I was asked to add this piece of code to a c program which I will execute through the shell:
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 if the post comes after this critical section ?.
From my understanding post is the action that wakes up the thread in the queue, or increasing the semaphore by 1 if no threads are waiting.
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)
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)
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)
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)
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)
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
LEARN ABOUT HPUX
sem_post
sem_post(2) System Calls Manual sem_post(2)NAME
sem_post - unlock a POSIX semaphore
SYNOPSIS DESCRIPTION
is used to post the semaphore referenced by sem. The calling thread will not return from its call to unless it can either: increment the
semaphore value, if there are no blocked threads on this semaphore; give the semaphore to a blocked thread, if there are any blocked
threads on this semaphore; or have an error condition.
If the semaphore value is < 0, the semaphore has blocked threads, waiting for it to become available (the absolute value of the semaphore's
value indicates the number of waiters at that moment). If the semaphore value is >= 0, the semaphore has no waiters.
If the semaphore has no waiters at the time its value is checked, the semaphore's value will be atomically incremented, with respect to the
checking of its value, up to its maximum value as specified by If the semaphore has waiters at the time its value is checked, the semaphore
value is not changed. Instead, the calling thread will attempt to wake up a waiter. If the semaphore has waiters having realtime priori-
ties, the thread must wake up the highest priority waiter. Otherwise the thread at the head of the channel queue is woken up.
When a waiter is successfully woken, the semaphore being posted will be given to the woken waiter. In other words, the state of the sema-
phore remains unchanged. Instead, the semaphore being posted will be inherited by the waiter being woken from this call to
If the specified semaphore referred to by sem is a named semaphore, then this semaphore must have been opened by the calling process with
The calling process must have both read and write permissions on the semaphore to perform this operation. The routine may be called asyn-
chronously, i.e. from a signal handler.
To use this function, link in the realtime library by specifying on the compiler or linker command line.
EXAMPLES
The following call to will post the semaphore sem.
RETURN VALUE
A successful call to will return 0 and the calling thread would have posted the semaphore. Otherwise, the call to will return -1 with
errno set to the appropriate value of the error condition.
ERRORS
fails and does not perform the requested operation if any of the following conditions are encountered:
[EPERM] The calling process does not have the privileges necessary to post the semaphore.
[EINVAL] The argument sem does not refer to a valid semaphore.
SEE ALSO
<semaphore.h>.
STANDARDS CONFORMANCE sem_post(2)