1.1 --- /dev/null	Thu Jan 01 00:00:00 1970 +0000
     1.2 +++ b/src/osdep/unix/flockcyg.c	Mon Sep 14 15:17:45 2009 +0900
     1.3 @@ -0,0 +1,92 @@
     1.4 +/* ========================================================================
     1.5 + * Copyright 1988-2006 University of Washington
     1.6 + *
     1.7 + * Licensed under the Apache License, Version 2.0 (the "License");
     1.8 + * you may not use this file except in compliance with the License.
     1.9 + * You may obtain a copy of the License at
    1.10 + *
    1.11 + *     http://www.apache.org/licenses/LICENSE-2.0
    1.12 + *
    1.13 + * 
    1.14 + * ========================================================================
    1.15 + */
    1.16 +
    1.17 +/*
    1.18 + * Program:	flock emulation via fcntl() locking
    1.19 + *
    1.20 + * Author:	Mark Crispin
    1.21 + *		Networks and Distributed Computing
    1.22 + *		Computing & Communications
    1.23 + *		University of Washington
    1.24 + *		Administration Building, AG-44
    1.25 + *		Seattle, WA  98195
    1.26 + *		Internet: MRC@CAC.Washington.EDU
    1.27 + *
    1.28 + * Date:	10 April 2001
    1.29 + * Last Edited:	30 August 2006
    1.30 + */
    1.31 +
    1.32 +
    1.33 +/* Cygwin does not seem to have the design flaw in fcntl() locking that
    1.34 + * most other systems do (see flocksim.c for details).  If some cretin
    1.35 + * decides to implement that design flaw, then Cygwin will have to use
    1.36 + * flocksim.  Also, we don't test NFS either.
    1.37 + *
    1.38 + * However, Cygwin does have the Windows misfeature (introduced in NT 4.0)
    1.39 + * that you can not write to any segment which has a shared lock, and you
    1.40 + * can't lock a zero-byte segment either.  This screws up the shared-write
    1.41 + * mailbox drivers (mbx, mtx, mx, and tenex).  As a workaround, we'll only
    1.42 + * lock the first byte of the file, meaning that you can't write that byte
    1.43 + * shared.  It's been suggested to lock the maximum off_t type, but that
    1.44 + * risks having a future version of Windows (or Cygwin) deciding that this
    1.45 + * also means "no lock".
    1.46 + */
    1.47 +
    1.48 +#undef flock			/* name is used as a struct for fcntl */
    1.49 +
    1.50 +/* Emulator for flock() call
    1.51 + * Accepts: file descriptor
    1.52 + *	    operation bitmask
    1.53 + * Returns: 0 if successful, -1 if failure under BSD conditions
    1.54 + */
    1.55 +
    1.56 +int flocksim (int fd,int op)
    1.57 +{
    1.58 +  char tmp[MAILTMPLEN];
    1.59 +  int logged = 0;
    1.60 +  struct flock fl;
    1.61 +				/* lock one bytes at byte 0 */
    1.62 +  fl.l_whence = SEEK_SET; fl.l_start = 0; fl.l_len = 1;
    1.63 +  fl.l_pid = getpid ();		/* shouldn't be necessary */
    1.64 +  switch (op & ~LOCK_NB) {	/* translate to fcntl() operation */
    1.65 +  case LOCK_EX:			/* exclusive */
    1.66 +    fl.l_type = F_WRLCK;
    1.67 +    break;
    1.68 +  case LOCK_SH:			/* shared */
    1.69 +    fl.l_type = F_RDLCK;
    1.70 +    break;
    1.71 +  case LOCK_UN:			/* unlock */
    1.72 +    fl.l_type = F_UNLCK;
    1.73 +    break;
    1.74 +  default:			/* default */
    1.75 +    errno = EINVAL;
    1.76 +    return -1;
    1.77 +  }
    1.78 +  while (fcntl (fd,(op & LOCK_NB) ? F_SETLK : F_SETLKW,&fl))
    1.79 +    if (errno != EINTR) {
    1.80 +      /* Can't use switch here because these error codes may resolve to the
    1.81 +       * same value on some systems.
    1.82 +       */
    1.83 +      if ((errno != EWOULDBLOCK) && (errno != EAGAIN) && (errno != EACCES)) {
    1.84 +	sprintf (tmp,"Unexpected file locking failure: %s",strerror (errno));
    1.85 +				/* give the user a warning of what happened */
    1.86 +	MM_NOTIFY (NIL,tmp,WARN);
    1.87 +	if (!logged++) syslog (LOG_ERR,"%s",tmp);
    1.88 +	if (op & LOCK_NB) return -1;
    1.89 +	sleep (5);		/* slow things down for loops */
    1.90 +      }
    1.91 +				/* return failure for non-blocking lock */
    1.92 +      else if (op & LOCK_NB) return -1;
    1.93 +    }
    1.94 +  return 0;			/* success */
    1.95 +}