Francois Gouget : testbot/lib: Make Collections try harder to return existing Item objects to avoid inconsistencies.

[Alexandre Julliard]

Module: tools
Branch: master
Commit: c1658af0dac543ad77c327eecb7216b8cadc0fdc
URL:    http://source.winehq.org/git/tools.git/?a=commit;h=c1658af0dac543ad77c327eecb7216b8cadc0fdc

Author: Francois Gouget <fgouget at codeweavers.com>
Date:   Tue May  6 12:40:27 2014 +0200

testbot/lib: Make Collections try harder to return existing Item objects to avoid inconsistencies.

Assume we have the following code:
   1: my $Jobs = CreateJobs();
   2: my $VM1 = $Jobs->GetItem(100)->Steps->GetItem(1)->Tasks->GetItem(1)->VM;
   3: my $VM2 = $Jobs->GetItem(101)->Steps->GetItem(1)->Tasks->GetItem(1)->VM;
   4: my $VM2b = $Jobs->GetItem(101)->Steps->GetItem(1)->Tasks->GetItem(1)->VM;
   5: print $VM1->Name, " is ", $VM1->Status, "\n"; # Prints 'buildvm is idle'
   6: print $VM2->Name, " is ", $VM2->Status, "\n"; # Prints 'buildvm is idle'
   7: $VM1->Status('running');
   8: $VM1->Save();
   9: print $VM1->Name, " is ", $VM1->Status, "\n"; # Prints 'buildvm is running'
  10: print $VM2->Name, " is ", $VM2->Status, "\n"; # Prints 'buildvm is idle' !!!
  11: print $VM2b->Name, " is ", $VM2b->Status, "\n"; # Prints 'buildvm is running'

The problem is that although $VM1, $VM2 and $VM2b refer to the same
VM (buildvm), they are all separate objects. Then $VM2->Status gets
loaded from the database for the print statement on line 6, and is
then never refreshed; hence the out-of-date value printed on line
10. In contrast $VM2b->Status is loaded from database for the print
statement on line 11 and thus shows the up-to-date value that was
saved on line 8. This is very confusing.

This patch associates a scope to each Collection and ensures that
there is no duplicate Item objects within that scope. Further, any
object created from a Collection inherits its scope. So in the example
above, because all objects can ultimately be traced back to the $Jobs
collection, $VM1, $VM2 and $VM2b all point to the same object which
avoids any inconsistency.

It's also possible to ensure that two Collections share the same scope
by passing the reference collection as a parameter. For instance, in
the above sample code, CreateVMs($Jobs)->GetItem('buildvm') will
return $VM1.

As before, creating a new Collection normally, CreateVMs() for
instance, ensures gets a new, empty, scope and thus reload the objects
from the database. This ensures the new objects will reflect changes
made to the database by other processes. This is also why having a
global persistent cache would not work.

---

 testbot/bin/WineSendLog.pl                  |    2 +-
 testbot/lib/ObjectModel/Collection.pm       |  199 +++++++++++++++++++++++----
 testbot/lib/ObjectModel/DBIBackEnd.pm       |   10 +-
 testbot/lib/ObjectModel/Item.pm             |   27 +++-
 testbot/lib/WineTestBot/Branches.pm         |    6 +-
 testbot/lib/WineTestBot/CGI/Sessions.pm     |    5 +-
 testbot/lib/WineTestBot/Jobs.pm             |    6 +-
 testbot/lib/WineTestBot/Patches.pm          |    5 +-
 testbot/lib/WineTestBot/PendingPatchSets.pm |    5 +-
 testbot/lib/WineTestBot/PendingPatches.pm   |    6 +-
 testbot/lib/WineTestBot/Roles.pm            |    5 +-
 testbot/lib/WineTestBot/Steps.pm            |    7 +-
 testbot/lib/WineTestBot/StepsTasks.pm       |    6 +-
 testbot/lib/WineTestBot/Tasks.pm            |    7 +-
 testbot/lib/WineTestBot/UserRoles.pm        |    7 +-
 testbot/lib/WineTestBot/Users.pm            |    6 +-
 testbot/lib/WineTestBot/VMs.pm              |    6 +-
 testbot/web/JobDetails.pl                   |    2 +-
 18 files changed, 250 insertions(+), 67 deletions(-)

Diff:   http://source.winehq.org/git/tools.git/?a=commitdiff;h=c1658af0dac543ad77c327eecb7216b8cadc0fdc