ByteStreamStoragePlugins: thread-checker fixes for fReadDavix

Mark the POSIX API as thread-safe (confirmed by Davix documentation).

Event/ByteStreamStoragePlugins/CMakeLists.txt

-# Copyright (C) 2002-2020 CERN for the benefit of the ATLAS collaboration
+# Copyright (C) 2002-2022 CERN for the benefit of the ATLAS collaboration
 
 # Declare the package name:
 atlas_subdir( ByteStreamStoragePlugins )
@@ -29,4 +29,4 @@ atlas_add_library( fReadDavix
    PRIVATE_INCLUDE_DIRS ${TDAQ-COMMON_INCLUDE_DIRS}
    ${DAVIX_INCLUDE_DIRS} ${Boost_INCLUDE_DIRS}
    PRIVATE_LINK_LIBRARIES ${TDAQ-COMMON_LIBRARIES} ${DAVIX_LIBRARIES}
-   ${Boost_LIBRARIES} )
+   ${Boost_LIBRARIES} CxxUtils )

Event/ByteStreamStoragePlugins/src/fReadDavix.h

 /*
-  Copyright (C) 2002-2017 CERN for the benefit of the ATLAS collaboration
+  Copyright (C) 2002-2022 CERN for the benefit of the ATLAS collaboration
 */
 
 #ifndef FREADDAVIX_H
 #define FREADDAVIX_H
 
+#include "CxxUtils/checker_macros.h"
 #include "EventStorage/fRead.h"
 #include "davix.hpp"
 
@@ -31,7 +32,7 @@ class fReadDavix : public fRead
   Davix::Context m_c;
   Davix::RequestParams *m_davixParam;
   Davix::DavixError* m_err;
-  Davix::DavPosix *m_pos;
+  Davix::DavPosix *m_pos ATLAS_THREAD_SAFE;  // Davix documentation says this is thread-safe
   Davix::X509Credential *m_cert;
   DAVIX_FD* m_fd; // davix pointer to current file