Mercurial > hg-stable
view tests/cgienv @ 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.
author | Gregory Szorc <gregory.szorc@gmail.com> |
---|---|
date | Sun, 04 Oct 2015 11:17:43 -0700 |
parents | aa3f726a2bdb |
children |
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DOCUMENT_ROOT="/var/www/hg"; export DOCUMENT_ROOT GATEWAY_INTERFACE="CGI/1.1"; export GATEWAY_INTERFACE HTTP_ACCEPT="text/xml,application/xml,application/xhtml+xml,text/html;q=0.9,text/plain;q=0.8,image/png,*/*;q=0.5"; export HTTP_ACCEPT HTTP_ACCEPT_CHARSET="ISO-8859-1,utf-8;q=0.7,*;q=0.7"; export HTTP_ACCEPT_CHARSET HTTP_ACCEPT_ENCODING="gzip,deflate"; export HTTP_ACCEPT_ENCODING HTTP_ACCEPT_LANGUAGE="en-us,en;q=0.5"; export HTTP_ACCEPT_LANGUAGE HTTP_CACHE_CONTROL="max-age=0"; export HTTP_CACHE_CONTROL HTTP_CONNECTION="keep-alive"; export HTTP_CONNECTION HTTP_HOST="hg.omnifarious.org"; export HTTP_HOST HTTP_KEEP_ALIVE="300"; export HTTP_KEEP_ALIVE HTTP_USER_AGENT="Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.8.0.4) Gecko/20060608 Ubuntu/dapper-security Firefox/1.5.0.4"; export HTTP_USER_AGENT PATH_INFO="/"; export PATH_INFO PATH_TRANSLATED="/var/www/hg/index.html"; export PATH_TRANSLATED QUERY_STRING=""; export QUERY_STRING REMOTE_ADDR="127.0.0.2"; export REMOTE_ADDR REMOTE_PORT="44703"; export REMOTE_PORT REQUEST_METHOD="GET"; export REQUEST_METHOD REQUEST_URI="/test/"; export REQUEST_URI SCRIPT_FILENAME="/home/hopper/hg_public/test.cgi"; export SCRIPT_FILENAME SCRIPT_NAME="/test"; export SCRIPT_NAME SCRIPT_URI="http://hg.omnifarious.org/test/"; export SCRIPT_URI SCRIPT_URL="/test/"; export SCRIPT_URL SERVER_ADDR="127.0.0.1"; export SERVER_ADDR SERVER_ADMIN="eric@localhost"; export SERVER_ADMIN SERVER_NAME="hg.omnifarious.org"; export SERVER_NAME SERVER_PORT="80"; export SERVER_PORT SERVER_PROTOCOL="HTTP/1.1"; export SERVER_PROTOCOL SERVER_SIGNATURE="<address>Apache/2.0.53 (Fedora) Server at hg.omnifarious.org Port 80</address>"; export SERVER_SIGNATURE SERVER_SOFTWARE="Apache/2.0.53 (Fedora)"; export SERVER_SOFTWARE