flockfile, ftrylockfilefunlockfile, stdio - locking functions
#include <stdio.h>
void flockfile(
FILE * file ); int ftrylockfile
FILE * file ); void funlockfile
FILE * file );
Standard C Library (libc)
Interfaces documented on this reference page conform to
industry standards as follows:
flockfile, funlockfile: POSIX.1c, XSH5.0
ftrylockfile: XSH5.0
Refer to the standards(5) reference page for more information
about industry standards and associated tags.
Specifies the stream to be locked.
The flockfile(), ftrylockfile, and funlockfile functions
provide for explicit application-level locking of stdio
(FILE*) objects. 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 locks a stdio stream so that a
thread can have exclusive use of that stream for multiple
I/O operations. Use the flockfile() function for a thread
that wishes to ensure that the output of several printf()
functions, for example, is not garbled by another thread
also trying to use printf().
The ftrylockfile() function is used by a thread to acquire
ownership of a stdio (FILE*) object if the object is
available. The ftrylockfile() function is a non-blocking
version of flockfile().
The funlockfile() function unlocks a stdio stream, causing
the thread that had been holding the lock to relinquish
exclusive use of the stream.
The behavior of the flockfile() and funlockfile() functions
is unspecified if the file parameter does not point
to a valid FILE structure. The behavior of funlockfile()
is also unspecified if a thread other than the current
owner calls funlockfile().
Matching flockfile() and funlockfile() calls can be
nested. If the stream has been locked recursively, it will
remain locked until the last matching funlockfile() is
called.
None for flockfile() and funlockfile(). The ftrylockfile()
function returns zero for success and non-zero to
indicate that the lock cannot be acquired.
Functions: getc_unlocked(3), putc_unlocked(3)
flockfile(3)
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