09-27-2010
Thanks, My question is a general question without special user case.
Maybe we can create a example to insert data 1-10000 in process to log and run 3 processes at the same time .
As you point , lockfile in linux could lock the file for exclusive writing, so I assume if we don't use lockfile or similar command, the above situation will cause the race condition or outdated data.
If I am wrong in above, please let me know.
Thanks again for your comments.
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LEARN ABOUT SUNOS
maillock
maillock(3MAIL) User Mailbox Library Functions maillock(3MAIL)
NAME
maillock, mailunlock, touchlock - functions to manage lockfile(s) for user's mailbox
SYNOPSIS
cc [ flag ... ] file ... -lmail [ library ... ]
#include <maillock.h>
int maillock(const char *user, int retrycnt);
void mailunlock(void);
void touchlock(void);
DESCRIPTION
The maillock() function attempts to create a lockfile for the user's mailfile. If a lockfile already exists, and it has not been modified
in the last 5 minutes, maillock() will remove the lockfile and set its own lockfile.
It is crucial that programs locking mail files refresh their locks at least every three minutes to maintain the lock. Refresh the lockfile
by calling the touchlock() function with no arguments.
The algorithm used to determine the age of the lockfile takes into account clock drift between machines using a network file system. A zero
is written into the lockfile so that the lock will be respected by systems running the standard version of System V.
If the lockfile has been modified in the last 5 minutes the process will sleep until the lock is available. The sleep algorithm is to
sleep for 5 seconds times the attempt number. That is, the first sleep will be for 5 seconds, the next sleep will be for 10 seconds, etc.
until the number of attempts reaches retrycnt.
When the lockfile is no longer needed, it should be removed by calling mailunlock().
The user argument is the login name of the user for whose mailbox the lockfile will be created. maillock() assumes that user's mailfiles
are in the ``standard'' place as defined in <maillock.h>.
RETURN VALUES
Upon successful completion, .maillock() returns 0. Otherwise it returns -1.
FILES
/var/mail/* user mailbox files
/var/mail/*.lock user mailbox lockfiles
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
+-----------------------------+-----------------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+-----------------------------+-----------------------------+
|MT-Level |Unsafe |
+-----------------------------+-----------------------------+
SEE ALSO
libmail(3LIB),attributes(5)
NOTES
The mailunlock() function will only remove the lockfile created from the most previous call to maillock(). Calling maillock() for different
users without intervening calls to mailunlock() will cause the initially created lockfile(s) to remain, potentially blocking subsequent
message delivery until the current process finally terminates.
SunOS 5.10 29 Mar 1999 maillock(3MAIL)