semaphore.h(3HEAD) Headers semaphore.h(3HEAD)NAME
semaphore.h, semaphore - semaphores
SYNOPSIS
#include <semaphore.h>
DESCRIPTION
The <semaphore.h> header defines the sem_t type, used in performing semaphore operations. The semaphore can be implemented using a file
descriptor, in which case applications are able to open up at least a total of {OPEN_MAX} files and semaphores. The symbol SEM_FAILED is
defined (see sem_open(3RT)).
Inclusion of the <semaphore.h> header can make visible symbols defined in the headers <fcntl.h> and <sys/types.h>. See fcntl.h(3HEAD) and
types.h(3HEAD).
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
+-----------------------------+-----------------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+-----------------------------+-----------------------------+
|Interface Stability |Standard |
+-----------------------------+-----------------------------+
SEE ALSO fcntl.h(3HEAD), types.h(3HEAD), sem_destroy(3RT), sem_getvalue(3RT), sem_init(3RT), sem_open(3RT), sem_post(3RT), sem_timedwait(3RT),
sem_unlink(3RT), sem_wait(3RT), attributes(5), standards(5)SunOS 5.10 10 Sep 2004 semaphore.h(3HEAD)
Check Out this Related Man Page
sem_getvalue(3RT) Realtime Library Functions sem_getvalue(3RT)NAME
sem_getvalue - get the value of a semaphore
SYNOPSIS
cc [ flag... ] file... -lrt [ library... ]
#include <semaphore.h>
int sem_getvalue(sem_t *restrict sem, int *restrict sval);
DESCRIPTION
The sem_getvalue() function updates the location referenced by the sval argument to have the value of the semaphore referenced by sem with-
out affecting the state of the semaphore. The updated value represents an actual semaphore value that occurred at some unspecified time
during the call, but it need not be the actual value of the semaphore when it is returned to the calling process.
If sem is locked, then the value returned by sem_getvalue() is either zero or a negative number whose absolute value represents the number
of processes waiting for the semaphore at some unspecified time during the call.
The value set in sval may be 0 or positive. If sval is 0, there may be other processes (or LWPs or threads) waiting for the semaphore; if
sval is positive, no process is waiting.
RETURN VALUES
Upon successful completion, sem_getvalue() returns 0. Otherwise, it returns -1 and sets errno to indicate the error.
ERRORS
The sem_getvalue() function will fail if:
EINVAL The sem argument does not refer to a valid semaphore.
ENOSYS The sem_getvalue() function is not supported by the system.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
+-----------------------------+-----------------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+-----------------------------+-----------------------------+
|Interface Stability |Standard |
+-----------------------------+-----------------------------+
|MT-Level |MT-Safe |
+-----------------------------+-----------------------------+
SEE ALSO semctl(2), semget(2), semop(2), sem_post(3RT), sem_wait(3RT), attributes(5), standards(5)SunOS 5.10 1 Nov 2003 sem_getvalue(3RT)
I know UNIX user level commands, shell scripts. But i have no idea about kernel level programming and networking. I know the terms semaphore,IPC,socket programming. But i don't know in details what are these. I need to know the following.
1. Unix kernel level programming.
2. Unix Internals.
3.... (4 Replies)
Hi,
I've a problem with this simple code about of semaphore:
#include<stdio.h>
#include<stdlib.h>
#include<unistd.h>
#include<semaphore.h>
#include<sys/types.h>
#include<sys/mman.h>
#include<sys/fcntl.h>
#define SemName "/SEM_1"
int main (int argc, char **argv)
{
char name;... (5 Replies)
Hi All,
I am going through the semaphore concept and have a doubt regarding the same and hope to get a resolution here.
I have a file which has a number of records.
I want to write an application (in C) which will be able to do concurrent read/write on these records.
Of what I have... (8 Replies)
I'm having an issue implementing my semaphores....
The following is how I'm setting up the semaphore.
First: I get the semkey (which I've wrapped in an IF statement using perror() but in an attempt to keep the code clutter free I've removed it here)
semkey = ftok("./request", 'S' )
... (1 Reply)
I am investigating some locking scheme using semaphores. To evaluate basic system speed I run a loop of getting some semaphore info and display it:
while : ; do ./semshow; done > res.txt
I ran this on 3 boxes - two similar modern HP XEON boxes, one running SCO OpenServer 5, the other is... (46 Replies)
Hi,
I have created a posix semaphore.
Is it possible to have a functionality, wherein I can reset the semaphore.
ie All the tasks waiting for the semaphore will be signalled and will return with error values and the semaphore value will be set to its initial value.
Is there a way to get a... (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)
Hi friends,
I want to print the the following sequence of numbers using sempahores.
2 3 2 3 2 3 2 3
But something seems to be wrong regarding my concept of semaphores, I am using a single function, a single semaphore, and two threads, but I am not succeeding to achieve my goal,
it prints as... (1 Reply)
hallo!
if there are many processes running and I initialize the semaphore like this:
my_sem = sem_open(SEM_NAME, O_CREAT | O_RDWR,
S_IRUSR | S_IWUSR, 10);
(the last argument is 10)
and then i use
sem_wait(my_sem);
sleep(5);
sem_post;
Will 10 processes be able to access the... (0 Replies)