[/ 
  Copyright 2006-2007 John Maddock.
  Distributed under the Boost Software License, Version 1.0.
  (See accompanying file LICENSE_1_0.txt or copy at
  http://www.boost.org/LICENSE_1_0.txt).
]


[section:thread_safety Thread Safety]

The Boost.Regex library is thread safe when Boost is: you can verify that 
Boost is in thread safe mode by checking to see if `BOOST_HAS_THREADS` is 
defined: this macro is set automatically by the config system when 
threading support is turned on in your compiler.

Class [basic_regex] and its typedefs regex and wregex are thread safe, 
in that compiled regular expressions can safely be shared between threads. 
The matching algorithms [regex_match], [regex_search], and [regex_replace]
are all re-entrant and thread safe. Class [match_results] is now thread safe, 
in that the results of a match can be safely copied from one thread to 
another (for example one thread may find matches and push [match_results] 
instances onto a queue, while another thread pops them off the other end), 
otherwise use a separate instance of [match_results] per thread.

The [link boost_regex.ref.posix POSIX API functions] are all re-entrant and thread safe, regular 
expressions compiled with regcomp can also be shared between threads.

The [link boost_regex.ref.deprecated_interfaces.old_regex class RegEx] is 
only thread safe if each thread gets its own 
RegEx instance (apartment threading) - this is a consequence of 
RegEx handling both compiling and matching regular expressions.

Finally note that changing the global locale invalidates all compiled 
regular expressions, therefore calling `set_locale` from one thread 
while another uses regular expressions will produce unpredictable results.

There is also a requirement that there is only one thread executing prior 
to the start of main().
     
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