05-21-2011
what's the difference between signal and semaphore?
dear all~
I am just new here.I am very happy to see such a forum.
I am very puzzled by the difference between signal and semaphore.
What's the difference between signal() wait() and P V operation?
the linux kernel have implemented a good semaphore system,why we need the system V IPC semaphore?
10 More Discussions You Might Find Interesting
1. UNIX for Dummies Questions & Answers
hi, is there any command where we can monitor semaphores? (1 Reply)
Discussion started by: yls177
1 Replies
2. UNIX for Dummies Questions & Answers
Hi,
I'm new to UNIX.
I need to know what's a semaphore
Do reply.
Thanks
VJ (3 Replies)
Discussion started by: vjsony
3 Replies
3. Shell Programming and Scripting
can any one tell me how to run a semaphore. i understand roughly how they work code wise, but i'm not sure how to make use of them. i have two client programs in csh that perform tasks on a server file (flat file) how the i get the semaphore to lock the file when one has accessed it and how to use... (5 Replies)
Discussion started by: FDavid
5 Replies
4. Shell Programming and Scripting
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)
Discussion started by: Jaken
2 Replies
5. UNIX for Dummies Questions & Answers
what is semaphore? can any body explain it in a more simple way than the manual ??
replies appreciated
Regards
raguram R (7 Replies)
Discussion started by: raguramtgr
7 Replies
6. Programming
In my server code there is a thread per client...
The server call accept() and after that start the thread.
So there is a thread for client that save in RAM the client's message, that will be send to other clients.
Now in RAM I have created a shared memory in which thread read and write(save)... (2 Replies)
Discussion started by: italian_boy
2 Replies
7. Shell Programming and Scripting
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)
Discussion started by: gokult
0 Replies
8. Programming
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)
Discussion started by: rupeshkp728
0 Replies
9. Solaris
Can anyone tell me abt the Semaphore concept and what is semaphore???
is semaphore id is associated in terms as in resources like semaphore id 1 indicates cpu share unit is given and semaphore id 2 will indicate abt the memore or semaphore id 3 will tell us the i/o components (1 Reply)
Discussion started by: aarjun07
1 Replies
10. UNIX for Beginners Questions & Answers
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 OSF1
sem_wait
sem_wait(3) Library Functions Manual sem_wait(3)
NAME
sem_wait, sem_trywait - Performs (or conditionally performs) a semaphore lock (P1003.1b)
LIBRARY
Realtime Library (librt.so, librt.a)
SYNOPSIS
#include <semaphore.h>
int sem_wait (
sem_t *sem);
int sem_trywait (
sem_t *sem);
PARAMETERS
sem Specifies a pointer to the semaphore to be locked.
DESCRIPTION
The sem_wait function locks the semaphore referenced by sem by performing a semaphore lock operation on it. If the semaphore value is zero,
the sem_wait function blocks until it either locks the semaphore or is interrupted by a signal.
The sem_trywait function locks a semaphore only if the semaphore is currently not locked. If the semaphore value is zero, the sem_trywait
function returns without locking the semaphore.
These functions help ensure that the resource associated with the semaphore cannot be accessed by other processes. The semaphore remains
locked until the process unlocks it with a call to the sem_post function.
Use the sem_wait function instead of the sem_trywait function if the process should wait for access to the semaphore.
RETURN VALUES
If the sem_wait or sem_trywait function returns successfully, a value of 0 (zero) is returned and the function executes the semaphore lock
operation.
On an unsuccessful call, a value of -1 is returned and errno is set to indicate that an error occurred. The state of the semaphore remains
unchanged.
ERRORS
The sem_wait and sem_trywait functions fail under the following conditions:
[EAGAIN] The semaphore was already locked and cannot be locked by the sem_trywait operation (sem_trywait only).
[EINTR] A signal interrupted this function.
[EINVAL] The sem argument does not refer to a valid semaphore.
RELATED INFORMATION
Functions: sem_post(3)
Guide to Realtime Programming delim off
sem_wait(3)