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Re: lockf replacement?
- From: "Gerrit P. Haase" <gp at familiehaase dot de>
- To: Talk Amongst Yourselves <cygwin-talk at cygwin dot com>
- Date: 2004年10月26日 23:22:46 +0200
- Subject: Re: lockf replacement?
- Organization: Esse keine toten Tiere
- References: <417EA119.3070007@familiehaase.de> <20041026192539.GG32188@trixie.casa.cgf.cx>
- Reply-to: Talk Amongst Yourselves <cygwin-talk at cygwin dot com>
Christopher Faylor wrote:
On Tue, Oct 26, 2004 at 09:10:17PM +0200, Gerrit P. Haase wrote:
I found some sources where the guy uses _locking from the WIN API to
replace lockf, I adapted this and linked the Cygwin executable against
/usr/lib/mingw/libcrtdll.a.
Is this a possible way to go? Or does libcrtdll conflict with
libcygwin? At least the application seems to run basically, I have not
tested the relevant parts though.
Are you just trying to implement lockf?
Why are you talking about linking libcrtdll.a with a cygwin executable
rather than just modifying the cygwin DLL?
Yes, this is the right idea. If it could be done via a similar Windows
function it should be trivial. Is it trivial? Usually the _locking is
in msvcrt but I found that it is also exported from crtdll. From where
gets cygwin the _locking function in this case?
Would require the definitions from mingw/sys/locking.h maybe best place
would be unistd.h, at least according to opengroup specs the lockf
macros should go there? And maybe a lockf.h header which just includes
unistd.h?
#define _LK_UNLCK 0 /* Unlock */
#define _LK_LOCK 1 /* Lock */
#define _LK_NBLCK 2 /* Non-blocking lock */
#define _LK_RLCK 3 /* Lock for read only */
#define _LK_NBRLCK 4 /* Non-blocking lock for read only */
#define LK_UNLCK _LK_UNLCK
#define LK_LOCK _LK_LOCK
#define LK_NBLCK _LK_NBLCK
#define LK_RLCK _LK_RLCK
#define LK_NBRLCK _LK_NBRLCK
/* mappings for lockf */
#define lockf _locking
#define F_ULOCK _LK_UNLCK /* Unlock locked sections. */
#define F_LOCK _LK_LOCK /* Lock a section for exclusive use. */
#define F_TLOCK _LK_NBLCK /* Test and lock a section for exclusive use */
#define F_TEST _LK_RLCK /* Test section for locks by other processes. */
Actually it looks to me like they just took BSD source and renamed lockf
to _locking.
From msdn.microsoft.com/library/en-us/vclib/html/_crt__locking.asp:
_locking
Locks or unlocks bytes of a file.
int _locking(
int fd,
int mode,
long nbytes
);
Parameters
fd
File descriptor.
mode
Locking action to perform.
nbytes
Number of bytes to lock.
Return Value
_locking returns 0 if successful. A return value of â1 indicates
failure, in which case errno is set to one of the following values:
EACCES
Locking violation (file already locked or unlocked).
EBADF
Invalid file descriptor.
EDEADLOCK
Locking violation. Returned when the _LK_LOCK or _LK_RLCK flag is
specified and the file cannot be locked after 10 attempts.
EINVAL
An invalid argument was given to _locking.
Remarks
The _locking function locks or unlocks nbytes bytes of the file
specified by fd. Locking bytes in a file prevents access to those bytes
by other processes. All locking or unlocking begins at the current
position of the file pointer and proceeds for the next nbytes bytes. It
is possible to lock bytes past end of file.
mode must be one of the following manifest constants, which are defined
in LOCKING.H:
_LK_LOCK
Locks the specified bytes. If the bytes cannot be locked, the
program immediately tries again after 1 second. If, after 10
attempts, the bytes cannot be locked, the constant returns an error.
_LK_NBLCK
Locks the specified bytes. If the bytes cannot be locked, the
constant returns an error.
_LK_NBRLCK
Same as _LK_NBLCK.
_LK_RLCK
Same as _LK_LOCK.
_LK_UNLCK
Unlocks the specified bytes, which must have been previously locked.
Multiple regions of a file that do not overlap can be locked. A region
being unlocked must have been previously locked. _locking does not merge
adjacent regions; if two locked regions are adjacent, each region must
be unlocked separately. Regions should be locked only briefly and should
be unlocked before closing a file or exiting the program.
Requirements
Routine Required header Optional headers
_locking <io.h> and <sys/locking.h> <errno.h>
Compatibility
Win 98, Win Me, Win NT, Win 2000, Win XP
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