flockfile(3S)                  DG/UX R4.11MU05                 flockfile(3S)


NAME
       flockfile, funlockfile - synchronize stdio file operations for
       reentrant functions

SYNOPSIS
       #include <stdio.h>

       void flockfile(FILE *file);

       void funlockfile(FILE *file);

DESCRIPTION
       flockfile and funlockfile provide for explicit application level
       locking and unlocking of stdio (FILE *) objects.  They may be used by
       a thread to delineate a sequence of I/O statements that are to be
       executed as a unit.

       The flockfile function is used by a thread to advise the
       implementation that it is the current owner of a (FILE *) object.

       The funlockfile function is used to relinquish the ownership granted
       to the thread.  The behavior is undefined if a thread other than the
       current owner calls the funlockfile function.

       Logically, there is a lock count associated with each (FILE *)
       object.  This count is implicitly initialized to zero when the file
       is opened.  The (FILE *) object is unlocked when this count is zero.
       When the count is positive a single thread owns the (FILE *) object.
       Each call to funlockfile decrements the count.

       When the count is non-zero threads not owning the (FILE *) object
       suspend waiting for the count to return to zero.  The thread owning
       the (FILE *) object does not suspend on subsequent calls to
       flockfile.  This allows matching calls to flockfile and funlockfile
       to be nested.


   Considerations for Threads Programming
                    +------------+-----------------------------+
                    |            |                      async- |
                    |function    | reentrant   cancel   cancel |
                    |            |             point     safe  |
                    +------------+-----------------------------+
                    |flockfile   |     Y         N        N    |
                    |funlockfile |     Y         N        N    |
                    +------------+-----------------------------+
       The flockfile and funlockfile functions are only useful in a threaded
       applications.

DIAGNOSTICS
       There are no return values or errors.

SEE ALSO
       getcunlocked(3S), getcharunlocked(3S), and reentrant(3).

STANDARDS
       These functions are not available when using m88kbcs, m88kdguxcoff,
       or m88kocs as the Software Development Environment targets.


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