file locking

KDB

Hi,
I am trying the following code to get a write lock on a file.

#include <unistd.h>
#include <iostream.h>
#include <fcntl.h>

main()
{
int fd = open("file",O_RDWR);

/** lock file */
flock lock = { F_WRLCK, SEEK_SET, 0, 0, 0 };
fcntl(fd, F_SETLKW, &lock);

/** do some processing here */

/** unlock file */
flock lock1 = { F_UNLCK, SEEK_SET, 0, 0, 0 };
fcntl(fd, F_SETLKW, &lock1);

printf("file unlocked\n");

close(fd);
}

the problem i am facing is that this program blocks while locking the
file ( if the file is already locked by another process).

can anyone suggest how to get a lock in non blocking mode so that if
the lock can not be obtained the function should return indicating
that it could not lock the file.

Thanks in advance.

Nov 13 '05 #1

Martijn

KDB wrote:

/** lock file */
flock lock = { F_WRLCK, SEEK_SET, 0, 0, 0 };
fcntl(fd, F_SETLKW, &lock);

can anyone suggest how to get a lock in non blocking mode so that if
the lock can not be obtained the function should return indicating
that it could not lock the file.

Use F_SETLK instead of F_SETLKW (the W means Wait)

--
Martijn
http://www.sereneconcepts.nl

Nov 13 '05 #2

Richard Bos

ka*****@delhi.tcs.co.in (KDB) wrote:

I am trying the following code to get a write lock on a file.

#include <unistd.h>
#include <iostream.h>
#include <fcntl.h> the problem i am facing is that this program blocks

No, the problem you're facing is that this isn't ISO C - unistd.h and
fcntl.h are POSIX, and iostream.h is some kind of C++. I'm not sure
which newsgroup you'd need for this, a POSIX or a C++ one, but given the
nature of your problem my first guess would be comp.unix.programmer.

Richard

Nov 13 '05 #3

LibraryUser

Martijn wrote:

KDB wrote:

/** lock file */
flock lock = { F_WRLCK, SEEK_SET, 0, 0, 0 };
fcntl(fd, F_SETLKW, &lock);

can anyone suggest how to get a lock in non blocking mode so
that if the lock can not be obtained the function should return
indicating that it could not lock the file.

Use F_SETLK instead of F_SETLKW (the W means Wait)

Please do not answer off topic questions with something other
than a redirection to an appropriate group. There is (in theory)
nobody here to criticize your answers and to correct possible
errors.

--
Replies should be to the newsgroup
Chuck Falconer, on vacation.

Nov 13 '05 #4

Martijn

LibraryUser wrote:

/** lock file */
flock lock = { F_WRLCK, SEEK_SET, 0, 0, 0 };
fcntl(fd, F_SETLKW, &lock);

can anyone suggest how to get a lock in non blocking mode so
that if the lock can not be obtained the function should return
indicating that it could not lock the file.

Use F_SETLK instead of F_SETLKW (the W means Wait)

Please do not answer off topic questions with something other
than a redirection to an appropriate group. There is (in theory)
nobody here to criticize your answers and to correct possible
errors.

He says while, "Lo and Behold", he's engaging in an off-topic discussing in
another thread.

The question in question is so simple in nature that the user can easily
verify the correctness of the proposed solution himself.

--
Martijn
http://www.sereneconcepts.nl

Nov 13 '05 #5