apps/waiter/models.py

   1 from os.path import join, isfile
   2 from django.core.urlresolvers import reverse
   3 from django.db import models
   4 from waiter.settings import WAITER_URL, WAITER_MAX_QUEUE
   5 from waiter.utils import check_abspath
   6 from picklefield import PickledObjectField
   7
   8
   9 class WaitedFile(models.Model):
  10     path = models.CharField(max_length=255, unique=True, db_index=True)
  11     task_id = models.CharField(max_length=128, db_index=True, null=True, blank=True)
  12     task = PickledObjectField(null=True, editable=False)
  13     description = models.CharField(max_length=255, null=True, blank=True)
  14
  15     @classmethod
  16     def exists(cls, path):
  17         """Returns opened file or None.
  18
  19         `path` is relative to WAITER_ROOT.
  20         Won't open a path leading outside of WAITER_ROOT.
  21         """
  22         abs_path = check_abspath(path)
  23         # Pre-fetch objects for deletion to avoid minor race condition
  24         relevant = [o.id for o in cls.objects.filter(path=path)]
  25         if isfile(abs_path):
  26             cls.objects.filter(id__in=relevant).delete()
  27             return True
  28         else:
  29             return False
  30
  31     @classmethod
  32     def can_order(cls, path):
  33         return (cls.objects.filter(path=path).exists() or
  34                 cls.exists(path) or
  35                 cls.objects.count() < WAITER_MAX_QUEUE
  36                 )
  37
  38     def is_stale(self):
  39         if self.task is None:
  40             # Race; just let the other task roll.
  41             return False
  42         if self.task.status not in (u'PENDING', u'STARTED', u'SUCCESS', u'RETRY'):
  43             return True
  44         return False
  45
  46     @classmethod
  47     def order(cls, path, task_creator, description=None):
  48         """
  49         Returns an URL for the user to follow.
  50         If the file is ready, returns download URL.
  51         If not, starts preparing it and returns waiting URL.
  52
  53         task_creator: function taking a path and generating the file;
  54         description: a string or string proxy with a description for user;
  55         """
  56         already = cls.exists(path)
  57         if not already:
  58             waited, created = cls.objects.get_or_create(path=path)
  59             if created or waited.is_stale():
  60                 waited.task = task_creator(check_abspath(path))
  61                 waited.task_id = waited.task.task_id
  62                 waited.description = description
  63                 waited.save()
  64             return reverse("waiter", args=[path])
  65         return join(WAITER_URL, path)