Here is a simple C utility for locking file - it's combination of two
sources:
- reading lock info from here:
http://uw714doc.sco.com/en/SDK_sysprog/_Getting_Lock_Information.html
- acquiring file lock from here:
http://siber.cankaya.edu.tr/ozdogan/SystemsProgramming/ceng425/node161.html
Now, to make use of it.
Regards,
Stevo.
On Wed, Jan 4, 2012 at 6:10 PM, Stevo Slavić <[email protected]> wrote:
> Hello Steven,
>
> I guess license covers only 5.4. Anyway I'm just told it's not an option
> at the moment to do the upgrade.
>
>
> About locking used, ActiveMQ uses Java 6 standard API for trying to
> acquire file lock, here is javadoc for the method used:
>
>
> http://docs.oracle.com/javase/6/docs/api/java/nio/channels/FileChannel.html#tryLock%28long,%20long,%20boolean%29
>
> ActiveMQ tries to obtain non-shared (thus exclusive) lock on whole file on
> shared file system, with range from 0 to 1, since the file being locked is
> empty. As documentation states, tryLock is non-blocking, it executes
> immediately. If ActiveMQ fails to obtain a lock it will loop (pause and
> retry acquiring lock again) until lock is obtained. In initial state first
> node obtains lock and becomes master, second one fails to obtain lock and
> gets into this loop, as expected. Problem is that slave ActiveMQ on cannot
> obtain a lock even after first node gets fenced - it reports that the file
> on shared storage is still locked. Simple custom java tool that I made
> reports the same, that the file is locked.
>
> OpenJDK 1.6 update 20 is being used as Java runtime. I haven't yet found
> in openjdk source exact code which tryLock will call on Linux.
>
>
> Is there non-Java tool that could be used to reliably check if a file (on
> gfs2) is (or can be) exclusively locked (regardless of where the process
> holding lock is running, on same or different node where the tool is being
> run)?
>
>
> Regards,
> Stevo.
>
>
>
>
> On Tue, Jan 3, 2012 at 10:59 AM, Steven Whitehouse <[email protected]>wrote:
>
>> Hi,
>>
>> On Fri, 2011-12-30 at 14:39 +0100, Stevo Slavić wrote:
>> > Hello RedHat Linux cluster community,
>> >
>> > I'm in process of configuring shared filesystem storage master/slave
>> > Apache ActiveMQ setup. For it to work, it requires reliable
>> > distributed locking - master is node that holds exclusive lock on a
>> > file on shared filesystem storage.
>> >
>> How does it do this locking? There are several possible ways this might
>> be done, and some will work better than others.
>>
>> > On RHEL (5.4), using CLVM with GFS2 is one of the options that should
>> > work.
>> Why are you using RHEL 5.4 and not something more recent? Note that if
>> you are a Red Hat customer, then you should contact our support team who
>> will be very happy to assist.
>>
>> > Third party configured the CLVM/GFS2. I'd like to make sure that
>> > distributed locking works OK.
>> > What are my options for verifying this?
>> >
>> I think we need to verify which type of locking the application uses
>> before we can answer this,
>>
>> Steve.
>>
>> > Thanks in advance!
>> >
>> > Regards,
>> > Stevo.
>> > --
>> > Linux-cluster mailing list
>> > [email protected]
>> > https://www.redhat.com/mailman/listinfo/linux-cluster
>>
>>
>> --
>> Linux-cluster mailing list
>> [email protected]
>> https://www.redhat.com/mailman/listinfo/linux-cluster
>>
>
>
#include <fcntl.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
int main (int args, char* argv[])
{
char* file = argv[1];
int fd;
struct flock lock;
struct flock lck;
printf("opening %s\n", file);
/* Open a file descriptor to the file. */
fd = open(file, O_WRONLY);
printf("checking for locks\n");
(void) printf(" pid type start length\n");
lck.l_start = 0L;
do {
lck.l_whence = 0;
lck.l_len = 0L;
lck.l_type = F_WRLCK;
(void) fcntl(fd, F_GETLK, &lck);
if (lck.l_type != F_UNLCK) {
(void) printf(" %5d %c %8d %8d\n",
lck.l_pid,
(lck.l_type == F_WRLCK) ? 'W' : 'R',
lck.l_start,
lck.l_len);
/* if this lock goes to the end of the address
* space, no need to look further, so break out.
*/
if (lck.l_len == 0)
break;
/* otherwise, look for new lock after the one
* just found.
*/
lck.l_start += lck.l_len;
}
} while (lck.l_type != F_UNLCK);
printf("locking\n");
/* Initialize the flock structure. */
memset(&lock, 0, sizeof(lock));
lock.l_type = F_WRLCK;
/* Place a write lock on the file. */
fcntl(fd, F_SETLKW, &lock);
printf("locked; hit enter to unlock...");
/* Wait for the user to hit enter. */
getchar();
printf("unlocking\n");
/* Release the lock. */
lock.l_type = F_UNLCK;
fcntl(fd, F_SETLKW, &lock);
close(fd);
return 0;
}
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