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Philippe Wicker wrote:
What I suspect is happening is the thread is not being released
quickly enough after receiving the event. It is more noticable if I
move the mouse about on the desktop. I am playing a MIDI note every
500ms and I can hear the time not being correct.
Can you tell us some more about the threads that are involved: who is
the signaling thread?
In the case I am citing here, there is no actual signalling thread. The
event times out after the period. At this point, my scheduled object is
checked on the top of a priority Q (it is the only object on it in this
simple instance), and the time is compared with the time the object was
put on the queue. The function for obtaining the time is as follows
DWORD Scheduler::getTime ()
{
struct timeval current_time;
DWORD ret = 0;
if (gettimeofday(¤t_time, NULL))
{
printf("Unable to get current time");
}
else
{
ret = (current_time.tv_sec - initial_time.tv_sec) * 1000;
ret += current_time.tv_usec / 1000;
}
return ret;
}
How (when) do you decide to signal the waiter? Are there several
synchronization points in the waiter thread?
There are two mutexes involved, however, there are no other tasks
unblocked that are taking them (i.e. MIDI In task). There is a mutext to
control adding and removing from the priority Q, however, I know that
there is not a sequence problem here. I have seen the problem in another
part of the program using events.
What thread is sending the midi note?
This thread. I can also see on the display that there is a delay by
printing numbers to the console
This only started occuring after upgrading to Panther from Jaguar. I
am after a 5ms resolution. Can Panther offer me this reliably using
POSIX threads?
The OS X scheduler can give very sharp resolution using
cond_timedwait, a 5ms resolution (and even much better) is possible.
I was preferring 1ms, but I could live with 5ms.
Now the point is how is the midi note sender thread scheduled: is it a
time shared or a real time thread? If time shared, did you give it the
default priority or did you try to boost its priority?
I tried to boost the priority
struct sched_param sp;
memset(&sp, 0, sizeof(struct sched_param));
sp.sched_priority=8;
if (pthread_setschedparam(pthread_self(), SCHED_FIFO, &sp) == -1)
{
printf("Failed to change priority.\n");
}
What is the amount of work it has to execute when it wakes up?
It does not do a lot - In this case it sends the note and adds another
scheduled event to the queue. It then waits 500ms
Thanks for taking the time. I was wondering whether I should use
something instead of the pThreads API. I was, however, hoping to port to
Linux later.
There are those who seek knowledge for the sake of knowledge - that is CURIOSITY
There are those who seek knowledge to be known by others - that is VANITY
There are those who seek knowledge in order to serve - that is LOVE
Bernard of Clairvaux (1090 - 1153)
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