I checked the kernels. There were major changes in 1995 (before version 2.0), 1998 (before version 2.4), and then again with the introduction of the "O(1) scheduler" (not sure). Here's the code -- unchanged since 2.4 -- that does semctl(GETALL):
Here's the code from 2.0:
When you break it down, the only difference is in the semlock() call, which is needed on multi-CPU systems. It could be SCO is also similarly limited. Why don't you try a linux 2.0 distribution, like RedHat 5.2, which uses Linux 2.0.36 (and uses the same sem code as above). Install it and benchmark the same code. That would be a great help to all of us, I think.
Hello,
I have a Supermicro server with a P4SCI mother board running Debian Sarge 3.1. This is the "dmidecode" output related to RAM info:
RAM speed information is incomplete.. "Current Speed: Unknown", is there anyway/soft to get the speed of installed RAM modules? thanks!!
Regards :)... (0 Replies)
Hi,
I am looking to use a semaphore for the first time in one of my scripts. I am just wondering if there are any simple examples or tutorials around?
I am a beginner so the simpler the better :)
Thanks
-Jaken (2 Replies)
I analysed disk performance with blktrace and get some data:
read:
8,3 4 2141 2.882115217 3342 Q R 195732187 + 32
8,3 4 2142 2.882116411 3342 G R 195732187 + 32
8,3 4 2144 2.882117647 3342 I R 195732187 + 32
8,3 4 2145 ... (1 Reply)
Control two exclusively shared resources(semaphore). The two resources are two files. The producer will write even numbers to one file, and odd numbers to another one. The consumer respectively reads from each file until it gets 5 even numbers and 5 odd numbers.
Can any one help me with the... (0 Replies)
If I create a semaphore and then I fork a number of child processes then all the child process use that same semaphore.
Since the process address spaces are different rfom each other then how all the child process are able to access the same semaphore?
I understand that semaphore/mutex is at os... (0 Replies)
I was asked to add this piece of code to a c program which I will execute through the shell:
for(long i = 0; i < NITER; i++)
{ sem_wait( &sema);
count++;
sem_post( &sema); }
I didn't get it, which is the critical section ? if it's "count++" how would a thread wake up in order to enter it... (1 Reply)
Discussion started by: uniran
1 Replies
LEARN ABOUT ULTRIX
semget
semget(2) System Calls Manual semget(2)Name
semget - get set of semaphores
Syntax
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/sem.h>
int semget (key, nsems, semflg)
key_t key;
int nsems, semflg;
Description
The system call returns the semaphore identifier associated with key. A semaphore identifier and associated data structure and set con-
taining nsems semaphores are created for key, if one of the following is true:
o The key is equal to IPC_PRIVATE
o The key does not already have a semaphore identifier associated with it, and (semflg & IPC_CREAT ) is true.
For further information, see
Upon creation, the data structure associated with the new semaphore identifier is initialized as follows:
o The sem_perm.cuid, sem_perm.uid, sem_perm.cgid and sem_perm.gid are set equal to the effective user ID and effective group ID, respec-
tively, of the calling process.
o The low-order nine bits of sem_perm.mode are set equal to the low-order nine bits of semflg.
o The sem_nsems is set equal to the value of nsems.
o The sem_otime is set equal to zero (0) and sem_ctime is set equal to the current time.
Return Values
Upon successful completion, a nonnegative integer, namely a semaphore identifier, is returned. Otherwise, a value of -1 is returned and
errno is set to indicate the error.
Diagnostics
The semget system call fails if any of the following is true:
[EINVAL] The nsems is either less than or equal to zero or greater than the system-imposed limit
[EACCES] A semaphore identifier exists for key, but operation permission, as specified by the low-order nine bits of semflg would not
be granted. For further information, see
[EINVAL] A semaphore identifier exists for key, but the number of semaphores in the set associated with it is less than nsems and
nsems is not equal to zero.
[ENOENT] A semaphore identifier does not exist for key and (semflg & IPC_CREAT ) is false.
[ENOSPC] A semaphore identifier is to be created but the system-imposed limit on the maximum number of allowed semaphore identifiers
in the system would be exceeded.
[EEXIST] A semaphore identifier exists for key but ((semflg & IPC_CREAT ) & (semflg & IPC_EXCL )) is true.
See Alsosemctl(2), semop(2), ftok(3)semget(2)