merge develop

1 files changed, 94 insertions, 50 deletions

diff --git a/synapse/util/logcontext.py b/synapse/util/logcontext.py
index d660ec785b..a58c723403 100644
--- a/synapse/util/logcontext.py
+++ b/synapse/util/logcontext.py
@@ -59,8 +59,8 @@ class LoggingContext(object):
 
     __slots__ = [
         "previous_context", "name", "ru_stime", "ru_utime",
-        "db_txn_count", "db_txn_duration_ms", "db_sched_duration_ms",
-        "usage_start", "usage_end",
+        "db_txn_count", "db_txn_duration_sec", "db_sched_duration_sec",
+        "usage_start",
         "main_thread", "alive",
         "request", "tag",
     ]
@@ -84,14 +84,15 @@ class LoggingContext(object):
         def stop(self):
             pass
 
-        def add_database_transaction(self, duration_ms):
+        def add_database_transaction(self, duration_sec):
             pass
 
-        def add_database_scheduled(self, sched_ms):
+        def add_database_scheduled(self, sched_sec):
             pass
 
         def __nonzero__(self):
             return False
+        __bool__ = __nonzero__  # python3
 
     sentinel = Sentinel()
 
@@ -102,14 +103,16 @@ class LoggingContext(object):
         self.ru_utime = 0.
         self.db_txn_count = 0
 
-        # ms spent waiting for db txns, excluding scheduling time
-        self.db_txn_duration_ms = 0
+        # sec spent waiting for db txns, excluding scheduling time
+        self.db_txn_duration_sec = 0
 
-        # ms spent waiting for db txns to be scheduled
-        self.db_sched_duration_ms = 0
+        # sec spent waiting for db txns to be scheduled
+        self.db_sched_duration_sec = 0
 
+        # If alive has the thread resource usage when the logcontext last
+        # became active.
         self.usage_start = None
-        self.usage_end = None
+
         self.main_thread = threading.current_thread()
         self.request = None
         self.tag = ""
@@ -158,12 +161,12 @@ class LoggingContext(object):
         """Restore the logging context in thread local storage to the state it
         was before this context was entered.
         Returns:
-            None to avoid suppressing any exeptions that were thrown.
+            None to avoid suppressing any exceptions that were thrown.
         """
         current = self.set_current_context(self.previous_context)
         if current is not self:
             if current is self.sentinel:
-                logger.debug("Expected logging context %s has been lost", self)
+                logger.warn("Expected logging context %s has been lost", self)
             else:
                 logger.warn(
                     "Current logging context %s is not expected context %s",
@@ -184,47 +187,61 @@ class LoggingContext(object):
 
     def start(self):
         if threading.current_thread() is not self.main_thread:
+            logger.warning("Started logcontext %s on different thread", self)
             return
 
-        if self.usage_start and self.usage_end:
-            self.ru_utime += self.usage_end.ru_utime - self.usage_start.ru_utime
-            self.ru_stime += self.usage_end.ru_stime - self.usage_start.ru_stime
-            self.usage_start = None
-            self.usage_end = None
-
+        # If we haven't already started record the thread resource usage so
+        # far
         if not self.usage_start:
             self.usage_start = get_thread_resource_usage()
 
     def stop(self):
         if threading.current_thread() is not self.main_thread:
+            logger.warning("Stopped logcontext %s on different thread", self)
             return
 
+        # When we stop, let's record the resource used since we started
         if self.usage_start:
-            self.usage_end = get_thread_resource_usage()
+            usage_end = get_thread_resource_usage()
+
+            self.ru_utime += usage_end.ru_utime - self.usage_start.ru_utime
+            self.ru_stime += usage_end.ru_stime - self.usage_start.ru_stime
+
+            self.usage_start = None
+        else:
+            logger.warning("Called stop on logcontext %s without calling start", self)
 
     def get_resource_usage(self):
+        """Get CPU time used by this logcontext so far.
+
+        Returns:
+            tuple[float, float]: The user and system CPU usage in seconds
+        """
         ru_utime = self.ru_utime
         ru_stime = self.ru_stime
 
-        if self.usage_start and threading.current_thread() is self.main_thread:
+        # If we are on the correct thread and we're currently running then we
+        # can include resource usage so far.
+        is_main_thread = threading.current_thread() is self.main_thread
+        if self.alive and self.usage_start and is_main_thread:
             current = get_thread_resource_usage()
             ru_utime += current.ru_utime - self.usage_start.ru_utime
             ru_stime += current.ru_stime - self.usage_start.ru_stime
 
         return ru_utime, ru_stime
 
-    def add_database_transaction(self, duration_ms):
+    def add_database_transaction(self, duration_sec):
         self.db_txn_count += 1
-        self.db_txn_duration_ms += duration_ms
+        self.db_txn_duration_sec += duration_sec
 
-    def add_database_scheduled(self, sched_ms):
+    def add_database_scheduled(self, sched_sec):
         """Record a use of the database pool
 
         Args:
-            sched_ms (int): number of milliseconds it took us to get a
+            sched_sec (float): number of seconds it took us to get a
                 connection
         """
-        self.db_sched_duration_ms += sched_ms
+        self.db_sched_duration_sec += sched_sec
 
 
 class LoggingContextFilter(logging.Filter):
@@ -278,7 +295,7 @@ class PreserveLoggingContext(object):
         context = LoggingContext.set_current_context(self.current_context)
 
         if context != self.new_context:
-            logger.debug(
+            logger.warn(
                 "Unexpected logging context: %s is not %s",
                 context, self.new_context,
             )
@@ -301,31 +318,49 @@ def preserve_fn(f):
 def run_in_background(f, *args, **kwargs):
     """Calls a function, ensuring that the current context is restored after
     return from the function, and that the sentinel context is set once the
-    deferred returned by the funtion completes.
+    deferred returned by the function completes.
 
     Useful for wrapping functions that return a deferred which you don't yield
-    on.
+    on (for instance because you want to pass it to deferred.gatherResults()).
+
+    Note that if you completely discard the result, you should make sure that
+    `f` doesn't raise any deferred exceptions, otherwise a scary-looking
+    CRITICAL error about an unhandled error will be logged without much
+    indication about where it came from.
     """
     current = LoggingContext.current_context()
-    res = f(*args, **kwargs)
-    if isinstance(res, defer.Deferred) and not res.called:
-        # The function will have reset the context before returning, so
-        # we need to restore it now.
-        LoggingContext.set_current_context(current)
-
-        # The original context will be restored when the deferred
-        # completes, but there is nothing waiting for it, so it will
-        # get leaked into the reactor or some other function which
-        # wasn't expecting it. We therefore need to reset the context
-        # here.
-        #
-        # (If this feels asymmetric, consider it this way: we are
-        # effectively forking a new thread of execution. We are
-        # probably currently within a ``with LoggingContext()`` block,
-        # which is supposed to have a single entry and exit point. But
-        # by spawning off another deferred, we are effectively
-        # adding a new exit point.)
-        res.addBoth(_set_context_cb, LoggingContext.sentinel)
+    try:
+        res = f(*args, **kwargs)
+    except:   # noqa: E722
+        # the assumption here is that the caller doesn't want to be disturbed
+        # by synchronous exceptions, so let's turn them into Failures.
+        return defer.fail()
+
+    if not isinstance(res, defer.Deferred):
+        return res
+
+    if res.called and not res.paused:
+        # The function should have maintained the logcontext, so we can
+        # optimise out the messing about
+        return res
+
+    # The function may have reset the context before returning, so
+    # we need to restore it now.
+    ctx = LoggingContext.set_current_context(current)
+
+    # The original context will be restored when the deferred
+    # completes, but there is nothing waiting for it, so it will
+    # get leaked into the reactor or some other function which
+    # wasn't expecting it. We therefore need to reset the context
+    # here.
+    #
+    # (If this feels asymmetric, consider it this way: we are
+    # effectively forking a new thread of execution. We are
+    # probably currently within a ``with LoggingContext()`` block,
+    # which is supposed to have a single entry and exit point. But
+    # by spawning off another deferred, we are effectively
+    # adding a new exit point.)
+    res.addBoth(_set_context_cb, ctx)
     return res
 
 
@@ -340,11 +375,20 @@ def make_deferred_yieldable(deferred):
     returning a deferred. Then, when the deferred completes, restores the
     current logcontext before running callbacks/errbacks.
 
-    (This is more-or-less the opposite operation to preserve_fn.)
+    (This is more-or-less the opposite operation to run_in_background.)
     """
-    if isinstance(deferred, defer.Deferred) and not deferred.called:
-        prev_context = LoggingContext.set_current_context(LoggingContext.sentinel)
-        deferred.addBoth(_set_context_cb, prev_context)
+    if not isinstance(deferred, defer.Deferred):
+        return deferred
+
+    if deferred.called and not deferred.paused:
+        # it looks like this deferred is ready to run any callbacks we give it
+        # immediately. We may as well optimise out the logcontext faffery.
+        return deferred
+
+    # ok, we can't be sure that a yield won't block, so let's reset the
+    # logcontext, and add a callback to the deferred to restore it.
+    prev_context = LoggingContext.set_current_context(LoggingContext.sentinel)
+    deferred.addBoth(_set_context_cb, prev_context)
     return deferred