Atomicity Post: 50804

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Top Forums Programming Atomicity Post 50804 by S.P.Prasad on Monday 3rd of May 2004 06:56:38 AM

05-03-2004

Registered User

First of all I would like to state that the pseudo-code I have written in my initial post needs modification. Instead of writing LOCK () and REL() as two separate functions, it would be only one subroutine LOCK_REL() implementing the pseudo-code.

Quote:

How are the variables shared - using shared memory?

Yes. This concept is already implemented in the project. All I need to is add up the required variables.

Quote:

No, you can also use a single lock for all resources, so that you might get heavy lock contention but still permit multiple processes to operate independently.

I studied the pseudo-code but that's what exactly we do not want. For example there are 10 process. Assume 2 different process would like to implement LOCK on the array and while 3 different process tries to REL the LOCK on the same array. Only one of the process should succeed for a specific array operation.

Further more of the remaining 5, 3 different process are trying to implement LOCK on 3 different arrays and 2 are REL two separate arrays, then they very well should. I mean they should not wait other wise timing would become a major issue i.e. time to process one transaction would increase.

Here's a sample view of what I would like to implement atomically:

Process'xx'1'xxxxx'2'xxxxx'3'xxxx'4'xxxxx'5'xxxxx'6'
Array'xxxx'A'xxxxx'B'xxxxx'C'xxxx'D'xxxxx'E'xxxxx'F'

xxxxxxxx ..... xxxx..... xx..... xxxx..... xxx......xxx.........
xxxxxxxxL(D)xxxxL(D)xxR(D)xxxxL(E)xxxR(F)xxxL(A)
xxxxxxxx ..... xxxx..... xx..... xxxx..... xxx......xxx.........

Where L stands for LOCK and R stands for REL the lock on array passed as arguments and value at array index 1 states whether array is locked ( value 1 ) or unlock ( value 0 ) . Please ignore the x's as I have put it for alignment purpose

I hope that I am clear in my requirement.

Thanks in advance.

Last edited by S.P.Prasad; 05-03-2004 at 09:55 AM..

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LEARN ABOUT FREEBSD

lock

LOCK(1) 						    BSD General Commands Manual 						   LOCK(1)

NAME

     lock -- reserve a terminal

SYNOPSIS

     lock [-npv] [-t timeout]

DESCRIPTION

     The lock utility requests a password from the user, reads it again for verification and then will normally not relinquish the terminal until
     the password is repeated.	There are two other conditions under which it will terminate: it will timeout after some interval of time and it
     may be killed by someone with the appropriate permission.

     The following options are available:

     -n      Do not use a timeout value.  Terminal will be locked forever.

     -p      A password is not requested, instead the user's current login password is used.

     -t timeout
	     The time limit (default 15 minutes) is changed to timeout minutes.

     -v      Disable switching virtual terminals while this terminal is locked.  This option is implemented in a way similar to the -S option of
	     vidcontrol(1), and thus has the same restrictions.  It is only available if the terminal in question is a syscons(4) or vt(4) virtual
	     terminal.

SEE ALSO

     vidcontrol(1), syscons(4), vt(4)

HISTORY

     The lock command appeared in 3.0BSD.

BSD
								   July 10, 2002							       BSD