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1. 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
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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)
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In my server code there is a thread per client...
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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. 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
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7. 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
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8. 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)
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9. 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)
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10. UNIX for Dummies Questions & Answers
hi, is there any command where we can monitor semaphores? (1 Reply)
Discussion started by: yls177
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sem_getvalue(2) System Calls Manual sem_getvalue(2)
NAME
sem_getvalue - get the value of a POSIX semaphore
SYNOPSIS
DESCRIPTION
is used to read the value of the semaphore. The value of the semaphore specified by sem is read, at some unspecified time during the call,
and then stored into sval. If the semaphore value is <= 0, at that time, the semaphore is considered unavailable. If the semaphore value
is > 0, at that time, the semaphore is considered available.
If sval is positive, it is equal to the number of locks available on the semaphore, at the time the semaphore value was read. If sval is
negative, its absolute value is equal to the number of blocked threads waiting for the semaphore to become available, at the time the sema-
phore value was read.
If the specified semaphore referred to by sem is a named semaphore, then this semaphore must have been opened by the calling process with
and the process must have read permission on this 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 read the value of the semaphore sem and store it in sval.
RETURN VALUE
A successful call to will return 0. 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 read the semaphore.
[EINVAL] The argument sem does not refer to a valid semaphore.
SEE ALSO
sem_open(2), <semaphore.h>.
STANDARDS CONFORMANCE
sem_getvalue(2)