bugfix: calling ngx.thread.wait() on a user thread object that is already waited (i.e., already dead) would hang forever. thanks Sam Lawrence for the report.

src/ngx_http_lua_uthread.c

@@ -169,8 +169,23 @@ ngx_http_lua_uthread_wait(lua_State *L)
 
             return nrets;
 
+        case NGX_HTTP_LUA_CO_DEAD:
+            dd("uthread already waited: %p (parent %p)", sub_coctx,
+               coctx);
+
+            if (i < nargs) {
+                /* just ignore it if it is not the last one */
+                continue;
+            }
+
+            /* being the last one */
+            lua_pushnil(L);
+            lua_pushliteral(L, "already waited");
+            return 2;
+
         default:
-            /* still alive */
+            dd("uthread %p still alive, status: %d, parent %p", sub_coctx,
+               sub_coctx->co_status, coctx);
             break;
         }
 

t/098-uthread-wait.t

@@ -1223,3 +1223,58 @@ ok
 --- error_log
 lua user thread aborted: runtime error: [string "content_by_lua"]:5: f done
 
+
+
+=== TEST 21: waiting on a dead coroutine
+--- config
+    location /lua {
+        content_by_lua '
+            function f()
+                ngx.say("hello in thread")
+                return "done"
+            end
+
+            local t, err = ngx.thread.spawn(f)
+            if not t then
+                ngx.say("failed to spawn thread: ", err)
+                return
+            end
+
+            ngx.say("thread created: ", coroutine.status(t))
+
+            collectgarbage()
+
+            local ok, res = ngx.thread.wait(t)
+            if not ok then
+                ngx.say("failed to run thread: ", res)
+                return
+            end
+
+            local ok, res = ngx.thread.wait(t)
+            if not ok then
+                ngx.say("failed to run thread: ", res)
+                return
+            end
+
+            ngx.say(res)
+        ';
+    }
+--- request
+GET /lua
+--- stap2 eval: $::StapScript
+--- stap eval: $::GCScript
+--- stap_out
+create 2 in 1
+spawn user thread 2 in 1
+terminate 2: ok
+delete thread 2
+terminate 1: ok
+delete thread 1
+
+--- response_body
+hello in thread
+thread created: zombie
+failed to run thread: already waited
+--- no_error_log
+[error]
+