5 files changed, 71 insertions, 19 deletions

diff --git a/deep_test/deeptest.lua b/deep_test/deeptest.lua
index 99cf1e4..250eb98 100644
--- a/deep_test/deeptest.lua
+++ b/deep_test/deeptest.lua
@@ -1,6 +1,8 @@
 local lanes = require("lanes").configure{ with_timers = false}
 local l = lanes.linda "my linda"
 
+local table_unpack = table.unpack or unpack -- Lua 5.1 support
+
 -- we will transfer userdata created by this module, so we need to make Lanes aware of it
 local dt = lanes.require "deep_test"
 
@@ -93,24 +95,44 @@ if DEEP then
         print "================================================================"
         print "DEEP"
         local d = dt.new_deep(nupvals)
-        if DEEP == "gc" then
-                local thrasher = function(repeat_, size_)
-                        print "in thrasher"
-                        -- result is a table of repeat_ tables, each containing size_ entries
-                        local result = {}
-                        for i = 1, repeat_ do
-                                local batch_values = {}
-                                for j = 1, size_ do
-                                        table.insert(batch_values, j)
+        if type(DEEP) == "string" then
+                local gc_tests = {
+                        thrasher = function(repeat_, size_)
+                                print "in thrasher"
+                                -- result is a table of repeat_ tables, each containing size_ entries
+                                local result = {}
+                                for i = 1, repeat_ do
+                                        local batch_values = {}
+                                        for j = 1, size_ do
+                                                table.insert(batch_values, j)
+                                        end
+                                        table.insert(result, batch_values)
+                                end
+                                print "thrasher done"
+                                return result
+                        end,
+                        stack_abuser = function(repeat_, size_)
+                                print "in stack_abuser"
+                                for i = 1, repeat_ do
+                                        local batch_values = {}
+                                        for j = 1, size_ do
+                                                table.insert(batch_values, j)
+                                        end
+                                        -- return size_ values
+                                        local _ = table_unpack(batch_values)
                                 end
-                                table.insert(result, batch_values)
+                                print "stack_abuser done"
+                                return result
                         end
-                        print "thrasher done"
-                        return result
-                end
+                }
                 -- have the object call the function from inside one of its functions, to detect if it gets collected from there (while in use!)
-                local r = d:invoke(thrasher, REPEAT or 10, SIZE or 10)
-                print("invoke -> ", tostring(r))
+                local testf = gc_tests[DEEP]
+                if testf then
+                        local r = d:invoke(gc_tests[DEEP], REPEAT or 10, SIZE or 10)
+                        print("invoke -> ", tostring(r))
+                else
+                        print("unknown test '" .. DEEP .. "'")
+                end
         else
                 performTest(d)
         end
diff --git a/src/debug.h b/src/debug.h
index a0a4b8d..99fe48a 100644
--- a/src/debug.h
+++ b/src/debug.h
@@ -15,6 +15,7 @@ inline void LUA_ASSERT_IMPL(lua_State* L_, bool cond_, char const* file_, int co
 }
 
 #define LUA_ASSERT(L_, cond_) LUA_ASSERT_IMPL(L_, cond_, __FILE__, __LINE__, #cond_)
+#define LUA_ASSERT_CODE(code_) code_
 
 class StackChecker
 {
@@ -102,6 +103,7 @@ class StackChecker
 #else // HAVE_LUA_ASSERT()
 
 #define LUA_ASSERT(L_, c) nullptr // nothing
+#define LUA_ASSERT_CODE(code_) nullptr
 
 #define STACK_CHECK_START_REL(L_, offset_)
 #define STACK_CHECK_START_ABS(L_, offset_)
diff --git a/src/linda.cpp b/src/linda.cpp
index 8b6df8e..3449f89 100644
--- a/src/linda.cpp
+++ b/src/linda.cpp
@@ -181,6 +181,8 @@ int Linda::ProtectedCall(lua_State* L_, lua_CFunction f_)
     lua_State* const _KL{ _K ? _K->L : nullptr };
     if (_KL == nullptr)
         return 0;
+
+    LUA_ASSERT_CODE(auto const _koip{ _linda->startKeeperOperation(L_) });
     // if we didn't do anything wrong, the keeper stack should be clean
     LUA_ASSERT(L_, lua_gettop(_KL) == 0);
 
diff --git a/src/linda.h b/src/linda.h
index 8db380a..809ade5 100644
--- a/src/linda.h
+++ b/src/linda.h
@@ -23,15 +23,39 @@ using LindaGroup = Unique<int>;
 class Linda
 : public DeepPrelude // Deep userdata MUST start with this header
 {
+    public:
+    class KeeperOperationInProgress
+    {
+        private:
+        Linda& linda;
+        [[maybe_unused]] lua_State* const L; // just here for inspection while debugging
+
+        public:
+        KeeperOperationInProgress(Linda& linda_, lua_State* const L_)
+        : linda{ linda_ }
+        , L{ L_ }
+        {
+            [[maybe_unused]] int const _prev{ linda.keeperOperationCount.fetch_add(1, std::memory_order_seq_cst) };
+        }
+
+        public:
+        ~KeeperOperationInProgress()
+        {
+            [[maybe_unused]] int const _prev{ linda.keeperOperationCount.fetch_sub(1, std::memory_order_seq_cst) };
+        }
+    };
+
     private:
     static constexpr size_t kEmbeddedNameLength = 24;
     using EmbeddedName = std::array<char, kEmbeddedNameLength>;
     // depending on the name length, it is either embedded inside the Linda, or allocated separately
-    std::variant<std::string_view, EmbeddedName> nameVariant;
+    std::variant<std::string_view, EmbeddedName> nameVariant{};
+    // counts the keeper operations in progress
+    std::atomic<int> keeperOperationCount{};
 
     public:
-    std::condition_variable readHappened;
-    std::condition_variable writeHappened;
+    std::condition_variable readHappened{};
+    std::condition_variable writeHappened{};
     Universe* const U{ nullptr }; // the universe this linda belongs to
     int const keeperIndex{ -1 }; // the keeper associated to this linda
     CancelRequest cancelRequest{ CancelRequest::None };
@@ -60,7 +84,9 @@ class Linda
     public:
     [[nodiscard]] Keeper* acquireKeeper() const;
     [[nodiscard]] std::string_view getName() const;
+    [[nodiscard]] bool inKeeperOperation() const { return keeperOperationCount.load(std::memory_order_seq_cst) != 0; }
     void releaseKeeper(Keeper* keeper_) const;
     [[nodiscard]] static int ProtectedCall(lua_State* L_, lua_CFunction f_);
+    [[nodiscard]] KeeperOperationInProgress startKeeperOperation(lua_State* const L_) { return KeeperOperationInProgress{ *this, L_ }; };
     [[nodiscard]] Keeper* whichKeeper() const { return U->keepers.getKeeper(keeperIndex); }
 };
diff --git a/src/lindafactory.cpp b/src/lindafactory.cpp
index 3f4b9b0..6a2b000 100644
--- a/src/lindafactory.cpp
+++ b/src/lindafactory.cpp
@@ -69,7 +69,7 @@ void LindaFactory::createMetatable(lua_State* L_) const
 void LindaFactory::deleteDeepObjectInternal(lua_State* L_, DeepPrelude* o_) const
 {
     Linda* const _linda{ static_cast<Linda*>(o_) };
-    LUA_ASSERT(L_, _linda);
+    LUA_ASSERT(L_, _linda && !_linda->inKeeperOperation());
     Keeper* const _myK{ _linda->whichKeeper() };
     // if collected after the universe, keepers are already destroyed, and there is nothing to clear
     if (_myK) {