hold strong ref for returned objects (#91)

src/cpp/channel.cpp

@@ -63,8 +63,10 @@ StoredArray Channel::pop(const sol::optional<int>& duration,
     }
 
     auto ret = data_->channel_.front();
-    for (const auto& obj: ret)
+    for (const auto& obj: ret) {
+        obj->holdStrongReference();
         removeReference(obj->gcHandle());
+    }
 
     data_->channel_.pop();
     return ret;

src/cpp/stored-object.cpp

@@ -97,6 +97,12 @@ public:
         strongRef_ = sol::nullopt;
     }
 
+    void holdStrongReference() override {
+        if (!strongRef_) {
+            strongRef_ = GC::instance().get<T>(handle_);
+        }
+    }
+
 private:
     GCObjectHandle handle_;
     sol::optional<T> strongRef_;

src/cpp/stored-object.h

@@ -24,6 +24,7 @@ public:
     virtual sol::object unpack(sol::this_state state) const = 0;
     virtual GCObjectHandle gcHandle() const { return GCNull; }
     virtual void releaseStrongReference() { }
+    virtual void holdStrongReference() { }
 
 private:
     BaseHolder(const BaseHolder&) = delete;

tests/lua/channel-stress.lua

@@ -68,4 +68,25 @@ if not os.getenv("APPVEYOR") then
         test.equal(chan:pop(10), "hello!")
         test.is_true(os.time() < start_time + 10)
     end
-end
+end
+
+-- regress for channel returns
+test.channel_stress.retun_tables = function ()
+    local function worker()
+        local effil = require "effil"
+        local ch = effil.channel()
+        for i = 1, 1000 do
+            ch:push(effil.table())
+            local ret = { ch:pop() }
+        end
+    end
+
+    local threads = {}
+
+    for i = 1, 20 do
+        table.insert(threads, effil.thread(worker)())
+    end
+    for _, thr in ipairs(threads) do
+        thr:wait()
+    end
+end