actor: a declared actor without its own drop gets one that awaits owed replies and closes the endpoint; the handler reaches the struct through endpoint.state so the struct isn't shared; spawn hint skips mailbox structs

1 files changed, 3 insertions, 1 deletions

diff --git a/src/compiler/builtins.zc b/src/compiler/builtins.zc
index fb2dcb2..be8c3b4 100644
--- a/src/compiler/builtins.zc
+++ b/src/compiler/builtins.zc
@@ -858,11 +858,13 @@ int tdroppable(word t) {
 int ldroppable(int i) { return (local_dropset && local_dropset[i]) || tdroppable(ltype[i]); }
 // x.spawn() on a mailbox struct snapshots the whole vm into a worker process, so an
 // owned value with a drop that is live there is dropped once in each process (6.15.4)
+// a pointer to a struct with a mailbox: its drop knows a worker's copy closes nothing
+int mailbox_type(word t) { return t && isptr(t) && t[4][0] == TY_STRUCT && tfindfield(t[4], intern("__mailbox")) >= 0; }
 int spawn_hint() {
 	int i = lbase;
 	if (!fchk || !local_dropset) return 0;
 	while (i < nloc) {
-		if (!empty(lstate[i]) && !isalias(i) && lstate[i] != S_BORROW && ldroppable(i) && hint_begin(tpack(), HINT_SMALL)) {
+		if (!empty(lstate[i]) && !isalias(i) && lstate[i] != S_BORROW && ldroppable(i) && !mailbox_type(ltype[i]) && hint_begin(tpack(), HINT_SMALL)) {
 			rt.put_s(lname[i]); rt.put_s(": has drop and is live at spawn; the worker's copy drops it too"); dg_close();
 		}
 		i++;