fix: 100% busy main thread while bot is not playing audio in vc (#1578)

Author: usyless

src/dpp/voice/enabled/read_write.cpp

@@ -34,8 +34,17 @@ void discord_voice_client::send(const char* packet, size_t len, uint64_t duratio
 		frame.packet.assign(packet, packet + len);
 		frame.duration = duration;
 
-		std::lock_guard<std::mutex> lock(this->stream_mutex);
-		outbuf.emplace_back(frame);
+		bool was_empty = false;
+		{
+			std::lock_guard<std::mutex> lock(this->stream_mutex);
+			was_empty = outbuf.empty();
+			outbuf.emplace_back(frame);
+		}
+
+		if (was_empty) {
+			udp_events.flags = WANT_READ | WANT_WRITE | WANT_ERROR;
+			owner->socketengine->update_socket(udp_events);
+		}
 	} else [[unlikely]] {
 		this->udp_send(packet, len);
 	}

src/dpp/voice/enabled/write_ready.cpp

@@ -31,12 +31,18 @@
 namespace dpp {
 
 void discord_voice_client::write_ready() {
-	/* 
-	 * WANT_WRITE has been reset everytime this method is being called,
-	 * ALWAYS set it again no matter what we're gonna do.
-	 */
-	udp_events.flags = WANT_READ | WANT_WRITE | WANT_ERROR;
-	owner->socketengine->update_socket(udp_events);
+	bool needs_write = false;
+	{
+		std::lock_guard<std::mutex> lock(this->stream_mutex);
+		const bool needs_stop_frames = this->paused && !this->sent_stop_frames;
+		const bool has_audio = !outbuf.empty();
+		needs_write = needs_stop_frames || has_audio;
+	}
+
+	if (needs_write) {
+		udp_events.flags = WANT_READ | WANT_WRITE | WANT_ERROR;
+		owner->socketengine->update_socket(udp_events);
+	}
 
 	uint64_t duration = 0;
 	bool track_marker_found = false;