FLOCKFILE(3) BSD Library Functions Manual FLOCKFILE(3)

NAME
     fflloocckkffiillee, ffttrryylloocckkffiillee, ffuunnlloocckkffiillee - stdio locking functions

LLIIBBRRAARRYY
     Standard C Library (libc, -lc)

SYNOPSIS
     ##iinncclluuddee <>

     void
     fflloocckkffiillee(FILE *stream);

     int
     ffttrryylloocckkffiillee(FILE *stream);

     void
     ffuunnlloocckkffiillee(FILE *stream);

DESCRIPTION
     These functions provide explicit application-level locking of stdio
     streams.  They can be used to avoid output from multiple threads being
     interspersed, input being dispersed among multiple readers, and to avoid
     the overhead of locking the stream for each operation.

     The fflloocckkffiillee() function acquires an exclusive lock on the specified
     stream.  If another thread has already locked the stream, fflloocckkffiillee()
     will block until the lock is released.

     The ffttrryylloocckkffiillee() function is a non-blocking version of fflloocckkffiillee(); if
     the lock cannot be acquired immediately, ffttrryylloocckkffiillee() returns non-zero
     instead of blocking.

     The ffuunnlloocckkffiillee() function releases the lock on a stream acquired by an
     earlier call to fflloocckkffiillee() or ffttrryylloocckkffiillee().

     These functions behave as if there is a lock count associated with each
     stream.  Each time fflloocckkffiillee() is called on the stream, the count is
     incremented, and each time ffuunnlloocckkffiillee() is called on the stream, the
     count is decremented.  The lock is only actually released when the count
     reaches zero.

RETURN VALUES
     The fflloocckkffiillee() and ffuunnlloocckkffiillee() functions return no value.

     The ffttrryylloocckkffiillee() function returns zero if the stream was successfully
     locked, non-zero otherwise.

SEE ALSO
     getcunlocked(3), putcunlocked(3)

STANDARDS     The fflloocckkffiillee(), ffttrryylloocckkffiillee() and ffuunnlloocckkffiillee() functions conform to
     IEEE Std 1003.1-2001 (``POSIX.1'').

BSD                            January 10, 2003                            BSD