Shared Memeory size on V.4 and BSD

Shared Memeory size on V.4 and BSD

Post by 25421-flo » Sat, 09 May 1992 23:55:22

Does anyone out there know what, if any, the limitations are on
shared memory size on System V.4 and BSD/SunOS systems?  Most
seem to have 1-2 megs as a default upper limit.  Can this be expanded
by changing a few kernel config parameters?  We'd potentially need
a segment of 8-16 Meg on some systems. Is this workable?


1. Yet another shared memeory problem

Hello every one:
I have a very nasty problem, and I thought the only way I could get it resolved is writing
it to this news group. the problem is as follow: I am using a Sun SPARC 1+ with SUN os 4.1
I have two processes One gets forked from its parent. before the fork. I create a semaphore
lock, and then I create shared memory using shmget system call. Then I do an shmat to
attach my shared memory. to a static pointer in the program, and then I fork the child.
The parent gets data via a socket, and as soon as data arrives. it gets the semaphore lock locked.
Thewn writes the data to the shared memory, and then unlocks the semaphore lock. It then sends SIGUSR1 signal to the child that is in pause until receiving this signal. The child does the same
procedure for locking and unlocking of the semaphore, and it only reads the data. This works fine
and everything is great, until I decide to kill both processes, and attempt to restart them again.
I might add that I also go and remove the semaphore lock and shared memory via ipcrm. Once I
restart this process, I can get the shared memory via shmget, however I can not attach it via shmat!
I keep getting EINVAL error. This situation continues until I reboot my machine, and then again
everything is ok. Does anybody have any clue of what is going on? I mean I can understand if
I did not remove the shared memory, I would have problem creating it with the same key, but
after deleting it via ipcrm, I should be able to attach it again.
Thanks for the input if any??

Ali Sadjadi
Cray Research Inc.
655 Lone Oak DR.
Eagan,MN 5121

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