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Fix a race in transaction queue

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It was theoretically possible for a PDU to get queued and not sent for ages. On
closer inspection I think there were bigger problems elsewhere, but we might as
well fix this since it's easy.
This commit is contained in:
Richard van der Hoff 2017-02-20 16:43:29 +00:00
parent b5c268738b
commit 0c4cf9372b
1 changed files with 21 additions and 9 deletions
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30
synapse/federation/transaction_queue.py
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@ -303,18 +303,10 @@ class TransactionQueue(object):
try:
self.pending_transactions[destination] = 1
# XXX: what's this for?
yield run_on_reactor()
while True:
pending_pdus = self.pending_pdus_by_dest.pop(destination, [])
pending_edus = self.pending_edus_by_dest.pop(destination, [])
pending_presence = self.pending_presence_by_dest.pop(destination, {})
pending_failures = self.pending_failures_by_dest.pop(destination, [])
pending_edus.extend(
self.pending_edus_keyed_by_dest.pop(destination, {}).values()
)
limiter = yield get_retry_limiter(
destination,
self.clock,
@ -326,6 +318,24 @@ class TransactionQueue(object):
yield self._get_new_device_messages(destination)
)
# BEGIN CRITICAL SECTION
#
# In order to avoid a race condition, we need to make sure that
# the following code (from popping the queues up to the point
# where we decide if we actually have any pending messages) is
# atomic - otherwise new PDUs or EDUs might arrive in the
# meantime, but not get sent because we hold the
# pending_transactions flag.
pending_pdus = self.pending_pdus_by_dest.pop(destination, [])
pending_edus = self.pending_edus_by_dest.pop(destination, [])
pending_presence = self.pending_presence_by_dest.pop(destination, {})
pending_failures = self.pending_failures_by_dest.pop(destination, [])
pending_edus.extend(
self.pending_edus_keyed_by_dest.pop(destination, {}).values()
)
pending_edus.extend(device_message_edus)
if pending_presence:
pending_edus.append(
@ -355,6 +365,8 @@ class TransactionQueue(object):
)
return
# END CRITICAL SECTION
success = yield self._send_new_transaction(
destination, pending_pdus, pending_edus, pending_failures,
limiter=limiter,