util: add a popoldest() method to lrucachedict
This allows consumers to prune the oldest item from the cache. This
could be useful for e.g. a consumer that wishes for the size of
items tracked by the cache to remain under a high water mark.
Differential Revision: https://phab.mercurial-scm.org/D4501
--- a/mercurial/util.py Thu Sep 06 11:40:20 2018 -0700
+++ b/mercurial/util.py Wed Sep 05 23:15:20 2018 -0700
@@ -1341,6 +1341,28 @@
return result
+ def popoldest(self):
+ """Remove the oldest item from the cache.
+
+ Returns the (key, value) describing the removed cache entry.
+ """
+ if not self._cache:
+ return
+
+ # Walk the linked list backwards starting at tail node until we hit
+ # a non-empty node.
+ n = self._head.prev
+ while n.key is _notset:
+ n = n.prev
+
+ key, value = n.key, n.value
+
+ # And remove it from the cache and mark it as empty.
+ del self._cache[n.key]
+ n.markempty()
+
+ return key, value
+
def _movetohead(self, node):
"""Mark a node as the newest, making it the new head.
--- a/tests/test-lrucachedict.py Thu Sep 06 11:40:20 2018 -0700
+++ b/tests/test-lrucachedict.py Wed Sep 05 23:15:20 2018 -0700
@@ -172,5 +172,30 @@
self.assertIn(key, d)
self.assertEqual(d[key], 'v%s' % key)
+ def testpopoldest(self):
+ d = util.lrucachedict(4)
+ d['a'] = 'va'
+ d['b'] = 'vb'
+
+ self.assertEqual(len(d), 2)
+ self.assertEqual(d.popoldest(), ('a', 'va'))
+ self.assertEqual(len(d), 1)
+ self.assertEqual(d.popoldest(), ('b', 'vb'))
+ self.assertEqual(len(d), 0)
+ self.assertIsNone(d.popoldest())
+
+ d['a'] = 'va'
+ d['b'] = 'vb'
+ d['c'] = 'vc'
+ d['d'] = 'vd'
+
+ self.assertEqual(d.popoldest(), ('a', 'va'))
+ self.assertEqual(len(d), 3)
+ for key in ('b', 'c', 'd'):
+ self.assertEqual(d[key], 'v%s' % key)
+
+ d['a'] = 'va'
+ self.assertEqual(d.popoldest(), ('b', 'vb'))
+
if __name__ == '__main__':
silenttestrunner.main(__name__)