branchcache: skip entries that are topological heads in the on disk file
In the majority of cases, topological heads are also branch heads. We have
efficient way to get the topological heads and efficient way to retrieve
their branch information. So there is little value in putting them in the branch
cache file explicitly. On the contrary, writing them explicitly tend to create
very large cache file that are inefficient to read and update.
So the branch cache v3 format is no longer including them. This changeset focus
on the format aspect and have no focus on the performance aspect. We will cover
that later.
from mercurial import extensions
def genwrapper(x):
def f(orig, *args, **kwds):
return [x] + orig(*args, **kwds)
f.x = x
return f
def getid(wrapper):
return getattr(wrapper, 'x', '-')
wrappers = [genwrapper(i) for i in range(5)]
class dummyclass:
def getstack(self):
return ['orig']
dummy = dummyclass()
def batchwrap(wrappers):
for w in wrappers:
extensions.wrapfunction(dummy, 'getstack', w)
print('wrap %d: %s' % (getid(w), dummy.getstack()))
def batchunwrap(wrappers):
for w in wrappers:
result = None
try:
result = extensions.unwrapfunction(dummy, 'getstack', w)
msg = str(dummy.getstack())
except (ValueError, IndexError) as e:
msg = e.__class__.__name__
print('unwrap %s: %s: %s' % (getid(w), getid(result), msg))
batchwrap(wrappers + [wrappers[0]])
batchunwrap(
[
(wrappers[i] if i is not None and i >= 0 else None)
for i in [3, None, 0, 4, 0, 2, 1, None]
]
)
wrap0 = extensions.wrappedfunction(dummy, 'getstack', wrappers[0])
wrap1 = extensions.wrappedfunction(dummy, 'getstack', wrappers[1])
# Use them in a different order from how they were created to check that
# the wrapping happens in __enter__, not in __init__
print('context manager', dummy.getstack())
with wrap1:
print('context manager', dummy.getstack())
with wrap0:
print('context manager', dummy.getstack())
# Bad programmer forgets to unwrap the function, but the context
# managers still unwrap their wrappings.
extensions.wrapfunction(dummy, 'getstack', wrappers[2])
print('context manager', dummy.getstack())
print('context manager', dummy.getstack())
print('context manager', dummy.getstack())
# Wrap callable object which has no __name__
class callableobj:
def __call__(self):
return ['orig']
dummy.cobj = callableobj()
extensions.wrapfunction(dummy, 'cobj', wrappers[0])
print('wrap callable object', dummy.cobj())