Implement a new class, save_blocker,

...analogous to input_blocker and update_locker, which effectively
masks requests to save the game and processes them after the
save_blocker has been destructed.  Wrap one around
playsingle_controller::init_side(), fixing bug #9496.  See also bug
#13298.

src/play_controller.cpp

@@ -27,7 +27,7 @@
 #include "sound.hpp"
 #include "unit_id.hpp"
 #include "terrain_filter.hpp"
-
+#include "savegame.hpp"
 
 #define LOG_NG LOG_STREAM(info, engine)
 
@@ -286,15 +286,30 @@ void play_controller::status_table(){
 }
 
 void play_controller::save_game(){
-	menu_handler_.save_game("",gui::OK_CANCEL);
+	if(save_blocker::try_block()) {
+		save_blocker::save_unblocker unblocker;
+		menu_handler_.save_game("",gui::OK_CANCEL);
+	} else {
+		save_blocker::on_unblock(this,&play_controller::save_game);
+	}
 }
 
 void play_controller::save_replay(){
-	menu_handler_.save_replay("", gui::OK_CANCEL, false);
+	if(save_blocker::try_block()) {
+		save_blocker::save_unblocker unblocker;
+		menu_handler_.save_game("", gui::OK_CANCEL, false);
+	} else {
+		save_blocker::on_unblock(this,&play_controller::save_replay);
+	}
 }
 
 void play_controller::save_map(){
-	menu_handler_.save_map();
+	if(save_blocker::try_block()) {
+		save_blocker::save_unblocker unblocker;
+		menu_handler_.save_map();
+	} else {
+		save_blocker::on_unblock(this,&play_controller::save_map);
+	}
 }
 
 void play_controller::load_game(){

src/playsingle_controller.cpp

@@ -33,6 +33,7 @@
 #include "upload_log.hpp"
 #include "formula_string_utils.hpp"
 #include "events.hpp"
+#include "savegame.hpp"
 
 #define ERR_NG LOG_STREAM(err, engine)
 #define LOG_NG LOG_STREAM(info, engine)
@@ -529,13 +530,7 @@ void playsingle_controller::play_turn(bool save)
 				skip_next_turn_ = false;
 				throw end_turn_exception();
 			}
-			/*
-			 * Commented this out at dfranke's request,
-			 * effectively reverting his commit 34278,
-			 * because it introduced blocker bug #13298:
-			 * reproducible hang in dialog code
-			 */
-			//input_blocker blocker;
+			save_blocker blocker;
 			init_side(player_number_ - 1);
 		} catch (end_turn_exception) {
 			if (current_team().is_network() == false) {

src/savegame.cpp

@@ -22,6 +22,51 @@
 
 #define LOG_SAVE LOG_STREAM(info, engine)
 
+
+play_controller* save_blocker::controller_ = NULL;
+void (play_controller::*save_blocker::callback_)() = NULL;
+SDL_sem* save_blocker::sem_ = SDL_CreateSemaphore(1);
+
+save_blocker::save_blocker() {
+	block();
+}
+
+save_blocker::~save_blocker() {
+	unblock();
+	if(controller_ && callback_) {
+		(controller_->*callback_)();
+		controller_ = NULL;
+		callback_ = NULL;
+	}
+}
+
+void save_blocker::on_unblock(play_controller* controller, void (play_controller::*callback)()) {
+	if(try_block()) {
+		unblock();
+		(controller->*callback)();
+	} else {
+		controller_ = controller;
+		callback_ = callback;
+	}
+}
+
+bool save_blocker::saves_are_blocked() {
+	return SDL_SemValue(sem_) == 0;
+}
+
+void save_blocker::block() {
+	SDL_SemWait(sem_);
+}
+
+bool save_blocker::try_block() {
+	return SDL_SemTryWait(sem_) == 0;
+}
+
+void save_blocker::unblock() {
+	assert(SDL_SemValue(sem_) == 0);
+	SDL_SemPost(sem_);
+}
+
 // Prototypes
 
 // Interactive replay save

src/savegame.hpp

@@ -18,9 +18,37 @@
 
 #include "global.hpp"
 #include "gamestatus.hpp"
+#include "play_controller.hpp"
 
 #include <string>
 
+#include "SDL_mutex.h"
+
+class save_blocker {
+public:
+	save_blocker();
+	~save_blocker();
+	static bool saves_are_blocked();
+	static void on_unblock(play_controller* controller, void (play_controller::*callback)());
+
+protected:
+	friend class play_controller;
+	static void block();
+	static bool try_block();
+	static void unblock();
+
+	class save_unblocker {
+	public:
+		save_unblocker() {}
+		~save_unblocker() { save_blocker::unblock(); }
+	};
+
+private:
+	static play_controller *controller_;
+	static void (play_controller::*callback_)();
+	static SDL_sem* sem_;
+};
+
 /** Autosave */
 std::string save_autosave(unsigned turn, const config& snapshot, game_state& gamestate);