Convert uses of boost::thread to std::thread

Also covers uses of boost::this_thread.

Turns out std::thread calls std::terminate if it's destroyed while still joinable.
thread::detach needs to be called or else the program will crash.

There's also no standard library equivalent of boost:🧵:timed_join so I just
replaced it with the is_worker_running_ variable.

src/events.cpp

@@ -31,11 +31,11 @@
 #include <iterator>
 #include <utility>
 #include <vector>
+#include <thread>
 
 #include <SDL.h>
 
 #include <boost/range/adaptor/reversed.hpp>
-#include <boost/thread.hpp>
 
 #define ERR_GEN LOG_STREAM(err, lg::general)
 
@@ -415,11 +415,11 @@ void finalize()
 }
 
 // TODO: I'm uncertain if this is always safe to call at static init; maybe set in main() instead?
-static const boost::thread::id main_thread = boost::this_thread::get_id();
+static const std::thread::id main_thread = std::this_thread::get_id();
 
 void run_event_loop()
 {
-	if(boost::this_thread::get_id() != main_thread) {
+	if(std::this_thread::get_id() != main_thread) {
 		// Can only call this on the main thread!
 		return;
 	}
@@ -746,7 +746,7 @@ void peek_for_resize()
 
 void call_in_main_thread(const std::function<void(void)>& f)
 {
-	if(boost::this_thread::get_id() == main_thread) {
+	if(std::this_thread::get_id() == main_thread) {
 		// nothing special to do if called from the main thread.
 		f();
 		return;

src/gui/dialogs/loading_screen.cpp

@@ -32,8 +32,6 @@
 #include "utils/functional.hpp"
 #include "video.hpp"
 
-#include <boost/thread.hpp>
-
 #include <cstdlib>
 
 #if defined(_MSC_VER) && _MSC_VER <= 1800
@@ -109,7 +107,7 @@ loading_screen::loading_screen(std::function<void()> f)
 void loading_screen::pre_show(window& window)
 {
 	if(work_) {
-		worker_.reset(new boost::thread([this]() {
+		worker_.reset(new std::thread([this]() {
 			is_worker_running_ = true;
 
 			try {
@@ -154,12 +152,13 @@ loading_screen* loading_screen::current_load = nullptr;
 
 void loading_screen::timer_callback(window& window)
 {
-	if(!work_ || !worker_ || worker_->timed_join(boost::posix_time::milliseconds(0))) {
+	if(!work_ || !worker_ || !is_worker_running_) {
 		if(exception_) {
 			clear_timer();
 			std::rethrow_exception(exception_);
 		}
 
+		worker_->detach();
 		window.close();
 	}
 

src/gui/dialogs/loading_screen.hpp

@@ -19,11 +19,8 @@
 #include <map>
 #include <vector>
 #include <atomic>
+#include <thread>
 
-namespace boost
-{
-	class thread;
-}
 namespace cursor
 {
 	struct setter;
@@ -86,7 +83,7 @@ private:
 	std::size_t timer_id_;
 	int animation_counter_;
 	std::function<void()> work_;
-	std::unique_ptr<boost::thread> worker_;
+	std::unique_ptr<std::thread> worker_;
 	std::unique_ptr<cursor::setter> cursor_setter_;
 	std::exception_ptr exception_;
 	void clear_timer();

src/wesnothd_connection.cpp

@@ -21,8 +21,6 @@
 
 #include <SDL_timer.h>
 
-#include <boost/thread.hpp>
-
 #include <cstdint>
 #include <deque>
 
@@ -82,6 +80,7 @@ wesnothd_connection::wesnothd_connection(const std::string& host, const std::str
 
 wesnothd_connection::~wesnothd_connection()
 {
+	worker_thread_->detach();
 	MPTEST_LOG;
 }
 
@@ -150,7 +149,7 @@ void wesnothd_connection::handle_handshake(const error_code& ec)
 	handshake_finished_ = true;
 	recv();
 
-	worker_thread_.reset(new boost::thread([this]() {
+	worker_thread_.reset(new std::thread([this]() {
 		// worker thread
 		std::shared_ptr<wesnothd_connection> this_ptr = this->shared_from_this();
 

src/wesnothd_connection.hpp

@@ -41,13 +41,9 @@
 
 #include <deque>
 #include <list>
+#include <thread>
 #include <mutex>
 
-namespace boost
-{
-class thread;
-}
-
 class config;
 class wesnothd_connection_ptr;
 enum class loading_stage;
@@ -139,7 +135,7 @@ public:
 	}
 
 private:
-	std::unique_ptr<boost::thread> worker_thread_;
+	std::unique_ptr<std::thread> worker_thread_;
 
 	boost::asio::io_service io_service_;