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NAME
     stream_MT - base class to provide dynamic changing  of  ios-
     tream class objects to and from MT safety.

SYNOPSIS
     #include <rlocks.h>
     typedef char stream_bool_t;

     class stream_MT {
     public:
          enum { unsafe_object=0, safe_object=1 };
          stream_MT();
          stream_MT(stream_bool_t);
          stream_bool_t test_safe_flag();
          void set_safe_flag(stream_bool_t);
          friend class stream_locker;
     };


  ENVIRONMENT
     The discussion about thread safety applies only  to  Solaris
     2.x.   On  Solaris 1.x the ``safe'' and ``unsafe'' functions
     behave identically.

DESCRIPTION
     Class stream_MT is a base class  that  allows  the  iostream
     classes  in  libC  to  work  correctly  in  a multi-threaded
     environment. The classes ios and streambuf are derived  from
     stream_MT.

     The multi-thread (MT) safety of an iostream  object  can  be
     dynamically  changed by setting a safe flag using the member
     function: set_safe_flag(). An argument  with  the  value  of
     stream_MT::safe_object  sets  the  iostream  object to be MT
     safe, an argument with the value of stream_MT::unsafe_object
     sets  the  object  to be MT-unsafe. The current state of the
     iostream object can be determined by  the  member  function:
     test_safe_flag().  When  an iostream object is MT safe there
     is a certain amount of  overhead  associated  with  internal
     locking  in  the object. The overhead can be avoided by set-
     ting the safe flag to zero which disables internal locking.


  Constructors
     stream_MT();

          By default the safe_flag of the class object is set  to
          stream_MT::safe_object

     stream_MT(stream_bool_t);

          The default can be changed  by  providing  an  explicit
          value for the safe flag.

  Member functions
     stream_bool_t test_safe_flag();

          Returns the current value of the  safe  flag.  A  value
          other  than stream_MT::unsafe_object indicates the ios-
          tream object is MT safe and locking is enabled.

     void set_safe_flag(stream_bool_t);

          Sets the internal safe flag of the iostream  object  to
          the  value  given  as an argument. Setting the value to
          non-zero enables locking and makes the object MT  safe.
          Setting the value to zero does the reverse.

SEE ALSO
     C++ 4.1 Library Reference Manual:

             Chapter 5, "Using libC in a Multithreaded Environment."

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