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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++;
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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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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
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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
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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)
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8. Programming
I'm running one multithreaded application, in that one of my thread
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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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msem_lock(2) System Calls Manual msem_lock(2)
NAME
msem_lock() - lock a semaphore
SYNOPSIS
DESCRIPTION
attempts to lock a binary semaphore.
sem points to an structure which specifies the semaphore to be locked.
If the semaphore is not currently locked, it becomes locked and the function returns successfully.
If the semaphore is currently locked, and condition is then the function returns with an error. If the semaphore is currently locked and
condition is zero, the function does not return until either the calling process is able to successfully lock the semaphore, or an error
condition occurs.
All calls to and by multiple processes sharing a common structure behave as if the calls were serialized.
If the structure contains any value not resulting from a call to followed by a (possibly empty) sequence of calls to and the results are
undefined. The address of an uniquely identifies the semaphore. If the structure contains any value copied from an structure at a differ-
ent address, the result is undefined.
IMPLEMENTATION NOTES
If blocked on a locked semaphore, suspends the calling process at a priority such that the process can be interrupted by a signal.
The system attempts to ignore or recover from invalid values written to the structure, but this is not guaranteed for all cases.
successfully acquires a semaphore that is locked by a process that has exited.
RETURN VALUE
returns one of the following values:
Success.
Failure.
is set to indicate the error.
ERRORS
sets to one of the following values if the corresponding condition is encountered.
was specified and the semaphore was already locked.
sem points to an structure that has been removed, or condition is invalid.
was interrupted by a signal that was caught.
The semaphore is currently locked,
condition is zero, and waiting to lock the semaphore would create a deadlock.
sem is not a properly aligned address or is otherwise an invalid pointer.
AUTHOR
was developed by HP and OSF.
SEE ALSO
msem_init(2), msem_remove(2), msem_unlock(2), mman(5).
STANDARDS CONFORMANCE
msem_lock(2)