From this I want to conclude that phase d) does not change
I've just discovered the existence of these manifest constants in spirit and checked the documentation and code to determine what they do. Of course figuring what spirt code does and how it does is not easy to get right for the casual observer so feel free to correct and any mis-conceptions / conclusions that I 've got. My general conception is that parsing can be consider as various quasi - independent phases. a) specification of grammar - source code preparation b) compiliation c) instantiontion/construction of grammar definition d) usage of c) to parse a text string e) destruction of instance. the grammar definition so so that in a multi-threading environment, the invocation of the scoped_lock would be limited to phases c) and e). That is, I want to believe that the following example adapted from the spirit documentation would work: const my_grammar g; // note addition of const if (parse(first, last, g, space_p).full) cout << "parsing succeeded\n"; else cout << "parsing failed\n"; The reason I ask is that the serialization library uses spirit to parse xml archives. Recently, I made changes to make the library thread-safe. I did this without using mutexes/locks by confine all non-const operations to construction and destruction and using static object constructed/destructed at pre-main and post main time time. Although the jury is still out on this, I believe it will make the serialization library thread safe without the need for using threading primitives and libraries. I never realised that spirt wasn't thread-safe. I would like this approach to include xml_archives. So my quesion is: Can I instantiate my xml grammar as a static variable at pre-execution time and permit it to be used by mulitipe threads without locking? Robert Ramey