Make random state thread-local.

include/plugin.hpp

@@ -14,13 +14,6 @@ namespace rack {
 namespace plugin {
 
 
-struct Update {
-	std::string pluginSlug;
-	std::string version;
-	std::string changelogUrl;
-};
-
-
 void init();
 void destroy();
 void logIn(const std::string &email, const std::string &password);
@@ -36,6 +29,13 @@ std::string normalizeTag(const std::string &tag);
 bool isSlugValid(const std::string &slug);
 
 
+struct Update {
+	std::string pluginSlug;
+	std::string version;
+	std::string changelogUrl;
+};
+
+
 extern const std::set<std::string> allowedTags;
 extern std::vector<Plugin*> plugins;
 

include/random.hpp

@@ -11,7 +11,9 @@ namespace rack {
 namespace random {
 
 
-/** Seeds the RNG with the current time */
+/** Initializes the thread-local RNG state.
+Must call per-thread, otherwise the RNG will always return 0.
+*/
 void init();
 /** Returns a uniform random uint32_t from 0 to UINT32_MAX */
 uint32_t u32();

src/engine/Engine.cpp

@@ -150,6 +150,7 @@ struct EngineWorker {
 
 	void start() {
 		thread = std::thread([&] {
+			random::init();
 			run();
 		});
 	}
@@ -436,7 +437,10 @@ static void Engine_run(Engine *that) {
 
 void Engine::start() {
 	internal->running = true;
-	internal->thread = std::thread(Engine_run, this);
+	internal->thread = std::thread([&] {
+		random::init();
+		Engine_run(this);
+	});
 }
 
 void Engine::stop() {

src/random.cpp

@@ -11,7 +11,7 @@ namespace random {
 // xoroshiro128+
 // from http://xoroshiro.di.unimi.it/xoroshiro128plus.c
 
-static uint64_t xoroshiro128plus_state[2] = {};
+thread_local uint64_t xoroshiro128plus_state[2];
 
 static uint64_t rotl(const uint64_t x, int k) {
 	return (x << k) | (x >> (64 - k));
@@ -30,8 +30,6 @@ static uint64_t xoroshiro128plus_next(void) {
 }
 
 void init() {
-	// Only allow the seed to be initialized once during the lifetime of the program.
-	assert(xoroshiro128plus_state[0] == 0 && xoroshiro128plus_state[1] == 0);
 	struct timeval tv;
 	gettimeofday(&tv, NULL);
 	xoroshiro128plus_state[0] = tv.tv_sec;