Add concept of cache contexts

1 files changed, 64 insertions, 13 deletions

diff --git a/synapse/util/caches/descriptors.py b/synapse/util/caches/descriptors.py
index f31dfb22b7..5cd277f2f2 100644
--- a/synapse/util/caches/descriptors.py
+++ b/synapse/util/caches/descriptors.py
@@ -55,7 +55,7 @@ class Cache(object):
     )
 
     def __init__(self, name, max_entries=1000, keylen=1, lru=True, tree=False):
-        if lru:
+        if True:
             cache_type = TreeCache if tree else dict
             self.cache = LruCache(
                 max_size=max_entries, keylen=keylen, cache_type=cache_type
@@ -81,8 +81,8 @@ class Cache(object):
                     "Cache objects can only be accessed from the main thread"
                 )
 
-    def get(self, key, default=_CacheSentinel):
-        val = self.cache.get(key, _CacheSentinel)
+    def get(self, key, default=_CacheSentinel, callback=None):
+        val = self.cache.get(key, _CacheSentinel, callback=callback)
         if val is not _CacheSentinel:
             self.metrics.inc_hits()
             return val
@@ -94,19 +94,19 @@ class Cache(object):
         else:
             return default
 
-    def update(self, sequence, key, value):
+    def update(self, sequence, key, value, callback=None):
         self.check_thread()
         if self.sequence == sequence:
             # Only update the cache if the caches sequence number matches the
             # number that the cache had before the SELECT was started (SYN-369)
-            self.prefill(key, value)
+            self.prefill(key, value, callback=callback)
 
-    def prefill(self, key, value):
+    def prefill(self, key, value, callback=None):
         if self.max_entries is not None:
             while len(self.cache) >= self.max_entries:
-                self.cache.popitem(last=False)
+                self.cache.popitem(last=False, callback=None)
 
-        self.cache[key] = value
+        self.cache.set(key, value, callback=callback)
 
     def invalidate(self, key):
         self.check_thread()
@@ -151,6 +151,18 @@ class CacheDescriptor(object):
     The wrapped function has another additional callable, called "prefill",
     which can be used to insert values into the cache specifically, without
     calling the calculation function.
+
+    Cached functions can be "chained" (i.e. a cached function can call other cached
+    functions and get appropriately invalidated when they called caches are
+    invalidated) by adding a special "cache_context" argument to the function
+    and passing that as a kwarg to all caches called. For example::
+
+        @cachedInlineCallbacks()
+        def foo(self, key, cache_context):
+            r1 = yield self.bar1(key, cache_context=cache_context)
+            r2 = yield self.bar2(key, cache_context=cache_context)
+            defer.returnValue(r1 + r2)
+
     """
     def __init__(self, orig, max_entries=1000, num_args=1, lru=True, tree=False,
                  inlineCallbacks=False):
@@ -168,7 +180,13 @@ class CacheDescriptor(object):
         self.lru = lru
         self.tree = tree
 
-        self.arg_names = inspect.getargspec(orig).args[1:num_args + 1]
+        all_args = inspect.getargspec(orig)
+        self.arg_names = all_args.args[1:num_args + 1]
+
+        if "cache_context" in self.arg_names:
+            self.arg_names.remove("cache_context")
+
+        self.add_cache_context = "cache_context" in all_args.args
 
         if len(self.arg_names) < self.num_args:
             raise Exception(
@@ -188,10 +206,23 @@ class CacheDescriptor(object):
 
         @functools.wraps(self.orig)
         def wrapped(*args, **kwargs):
+            cache_context = kwargs.pop("cache_context", None)
+            if cache_context:
+                context_callback = cache_context.invalidate
+            else:
+                context_callback = None
+
+            self_context = _CacheContext(cache, None)
+            if self.add_cache_context:
+                kwargs["cache_context"] = self_context
+
             arg_dict = inspect.getcallargs(self.orig, obj, *args, **kwargs)
             cache_key = tuple(arg_dict[arg_nm] for arg_nm in self.arg_names)
+
+            self_context.key = cache_key
+
             try:
-                cached_result_d = cache.get(cache_key)
+                cached_result_d = cache.get(cache_key, callback=context_callback)
 
                 observer = cached_result_d.observe()
                 if DEBUG_CACHES:
@@ -228,7 +259,7 @@ class CacheDescriptor(object):
                 ret.addErrback(onErr)
 
                 ret = ObservableDeferred(ret, consumeErrors=True)
-                cache.update(sequence, cache_key, ret)
+                cache.update(sequence, cache_key, ret, callback=context_callback)
 
                 return preserve_context_over_deferred(ret.observe())
 
@@ -297,6 +328,12 @@ class CacheListDescriptor(object):
 
         @functools.wraps(self.orig)
         def wrapped(*args, **kwargs):
+            cache_context = kwargs.pop("cache_context", None)
+            if cache_context:
+                context_callback = cache_context.invalidate
+            else:
+                context_callback = None
+
             arg_dict = inspect.getcallargs(self.orig, obj, *args, **kwargs)
             keyargs = [arg_dict[arg_nm] for arg_nm in self.arg_names]
             list_args = arg_dict[self.list_name]
@@ -311,7 +348,7 @@ class CacheListDescriptor(object):
                 key[self.list_pos] = arg
 
                 try:
-                    res = cache.get(tuple(key))
+                    res = cache.get(tuple(key), callback=context_callback)
                     if not res.has_succeeded():
                         res = res.observe()
                         res.addCallback(lambda r, arg: (arg, r), arg)
@@ -345,7 +382,10 @@ class CacheListDescriptor(object):
 
                     key = list(keyargs)
                     key[self.list_pos] = arg
-                    cache.update(sequence, tuple(key), observer)
+                    cache.update(
+                        sequence, tuple(key), observer,
+                        callback=context_callback
+                    )
 
                     def invalidate(f, key):
                         cache.invalidate(key)
@@ -376,6 +416,17 @@ class CacheListDescriptor(object):
         return wrapped
 
 
+class _CacheContext(object):
+    __slots__ = ["cache", "key"]
+
+    def __init__(self, cache, key):
+        self.cache = cache
+        self.key = key
+
+    def invalidate(self):
+        self.cache.invalidate(self.key)
+
+
 def cached(max_entries=1000, num_args=1, lru=True, tree=False):
     return lambda orig: CacheDescriptor(
         orig,