stock/BasicStock: convert StockHandler to BasicStock virtual method

This moves the complexity of the DeferEvent to class MapStock, its
only user so far.

src/stock/BasicStock.cxx

@@ -16,7 +16,7 @@ BasicStock::FadeAll() noexcept
 		i.Fade();
 
 	ClearIdle();
-	ScheduleCheckEmpty();
+	CheckEmpty();
 
 	// TODO: restart the "num_create" list?
 }
@@ -38,15 +38,8 @@ BasicStock::Shutdown() noexcept
 void
 BasicStock::CheckEmpty() noexcept
 {
-	if (IsEmpty() && handler != nullptr)
-		handler->OnStockEmpty(*this);
-}
-
-void
-BasicStock::ScheduleCheckEmpty() noexcept
-{
-	if (IsEmpty() && handler != nullptr)
-		empty_event.Schedule();
+	if (IsEmpty())
+		OnEmpty();
 }
 
 
@@ -106,14 +99,11 @@ BasicStock::ClearEventCallback() noexcept
 
 BasicStock::BasicStock(EventLoop &event_loop, StockClass &_cls,
 		       const char *_name, std::size_t _max_idle,
-		       Event::Duration _clear_interval,
-		       StockHandler *_handler) noexcept
+		       Event::Duration _clear_interval) noexcept
 	:cls(_cls),
 	 name(_name),
 	 max_idle(_max_idle),
 	 clear_interval(_clear_interval),
-	 handler(_handler),
-	 empty_event(event_loop, BIND_THIS_METHOD(CheckEmpty)),
 	 cleanup_event(event_loop, BIND_THIS_METHOD(CleanupEventCallback)),
 	 clear_event(event_loop, BIND_THIS_METHOD(ClearEventCallback))
 {
@@ -165,7 +155,7 @@ BasicStock::GetIdle() noexcept
 		delete &item;
 	}
 
-	ScheduleCheckEmpty();
+	CheckEmpty();
 	return nullptr;
 }
 
@@ -221,7 +211,7 @@ BasicStock::ItemCreateError(StockGetHandler &get_handler,
 	assert(num_create > 0);
 	--num_create;
 
-	ScheduleCheckEmpty();
+	CheckEmpty();
 
 	get_handler.OnStockItemError(ep);
 }
@@ -232,7 +222,7 @@ BasicStock::ItemCreateAborted() noexcept
 	assert(num_create > 0);
 	--num_create;
 
-	ScheduleCheckEmpty();
+	CheckEmpty();
 }
 
 PutAction
@@ -250,7 +240,7 @@ BasicStock::Put(StockItem &item, PutAction action) noexcept
 	if (action == PutAction::DESTROY ||
 	    item.IsFading() || !item.Release()) {
 		delete &item;
-		ScheduleCheckEmpty();
+		CheckEmpty();
 		return PutAction::DESTROY;
 	} else {
 		InjectIdle(item);
@@ -287,7 +277,7 @@ BasicStock::ItemIdleDisconnect(StockItem &item) noexcept
 		UnscheduleCleanup();
 
 	delete &item;
-	ScheduleCheckEmpty();
+	CheckEmpty();
 }
 
 void

src/stock/BasicStock.hxx

@@ -9,7 +9,6 @@
 #include "Request.hxx"
 #include "Stats.hxx"
 #include "event/CoarseTimerEvent.hxx"
-#include "event/DeferEvent.hxx"
 #include "util/DeleteDisposer.hxx"
 #include "util/IntrusiveList.hxx"
 
@@ -23,15 +22,6 @@ class BasicStock;
 class StockClass;
 class StockGetHandler;
 
-class StockHandler {
-public:
-	/**
-	 * The stock has become empty.  It is safe to delete it from
-	 * within this method.
-	 */
-	virtual void OnStockEmpty(BasicStock &stock) noexcept = 0;
-};
-
 /**
  * Objects in stock.  May be used for connection pooling.
  *
@@ -52,14 +42,6 @@ private:
 
 	const Event::Duration clear_interval;
 
-	StockHandler *const handler;
-
-	/**
-	 * This event is used to move the "empty" check out of the current
-	 * stack, to invoke the handler method in a safe environment.
-	 */
-	DeferEvent empty_event;
-
 	CoarseTimerEvent cleanup_event;
 	CoarseTimerEvent clear_event;
 
@@ -82,16 +64,15 @@ public:
 	 */
 	BasicStock(EventLoop &event_loop, StockClass &cls,
 		   const char *name, std::size_t max_idle,
-		   Event::Duration _clear_interval,
-		   StockHandler *handler=nullptr) noexcept;
+		   Event::Duration _clear_interval) noexcept;
 
 	~BasicStock() noexcept;
 
 	BasicStock(const BasicStock &) = delete;
 	BasicStock &operator=(const BasicStock &) = delete;
 
 	EventLoop &GetEventLoop() const noexcept override {
-		return empty_event.GetEventLoop();
+		return cleanup_event.GetEventLoop();
 	}
 
 	StockClass &GetClass() noexcept {
@@ -136,7 +117,7 @@ public:
 
 		ClearIdleIf(predicate);
 
-		ScheduleCheckEmpty();
+		CheckEmpty();
 		// TODO: restart the "num_create" list?
 	}
 
@@ -160,12 +141,17 @@ protected:
 		return busy.size() + num_create;
 	}
 
+	/**
+	 * The stock has become empty.  It is not safe to delete it
+	 * from within this method.
+	 */
+	virtual void OnEmpty() noexcept {}
+
 private:
 	/**
 	 * Check if the stock has become empty, and invoke the handler.
 	 */
 	void CheckEmpty() noexcept;
-	void ScheduleCheckEmpty() noexcept;
 
 	void ScheduleClear() noexcept {
 		if (clear_interval > Event::Duration::zero())

src/stock/MapStock.cxx

@@ -7,6 +7,13 @@
 #include "util/DeleteDisposer.hxx"
 #include "util/StringAPI.hxx"
 
+void
+StockMap::Item::OnDeferredEmpty() noexcept
+{
+	if (IsEmpty() && !sticky)
+		map.Erase(*this);
+}
+
 inline size_t
 StockMap::Item::Hash::operator()(const char *key) const noexcept
 {
@@ -45,27 +52,16 @@ StockMap::Erase(Item &item) noexcept
 	map.erase_and_dispose(i, DeleteDisposer());
 }
 
-void
-StockMap::OnStockEmpty(BasicStock &stock) noexcept
-{
-	auto &item = static_cast<Item &>(stock);
-	if (item.sticky)
-		return;
-
-	Erase(item);
-}
-
 Stock &
 StockMap::GetStock(const char *uri, void *request) noexcept
 {
 	auto [position, inserted] = map.insert_check(uri);
 	if (inserted) {
-		auto *item = new Item(event_loop, cls,
+		auto *item = new Item(*this, event_loop, cls,
 				      uri,
 				      GetLimit(request, limit),
 				      max_idle,
-				      GetClearInterval(request),
-				      this);
+				      GetClearInterval(request));
 		map.insert_commit(position, *item);
 		return *item;
 	} else

src/stock/MapStock.hxx

@@ -6,25 +6,41 @@
 
 #include "Stock.hxx"
 #include "event/Chrono.hxx"
+#include "event/DeferEvent.hxx"
 #include "util/IntrusiveHashSet.hxx"
-#include "util/StringAPI.hxx"
 
-#include <cassert>
 #include <concepts> // for std::predicate
 #include <cstddef>
 
 /**
  * A hash table of any number of Stock objects, each with a different
  * URI.
  */
-class StockMap : StockHandler {
+class StockMap {
 	struct Item final : IntrusiveHashSetHook<IntrusiveHookMode::NORMAL>, Stock {
+		StockMap &map;
+
+		DeferEvent defer_empty{GetEventLoop(), BIND_THIS_METHOD(OnDeferredEmpty)};
+
 		bool sticky = false;
 
+		template<typename... Args>
+		explicit Item(StockMap &_map, Args&&... args) noexcept
+			:Stock(std::forward<Args>(args)...), map(_map) {}
+
 		template<typename... Args>
 		explicit Item(Args&&... args) noexcept
 			:Stock(std::forward<Args>(args)...) {}
 
+	protected:
+		virtual void OnEmpty() noexcept override {
+			defer_empty.Schedule();
+		}
+
+	private:
+		void OnDeferredEmpty() noexcept;
+
+	public:
 		struct Hash {
 			[[gnu::pure]]
 			size_t operator()(const char *key) const noexcept;
@@ -158,8 +174,4 @@ protected:
 	virtual Event::Duration GetClearInterval([[maybe_unused]] const void *request) const noexcept {
 		return clear_interval;
 	}
-
-private:
-	/* virtual methods from class StockHandler */
-	void OnStockEmpty(BasicStock &stock) noexcept override;
 };

src/stock/Stock.cxx

@@ -139,12 +139,10 @@ Stock::ScheduleRetryWaiting() noexcept
 
 Stock::Stock(EventLoop &event_loop, StockClass &_cls,
 	     const char *_name, std::size_t _limit, std::size_t _max_idle,
-	     Event::Duration _clear_interval,
-	     StockHandler *_handler) noexcept
+	     Event::Duration _clear_interval) noexcept
 	:BasicStock(event_loop, _cls, _name,
 		    _max_idle,
-		    _clear_interval,
-		    _handler),
+		    _clear_interval),
 	 limit(_limit),
 	 retry_event(event_loop, BIND_THIS_METHOD(RetryWaiting))
 {

src/stock/Stock.hxx

@@ -52,8 +52,7 @@ public:
 	 */
 	Stock(EventLoop &event_loop, StockClass &cls,
 	      const char *name, std::size_t limit, std::size_t max_idle,
-	      Event::Duration _clear_interval,
-	      StockHandler *handler=nullptr) noexcept;
+	      Event::Duration _clear_interval) noexcept;
 
 	~Stock() noexcept;