templog: web/settings.py comparison

long polling config updates

comparison

equal deleted inserted replaced

-:b6079cb0c665
+:0a1b642e3086
+import gevent
+import fcntl
+import hashlib
+class Settings(object):
+RAND_SIZE = 15 # 120 bits
+""" Handles state updates from both the web UI and from the fridge client.
+The fridge client is canonical. It provides the epoch (apart from 'startepoch'), that
+is changed any time the fridge reloads its local config. The fridge only accepts
+updates that have the same epoch.
+When the web UI changes it keeps the same epoch but generates a new tag. The fridge sends
+its current known tag and waits for it to change.
+content is opaque, presently a dictionary of decoded json
+"""
+def __init__(self):
+self.event = gevent.event.Event()
+self.contents = None
+self.epoch = None
+self.tag = None
+self.update(self, None, 'startepoch')
+def wait(self, epoch_tag = None, timeout = None):
+""" returns false if the timeout was hit """
+if self.epoch_tag() != epoch_tag:
+# has alredy changed
+return True
+return self.event.wait(timeout)
+def epoch_tag(self):
+return '%s-%s' % (self.epoch, self.tag)
+def random(self):
+return binascii.hexlify(os.urandom(self.RAND_SIZE))
+def update(self, contents, epoch = None):
+""" replaces settings contents and updates waiters if changed """
+if epoch:
+if self.epoch == epoch:
+return
+else:
+self.epoch = epoch
+self.tag = self.random()
+self.contents = contents
+self.event.set()
+self.event.clear()
+def get(self):
+""" Returns (contents, epoch-tag) """
+return self.contents, self.epoch_tag()

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