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[mLib] / lock.3
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b6b9d458 1.\" -*-nroff-*-
fbf20b5b 2.TH lock 3 "23 May 1999" "Straylight/Edgeware" "mLib utilities library"
b6b9d458 3.SH NAME
4lock \- oversimplified file locking interface
08da152e 5.\" @lock_file
b6b9d458 6.SH SYNOPSIS
7.nf
d2a91066 8.B "#include <mLib/lock.h>"
b6b9d458 9
10.BI "int lock_file(int " fd ", unsigned " how );
11.fi
12.SH DESCRIPTION
13The
14.B lock_file
15function provides an extremely simplistic interface to POSIX
16.BR fcntl (2)
17locking. It locks only entire files, not sections of files. It doesn't
18have a nonblocking `is this file locked?' function.
19.PP
20On entry,
21.I fd
22should be a file descriptor on an open file, and
23.I how
24is a constant which describes how the file is to be locked. The
25possible values of
26.I how
27are:
28.TP
29.B LOCK_EXCL
30Lock the file exclusively. Attempts to lock the file exclusively or
31nonexclusively will fail until the file is unlocked.
32.TP
33.B LOCK_NONEXCL
34Lock the file nonexclusively. Until the file is unlocked, attempts to
35lock it exclusively will fail, but other nonexclusive locks will
36succeed.
37.TP
38.B LOCK_UNLOCK
39Unlocks a locked file. Any locks afterwards can succeed.
40.PP
41The
42.B lock_file
43function will block if it can't obtain a lock immediately. It will time
44itself out after a short while (10 seconds in the current
45implementation) if the lock doesn't become available.
46.PP
47If the call succeeds,
48.B lock_file
49returns zero. On failure, \-1 is returned, and
50.B errno
51is set to an appropriate value. Most of the error returns are from
52.BR fcntl (2)
53(q.v.). If the lock operation times out,
54.B errno
55is set to
56.BR EINTR .
08da152e 57.SH "SEE ALSO"
58.BR fcntl (2),
59.BR mLib (3).
b6b9d458 60.SH AUTHOR
9b5ac6ff 61Mark Wooding, <mdw@distorted.org.uk>