Codechange: Use atomic variables for thread synchronization where useful.

src/network/network_gamelist.cpp

@@ -18,16 +18,14 @@
 #include "network_internal.h"
 #include "network_udp.h"
 #include "network_gamelist.h"
-#include <mutex>
+#include <atomic>
 
 #include "../safeguards.h"
 
 NetworkGameList *_network_game_list = NULL;
 
-/** Mutex for handling delayed insertion/querying of servers. */
-static std::mutex _network_game_list_mutex;
 /** The games to insert when the GUI thread has time for us. */
-static NetworkGameList *_network_game_delayed_insertion_list = NULL;
+static std::atomic<NetworkGameList *> _network_game_delayed_insertion_list(NULL);
 
 /**
  * Add a new item to the linked gamelist, but do it delayed in the next tick
@@ -36,18 +34,17 @@ static NetworkGameList *_network_game_delayed_insertion_list = NULL;
  */
 void NetworkGameListAddItemDelayed(NetworkGameList *item)
 {
-	std::lock_guard<std::mutex> lock(_network_game_list_mutex);
+	item->next = _network_game_delayed_insertion_list.load(std::memory_order_relaxed);
-	item->next = _network_game_delayed_insertion_list;
+	while (!_network_game_delayed_insertion_list.compare_exchange_weak(item->next, item, std::memory_order_acq_rel)) {}
-	_network_game_delayed_insertion_list = item;
 }
 
 /** Perform the delayed (thread safe) insertion into the game list */
 static void NetworkGameListHandleDelayedInsert()
 {
-	std::lock_guard<std::mutex> lock(_network_game_list_mutex);
+	while (true) {
-	while (_network_game_delayed_insertion_list != NULL) {
+		NetworkGameList *ins_item = _network_game_delayed_insertion_list.load(std::memory_order_relaxed);
-		NetworkGameList *ins_item = _network_game_delayed_insertion_list;
+		while (ins_item != NULL && !_network_game_delayed_insertion_list.compare_exchange_weak(ins_item, ins_item->next, std::memory_order_acq_rel)) {}
-		_network_game_delayed_insertion_list = ins_item->next;
+		if (ins_item == NULL) break; // No item left.
 
 		NetworkGameList *item = NetworkGameListAddItem(ins_item->address);
 

src/saveload/saveload.cpp

@@ -45,6 +45,7 @@
 #include "../string_func.h"
 #include "../fios.h"
 #include "../error.h"
+#include <atomic>
 
 #include "table/strings.h"
 
@@ -370,9 +371,9 @@ void NORETURN SlErrorCorruptFmt(const char *format, ...)
 }
 
 
-typedef void (*AsyncSaveFinishProc)();                ///< Callback for when the savegame loading is finished.
+typedef void (*AsyncSaveFinishProc)();                      ///< Callback for when the savegame loading is finished.
-static AsyncSaveFinishProc _async_save_finish = NULL; ///< Callback to call when the savegame loading is finished.
+static std::atomic<AsyncSaveFinishProc> _async_save_finish; ///< Callback to call when the savegame loading is finished.
-static std::thread _save_thread;                      ///< The thread we're using to compress and write a savegame
+static std::thread _save_thread;                            ///< The thread we're using to compress and write a savegame
 
 /**
  * Called by save thread to tell we finished saving.
@@ -381,9 +382,9 @@ static std::thread _save_thread;                      ///< The thread we're usin
 static void SetAsyncSaveFinish(AsyncSaveFinishProc proc)
 {
 	if (_exit_game) return;
-	while (_async_save_finish != NULL) CSleep(10);
+	while (_async_save_finish.load(std::memory_order_acquire) != NULL) CSleep(10);
 
-	_async_save_finish = proc;
+	_async_save_finish.store(proc, std::memory_order_release);
 }
 
 /**
@@ -391,11 +392,10 @@ static void SetAsyncSaveFinish(AsyncSaveFinishProc proc)
  */
 void ProcessAsyncSaveFinish()
 {
-	if (_async_save_finish == NULL) return;
+	AsyncSaveFinishProc proc = _async_save_finish.exchange(NULL, std::memory_order_acq_rel);
+	if (proc == NULL) return;
 
-	_async_save_finish();
+	proc();
-
-	_async_save_finish = NULL;
 
 	if (_save_thread.joinable()) {
 		_save_thread.join();