Reload cache factors from disk on SIGHUP

changelog.d/12673.feature

@@ -0,0 +1 @@
+Synapse will now reload [cache config](https://matrix-org.github.io/synapse/latest/usage/configuration/config_documentation.html#caching) when it receives a [SIGHUP](https://en.wikipedia.org/wiki/SIGHUP) signal.

synapse/app/_base.py

@@ -51,6 +51,8 @@
 from synapse.api.constants import MAX_PDU_SIZE
 from synapse.app import check_bind_error
 from synapse.app.phone_stats_home import start_phone_stats_home
+from synapse.config import ConfigError
+from synapse.config._base import format_config_error
 from synapse.config.homeserver import HomeServerConfig
 from synapse.config.server import ManholeConfig
 from synapse.crypto import context_factory
@@ -426,6 +428,7 @@ def run_sighup(*args: Any, **kwargs: Any) -> None:
         signal.signal(signal.SIGHUP, run_sighup)
 
         register_sighup(refresh_certificate, hs)
+        register_sighup(reload_cache_config, hs.config)
 
     # Load the certificate from disk.
     refresh_certificate(hs)
@@ -480,6 +483,22 @@ def run_sighup(*args: Any, **kwargs: Any) -> None:
         atexit.register(gc.freeze)
 
 
+def reload_cache_config(config: HomeServerConfig) -> None:
+    # For mypy's benefit. It can't know that we haven't altered `config` by the time
+    # we call this closure.
+    assert config is not None
+    try:
+        # This will call CacheConfig.read_config, which will automatically call
+        # CacheConfig.resize_all_caches.
+        config.reload_config_section("caches")
+    except ConfigError as e:
+        logger.warning("Failed to reload cache config")
+        for f in format_config_error(e):
+            logger.warning(f)
+    else:
+        logger.debug("New cache config: %s", config.caches.__dict__)
+
+
 def setup_sentry(hs: "HomeServer") -> None:
     """Enable sentry integration, if enabled in configuration"""
 

synapse/app/homeserver.py

@@ -16,7 +16,7 @@
 import logging
 import os
 import sys
-from typing import Dict, Iterable, Iterator, List
+from typing import Dict, Iterable, List
 
 from matrix_common.versionstring import get_distribution_version_string
 
@@ -45,7 +45,7 @@
     redirect_stdio_to_logs,
     register_start,
 )
-from synapse.config._base import ConfigError
+from synapse.config._base import ConfigError, format_config_error
 from synapse.config.emailconfig import ThreepidBehaviour
 from synapse.config.homeserver import HomeServerConfig
 from synapse.config.server import ListenerConfig
@@ -399,38 +399,6 @@ async def start() -> None:
     return hs
 
 
-def format_config_error(e: ConfigError) -> Iterator[str]:
-    """
-    Formats a config error neatly
-
-    The idea is to format the immediate error, plus the "causes" of those errors,
-    hopefully in a way that makes sense to the user. For example:
-
-        Error in configuration at 'oidc_config.user_mapping_provider.config.display_name_template':
-          Failed to parse config for module 'JinjaOidcMappingProvider':
-            invalid jinja template:
-              unexpected end of template, expected 'end of print statement'.
-
-    Args:
-        e: the error to be formatted
-
-    Returns: An iterator which yields string fragments to be formatted
-    """
-    yield "Error in configuration"
-
-    if e.path:
-        yield " at '%s'" % (".".join(e.path),)
-
-    yield ":\n  %s" % (e.msg,)
-
-    parent_e = e.__cause__
-    indent = 1
-    while parent_e:
-        indent += 1
-        yield ":\n%s%s" % ("  " * indent, str(parent_e))
-        parent_e = parent_e.__cause__
-
-
 def run(hs: HomeServer) -> None:
     _base.start_reactor(
         "synapse-homeserver",

synapse/config/_base.py

@@ -16,14 +16,18 @@
 
 import argparse
 import errno
+import logging
 import os
 from collections import OrderedDict
 from hashlib import sha256
 from textwrap import dedent
 from typing import (
     Any,
+    ClassVar,
+    Collection,
     Dict,
     Iterable,
+    Iterator,
     List,
     MutableMapping,
     Optional,
@@ -40,6 +44,8 @@
 
 from synapse.util.templates import _create_mxc_to_http_filter, _format_ts_filter
 
+logger = logging.getLogger(__name__)
+
 
 class ConfigError(Exception):
     """Represents a problem parsing the configuration
@@ -55,6 +61,38 @@ def __init__(self, msg: str, path: Optional[Iterable[str]] = None):
         self.path = path
 
 
+def format_config_error(e: ConfigError) -> Iterator[str]:
+    """
+    Formats a config error neatly
+
+    The idea is to format the immediate error, plus the "causes" of those errors,
+    hopefully in a way that makes sense to the user. For example:
+
+        Error in configuration at 'oidc_config.user_mapping_provider.config.display_name_template':
+          Failed to parse config for module 'JinjaOidcMappingProvider':
+            invalid jinja template:
+              unexpected end of template, expected 'end of print statement'.
+
+    Args:
+        e: the error to be formatted
+
+    Returns: An iterator which yields string fragments to be formatted
+    """
+    yield "Error in configuration"
+
+    if e.path:
+        yield " at '%s'" % (".".join(e.path),)
+
+    yield ":\n  %s" % (e.msg,)
+
+    parent_e = e.__cause__
+    indent = 1
+    while parent_e:
+        indent += 1
+        yield ":\n%s%s" % ("  " * indent, str(parent_e))
+        parent_e = parent_e.__cause__
+
+
 # We split these messages out to allow packages to override with package
 # specific instructions.
 MISSING_REPORT_STATS_CONFIG_INSTRUCTIONS = """\
@@ -119,7 +157,7 @@ class Config:
             defined in subclasses.
     """
 
-    section: str
+    section: ClassVar[str]
 
     def __init__(self, root_config: "RootConfig" = None):
         self.root = root_config
@@ -309,9 +347,12 @@ class RootConfig:
     class, lower-cased and with "Config" removed.
     """
 
-    config_classes = []
+    config_classes: List[Type[Config]] = []
+
+    def __init__(self, config_files: Collection[str] = ()):
+        # Capture absolute paths here, so we can reload config after we daemonize.
+        self.config_files = [os.path.abspath(path) for path in config_files]
 
-    def __init__(self):
         for config_class in self.config_classes:
             if config_class.section is None:
                 raise ValueError("%r requires a section name" % (config_class,))
@@ -512,12 +553,10 @@ def load_config_with_parser(
             object from parser.parse_args(..)`
         """
 
-        obj = cls()
-
         config_args = parser.parse_args(argv)
 
         config_files = find_config_files(search_paths=config_args.config_path)
-
+        obj = cls(config_files)
         if not config_files:
             parser.error("Must supply a config file.")
 
@@ -627,7 +666,7 @@ def load_or_generate_config(
 
         generate_missing_configs = config_args.generate_missing_configs
 
-        obj = cls()
+        obj = cls(config_files)
 
         if config_args.generate_config:
             if config_args.report_stats is None:
@@ -727,6 +766,20 @@ def generate_missing_files(
     ) -> None:
         self.invoke_all("generate_files", config_dict, config_dir_path)
 
+    def reload_config_section(self, section_name: str) -> None:
+        """Reconstruct the given config section, leaving all others unchanged.
+
+        :raises ValueError: if the given `section` does not exist.
+        :raises ConfigError: for any other problems reloading config.
+        """
+        existing_config: Optional[Config] = getattr(self, section_name, None)
+        if existing_config is None:
+            raise ValueError(f"Unknown config section '{section_name}'")
+        logger.info("Reloading config section '%s'", section_name)
+
+        new_config_data = read_config_files(self.config_files)
+        existing_config.read_config(new_config_data)
+
 
 def read_config_files(config_files: Iterable[str]) -> Dict[str, Any]:
     """Read the config files into a dict

synapse/config/_base.pyi

@@ -1,8 +1,10 @@
 import argparse
 from typing import (
     Any,
+    Collection,
     Dict,
     Iterable,
+    Iterator,
     List,
     MutableMapping,
     Optional,
@@ -64,6 +66,8 @@ class ConfigError(Exception):
         self.msg = msg
         self.path = path
 
+def format_config_error(e: ConfigError) -> Iterator[str]: ...
+
 MISSING_REPORT_STATS_CONFIG_INSTRUCTIONS: str
 MISSING_REPORT_STATS_SPIEL: str
 MISSING_SERVER_NAME: str
@@ -117,7 +121,8 @@ class RootConfig:
     background_updates: background_updates.BackgroundUpdateConfig
 
     config_classes: List[Type["Config"]] = ...
-    def __init__(self) -> None: ...
+    config_files: List[str]
+    def __init__(self, config_files: Collection[str] = ...) -> None: ...
     def invoke_all(
         self, func_name: str, *args: Any, **kwargs: Any
     ) -> MutableMapping[str, Any]: ...
@@ -157,6 +162,7 @@ class RootConfig:
     def generate_missing_files(
         self, config_dict: dict, config_dir_path: str
     ) -> None: ...
+    def reload_config_section(self, section_name: str) -> None: ...
 
 class Config:
     root: RootConfig

synapse/config/cache.py

@@ -69,11 +69,11 @@ def _canonicalise_cache_name(cache_name: str) -> str:
 def add_resizable_cache(
     cache_name: str, cache_resize_callback: Callable[[float], None]
 ) -> None:
-    """Register a cache that's size can dynamically change
+    """Register a cache whose size can dynamically change
 
     Args:
         cache_name: A reference to the cache
-        cache_resize_callback: A callback function that will be ran whenever
+        cache_resize_callback: A callback function that will run whenever
             the cache needs to be resized
     """
     # Some caches have '*' in them which we strip out.
@@ -180,9 +180,7 @@ def read_config(self, config: JsonDict, **kwargs: Any) -> None:
         self.cache_factors: Dict[str, float] = {}
 
         cache_config = config.get("caches") or {}
-        self.global_factor = cache_config.get(
-            "global_factor", properties.default_factor_size
-        )
+        self.global_factor = cache_config.get("global_factor", _DEFAULT_FACTOR_SIZE)
         if not isinstance(self.global_factor, (int, float)):
             raise ConfigError("caches.global_factor must be a number.")