=None):
+        pass
+
+    def getmetrics(self):
+        return {}
+
+    def getancestors(self, name, node, known=None):
+        self._generatetrees(name, node)
+        return self._sharedhistory.getancestors(name, node, known=known)
+
+    def getnodeinfo(self, name, node):
+        self._generatetrees(name, node)
+        return self._sharedhistory.getnodeinfo(name, node)
+
+class remotetreestore(generatingdatastore):
     def _generatetrees(self, name, node):
         # Only look at the server if not root or is public
         basemfnodes = []
@@ -1706,34 +1746,6 @@ class remotetreestore(object):
         self._shareddata.markforrefresh()
         self._sharedhistory.markforrefresh()
 
-    def get(self, name, node):
-        self._generatetrees(name, node)
-        return self._shareddata.get(name, node)
-
-    def getdeltachain(self, name, node):
-        self._generatetrees(name, node)
-        return self._shareddata.getdeltachain(name, node)
-
-    def add(self, name, node, data):
-        raise RuntimeError("cannot add to a remote store")
-
-    def getmissing(self, keys):
-        return keys
-
-    def markledger(self, ledger, options=None):
-        pass
-
-    def getmetrics(self):
-        return {}
-
-    def getancestors(self, name, node, known=None):
-        self._generatetrees(name, node)
-        return self._sharedhistory.getancestors(name, node, known=known)
-
-    def getnodeinfo(self, name, node):
-        self._generatetrees(name, node)
-        return self._sharedhistory.getnodeinfo(name, node)
-
 def serverrepack(repo, incremental=False, options=None):
     packpath = repo.vfs.join('cache/packs/%s' % PACK_CATEGORY)