box: always wait box loading in box.execute()

<box_load_and_execute> checks whether box is configured with appropriate
locking and configures it when necessary. However it is not so for
<lbox_execute>. We should replace the former with the latter only when
box is fully loaded.

Follow-up #4231

src/box/lua/load_cfg.lua

@@ -570,6 +570,11 @@ local box_cfg_guard_whitelist = {
     NULL = true;
 };
 
+-- List of box members that requires full box loading.
+local box_restore_after_full_load_list = {
+    execute = true,
+}
+
 local box = require('box')
 -- Move all box members except the whitelisted to box_configured
 local box_configured = {}
@@ -618,12 +623,13 @@ local function load_cfg(cfg)
     -- It also would be counter-intuitive to receive an error from
     -- box.cfg({<...>}), but find that box is actually configured.
 
-    -- Restore box members after initial configuration
+    -- Restore box members after initial configuration.
     for k, v in pairs(box_configured) do
-        box[k] = v
+        if not box_restore_after_full_load_list[k] then
+            box[k] = v
+        end
     end
     setmetatable(box, nil)
-    box_configured = nil
     box.cfg = setmetatable(cfg,
         {
             __newindex = function(table, index)
@@ -658,6 +664,14 @@ local function load_cfg(cfg)
         box.schema.upgrade{auto = true}
     end
 
+    -- Restore box members that requires full box loading.
+    for k, v in pairs(box_configured) do
+        if box_restore_after_full_load_list[k] then
+            box[k] = v
+        end
+    end
+    box_configured = nil
+
     box_is_configured = true
 end
 box.cfg = locked(load_cfg)

test/box-tap/gh-4231-box-execute-locking.test.lua

@@ -4,20 +4,43 @@
 -- before box will be loaded) in several fibers in parallel and
 -- ensure that it returns correct results (i.e. that the function
 -- waits until box will be fully configured).
+--
+-- The test can be configured to call box.execute() from a fiber
+-- instead of box_load_and_execute(): it can be done either via
+-- test-run using confguration feature or using an argument when
+-- the test is invoked directly.
 
 local fiber = require('fiber')
 local tap = require('tap')
 
+-- Determine configuration.
+local conf = 'box_load_and_execute'
+local ok, test_run = pcall(require, 'test_run')
+if ok then
+    test_run = test_run.new()
+    conf = test_run:get_cfg('conf')
+elseif #arg >= 1 then
+    conf = arg[1]
+end
+assert(conf == 'box_load_and_execute' or
+       conf == 'box.execute')
+
 local box_load_and_execute = box.execute
 local fiber_count = 10
 local results = fiber.channel(fiber_count)
 
 local function select_from_vindex()
-    local res = box_load_and_execute('SELECT * FROM "_vindex"')
+    local box_execute_func =
+        conf == 'box_load_and_execute' and box_load_and_execute or
+        conf == 'box.execute' and box.execute or
+        function() return false end
+
+    local res = box_execute_func('SELECT * FROM "_vindex"')
     results:put(res)
 end
 
 local test = tap.test('gh-4231-box-execute-locking')
+test:diag('configuration: %s', conf)
 
 test:plan(fiber_count)
 

test/box-tap/suite.cfg

+{
+    "gh-4231-box-execute-locking.test.lua": {
+        "box_load_and_execute": {"conf": "box_load_and_execute"},
+        "box.execute": {"conf": "box.execute"}
+    }
+}

test/box-tap/suite.ini

@@ -6,3 +6,4 @@ pretest_clean = True
 use_unix_sockets_iproto = True
 fragile = cfg.test.lua     ; gh-4344
           key_def.test.lua ; gh-4252
+config = suite.cfg