Rewrite of sigslot that avoids vtables.

This reduces binary size considerably and solves some other problems.

Also rewrote using variadic templates.

Initial patch contributed by andrey.semashev@gmail.com.

BUG=webrtc:2305

Review-Url: https://codereview.webrtc.org/2509733003
Cr-Commit-Position: refs/heads/master@{#16703}

webrtc/base/sigslot.cc

@@ -12,43 +12,11 @@ namespace sigslot {
 
 #ifdef _SIGSLOT_HAS_POSIX_THREADS
 
-multi_threaded_global::multi_threaded_global() {
-  pthread_mutex_init(get_mutex(), NULL);
-}
-
-multi_threaded_global::multi_threaded_global(const multi_threaded_global&) {
-}
-
-multi_threaded_global::~multi_threaded_global() = default;
-
-void multi_threaded_global::lock() {
-  pthread_mutex_lock(get_mutex());
-}
-
-void multi_threaded_global::unlock() {
-  pthread_mutex_unlock(get_mutex());
-}
-
-multi_threaded_local::multi_threaded_local() {
-  pthread_mutex_init(&m_mutex, NULL);
-}
-
-multi_threaded_local::multi_threaded_local(const multi_threaded_local&) {
-  pthread_mutex_init(&m_mutex, NULL);
-}
-
-multi_threaded_local::~multi_threaded_local() {
-  pthread_mutex_destroy(&m_mutex);
-}
-
-void multi_threaded_local::lock() {
-  pthread_mutex_lock(&m_mutex);
-}
-
-void multi_threaded_local::unlock() {
-  pthread_mutex_unlock(&m_mutex);
+pthread_mutex_t* multi_threaded_global::get_mutex() {
+  static pthread_mutex_t g_mutex = PTHREAD_MUTEX_INITIALIZER;
+  return &g_mutex;
 }
 
 #endif  // _SIGSLOT_HAS_POSIX_THREADS
 
-};  // namespace sigslot
+}  // namespace sigslot

webrtc/base/sigslot_unittest.cc

@@ -103,12 +103,8 @@ class multi_threaded_local_fake : public sigslot::multi_threaded_local {
   multi_threaded_local_fake() : lock_count_(0), unlock_count_(0) {
   }
 
-  virtual void lock() {
-    ++lock_count_;
-  }
-  virtual void unlock() {
-    ++unlock_count_;
-  }
+  void lock() { ++lock_count_; }
+  void unlock() { ++unlock_count_; }
 
   int lock_count() { return lock_count_; }
 

webrtc/media/sctp/sctptransport_unittest.cc

@@ -50,8 +50,8 @@ class SctpFakeDataReceiver : public sigslot::has_slots<> {
     last_params_ = ReceiveDataParams();
   }
 
-  virtual void OnDataReceived(const ReceiveDataParams& params,
-                              const rtc::CopyOnWriteBuffer& data) {
+  void OnDataReceived(const ReceiveDataParams& params,
+                      const rtc::CopyOnWriteBuffer& data) {
     received_ = true;
     last_data_ = std::string(data.data<char>(), data.size());
     last_params_ = params;

webrtc/p2p/base/stunserver.h

@@ -25,7 +25,7 @@ class StunServer : public sigslot::has_slots<> {
   // Creates a STUN server, which will listen on the given socket.
   explicit StunServer(rtc::AsyncUDPSocket* socket);
   // Removes the STUN server from the socket and deletes the socket.
-  ~StunServer();
+  ~StunServer() override;
 
  protected:
   // Slot for AsyncSocket.PacketRead: