proxy: fix lifecycle of backend connections

A backend's connection object is technically owned by the IO thread
after it has been created. An error in how this was done lead to invalid
backends being infinitely retried despite the underlying object being
collected.

This change adds an extra indirection to backend objects: a backend_wrap
object, which just turns the backend connection into an arbitrary
pointer instead of lua memory owned by the config VM.

- When backend connections are created, this pointer is shipped to the
  IO thread to have its connection instantiated.
- When the wrap object is garbage collected (ie; no longer referenced by
  any pool object), the be conn. pointer is again shipped to the IO
  thread, which then removes any pending events, closes the sock, and
  frees data.

1 files changed, 5 insertions, 0 deletions

diff --git a/proxy_config.c b/proxy_config.c
index 47414fa..6bb54be 100644
--- a/proxy_config.c
+++ b/proxy_config.c
@@ -78,6 +78,11 @@ static void *_proxy_manager_thread(void *arg) {
             luaL_unref(L, LUA_REGISTRYINDEX, p->self_ref);
         }
         pthread_mutex_unlock(&ctx->config_lock);
+        // force lua garbage collection so any resources close out quickly.
+        lua_gc(L, LUA_GCCOLLECT);
+        // twice because objects with garbage collector handlers are only
+        // marked on the first collection cycle.
+        lua_gc(L, LUA_GCCOLLECT);
 
         // done.
         pthread_mutex_lock(&ctx->manager_lock);