allow an easy way to fix an upper limit to the number of threads used,

...limit is 1 for client and unlimited for wesnothd and
campaignd. limits for the servers can be set via CLI

changelog

@@ -217,7 +217,8 @@ Version 1.3-svn:
    * better handling of SDL_ListModes return code (no user impact)
    * first turn of a game is saved again (fixes bug #7909 and bug #8117)
    * reduce CPU usage by removing calls to SDL_GetTicks for idle animations
-   * changed network thread management to be more scalable
+   * changed network thread management to be more scalable, both with an upper
+   and lower number of threads
    * enabled python as default, to disable it use --disable-python
    * various code cleanups
 

src/campaign_server/campaign_server.cpp

@@ -46,7 +46,7 @@ namespace {
 	class campaign_server
 	{
 		public:
-			explicit campaign_server(const std::string& cfgfile,unsigned int nthread = 10);
+			explicit campaign_server(const std::string& cfgfile,size_t min_thread = 10,size_t max_thread = 0);
 			void run();
 		private:
 			int load_config(); // return the server port
@@ -66,8 +66,8 @@ namespace {
 		return lexical_cast_default<int>(cfg_["port"], 15003);
 	}
 
-	campaign_server::campaign_server(const std::string& cfgfile,unsigned int nthread)
-		: file_(cfgfile), net_manager_(nthread), server_manager_(load_config())
+	campaign_server::campaign_server(const std::string& cfgfile,size_t min_thread,size_t max_thread)
+		: file_(cfgfile), net_manager_(min_thread,max_thread), server_manager_(load_config())
 	{
 		if(cfg_.child("campaigns") == NULL) {
 			cfg_.add_child("campaigns");

src/network.cpp

@@ -183,7 +183,7 @@ void error::disconnect()
 	network::disconnect(socket);
 }
 
-manager::manager(size_t nthreads) : free_(true)
+manager::manager(size_t min_threads, size_t max_threads) : free_(true)
 {
 	//if the network is already being managed
 	if(socket_set) {
@@ -204,7 +204,7 @@ manager::manager(size_t nthreads) : free_(true)
 
 	socket_set = SDLNet_AllocSocketSet(512);
 
-	worker_pool_man = new network_worker_pool::manager(nthreads);
+	worker_pool_man = new network_worker_pool::manager(min_threads, max_threads);
 }
 
 manager::~manager()

src/network.hpp

@@ -31,8 +31,14 @@ namespace network {
 
 //a network manager must be created before networking can be used.
 //it must be destroyed only after all networking activity stops.
+
+// min_threads is the maximum number we allow to wait, of more threads attempt to wait, they will die
+// if min_threads == 0 no thread will ever be destroyed, and we will stay at the max number of threads ever needed
+
+// max_threads is the overall max number of helper threads. if we have that many threads already running, we will never create more
+// if max_threads == 0 we will alway create a thread if we need it
 struct manager {
-	explicit manager(size_t nthreads=2);
+	explicit manager(size_t min_threads = 1,size_t max_threads = 0);
 	~manager();
 
 private:

src/network_worker.cpp

@@ -80,7 +80,8 @@ struct _TCPsocket {
 };
 unsigned int buf_id = 0;
 unsigned int waiting_threads = 0;
-unsigned int thread_pool = 0;
+size_t min_threads = 0;
+size_t max_threads = 0;
 
 struct buffer {
 	explicit buffer(TCPsocket sock) : sock(sock) {}
@@ -302,7 +303,7 @@ int process_queue(void*)
 				delete zombie;
 
 			}
-			if(waiting_threads >= thread_pool) {
+			if(min_threads && waiting_threads >= min_threads) {
 					LOG_NW << "worker thread exiting... not enough job\n";
 					to_clear.push_back(threading::get_current_thread_id());
 					return 0;
@@ -354,8 +355,11 @@ int process_queue(void*)
 			waiting_threads--;
 			// if we are the last thread in the pool, create a new one
 			if(!waiting_threads && managed == true) {
-				threading::thread * tmp = new threading::thread(process_queue,NULL);
-				threads[tmp->get_id()] =tmp;
+				// max_threads of 0 is unlimited
+				if(!max_threads || max_threads >threads.size()) {
+					threading::thread * tmp = new threading::thread(process_queue,NULL);
+					threads[tmp->get_id()] =tmp;
+				}
 			}
 		}
 
@@ -398,15 +402,16 @@ int process_queue(void*)
 namespace network_worker_pool
 {
 
-manager::manager(size_t nthreads) : active_(!managed)
+manager::manager(size_t p_min_threads,size_t p_max_threads) : active_(!managed)
 {
 	if(active_) {
 		managed = true;
 		global_mutex = new threading::mutex();
 		cond = new threading::condition();
-		thread_pool = nthreads;
+		min_threads = p_min_threads;
+		max_threads = p_max_threads;
 
-		for(size_t n = 0; n != nthreads; ++n) {
+		for(size_t n = 0; n != min_threads; ++n) {
 			threading::thread * tmp = new threading::thread(process_queue,NULL);
 			threads[tmp->get_id()] =tmp;
 		}

src/network_worker.hpp

@@ -29,7 +29,7 @@ namespace network_worker_pool
 
 struct manager
 {
-	explicit manager(size_t nthreads=2);
+	explicit manager(size_t min_threads,size_t max_threads);
 	~manager();
 
 private:

src/server/server.cpp

@@ -88,7 +88,7 @@ void truncate_message(t_string& str)
 class server
 {
 public:
-	server(int port, input_stream& input, const config& cfg, size_t nthreads);
+	server(int port, input_stream& input, const config& cfg, size_t min_threads,size_t max_threads);
 	void run();
 private:
 	void process_data(network::connection sock, config& data, config& gamelist);
@@ -152,7 +152,7 @@ private:
 	std::string motd_;
 };
 
-server::server(int port, input_stream& input, const config& cfg, size_t nthreads) : net_manager_(nthreads), server_(port),
+server::server(int port, input_stream& input, const config& cfg, size_t min_threads,size_t max_threads) : net_manager_(min_threads,max_threads), server_(port),
     not_logged_in_(players_), lobby_players_(players_), last_stats_(time(NULL)), input_(input), cfg_(cfg), admin_passwd_(cfg["passwd"]), motd_(cfg["motd"])
 {
 	version_query_response_.add_child("version");
@@ -1343,7 +1343,8 @@ void server::delete_game(std::vector<game>::iterator i)
 int main(int argc, char** argv)
 {
 	int port = 15000;
-	size_t nthreads = 5;
+	size_t min_threads = 5;
+	size_t max_threads = 0;
 
 	config configuration;
 
@@ -1407,10 +1408,12 @@ int main(int argc, char** argv)
 			setsid();
 #endif
 		} else if((val == "--threads" || val == "-t") && arg+1 != argc) {
-			nthreads = atoi(argv[++arg]);
-			if(nthreads > 30) {
-				nthreads = 30;
+			min_threads = atoi(argv[++arg]);
+			if(min_threads > 30) {
+				min_threads = 30;
 			}
+		} else if((val == "--max-threads" || val == "-T") && arg+1 != argc) {
+			max_threads = atoi(argv[++arg]);
 		} else if(val[0] == '-') {
 			std::cerr << "unknown option: " << val << "\n";
 			return 0;
@@ -1422,7 +1425,7 @@ int main(int argc, char** argv)
 	input_stream input(fifo_path);
 
 	try {
-		server(port,input,configuration,nthreads).run();
+		server(port,input,configuration,min_threads,max_threads).run();
 	} catch(network::error& e) {
 		std::cerr << "caught network error while server was running. aborting.: " << e.message << "\n";
 		return -1;