util: add an LRU cache dict
In certain cases we would like to have a cache of the last N results of a
given computation, where N is small. This will be used in an upcoming patch to
increase the size of the manifest cache from 1 to 3.
from mercurial import util
def printifpresent(d, xs):
for x in xs:
present = x in d
print "'%s' in d: %s" % (x, present)
if present:
print "d['%s']: %s" % (x, d[x])
def test_lrucachedict():
d = util.lrucachedict(4)
d['a'] = 'va'
d['b'] = 'vb'
d['c'] = 'vc'
d['d'] = 'vd'
# all of these should be present
printifpresent(d, ['a', 'b', 'c', 'd'])
# 'a' should be dropped because it was least recently used
d['e'] = 've'
printifpresent(d, ['a', 'b', 'c', 'd', 'e'])
# touch entries in some order (get or set).
d['e']
d['c'] = 'vc2'
d['d']
d['b'] = 'vb2'
# 'e' should be dropped now
d['f'] = 'vf'
printifpresent(d, ['b', 'c', 'd', 'e', 'f'])
if __name__ == '__main__':
test_lrucachedict()