egencache: tweak redundant write check condition

We can use the raise_stat_collision attribute to determine when it is
necessary to check for redundant writes.

diff --git a/bin/egencache b/bin/egencache
index afd2baafb4df4dde8e3a8cb5c7d74406398ebc78..02ef4bdf858f1dd9a8f96458848f273a9b4ca04d 100755 (executable)
--- a/bin/egencache
+++ b/bin/egencache
@@ -226,18 +226,15 @@ class GenCache(object):
                        raise Exception("cache formats '%s' aren't supported" %
                                (" ".join(conf.cache_formats),))
 
-               self._avoid_redundant_write = set()
-               from portage.cache.metadata import database as pms_database
-               for trg_cache in self._trg_caches:
-                       if not isinstance(trg_cache, pms_database):
-                               self._avoid_redundant_write.add(id(trg_cache))
-                       elif rsync:
-                               trg_cache.raise_stat_collision = True
-                               # Make _metadata_callback write this cache first, in case
-                               # it raises a StatCollision and triggers mtime
-                               # modification.
-                               self._trg_caches = tuple([trg_cache] +
-                                       [x for x in self._trg_caches if x is not trg_cache])
+               if rsync:
+                       for trg_cache in self._trg_caches:
+                               if hasattr(trg_cache, 'raise_stat_collision'):
+                                       trg_cache.raise_stat_collision = True
+                                       # Make _metadata_callback write this cache first, in case
+                                       # it raises a StatCollision and triggers mtime
+                                       # modification.
+                                       self._trg_caches = tuple([trg_cache] +
+                                               [x for x in self._trg_caches if x is not trg_cache])
 
                self._existing_nodes = set()
 
@@ -253,7 +250,7 @@ class GenCache(object):
 
        def _write_cache(self, trg_cache, cpv, repo_path, metadata, ebuild_hash):
 
-                       if id(trg_cache) in self._avoid_redundant_write:
+                       if not hasattr(trg_cache, 'raise_stat_collision'):
                                # This cache does not avoid redundant writes automatically,
                                # so check for an identical existing entry before writing.
                                # This prevents unecessary disk writes and can also prevent
@@ -285,10 +282,12 @@ class GenCache(object):
                                        # exception from _setitem() if they detect this type of stat
                                        # collision. These exceptions are handled by bumping the
                                        # mtime on the ebuild (and the corresponding cache entry).
-                                       # This type of cache must not be included in the above
-                                       # _avoid_redundant_write set, since __setitem__ must be
-                                       # called in order to detect the StatCollision (redundant
-                                       # writes will be avoided internally). See bug #139134.
+                                       # See bug #139134. It is convenient to include checks for
+                                       # redundant writes along with the interal StatCollision
+                                       # detection code, so for caches with the
+                                       # raise_stat_collision attribute, we do not need to
+                                       # explicitly check for redundant writes like we do for the
+                                       # other cache types above.
                                        max_mtime = sc.mtime
                                        for ec, ec_hash in metadata['_eclasses_'].items():
                                                if max_mtime < ec_hash.mtime: