imapext-2007
view src/osdep/unix/flockcyg.c @ 0:ada5e610ab86
imap-2007e
| author | yuuji@gentei.org |
|---|---|
| date | Mon, 14 Sep 2009 15:17:45 +0900 |
| parents | |
| children |
line source
1 /* ========================================================================
2 * Copyright 1988-2006 University of Washington
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 *
11 * ========================================================================
12 */
14 /*
15 * Program: flock emulation via fcntl() locking
16 *
17 * Author: Mark Crispin
18 * Networks and Distributed Computing
19 * Computing & Communications
20 * University of Washington
21 * Administration Building, AG-44
22 * Seattle, WA 98195
23 * Internet: MRC@CAC.Washington.EDU
24 *
25 * Date: 10 April 2001
26 * Last Edited: 30 August 2006
27 */
30 /* Cygwin does not seem to have the design flaw in fcntl() locking that
31 * most other systems do (see flocksim.c for details). If some cretin
32 * decides to implement that design flaw, then Cygwin will have to use
33 * flocksim. Also, we don't test NFS either.
34 *
35 * However, Cygwin does have the Windows misfeature (introduced in NT 4.0)
36 * that you can not write to any segment which has a shared lock, and you
37 * can't lock a zero-byte segment either. This screws up the shared-write
38 * mailbox drivers (mbx, mtx, mx, and tenex). As a workaround, we'll only
39 * lock the first byte of the file, meaning that you can't write that byte
40 * shared. It's been suggested to lock the maximum off_t type, but that
41 * risks having a future version of Windows (or Cygwin) deciding that this
42 * also means "no lock".
43 */
45 #undef flock /* name is used as a struct for fcntl */
47 /* Emulator for flock() call
48 * Accepts: file descriptor
49 * operation bitmask
50 * Returns: 0 if successful, -1 if failure under BSD conditions
51 */
53 int flocksim (int fd,int op)
54 {
55 char tmp[MAILTMPLEN];
56 int logged = 0;
57 struct flock fl;
58 /* lock one bytes at byte 0 */
59 fl.l_whence = SEEK_SET; fl.l_start = 0; fl.l_len = 1;
60 fl.l_pid = getpid (); /* shouldn't be necessary */
61 switch (op & ~LOCK_NB) { /* translate to fcntl() operation */
62 case LOCK_EX: /* exclusive */
63 fl.l_type = F_WRLCK;
64 break;
65 case LOCK_SH: /* shared */
66 fl.l_type = F_RDLCK;
67 break;
68 case LOCK_UN: /* unlock */
69 fl.l_type = F_UNLCK;
70 break;
71 default: /* default */
72 errno = EINVAL;
73 return -1;
74 }
75 while (fcntl (fd,(op & LOCK_NB) ? F_SETLK : F_SETLKW,&fl))
76 if (errno != EINTR) {
77 /* Can't use switch here because these error codes may resolve to the
78 * same value on some systems.
79 */
80 if ((errno != EWOULDBLOCK) && (errno != EAGAIN) && (errno != EACCES)) {
81 sprintf (tmp,"Unexpected file locking failure: %s",strerror (errno));
82 /* give the user a warning of what happened */
83 MM_NOTIFY (NIL,tmp,WARN);
84 if (!logged++) syslog (LOG_ERR,"%s",tmp);
85 if (op & LOCK_NB) return -1;
86 sleep (5); /* slow things down for loops */
87 }
88 /* return failure for non-blocking lock */
89 else if (op & LOCK_NB) return -1;
90 }
91 return 0; /* success */
92 }