Accessing a semaphore - assuming there is no deadlock - it is a direct memory access operation, adding a whole page or multiples to process memory has overhead. It can involve an expensive call: brk(), if no memory is already there.
It depends on what
says in total, rounded up to a minimum of the PAGE_SIZE (mutiple) boundary (stack frame boundary usually), which can leave extra multiple pages of memory. Look at what is show to be allocated to heap. As a start. You can call sbrk(0) to find the end of process memory.
shmget allocates from heap in most implementations: /proc/sys/kernel/sh* proc directories have shared memory information. kernel settings control shared memory operations.
try this:
That will display cum time spent + # calls for each of the function calls. You can see if/where there is a problem. If there is one with semaphores then semget will be your most likely problem - allocating pages of memory.
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 HPUX
sem_unlink
sem_unlink(2) System Calls Manual sem_unlink(2)NAME
sem_unlink - unlink a named POSIX semaphore
SYNOPSIS DESCRIPTION
is used to unlink named semaphores. A successful call to marks the semaphore, specified by name, for removal. Calling does not affect
processes, including the calling process, which currently have a descriptor, obtained from a call to Named semaphores are uniquely identi-
fied by character strings. All character string names will be pre-processed to ensure variations of a pathname resolve to the same sema-
phore name. If the semaphore is successfully marked for removal by a call to the semaphore will be removed when all processes remove their
descriptors to the specified semaphore by calling Subsequent calls to using the string name will refer to a new semaphore.
To use this function, link in the realtime library by specifying on the compiler or linker command line.
EXAMPLES
The following call to will remove the named semaphore named by the string name. If the semaphore is currently referenced by one or more
processes, the semaphore will be marked for removal and removed when there are no more processes referencing it.
RETURN VALUE
If the semaphore was unlinked successfully, returns 0.
If the semaphore could not be unlinked, the call returns -1 and sets to indicate the error.
ERRORS
fails and does not perform the requested operation if any of the following conditions are encountered:
[EACCES] The named semaphore exists and the process does not have the permissions to unlink the semaphore.
[ENAMETOOLONG] The name string is longer than
[ENOENT] The flag is not set in oflag (see sem_open(2)) and the named semaphore does not exist.
SEE ALSO sem_close(2), sem_open(2), privileges(5), <semaphore.h>.
STANDARDS CONFORMANCE sem_unlink(2)