flockfile man page on DigitalUNIX

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flockfile(3)							  flockfile(3)

       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 stan‐
       dards 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 state‐
       ments 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

       The behavior of the flockfile() and funlockfile() functions is unspeci‐
       fied  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)


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