Protect access to create_stream() with a mutex

Multiple threads may access create_stream() for the same session
simultaneously which can cause problems if the access is not protected.

include/session.hh

@@ -1,5 +1,6 @@
 #pragma once
 
+#include <mutex>
 #include <string>
 #include <vector>
 
@@ -47,5 +48,7 @@ namespace uvg_rtp {
 
             /* All media streams of this session */
             std::unordered_map<uint32_t, uvg_rtp::media_stream *> streams_;
+
+            std::mutex session_mtx_;
     };
 };

src/session.cc

@@ -30,6 +30,8 @@ uvg_rtp::session::~session()
 
 uvg_rtp::media_stream *uvg_rtp::session::create_stream(int r_port, int s_port, rtp_format_t fmt, int flags)
 {
+    std::lock_guard<std::mutex> m(session_mtx_);
+
     uvg_rtp::media_stream *stream = nullptr;
 
     if (flags & RCE_SYSTEM_CALL_DISPATCHER) {