funlockfile(3C)
NAME
flockfile, funlockfile, ftrylockfile - acquire and release
stream lock
SYNOPSIS
#include <stdio.h>
void flockfile(FILE *stream);
void funlockfile(FILE *stream);
int ftrylockfile(FILE *stream);
DESCRIPTION
The flockfile() function acquires an internal lock of a
stream stream. If the lock is already acquired by another
thread, the thread calling flockfile() is suspended until it
can acquire the lock. In the case that the stream lock is
available, flockfile() not only acquires the lock, but keeps
track of the number of times it is being called by the
current thread. This implies that the stream lock can be
acquired more than once by the same thread.
The funlockfile() function releases the lock being held by
the current thread. In the case of recursive locking, this
function must be called the same number of times flockfile()
was called. After the number of funlockfile() calls is
equal to the number of flockfile() calls, the stream lock is
available for other threads to acquire.
The ftrylockfile() function acquires an internal lock of a
stream stream, only if that object is available. In essence
ftrylockfile() is a non-blocking version of flockfile().
RETURN VALUES
The ftrylockfile() function returns 0 on success and non-
zero to indicate a lock cannot be acquired.
EXAMPLES
Example 1: A sample program of flockfile().
The following example prints everything out together, block-
ing other threads that might want to write to the same file
between calls to fprintf(3C):
FILE iop;
flockfile(iop);
fprintf(iop, "hello ");
fprintf(iop, "world);
fputc(iop, 'a');
funlockfile(iop);
An unlocked interface is available in case performance is an
issue. For example:
flockfile(iop);
while (!feof(iop)) {
*c++ = getc_unlocked(iop);
}
funlockfile(iop);
ATTRIBUTES
See attributes(5) for descriptions of the following attri-
butes:
____________________________________________________________
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
|_____________________________|_____________________________|
| MT-Level | MT-Safe |
|_____________________________|_____________________________|
SEE ALSO
intro(3), ferror(3C), fprintf(3C), getc(3C), putc(3C),
stdio(3C), ungetc(3C), attributes(5), standards(5)
NOTES
The interfaces on this page are as specified in IEEE Std
1003.1c. See standards(5).
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