05-21-2009
Quote:
Originally Posted by
jim mcnamara
The simplest way would be to use a lock file - let the contents of a text file act as a traffic cop.
Hmmm...
contents of the file?
How would you make sure that, in between the point in time you check the file and the point in time you set the lock, no other process does the same resulting in two processes running?
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plock(3C) Standard C Library Functions plock(3C)
NAME
plock - lock or unlock into memory process, text, or data
SYNOPSIS
#include <sys/lock.h>
int plock(int op);
DESCRIPTION
The plock() function allows the calling process to lock or unlock into memory its text segment (text lock), its data segment (data lock),
or both its text and data segments (process lock). Locked segments are immune to all routine swapping. The effective user ID of the calling
process must be super-user to use this call.
The plock() function performs the function specified by op:
PROCLOCK Lock text and data segments into memory (process lock).
TXTLOCK Lock text segment into memory (text lock).
DATLOCK Lock data segment into memory (data lock).
UNLOCK Remove locks.
RETURN VALUES
Upon successful completion, 0 is returned. Otherwise, -1 is returned and errno is set to indicate the error.
ERRORS
The plock() function fails and does not perform the requested operation if:
EAGAIN Not enough memory.
EINVAL The op argument is equal to PROCLOCK and a process lock, a text lock, or a data lock already exists on the calling process; the op
argument is equal to TXTLOCK and a text lock or a process lock already exists on the calling process; the op argument is equal to
DATLOCK and a data lock or a process lock already exists on the calling process; or the op argument is equal to UNLOCK and no lock
exists on the calling process.
EPERM The {PRIV_PROC_LOCK_MEMORY} privilege is not asserted in the effective set of the calling process.
USAGE
The mlock(3C) and mlockall(3C) functions are the preferred interfaces for process locking.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
+-----------------------------+-----------------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+-----------------------------+-----------------------------+
|MT-Level |MT-Safe |
+-----------------------------+-----------------------------+
SEE ALSO
exec(2), exit(2), fork(2), memcntl(2), mlock(3C), mlockall(3C), attributes(5)
SunOS 5.10 22 Mar 2004 plock(3C)