WC lock idea and patch with stub functions
joey
parent
d72c5c558b
commit
9586107d13
|
|
@ -3,19 +3,118 @@ changes at once with its commit message (see r2779). The loser gets a
|
|||
message that there were conflicts and gets to see his own edits as the
|
||||
conflicting edits he's supposed to resolve.
|
||||
|
||||
This can happen because CGI.pm writes the change, then drops the lock
|
||||
before calling rcs_commit. It can't keep the lock because the commit hook
|
||||
needs to be able to lock.
|
||||
This can happen because CGI.pm writes the change, then drops the main wiki
|
||||
lock before calling rcs_commit. It can't keep the lock because the commit
|
||||
hook needs to be able to lock.
|
||||
|
||||
Using a shared reader lock plus an exclusive writer lock would seem to
|
||||
allow getting around this. The CGI would need the exclusive lock when
|
||||
editing the WC, then it could drop/convert that to the reader lock, keep
|
||||
the lock open, and lauch the post-commit hook, which would use the reader
|
||||
lock.
|
||||
We batted this around for an hour or two on irc. The best solution seems to
|
||||
be adding a subsidiary second lock, which is only used to lock the working
|
||||
copy and is a blocking read/write lock.
|
||||
|
||||
One problem with the reader/writer idea is that the post-commit hook writes
|
||||
wiki state.
|
||||
* As before, the CGI will take the main wiki lock when starting up.
|
||||
* Before writing to the WC, the CGI takes an exclusive lock on the WC.
|
||||
* After writing to the WC, the CGI can downgrade it to a shared lock.
|
||||
(This downgrade has to happen atomically, to prevent other CGIs from
|
||||
stealing the exclusive lock.)
|
||||
* Then the CGI, as before, drops the main wiki lock to prevent deadlock. It
|
||||
keeps its shared WC lock.
|
||||
* The commit hook takes first the main wiki lock and then the shared WC lock
|
||||
when starting up, and holds them until it's done.
|
||||
* Once the commit is done, the CGI, as before, does not attempt to regain
|
||||
the main wiki lock (that could deadlock). It does its final stuff and
|
||||
exits, dropping the shared WC lock.
|
||||
|
||||
An alternative approach might be setting a flag that prevents the
|
||||
post-commit hook from doing anything, and keeping the lock. Then the CGI
|
||||
would do the render & etc that the post-commit hook normally does.
|
||||
Sample patch, with stub functions for the new lock:
|
||||
|
||||
<pre>
|
||||
Index: IkiWiki/CGI.pm
|
||||
===================================================================
|
||||
--- IkiWiki/CGI.pm (revision 2774)
|
||||
+++ IkiWiki/CGI.pm (working copy)
|
||||
@@ -494,9 +494,14 @@
|
||||
$content=~s/\r\n/\n/g;
|
||||
$content=~s/\r/\n/g;
|
||||
|
||||
+ lockwc_exclusive();
|
||||
+
|
||||
$config{cgi}=0; # avoid cgi error message
|
||||
eval { writefile($file, $config{srcdir}, $content) };
|
||||
$config{cgi}=1;
|
||||
+
|
||||
+ lockwc_shared();
|
||||
+
|
||||
if ($@) {
|
||||
$form->field(name => "rcsinfo", value => rcs_prepedit($file),
|
||||
force => 1);
|
||||
Index: IkiWiki/Plugin/poll.pm
|
||||
===================================================================
|
||||
--- IkiWiki/Plugin/poll.pm (revision 2770)
|
||||
+++ IkiWiki/Plugin/poll.pm (working copy)
|
||||
@@ -120,7 +120,9 @@
|
||||
$content =~ s{(\\?)\[\[poll\s+([^]]+)\s*\]\]}{$edit->($1, $2)}seg;
|
||||
|
||||
# Store their vote, update the page, and redirect to it.
|
||||
+ IkiWiki::lockwc_exclusive();
|
||||
writefile($pagesources{$page}, $config{srcdir}, $content);
|
||||
+ IkiWiki::lockwc_shared();
|
||||
$session->param($choice_param, $choice);
|
||||
IkiWiki::cgi_savesession($session);
|
||||
$oldchoice=$session->param($choice_param);
|
||||
@@ -130,6 +132,10 @@
|
||||
IkiWiki::rcs_commit($pagesources{$page}, "poll vote ($choice)",
|
||||
IkiWiki::rcs_prepedit($pagesources{$page}),
|
||||
$session->param("name"), $ENV{REMOTE_ADDR});
|
||||
+ # Make sure that the repo is up-to-date;
|
||||
+ # locking prevents the post-commit hook
|
||||
+ # from updating it.
|
||||
+ rcs_update();
|
||||
}
|
||||
else {
|
||||
require IkiWiki::Render;
|
||||
Index: ikiwiki.in
|
||||
===================================================================
|
||||
--- ikiwiki.in (revision 2770)
|
||||
+++ ikiwiki.in (working copy)
|
||||
@@ -121,6 +121,7 @@
|
||||
lockwiki();
|
||||
loadindex();
|
||||
require IkiWiki::Render;
|
||||
+ lockwc_shared();
|
||||
rcs_update();
|
||||
refresh();
|
||||
rcs_notify() if $config{notify};
|
||||
Index: IkiWiki.pm
|
||||
===================================================================
|
||||
--- IkiWiki.pm (revision 2770)
|
||||
+++ IkiWiki.pm (working copy)
|
||||
@@ -617,6 +617,29 @@
|
||||
close WIKILOCK;
|
||||
} #}}}
|
||||
|
||||
+sub lockwc_exclusive () { #{{{
|
||||
+ # Take an exclusive lock on the working copy.
|
||||
+ # The lock will be dropped on program exit.
|
||||
+ # Note: This lock should only be taken _after_ the main wiki
|
||||
+ # lock.
|
||||
+
|
||||
+ # TODO
|
||||
+} #}}}
|
||||
+
|
||||
+sub lockwc_shared () { #{{{
|
||||
+ # Take a shared lock on the working copy. If an exclusive lock
|
||||
+ # already exists, downgrade it to a shared lock.
|
||||
+ # The lock will be dropped on program exit.
|
||||
+ # Note: This lock should only be taken _after_ the main wiki
|
||||
+ # lock.
|
||||
+
|
||||
+ # TODO
|
||||
+} #}}}
|
||||
+
|
||||
+sub unlockwc () { #{{{
|
||||
+ close WIKIWCLOCK;
|
||||
+} #}}}
|
||||
+
|
||||
sub loadindex () { #{{{
|
||||
open (IN, "$config{wikistatedir}/index") || return;
|
||||
while (<IN>) {
|
||||
</pre>
|
||||
|
|
|
|||
Loading…
Reference in New Issue