From 02118901347ab5067fbb47169b36a8424e671bfb Mon Sep 17 00:00:00 2001
From: Erik Johnston <erik@matrix.org>
Date: Fri, 7 Aug 2015 18:14:49 +0100
Subject: [PATCH] Implement a CacheListDescriptor

---
 synapse/storage/_base.py | 106 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 106 insertions(+)

diff --git a/synapse/storage/_base.py b/synapse/storage/_base.py
index 32089b05e5..556aa3b523 100644
--- a/synapse/storage/_base.py
+++ b/synapse/storage/_base.py
@@ -16,6 +16,7 @@ import logging
 
 from synapse.api.errors import StoreError
 from synapse.util.async import ObservableDeferred
+from synapse.util import unwrapFirstError
 from synapse.util.logutils import log_function
 from synapse.util.logcontext import preserve_context_over_fn, LoggingContext
 from synapse.util.lrucache import LruCache
@@ -231,6 +232,101 @@ class CacheDescriptor(object):
         return wrapped
 
 
+class CacheListDescriptor(object):
+    def __init__(self, orig, cache, list_name, num_args=1, inlineCallbacks=False):
+        self.orig = orig
+
+        if inlineCallbacks:
+            self.function_to_call = defer.inlineCallbacks(orig)
+        else:
+            self.function_to_call = orig
+
+        self.num_args = num_args
+        self.list_name = list_name
+
+        self.arg_names = inspect.getargspec(orig).args[1:num_args+1]
+        self.list_pos = self.arg_names.index(self.list_name)
+
+        self.cache = cache
+
+        self.sentinel = object()
+
+        if len(self.arg_names) < self.num_args:
+            raise Exception(
+                "Not enough explicit positional arguments to key off of for %r."
+                " (@cached cannot key off of *args or **kwars)"
+                % (orig.__name__,)
+            )
+
+        if self.list_name not in self.arg_names:
+            raise Exception(
+                "Couldn't see arguments %r for %r."
+                % (self.list_name, cache.name,)
+            )
+
+    def __get__(self, obj, objtype=None):
+
+        @functools.wraps(self.orig)
+        def wrapped(*args, **kwargs):
+            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]
+
+            cached = {}
+            missing = []
+            for arg in list_args:
+                key = list(keyargs)
+                key[self.list_pos] = arg
+
+                try:
+                    res = self.cache.get(tuple(key)).observe()
+                    res.addCallback(lambda r, arg: (arg, r), arg)
+                    cached[arg] = res
+                except KeyError:
+                    missing.append(arg)
+
+            if missing:
+                sequence = self.cache.sequence
+                args_to_call = dict(arg_dict)
+                args_to_call[self.list_name] = missing
+
+                ret_d = defer.maybeDeferred(
+                    self.function_to_call,
+                    **args_to_call
+                )
+
+                ret_d = ObservableDeferred(ret_d)
+
+                for arg in missing:
+                    observer = ret_d.observe()
+                    observer.addCallback(lambda r, arg: r[arg], arg)
+
+                    observer = ObservableDeferred(observer)
+
+                    key = list(keyargs)
+                    key[self.list_pos] = arg
+                    self.cache.update(sequence, tuple(key), observer)
+
+                    def invalidate(f, key):
+                        self.cache.invalidate(key)
+                        return f
+                    observer.addErrback(invalidate, tuple(key))
+
+                    res = observer.observe()
+                    res.addCallback(lambda r, arg: (arg, r), arg)
+
+                    cached[arg] = res
+
+            return defer.gatherResults(
+                cached.values(),
+                consumeErrors=True,
+            ).addErrback(unwrapFirstError).addCallback(lambda res: dict(res))
+
+        obj.__dict__[self.orig.__name__] = wrapped
+
+        return wrapped
+
+
 def cached(max_entries=1000, num_args=1, lru=True):
     return lambda orig: CacheDescriptor(
         orig,
@@ -250,6 +346,16 @@ def cachedInlineCallbacks(max_entries=1000, num_args=1, lru=False):
     )
 
 
+def cachedList(cache, list_name, num_args=1, inlineCallbacks=False):
+    return lambda orig: CacheListDescriptor(
+        orig,
+        cache=cache,
+        list_name=list_name,
+        num_args=num_args,
+        inlineCallbacks=inlineCallbacks,
+    )
+
+
 class LoggingTransaction(object):
     """An object that almost-transparently proxies for the 'txn' object
     passed to the constructor. Adds logging and metrics to the .execute()