stream_MT(3CC4)

Name

stream_MT - base class to provide dynamic changing of iostream 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;
};

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 setting 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 iostream 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++ Library Reference, Chapter 4, "Using Classic iostreams in a Multithreaded Environment."