Using directory approach

  //----- BLOCK THIS FUNCTION BEING RUN SIMULTANEOUSLY ON DIFFERENT THREADS -----
  //Creating and deleting a directory is a good way tot do this in PHP because although files may be opened by two different processes (which happily overwrite each other), 
  //directories don’t have such problems (they may be created and removed, but they can’t be written)
  //We check for the presence of a directory by creating one. If the creation fails, then the directory is already there. If the creation succeed, then, the directory was not there.
  if (mkdir('/tmp/mysemaphorefile.lock', 0700))
  {
    //We are OK to run
  

    rmdir('/tmp/mysemaphorefile.lock') ;
  }
  else
  {
    //Another script is already running
    
  }