On Wed, Sep 16, 2009 at 8:04 PM, Jeff Peery <jeffpe...@yahoo.com> wrote: > > Hello, > Does anyone know if there is there a way to look at a queue's contents? Or > prevent duplicate messages from being put into a queue? The docs don't show > anything useful. The reason is that I'm collecting and drawing data. one > thread collects, and one thread draws. each time one sample is collected by > the collector thread, a "draw message" is put into the queue to notify the > drawing thread. the dataset is shared between the threads and is continuously > growing as data is appended. The queue is used to notify the drawing thread > that it should draw. I use threading.Lock() to prevent any "sharing issues". > > The problem is that if the data collector thread is putting messages into the > queue faster than the drawing thread is getting them, then the drawing thread > is forced to redraw more times than it needs to and appears slow. However > since the dataset is shared the drawing thread only needs to draw once to be > updated for all the new samples. For example if 10 samples have been appended > by the data collector thread while the drawing thread drew once, then there > are now 10 messages for the drawing thread to get. yet it only needs to draw > once to reflect the 10 samples. so there are 9 redraws that are a waste of > energy.
It sounds like what you really want is a flag. The collector thread sets the flag when data is available, the draw thread clears the flag when it starts to draw. If the flag is set multiple times before the draw, it still only triggers one draw. Take a look at threading.Event, it might work better than Queue. You could try to use qsize() to avoid putting an item in the queue if there is already something there, but you may have to introduce additional locks to avoid race conditions. Kent _______________________________________________ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
