stock/AbstractStock: eliminate ItemCreateAborted()

Allocate a Create object which updates the BasicStock state
automatically without requiring an extra method.  This reduces code
complexity and prepares implementing continue-after-cancel.

src/pg/Stock.cxx

@@ -83,7 +83,7 @@ class Stock::Item final : public StockItem, Cancellable, AsyncConnectionHandler
 	void Cancel() noexcept override {
 		assert(!initialized || defer_initialized.IsPending());
 
-		InvokeCreateAborted();
+		delete this;
 	}
 
 	/* virtual methods from class AsyncConnectionHandler */

src/stock/AbstractStock.cxx

@@ -12,10 +12,3 @@ AbstractStock::ItemCreateError(StockItem &item, StockGetHandler &get_handler,
 	ItemCreateError(get_handler, ep);
 	delete &item;
 }
-
-void
-AbstractStock::ItemCreateAborted(StockItem &item) noexcept
-{
-	ItemCreateAborted();
-	delete &item;
-}

src/stock/AbstractStock.hxx

@@ -33,7 +33,5 @@ public:
 			     std::exception_ptr ep) noexcept;
 	virtual void ItemCreateError(StockGetHandler &get_handler,
 				     std::exception_ptr ep) noexcept = 0;
-	void ItemCreateAborted(StockItem &item) noexcept;
-	virtual void ItemCreateAborted() noexcept = 0;
 	virtual void ItemUncleanFlagCleared() noexcept {}
 };

src/stock/BasicStock.cxx

@@ -9,6 +9,39 @@
 
 #include <cassert>
 
+struct BasicStock::Create final
+	: IntrusiveListHook<>, StockGetHandler, Cancellable
+{
+	BasicStock &stock;
+
+	StockGetHandler &handler;
+
+	CancellablePointer cancel_ptr;
+
+	Create(BasicStock &_stock,
+	       StockGetHandler &_handler, CancellablePointer &_cancel_ptr) noexcept
+		:stock(_stock), handler(_handler)
+	{
+		_cancel_ptr = *this;
+	}
+
+	[[noreturn]]
+	void OnStockItemReady(StockItem &) noexcept override {
+		// unreachable
+		std::terminate();
+	}
+
+	[[noreturn]]
+	void OnStockItemError(std::exception_ptr) noexcept override {
+		// unreachable
+		std::terminate();
+	}
+
+	void Cancel() noexcept override {
+		stock.CreateCanceled(*this);
+	}
+};
+
 void
 BasicStock::FadeAll() noexcept
 {
@@ -114,7 +147,7 @@ BasicStock::BasicStock(EventLoop &event_loop, StockClass &_cls,
 
 BasicStock::~BasicStock() noexcept
 {
-	assert(num_create == 0);
+	assert(create.empty());
 
 	/* must not delete the Stock when there are busy items left */
 	assert(busy.empty());
@@ -182,46 +215,49 @@ BasicStock::GetCreate(StockRequest request,
 		      StockGetHandler &get_handler,
 		      CancellablePointer &cancel_ptr) noexcept
 {
-	++num_create;
+	auto *c = new Create(*this, get_handler, cancel_ptr);
+	create.push_front(*c);
 
 	try {
-		cls.Create({*this}, std::move(request),
-			   get_handler, cancel_ptr);
+		cls.Create({*this}, std::move(request), *c, c->cancel_ptr);
 	} catch (...) {
-		ItemCreateError(get_handler, std::current_exception());
+		ItemCreateError(*c, std::current_exception());
 	}
 }
 
 void
-BasicStock::ItemCreateSuccess(StockGetHandler &get_handler,
+BasicStock::ItemCreateSuccess(StockGetHandler &_handler,
 			      StockItem &item) noexcept
 {
-	assert(num_create > 0);
-	--num_create;
+	auto &c = static_cast<Create &>(_handler);
+	auto &get_handler = c.handler;
+
+	DeleteCreate(c);
 
 	busy.push_front(item);
 
 	get_handler.OnStockItemReady(item);
 }
 
 void
-BasicStock::ItemCreateError(StockGetHandler &get_handler,
+BasicStock::ItemCreateError(StockGetHandler &_handler,
 			    std::exception_ptr ep) noexcept
 {
-	assert(num_create > 0);
-	--num_create;
+	auto &c = static_cast<Create &>(_handler);
+	auto &get_handler = c.handler;
+
+	DeleteCreate(c);
 
 	CheckEmpty();
 
 	get_handler.OnStockItemError(ep);
 }
 
-void
-BasicStock::ItemCreateAborted() noexcept
+inline void
+BasicStock::CreateCanceled(Create &c) noexcept
 {
-	assert(num_create > 0);
-	--num_create;
-
+	DeleteCreate(c);
+	OnCreateCanceled();
 	CheckEmpty();
 }
 
@@ -288,3 +324,13 @@ BasicStock::ItemBusyDisconnect(StockItem &item) noexcept
 	/* this item will be destroyed by Put() */
 	item.Fade();
 }
+
+
+inline void
+BasicStock::DeleteCreate(Create &c) noexcept
+{
+	assert(!create.empty());
+
+	create.erase_and_dispose(create.iterator_to(c),
+				 DeleteDisposer{});
+}

src/stock/BasicStock.hxx

@@ -60,13 +60,17 @@ private:
 	 */
 	ItemList busy;
 
+	struct Create;
+
 	/**
-	 * The number of items that are currently being created.  We
-	 * keep track of this because we need to know whether this
-	 * stock is empty (see OnEmpty()) and whether this stock is
-	 * full (see Stock::IsFull()).
+	 * The items that are currently being created.  We keep track
+	 * of this because we need to know whether this stock is empty
+	 * (see OnEmpty()) and whether this stock is full (see
+	 * Stock::IsFull()).
 	 */
-	std::size_t num_create = 0;
+	IntrusiveList<Create,
+		IntrusiveListBaseHookTraits<Create>,
+		IntrusiveListOptions{.constant_time_size = true}> create;
 
 protected:
 	bool may_clear = false;
@@ -104,7 +108,7 @@ public:
 	 */
 	[[gnu::pure]]
 	bool IsEmpty() const noexcept {
-		return idle.empty() && busy.empty() && num_create == 0;
+		return idle.empty() && busy.empty() && create.empty();
 	}
 
 	/**
@@ -133,7 +137,7 @@ public:
 		ClearIdleIf(predicate);
 
 		CheckEmpty();
-		// TODO: restart the "num_create" list?
+		// TODO: restart the "create" list?
 	}
 
 	/**
@@ -149,13 +153,15 @@ protected:
 
 	/**
 	 * Determine the number of "active" items, i.e. the busy items
-	 * and the ones being created (#num_create).  This number is
-	 * used to compare with the configured #limit.
+	 * and the ones being created (#create).  This number is used
+	 * to compare with the configured #limit.
 	 */
 	std::size_t GetActiveCount() const noexcept {
-		return busy.size() + num_create;
+		return busy.size() + create.size();
 	}
 
+	virtual void OnCreateCanceled() noexcept {}
+
 	/**
 	 * The stock has become empty.  It is not safe to delete it
 	 * from within this method.
@@ -225,9 +231,11 @@ public:
 			       StockItem &item) noexcept override;
 	void ItemCreateError(StockGetHandler &get_handler,
 			     std::exception_ptr ep) noexcept override;
-	void ItemCreateAborted() noexcept override;
 
 private:
+	void DeleteCreate(Create &c) noexcept;
+	void CreateCanceled(Create &c) noexcept;
+
 	void ScheduleCleanup() noexcept {
 		cleanup_event.Schedule(std::chrono::seconds(20));
 	}

src/stock/Item.cxx

@@ -18,12 +18,6 @@ CreateStockItem::InvokeCreateError(StockGetHandler &handler,
 	stock.ItemCreateError(handler, ep);
 }
 
-void
-CreateStockItem::InvokeCreateAborted() noexcept
-{
-	stock.ItemCreateAborted();
-}
-
 StockItem::~StockItem() noexcept
 {
 }
@@ -53,12 +47,6 @@ StockItem::InvokeCreateError(StockGetHandler &handler,
 	stock.ItemCreateError(*this, handler, ep);
 }
 
-void
-StockItem::InvokeCreateAborted() noexcept
-{
-	stock.ItemCreateAborted(*this);
-}
-
 void
 StockItem::InvokeIdleDisconnect() noexcept
 {

src/stock/Item.hxx

@@ -27,12 +27,6 @@ struct CreateStockItem {
 	 */
 	void InvokeCreateError(StockGetHandler &handler,
 			       std::exception_ptr ep) noexcept;
-
-	/**
-	 * Announce that the creation of this item has been aborted by the
-	 * caller.
-	 */
-	void InvokeCreateAborted() noexcept;
 };
 
 class StockItem
@@ -124,12 +118,6 @@ public:
 	void InvokeCreateError(StockGetHandler &handler,
 			       std::exception_ptr ep) noexcept;
 
-	/**
-	 * Announce that the creation of this item has been aborted by the
-	 * caller.
-	 */
-	void InvokeCreateAborted() noexcept;
-
 	/**
 	 * Announce that the item has been disconnected by the peer while
 	 * it was idle.

src/stock/MultiStock.cxx

@@ -240,12 +240,6 @@ MultiStock::OuterItem::ItemCreateError(StockGetHandler &get_handler,
 	get_handler.OnStockItemError(std::move(ep));
 }
 
-void
-MultiStock::OuterItem::ItemCreateAborted() noexcept
-{
-	// unreachable
-}
-
 void
 MultiStock::OuterItem::ItemUncleanFlagCleared() noexcept
 {
@@ -545,12 +539,6 @@ MultiStock::MapItem::ItemCreateError(StockGetHandler &get_handler,
 	get_handler.OnStockItemError(ep);
 }
 
-void
-MultiStock::MapItem::ItemCreateAborted() noexcept
-{
-	assert(!get_cancel_ptr);
-}
-
 inline void
 MultiStock::MapItem::OnLeaseReleased(OuterItem &item) noexcept
 {

src/stock/MultiStock.hxx

@@ -149,7 +149,6 @@ class MultiStock {
 				       StockItem &item) noexcept override;
 		void ItemCreateError(StockGetHandler &get_handler,
 				     std::exception_ptr ep) noexcept override;
-		void ItemCreateAborted() noexcept override;
 		void ItemUncleanFlagCleared() noexcept override;
 	};
 
@@ -293,7 +292,6 @@ class MultiStock {
 				       StockItem &item) noexcept override;
 		void ItemCreateError(StockGetHandler &get_handler,
 				     std::exception_ptr ep) noexcept override;
-		void ItemCreateAborted() noexcept override;
 
 	public:
 		struct Hash {

src/stock/Stock.cxx

@@ -223,9 +223,8 @@ Stock::ItemCreateError(StockGetHandler &get_handler,
 }
 
 void
-Stock::ItemCreateAborted() noexcept
+Stock::OnCreateCanceled() noexcept
 {
-	BasicStock::ItemCreateAborted();
 	ScheduleRetryWaiting();
 }
 

src/stock/Stock.hxx

@@ -94,13 +94,14 @@ public:
 
 	void ItemCreateError(StockGetHandler &get_handler,
 			     std::exception_ptr ep) noexcept override;
-	void ItemCreateAborted() noexcept override;
 
 	void ItemUncleanFlagCleared() noexcept override {
 		ScheduleRetryWaiting();
 	}
 
 private:
+	void OnCreateCanceled() noexcept override;
+
 	[[gnu::pure]]
 	WaitingList::iterator PickWaiting() noexcept;
 

test/stock/TestMultiStock.cxx

@@ -308,7 +308,6 @@ MyStockClass::DeferredRequest::OnDeferred() noexcept
 void
 MyStockClass::DeferredRequest::Cancel() noexcept
 {
-	c.InvokeCreateAborted();
 	delete this;
 }