stdio/FreeBSD/flockfile.3

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  25 .\" $FreeBSD: src/lib/libc/stdio/flockfile.3,v 1.3 2003/01/13 01:29:14 tjr Exp $
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  27 .Dd January 10, 2003
  28 .Dt FLOCKFILE 3
  29 .Os
  30 .Sh NAME
  31 .Nm flockfile ,
  32 .Nm ftrylockfile ,
  33 .Nm funlockfile
  34 .Nd "stdio locking functions"
  35 .Sh LIBRARY
  36 .Lb libc
  37 .Sh SYNOPSIS
  38 .In stdio.h
  39 .Ft void
  40 .Fn flockfile "FILE *file"
  41 .Ft int
  42 .Fn ftrylockfile "FILE *file"
  43 .Ft void
  44 .Fn funlockfile "FILE *file"
  45 .Sh DESCRIPTION
  46 These functions provide explicit application-level locking
  47 of stdio FILE objects.
  48 They can be used to avoid output from multiple threads being interspersed,
  49 input being dispersed among multiple readers, and to avoid the overhead
  50 of locking the object for each operation.
  51 .Pp
  52 The
  53 .Fn flockfile
  54 function acquires an exclusive lock on the specified object.
  55 If another thread has already locked the object,
  56 .Fn flockfile
  57 will block until the lock is released.
  58 .Pp
  59 The
  60 .Fn ftrylockfile
  61 function is a non-blocking version of
  62 .Fn flockfile ;
  63 if the lock cannot be acquired immediately,
  64 .Fn ftrylockfile
  65 returns non-zero instead of blocking.
  66 .Pp
  67 The
  68 .Fn funlockfile
  69 function releases the lock on an object acquired by an earlier call to
  70 .Fn flockfile
  71 or
  72 .Fn ftrylockfile .
  73 .Pp
  74 These functions behave as if there is a lock count associated
  75 with each object.
  76 Each time
  77 .Fn flockfile
  78 is called on the object, the count is incremented,
  79 and each time
  80 .Fn funlockfile
  81 is called on the object, the count is decremented.
  82 The lock is only actually released when the count reaches zero.
  83 .Sh RETURN VALUES
  84 The
  85 .Fn flockfile
  86 and
  87 .Fn funlockfile
  88 functions return no value.
  89 .Pp
  90 The
  91 .Fn ftrylockfile
  92 function
  93 returns zero if the object was successfully locked,
  94 non-zero otherwise.
  95 .Sh SEE ALSO
  96 .Xr getc_unlocked 3 ,
  97 .Xr putc_unlocked 3
  98 .Sh STANDARDS
  99 The
 100 .Fn flockfile ,
 101 .Fn ftrylockfile ,
 102 and
 103 .Fn funlockfile
 104 functions conform to
 105 .St -p1003.1-2001 .