05-06-2007
Semaphore
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
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. Programming
I'm running one multithreaded application, in that one of my thread
is waiting infinitely in a semphore. Is there a way to determine, in
which semaphore the particular thread is waiting and which thread(s)
is holding the semaphore. (5 Replies)
Discussion started by: ptprabu
5 Replies
4. UNIX for Advanced & Expert Users
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)
Discussion started by: maverix
8 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 DEBIAN
coro::semaphore
Semaphore(3pm) User Contributed Perl Documentation Semaphore(3pm)
NAME
Coro::Semaphore - counting semaphores
SYNOPSIS
use Coro;
$sig = new Coro::Semaphore [initial value];
$sig->down; # wait for signal
# ... some other "thread"
$sig->up;
DESCRIPTION
This module implements counting semaphores. You can initialize a mutex with any level of parallel users, that is, you can intialize a
sempahore that can be "down"ed more than once until it blocks. There is no owner associated with semaphores, so one thread can "down" it
while another can "up" it.
Counting semaphores are typically used to coordinate access to resources, with the semaphore count initialized to the number of free
resources. Threads then increment the count when resources are added and decrement the count when resources are removed.
You don't have to load "Coro::Semaphore" manually, it will be loaded automatically when you "use Coro" and call the "new" constructor.
new [inital count]
Creates a new sempahore object with the given initial lock count. The default lock count is 1, which means it is unlocked by default.
Zero (or negative values) are also allowed, in which case the semaphore is locked by default.
$sem->count
Returns the current semaphore count.
$sem->adjust ($diff)
Atomically adds the amount given to the current semaphore count. If the count becomes positive, wakes up any waiters. Does not block if
the count becomes negative, however.
$sem->down
Decrement the counter, therefore "locking" the semaphore. This method waits until the semaphore is available if the counter is zero.
$sem->wait
Similar to "down", but does not actually decrement the counter. Instead, when this function returns, a following call to "down" or
"try" is guaranteed to succeed without blocking, until the next thread switch ("cede" etc.).
Note that using "wait" is much less efficient than using "down", so try to prefer "down" whenever possible.
$sem->wait ($callback)
If you pass a callback argument to "wait", it will not wait, but immediately return. The callback will be called as soon as the
semaphore becomes available (which might be instantly), and gets passed the semaphore as first argument.
The callback might "down" the semaphore exactly once, might wake up other threads, but is NOT allowed to block (switch to other
threads).
$sem->up
Unlock the semaphore again.
$sem->try
Try to "down" the semaphore. Returns true when this was possible, otherwise return false and leave the semaphore unchanged.
$sem->waiters
In scalar context, returns the number of threads waiting for this semaphore.
$guard = $sem->guard
This method calls "down" and then creates a guard object. When the guard object is destroyed it automatically calls "up".
AUTHOR
Marc Lehmann <schmorp@schmorp.de>
http://home.schmorp.de/
perl v5.14.2 2012-04-13 Semaphore(3pm)