Clean up some LoggingContext stuff (#7120)

* Pull Sentinel out of LoggingContext

... and drop a few unnecessary references to it

* Factor out LoggingContext.current_context

move `current_context` and `set_context` out to top-level functions.

Mostly this means that I can more easily trace what's actually referring to
LoggingContext, but I think it's generally neater.

* move copy-to-parent into `stop`

this really just makes `start` and `stop` more symetric. It also means that it
behaves correctly if you manually `set_log_context` rather than using the
context manager.

* Replace `LoggingContext.alive` with `finished`

Turn `alive` into `finished` and make it a bit better defined.

2 files changed, 7 insertions, 8 deletions

diff --git a/synapse/storage/data_stores/main/events_worker.py b/synapse/storage/data_stores/main/events_worker.py

index ca237c6f12..3013f49d32 100644
--- a/synapse/storage/data_stores/main/events_worker.py
+++ b/synapse/storage/data_stores/main/events_worker.py
@@ -35,7 +35,7 @@ from synapse.api.room_versions import (
 )
 from synapse.events import make_event_from_dict
 from synapse.events.utils import prune_event
-from synapse.logging.context import LoggingContext, PreserveLoggingContext
+from synapse.logging.context import PreserveLoggingContext, current_context
 from synapse.metrics.background_process_metrics import run_as_background_process
 from synapse.storage._base import SQLBaseStore, make_in_list_sql_clause
 from synapse.storage.database import Database
@@ -409,7 +409,7 @@ class EventsWorkerStore(SQLBaseStore):
         missing_events_ids = [e for e in event_ids if e not in event_entry_map]
 
         if missing_events_ids:
-            log_ctx = LoggingContext.current_context()
+            log_ctx = current_context()
             log_ctx.record_event_fetch(len(missing_events_ids))
 
             # Note that _get_events_from_db is also responsible for turning db rows
diff --git a/synapse/storage/database.py b/synapse/storage/database.py

index e61595336c..715c0346dd 100644
--- a/synapse/storage/database.py
+++ b/synapse/storage/database.py
@@ -32,6 +32,7 @@ from synapse.config.database import DatabaseConnectionConfig
 from synapse.logging.context import (
     LoggingContext,
     LoggingContextOrSentinel,
+    current_context,
     make_deferred_yieldable,
 )
 from synapse.metrics.background_process_metrics import run_as_background_process
@@ -483,7 +484,7 @@ class Database(object):
             end = monotonic_time()
             duration = end - start
 
-            LoggingContext.current_context().add_database_transaction(duration)
+            current_context().add_database_transaction(duration)
 
             transaction_logger.debug("[TXN END] {%s} %f sec", name, duration)
 
@@ -510,7 +511,7 @@ class Database(object):
         after_callbacks = []  # type: List[_CallbackListEntry]
         exception_callbacks = []  # type: List[_CallbackListEntry]
 
-        if LoggingContext.current_context() == LoggingContext.sentinel:
+        if not current_context():
             logger.warning("Starting db txn '%s' from sentinel context", desc)
 
         try:
@@ -547,10 +548,8 @@ class Database(object):
         Returns:
             Deferred: The result of func
         """
-        parent_context = (
-            LoggingContext.current_context()
-        )  # type: Optional[LoggingContextOrSentinel]
-        if parent_context == LoggingContext.sentinel:
+        parent_context = current_context()  # type: Optional[LoggingContextOrSentinel]
+        if not parent_context:
             logger.warning(
                 "Starting db connection from sentinel context: metrics will be lost"
             )