NAME

flockfile(), funlockfile() − explicit locking of streams within a multi-thread application

SYNOPSIS

#include <stdio.h>

void flockfile(FILE *stream);

void funlockfile(FILE *stream);

DESCRIPTION

The flockfile() and funlockfile() functions provide for explicit application-level locking of streams.  These functions can 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 stream. 

The funlock() 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 count associated with each stream.  This count is implicitly initialized to zero when the stream is created.  The stream is unlocked when the count is zero.  When the count is positive, a single thread owns the stream.  When the flockfile() function is called, if the count is zero or if the count is positive and the caller owns the stream, the count is incremented.  Otherwise, the calling thread is suspended, waiting for the count to return to zero.  Each call to funlockfile() decrements the count.  This allows matching calls to flockfile() and funlockfile() to be nested. 

RETURN VALUE

None. 

Hewlett-Packard Company  —  HP-UX Release 10.20:  July 1996