nodemap: update the index with the newly written data (when appropriate)

If we are to use mmap to read the nodemap data, and if the python code is
responsible for the IO, we need to refresh the mmap after each write and provide
it back to the index.

We start this dance without the mmap first.

Differential Revision: https://phab.mercurial-scm.org/D7893

mercurial/revlogutils/nodemap.py

@@ -100,6 +100,8 b' def _persist_nodemap(tr, revlog):'
             with revlog.opener(datafile, b'r+') as fd:
                 fd.seek(target_docket.data_length)
                 fd.write(data)
+                fd.seek(0)
+                new_data = fd.read(target_docket.data_length + len(data))
             target_docket.data_length += len(data)
             target_docket.data_unused += data_changed_count
 
@@ -113,6 +115,7 b' def _persist_nodemap(tr, revlog):'
             data = persistent_data(revlog.index)
         # EXP-TODO: if this is a cache, this should use a cache vfs, not a
         # store vfs
+        new_data = data
         with revlog.opener(datafile, b'w') as fd:
             fd.write(data)
         target_docket.data_length = len(data)
@@ -122,6 +125,9 b' def _persist_nodemap(tr, revlog):'
     with revlog.opener(revlog.nodemap_file, b'w', atomictemp=True) as fp:
         fp.write(target_docket.serialize())
     revlog._nodemap_docket = target_docket
+    if util.safehasattr(revlog.index, "update_nodemap_data"):
+        revlog.index.update_nodemap_data(target_docket, new_data)
+
     # EXP-TODO: if the transaction abort, we should remove the new data and
     # reinstall the old one.