Externalize templates to speed up build

Profiling the mcrouter OSS build with ninjatracing + clang's
-ftime-trace indicates that a significant amount of time is spent in
repeated template instantiations for ProxyConfig and ServiceInfo
(see attached speedscope profile).

Add extern template declarations for these classes with their most
common parameter (MemcacheRouterInfo) to reduce compile times.
On a full build of mcrouter OSS with all tests, this reduces the build
time from ~34 minutes to ~29 minutes.

mcrouter/Makefile.am

@@ -89,6 +89,7 @@ libmcroutercore_a_SOURCES = \
   ProxyBase.h \
   ProxyConfig-inl.h \
   ProxyConfig.h \
+  ProxyConfig.cpp \
   ProxyConfigBuilder.cpp \
   ProxyConfigBuilder.h \
   ProxyDestination.cpp \

mcrouter/ProxyConfig-inl.h

@@ -15,6 +15,7 @@
 #include "mcrouter/Proxy.h"
 #include "mcrouter/lib/config/RouteHandleFactory.h"
 #include "mcrouter/lib/fbi/cpp/util.h"
+#include "mcrouter/lib/network/gen/MemcacheRouterInfo.h"
 #include "mcrouter/routes/McRouteHandleProvider.h"
 #include "mcrouter/routes/PrefixSelectorRoute.h"
 #include "mcrouter/routes/ProxyRoute.h"
@@ -24,6 +25,8 @@ namespace facebook {
 namespace memcache {
 namespace mcrouter {
 
+extern template class ProxyConfig<facebook::memcache::MemcacheRouterInfo>;
+
 template <class RouterInfo>
 ProxyConfig<RouterInfo>::ProxyConfig(
     Proxy<RouterInfo>& proxy,

mcrouter/ProxyConfig.cpp

@@ -0,0 +1,7 @@
+#include "mcrouter/ProxyConfig.h"
+#include "mcrouter/ServiceInfo.h"
+#include "mcrouter/lib/network/gen/MemcacheRouterInfo.h"
+
+namespace facebook::memcache::mcrouter {
+template class ProxyConfig<facebook::memcache::MemcacheRouterInfo>;
+}

mcrouter/ServiceInfo-inl.h

@@ -39,6 +39,9 @@
 namespace facebook {
 namespace memcache {
 namespace mcrouter {
+
+extern template class ServiceInfo<facebook::memcache::MemcacheRouterInfo>;
+
 namespace detail {
 
 bool srHostInfoPtrFuncRouteHandlesCommandDispatcher(

mcrouter/ServiceInfo.cpp

@@ -8,8 +8,11 @@
 #include "mcrouter/ServiceInfo.h"
 #include "mcrouter/mcrouter_sr_deps.h"
 
-namespace facebook::memcache::mcrouter::detail {
+namespace facebook::memcache::mcrouter {
 
+template class ServiceInfo<facebook::memcache::MemcacheRouterInfo>;
+
+namespace detail {
 bool srHostInfoPtrFuncRouteHandlesCommandDispatcher(
     const HostInfoPtr& host,
     std::string& tree,
@@ -23,5 +26,5 @@ bool srHostInfoPtrFuncRouteHandlesCommandDispatcher(
       '\n');
   return false;
 }
-
-} // namespace facebook::memcache::mcrouter::detail
+} // namespace detail
+} // namespace facebook::memcache::mcrouter