view tests/test-bundle-type.t @ 26457:7e81305092a0

demandimport: replace more references to _demandmod instances

_demandmod instances may be referenced by multiple importing modules.
Before this patch, the _demandmod instance only maintained a reference
to its first consumer when using the "from X import Y" syntax. This is
because we only created a single _demandmod instance (attached to the
parent X module). If multiple modules A and B performed
"from X import Y", we'd produce a single _demandmod instance
"demandmod" with the following references:

  X.Y = <demandmod>
  A.Y = <demandmod>
  B.Y = <demandmod>

The locals from the first consumer (A) would be stored in <demandmod1>.
When <demandmod1> was loaded, we'd look at the locals for the first
consumer and replace the symbol, if necessary. This resulted in state:

  X.Y = <module>
  A.Y = <module>
  B.Y = <demandmod>

B's reference to Y wasn't updated and was still using the proxy object
because we just didn't record that B had a reference to <demandmod> that
needed updating!

With this patch, we add support for tracking which modules in addition
to the initial importer have a reference to the _demandmod instance and
we replace those references at module load time.

In the case of posix.py, this fixes an issue where the "encoding" module
was being proxied, resulting in hundreds of thousands of
__getattribute__ lookups on the _demandmod instance during dirstate
operations on mozilla-central, speeding up execution by many
milliseconds. There are likely several other operation that benefit from
this change as well.

The new mechanism isn't perfect: references in locals (not globals) may
likely linger. So, if there is an import inside a function and a symbol
from that module is used in a hot loop, we could have unwanted overhead
from proxying through _demandmod. Non-global imports are discouraged
anyway. So hopefully this isn't a big deal in practice. We could
potentially deploy a code checker that bans use of attribute lookups of
function-level-imported modules inside loops.

This deficiency in theory could be avoided by storing the set of globals
and locals dicts to update in the _demandmod instance. However, I tried
this and it didn't work. One reason is that some globals are _demandmod
instances. We could work around this, but it's a bit more work. There
also might be other module import foo at play. The solution as
implemented is better than what we had and IMO is good enough for the
time being.

It's worth noting that this sub-optimal behavior was made worse by the
introduction of absolute_import and its recommended "from . import X"
syntax for importing modules from the "mercurial" package. If we ever
wrote performance tests, measuring the amount of module imports and
__getattribute__ proxy calls through _demandmod instances would be
something I'd have it check.

bundle w/o type option

  $ hg init t1
  $ hg init t2
  $ cd t1
  $ echo blablablablabla > file.txt
  $ hg ci -Ama
  adding file.txt
  $ hg log | grep summary
  summary:     a
  $ hg bundle ../b1 ../t2
  searching for changes
  1 changesets found

  $ cd ../t2
  $ hg pull ../b1
  pulling from ../b1
  requesting all changes
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 1 changes to 1 files
  (run 'hg update' to get a working copy)
  $ hg up
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg log | grep summary
  summary:     a
  $ cd ..

test bundle types

  $ for t in "None" "bzip2" "gzip"; do
  >   echo % test bundle type $t
  >   hg init t$t
  >   cd t1
  >   hg bundle -t $t ../b$t ../t$t
  >   cut -b 1-6 ../b$t | head -n 1
  >   cd ../t$t
  >   hg pull ../b$t
  >   hg up
  >   hg log | grep summary
  >   cd ..
  > done
  % test bundle type None
  searching for changes
  1 changesets found
  HG10UN
  pulling from ../bNone
  requesting all changes
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 1 changes to 1 files
  (run 'hg update' to get a working copy)
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  summary:     a
  % test bundle type bzip2
  searching for changes
  1 changesets found
  HG10BZ
  pulling from ../bbzip2
  requesting all changes
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 1 changes to 1 files
  (run 'hg update' to get a working copy)
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  summary:     a
  % test bundle type gzip
  searching for changes
  1 changesets found
  HG10GZ
  pulling from ../bgzip
  requesting all changes
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 1 changes to 1 files
  (run 'hg update' to get a working copy)
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  summary:     a

test garbage file

  $ echo garbage > bgarbage
  $ hg init tgarbage
  $ cd tgarbage
  $ hg pull ../bgarbage
  pulling from ../bgarbage
  abort: ../bgarbage: not a Mercurial bundle
  [255]
  $ cd ..

test invalid bundle type

  $ cd t1
  $ hg bundle -a -t garbage ../bgarbage
  abort: unknown bundle type specified with --type
  [255]
  $ cd ..