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hitach__0
Beginner
118 Views

pipeline with concurrent_queue

I am developing my project using pipeline, but i am having small issue.
My task is read a video and display every fram in sequence, that is i have to display image in every 30ms.
so i planed to use concurrent_queue to output buffer and display image it.
but i dont know how to create new thread within output buffer and hanle display image in every 30ms. I have to wake up that thread every 30ms and run. How to do that?
0 Kudos
14 Replies
Dmitry_Vyukov
Valued Contributor I
118 Views

[cpp]
volatile bool stop = false;
tbb::tbb_thread t (bind(thread_func, ref(stop)));
...
stop = true;
t.join();

void thread_func(bool volatile& stop)
{
  while (stop == false)
  {
    do_your_work_here();
	tbb::this_tbb_thread::sleep(tbb::tick_count::interval_t(0.03));
  }
}


[/cpp]

hitach__0
Beginner
118 Views

thanks for quick reply,
can you explain how it works?
Dmitry_Vyukov
Valued Contributor I
118 Views

[cpp]
int main()
{
	volatile bool stop = false;
	// this creates new thread (what you asked for)
	tbb::tbb_thread t (bind(thread_func, ref(stop)));
	...
	start pipeline here
	...
	// this terminates the thread
	stop = true;
	t.join();
}

// this a thread's function
void thread_func(bool volatile& stop)
{
  while (stop == false)
  {
    // here you must poll an image from the queue and display it
    do_your_work_here();
	// this suspends the thread for 30 ms
	tbb::this_tbb_thread::sleep(tbb::tick_count::interval_t(0.03));
  }
}


[/cpp]

nikkey_c
Beginner
118 Views

Thanks I am also looking this.......
i think you miss something, isnt it?
tbb::tbb_threadt(bind(thread_func,ref(stop)));
what do u mean by ref?
Dmitry_Vyukov
Valued Contributor I
118 Views

I had in mind bost::bind/ref. However the code is just typed in a text editor.
You can use whatever method you are comfortable with to create the functor. The simplest way is as follows:

struct my_thread
{
bool volatile& stop;
queue_t& queue;

my_thread(bool volatile& stop, queue_t& queue) : stop(stop), queue(queue) {}

void operator ()
{
// put your code here
}
};


tbb::tbb_thread t (my_thread(stop, queue));
nikkey_c
Beginner
118 Views

This is the code i havewritten, but i coulndnt get the results, that i needed. It runs only my_thread function not InputFilterstage,TransformFilter stage and outputFilterstage.
class my_thread
{
public:
bool volatile& stop;
my_thread(bool volatile& st);
void operator ()();
};
my_thread::my_thread(bool volatile& st) : stop(st) {}
void my_thread::operator ()(){
while (stop == false)
{
printf("display \n"); // have to display image every 30ms. that means first 29 sec needed to do //other three stages job.
tbb::this_tbb_thread::sleep(tbb::tick_count::interval_t(3.));
}
}
//Outputbuffer of pipeline
void* MyOutputFilter::operator()( void* item ) {
MyBuffer& b = *static_cast(item);
//here b is ordered sequence of image frames.
//store those images into queue
volatile bool stop = false;
my_thread tt(stop);
//every 30th sec i have to run below thread and display image.
tbb::tbb_thread t (tt);
t.join();
return NULL;
}
(added) and i am using
static int NThread = tbb::task_scheduler_init::automatic;
for pipeline. I am developing code based on tbb's text_filter.cpp example
RafSchietekat
Black Belt
118 Views

You should never launch and join a thread from something done inside a task (MyOutputFilter::operator() is called for each data item): that's like the tail wagging the dog (always wanted to use that in a sentence). You could launch it outside the pipeline, and feed it work from the output stage through a concurrent_queue. As for sleep time, you'd probably want to check wall clock time first to compensate for various knowns and unknowns.
hitach__0
Beginner
118 Views

sorry sir, i ddnt get your answer, ya we have to createmy_thread outside of pipeline, and pass it as argument.
But i dont know where I have to run this code:
tbb::tbb_thread t (tt);
t.join
and concurrent_queue?
can you send small code for that?
(added)
My task is run a function every 30ms insideMyOutputFilter. that function pops data from concurrent_queue.
hitach__0
Beginner
118 Views

I think this code is for, after pipeline is finished.
But i want to run thread_func while pipeline s runing
RafSchietekat
Black Belt
118 Views

"But i dont know where I have to run this code:"
The constructor before you run the pipeline, the join() after you stop the pipeline? BTW, you should use an atomic to communicate between threads: using volatile is compiler-specific.
hitach__0
Beginner
118 Views

Thank, my code works well.
even thoughi follow above code, i couldnot able to get sequence output.
void my_thread::operator ()(){
cvNamedWindow("tacka", CV_WINDOW_AUTOSIZE);
while (stop == false)
{
IplImage *temp;
if(queue.try_pop(temp)){
cvShowImage("tacka", temp);
cvWaitKey(1);
}
tbb::tick_count t0 = tbb::tick_count::now();
tbb::this_tbb_thread::sleep(tbb::tick_count::interval_t(.04));
tbb::tick_count t1 = tbb::tick_count::now();
printf("time%g \n",(t1-t0).seconds());
}
}
the time period is not .04 second. it is more than that. i have to showimage every .04 second. what is the best way to do it.
RafSchietekat
Black Belt
118 Views

You didn't specify how much more, and if you want to show 25 images per second you should sleep less than 40 ms.

Try to find a timer utility, or write your code to tune itself. TBB uses Sleep(), which has only millisecond granularity, and I don't know how well the scheduler supports it: perhaps this could be rewritten to busy-wait the last few milliseconds for better accuracy?
hitach__0
Beginner
118 Views

My code is working, but using sleep() method we cant sure that it will run every 40ms. because by using sleep() we are saying that, that thread will runat least40ms.
But i have to force that method to run on every 40ms. can weinterruptthat method on every 40ms?
I didnt understand why your mentioning timer utility, sleep() can support ms value (i think it support upto for decimal point).
are you saying that instead of sleep(), we have to use timer?
Thanks
RafSchietekat
Black Belt
118 Views

"are you saying that instead of sleep(), we have to use timer?"
If you want to drive nails, why not use a hammer...

(Added) That means: yes. :-)
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