branchmap: remove the dict interface from the branchcache class (API)

The current branchmap computation involves reading the whole branchmap from
disk, validating all the nodes even if they are not required. This leads to a
lot of time on repos which have large branchmap or a lot of branches. On large
repos, this can validate around 1000's of nodes.

On some operations, like finding whether a branch exists or not, we don't need
to validate all the nodes. Or updating heads for a single branch.

Before this patch, branchcache class was having dict interface and it was hard
to keep track of reads.

This patch removes the dict interface. Upcoming patches will implement lazy
loading and validation of data and implement better API's.

Differential Revision: https://phab.mercurial-scm.org/D6151

mercurial/branchmap.py

@@ -127,7 +127,7 b' class BranchMapCache(object):'
         self._per_filter.clear()
 
 
-class branchcache(dict):
+class branchcache(object):
     """A dict like object that hold branches heads cache.
 
     This cache is used to avoid costly computations to determine all the
@@ -151,7 +151,6 b' class branchcache(dict):'
 
     def __init__(self, entries=(), tipnode=nullid, tiprev=nullrev,
                  filteredhash=None, closednodes=None):
-        super(branchcache, self).__init__(entries)
         self.tipnode = tipnode
         self.tiprev = tiprev
         self.filteredhash = filteredhash
@@ -162,6 +161,25 b' class branchcache(dict):'
             self._closednodes = set()
         else:
             self._closednodes = closednodes
+        self.entries = dict(entries)
+
+    def __iter__(self):
+        return iter(self.entries)
+
+    def __setitem__(self, key, value):
+        self.entries[key] = value
+
+    def __getitem__(self, key):
+        return self.entries[key]
+
+    def setdefault(self, *args):
+        return self.entries.setdefault(*args)
+
+    def iteritems(self):
+        return self.entries.iteritems()
+
+    def itervalues(self):
+        return self.entries.itervalues()
 
     @classmethod
     def fromfile(cls, repo):
@@ -271,8 +289,8 b' class branchcache(dict):'
 
     def copy(self):
         """return an deep copy of the branchcache object"""
-        return type(self)(
-            self, self.tipnode, self.tiprev, self.filteredhash,
+        return branchcache(
+            self.entries, self.tipnode, self.tiprev, self.filteredhash,
             self._closednodes)
 
     def write(self, repo):
@@ -295,7 +313,7 b' class branchcache(dict):'
             f.close()
             repo.ui.log('branchcache',
                         'wrote %s branch cache with %d labels and %d nodes\n',
-                        repo.filtername, len(self), nodecount)
+                        repo.filtername, len(self.entries), nodecount)
         except (IOError, OSError, error.Abort) as inst:
             # Abort may be raised by read only opener, so log and continue
             repo.ui.debug("couldn't write branch cache: %s\n" %
@@ -351,7 +369,7 b' class branchcache(dict):'
             # cache key are not valid anymore
             self.tipnode = nullid
             self.tiprev = nullrev
-            for heads in self.values():
+            for heads in self.itervalues():
                 tiprev = max(cl.rev(node) for node in heads)
                 if tiprev > self.tiprev:
                     self.tipnode = cl.node(tiprev)

mercurial/localrepo.py

@@ -1556,7 +1556,7 b' class localrepository(object):'
         return scmutil.revsymbol(self, key).node()
 
     def lookupbranch(self, key):
-        if key in self.branchmap():
+        if key in self.branchmap().entries:
             return key
 
         return scmutil.revsymbol(self, key).branch()
@@ -2730,7 +2730,7 b' class localrepository(object):'
         if branch is None:
             branch = self[None].branch()
         branches = self.branchmap()
-        if branch not in branches:
+        if branch not in branches.entries:
             return []
         # the cache returns heads ordered lowest to highest
         bheads = list(reversed(branches.branchheads(branch, closed=closed)))