phabstatus: batch peekahead for smartlog

Summary:
Phabstatus for smartlog uses `PeekeaheadList` rather than `PeekaheadRevsetIterator` as
all of the commits are known ahead of time, and we don't need to collect together
batches as we iterate across the revset.

However, we should still batch up requests to Phabricator, as users with very high
numbers of commits in their smartlog may hit timeouts.

Add a batching mechanism to `PeekaheadList` that splits the list into chunks to
return with each peekahead.

Reviewed By: liubov-dmitrieva

Differential Revision: D23840071

fbshipit-source-id: 68596c7eb4f7404ce6109e69914f328565e34582

eden/scm/edenscm/hgext/phabstatus.py

@@ -343,20 +343,32 @@ class PeekaheadList(object):
     the full list.
     """
 
-    def __init__(self, revs):
+    def __init__(self, revs, chunksize):
         self.revs = revs
+        self.chunksize = chunksize
+        self.offset = 0
         self.done = False
 
-    def peekahead(self):
-        self.done = True
-        return self.revs
+    def peekahead(self, chunksize=None):
+        chunksize = chunksize or self.chunksize
+        revs = self.revs[self.offset : self.offset + self.chunksize]
+        self.offset += self.chunksize
+        if self.offset >= len(self.revs):
+            self.done = True
+        return revs
 
 
 def _getsmartlogdag(orig, ui, repo, revs, *args):
     # smartlog just uses a plain list for its revisions, and not an
-    # abstractsmartset type.  We just save a copy of it.
-    repo._phabstatusrevs = PeekaheadList(revs)
-    return orig(ui, repo, revs, *args)
+    # abstractsmartset type.  We just save a copy of it in the order
+    # the commits appear in smartlog.
+    results, reserved = orig(ui, repo, revs, *args)
+
+    revs = [result[0] for result in results]
+    peekahead = repo.ui.configint("phabstatus", "logpeekaheadlist", 30)
+    repo._phabstatusrevs = PeekaheadList(revs, peekahead)
+
+    return results, reserved
 
 
 def extsetup(ui):