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Old 11-19-2004, 07:57 AM   #1
msriram_linux
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Registered: Nov 2004
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POSIX thread Programming


Hi!!
I would like to know how to set priorities for threads...
In the program I have been experimenting on, I have three threads and I want to set thier pririties as I wish. Is this possible?..
Could someone please mail an example application where different scheduling policies and scheduling attributes become clear?..
Thank you
 
Old 11-19-2004, 08:18 AM   #2
rjlee
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Registered: Jul 2004
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Linux doesn't allow you to set a thread's scheduling priority directly; instead, you can set the niceness value, using the nice(2) function:

Code:
#include <unistd.h>
int nice(int inc); //returns 0 on success or -1 on error (sets errno)
Edit: In response to your email, it seems that some implementations return the actual nice value. From the manpage:
Quote:
NOTES
Note that the routine is documented in SUSv2 and POSIX 1003.1-2003 to return the new nice value,
while the Linux syscall and (g)libc (earlier than glibc 2.2.4) routines return 0 on success. The
new nice value can be found using getpriority(2). Note that an implementation in which nice returns
the new nice value can legitimately return -1. To reliably detect an error, set errno to 0 before
the call, and check its value when nice returns -1.
The nice values range from -19 (most foreground; highest priority) to +20 (most background; lowest priority). The initial default is usually 0.

Reducing the nice value is a privilaged instruction that requires superuser powers.

The getpriority(2) call returns the current nice value, and the nice and renice programs can be used to change niceness from the shell.

The actual scheduling priority is set depending on the nice value, recent schedular performance, and other system loads.

Last edited by rjlee; 11-21-2004 at 10:49 AM.
 
Old 11-19-2004, 08:24 AM   #3
perfect_circle
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Registered: Oct 2004
Location: Athens, Greece
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you probably don't what to hack your kernel.
If you need to scedule your threads, what you need to do is to build a simple server,
who will be the sceduler. When a thread starts, make it connect to the server (through TCP if you want),
The severs may send simple messages to the threads, to block and unblock them.
So the sever is responsible for the sceduling, and the threads all they need to do is to listen on a socken. When they get a block message they stop and when they get a unblock message they continue doing what they do. When a thread finishes the work, it closes the connection, so that the server knows it. I had to do something like that for a project in the univercity, a few years ago. I don't remember all the details, but i think this is the basic consept. If i find the project i will e-mail it to you.
 
Old 11-19-2004, 09:23 AM   #4
LauroMoura
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Registered: Feb 2004
Location: Carpina, PE, Brazil
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Check these functions:

pthread_getschedparam
pthread_setschedparam

-----
Poxis Thread Programming
 
Old 11-21-2004, 03:14 PM   #5
msriram_linux
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Registered: Nov 2004
Posts: 19

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Hi Lauro!
Thank you for the suggestion.
However my problem was solved with nice fuction suggested by rjlee.
I tried with pthread_setschedparam (in a different program)but I have some
problems reagrding which I have stated a new thread subjected "Pthread scheduling..". Could you please take pains to go through it?
 
  


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