1 files changed, 44 insertions, 45 deletions
diff --git a/synapse/rest/client/transactions.py b/synapse/rest/client/transactions.py
index fceca2edeb..00b1b3066e 100644
--- a/synapse/rest/client/transactions.py
+++ b/synapse/rest/client/transactions.py
@@ -17,37 +17,20 @@
 to ensure idempotency when performing PUTs using the REST API."""
 import logging
 
-from synapse.api.auth import get_access_token_from_request
 from synapse.util.async import ObservableDeferred
+from synapse.util.logcontext import make_deferred_yieldable, run_in_background
 
 logger = logging.getLogger(__name__)
 
-
-def get_transaction_key(request):
-    """A helper function which returns a transaction key that can be used
-    with TransactionCache for idempotent requests.
-
-    Idempotency is based on the returned key being the same for separate
-    requests to the same endpoint. The key is formed from the HTTP request
-    path and the access_token for the requesting user.
-
-    Args:
-        request (twisted.web.http.Request): The incoming request. Must
-        contain an access_token.
-    Returns:
-        str: A transaction key
-    """
-    token = get_access_token_from_request(request)
-    return request.path + "/" + token
-
-
 CLEANUP_PERIOD_MS = 1000 * 60 * 30  # 30 mins
 
 
 class HttpTransactionCache(object):
 
-    def __init__(self, clock):
-        self.clock = clock
+    def __init__(self, hs):
+        self.hs = hs
+        self.auth = self.hs.get_auth()
+        self.clock = self.hs.get_clock()
         self.transactions = {
             # $txn_key: (ObservableDeferred<(res_code, res_json_body)>, timestamp)
         }
@@ -55,6 +38,23 @@ class HttpTransactionCache(object):
         # for at *LEAST* 30 mins, and at *MOST* 60 mins.
         self.cleaner = self.clock.looping_call(self._cleanup, CLEANUP_PERIOD_MS)
 
+    def _get_transaction_key(self, request):
+        """A helper function which returns a transaction key that can be used
+        with TransactionCache for idempotent requests.
+
+        Idempotency is based on the returned key being the same for separate
+        requests to the same endpoint. The key is formed from the HTTP request
+        path and the access_token for the requesting user.
+
+        Args:
+            request (twisted.web.http.Request): The incoming request. Must
+            contain an access_token.
+        Returns:
+            str: A transaction key
+        """
+        token = self.auth.get_access_token_from_request(request)
+        return request.path + "/" + token
+
     def fetch_or_execute_request(self, request, fn, *args, **kwargs):
         """A helper function for fetch_or_execute which extracts
         a transaction key from the given request.
@@ -63,7 +63,7 @@ class HttpTransactionCache(object):
             fetch_or_execute
         """
         return self.fetch_or_execute(
-            get_transaction_key(request), fn, *args, **kwargs
+            self._get_transaction_key(request), fn, *args, **kwargs
         )
 
     def fetch_or_execute(self, txn_key, fn, *args, **kwargs):
@@ -80,31 +80,30 @@ class HttpTransactionCache(object):
         Returns:
             Deferred which resolves to a tuple of (response_code, response_dict).
         """
-        try:
-            return self.transactions[txn_key][0].observe()
-        except (KeyError, IndexError):
-            pass  # execute the function instead.
-
-        deferred = fn(*args, **kwargs)
-
-        # if the request fails with a Twisted failure, remove it
-        # from the transaction map. This is done to ensure that we don't
-        # cache transient errors like rate-limiting errors, etc.
-        def remove_from_map(err):
-            self.transactions.pop(txn_key, None)
-            return err
-        deferred.addErrback(remove_from_map)
-
-        # We don't add any other errbacks to the raw deferred, so we ask
-        # ObservableDeferred to swallow the error. This is fine as the error will
-        # still be reported to the observers.
-        observable = ObservableDeferred(deferred, consumeErrors=True)
-        self.transactions[txn_key] = (observable, self.clock.time_msec())
-        return observable.observe()
+        if txn_key in self.transactions:
+            observable = self.transactions[txn_key][0]
+        else:
+            # execute the function instead.
+            deferred = run_in_background(fn, *args, **kwargs)
+
+            observable = ObservableDeferred(deferred)
+            self.transactions[txn_key] = (observable, self.clock.time_msec())
+
+            # if the request fails with an exception, remove it
+            # from the transaction map. This is done to ensure that we don't
+            # cache transient errors like rate-limiting errors, etc.
+            def remove_from_map(err):
+                self.transactions.pop(txn_key, None)
+                # we deliberately do not propagate the error any further, as we
+                # expect the observers to have reported it.
+
+            deferred.addErrback(remove_from_map)
+
+        return make_deferred_yieldable(observable.observe())
 
     def _cleanup(self):
         now = self.clock.time_msec()
-        for key in self.transactions.keys():
+        for key in list(self.transactions):
             ts = self.transactions[key][1]
             if now > (ts + CLEANUP_PERIOD_MS):  # after cleanup period
                 del self.transactions[key]