Re: PATCH: Microsecond sleep time

On 02.07.2008, at 14:29, Werner Coetzee wrote:

>
> Hi
>
> Can anyone explain why gwthread is using the poll function to sleep  
> (using milliseconds as timeout), and not maybe the select function  
> (using microseconds as timeout)?


Kannel can use poll or select. It's a platform specific decision by ./ 
configure as not all have poll as far as I remember.
Select has an issue if you have a lot of file descriptors open as it  
uses an array of many fd's. poll is much smarter there.

The reason why kannel uses poll on a pipe to sleep is for the simple  
reason that a thread can be  woken up before the sleep time expires by  
sending a byte to the pipe.

> We have the requirement to be able to sleep for less than a  
> millisecond, which the current gwthread_sleep can't provide.

If its for pure sleeping of such small time amounts, you might consult  
your operating system's documentation. maybe usleep() or nanosleep()  
is better for such cases. However be aware that if you sleep such  
small amounts, accuracy can become an issue. Unix kernels are not real  
time kernels.

usleep() on MacOS X says:

	DESCRIPTION
	     The usleep() function suspends execution of the calling thread  
until either useconds microseconds have elapsed or a signal is deliv-
	     ered to the thread whose action is to invoke a signal-catching  
function or to terminate the thread or process.  The actual time
	     slept may be longer, due to system latencies and possible  
limitations in the timer resolution of the hardware.

	     This function is implemented, using nanosleep(2), by pausing for  
useconds microseconds or until a signal occurs.  Consequently, in
	     this implementation, sleeping has no effect on the state of  
process timers and there is no special handling for SIGALRM.






Andreas Fink

Fink Consulting GmbH
Global Networks Schweiz AG
BebbiCell AG
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