Hi all,
A performance related question:
I've written a Cocoa app that continuously reads data from a USB device and
plots it on a graph. It consists of three of my own classes.
The first class is the model that submits asynchronous bulk reads to the USB
device. The callback for these reads copies the received data from the buffer
asynchronous filled by the request and into an NSData object that is allocated
and added to an NSArray. The buffer that the asynchronous request was using is
recycled into a new asynchronous request. So the pool of buffers is allocated
once and reused while the NSData objects are continuously allocated and
deallocated (when released by the controller).
The second class is the view that uses an NSTimer to call [self
setNeedsDisplay:YES] 24 times per second. The drawRect: method requests data
from the data source (the third, controller class) and draws it with OpenGL.
The third class is the controller class that serves as a data source for the
view. When the view calls the giveMeData: method, the controller class calls
the buffer: method in the model class, which removes and returns the oldest
NSData object in its NSArray. The controller then does some computations on it
and passes it off to the view in a new NSData object.
The application runs pretty well, and running it through the Leaks instrument
there are no leaks except for 16-bytes when the application is first starting
caused by IOUSBLib. However, looking at it in the Activity Monitor, the real
memory used starts off at 25 MB and steadily grows to 250+ MB while the virtual
memory starts off at about the same and steadily grows to about the same or
sometimes close to 500MB, over the course of several minutes. This especially
happens if I don't move the mouse for a while, or don't have the application in
focus. As soon as a move the mouse or bring the application into focus, it's as
if an autorelease pool is drained and the memory drops back down to 30-40MB
real and 30-40MB virtual. This is annoying since the application hangs for 5
seconds or so when this memory draining is occurring. Has anyone dealt with
this before? Any ideas on what could be causing this and how to work around it?
Another related question:
The number of asynchronous requests that the driver submits at once and the
maximum number of objects in the NSArray are set to some constant. Now in
theory, the requests should be added and drained "simultaneously" (i.e. by
separate threads), but if I make this constant larger, I notice a greater delay
between when data entering the USB device and being plotted. It's as if the
asynchronous requests are being filled and added to the NSArray all in a group,
and then drained by the view all in a group... maybe? Is this something subtle
from the way run loops work? Is the USB asynchronous bulk read run loop source
on the same thread as the view class's drawRect method?
My apologies for the length of this post and if the USB stuff isn't strictly
Cocoa related, but since it's so intertwined with Cocoa classes, I figured this
was the best place to ask. Advice is much appreciated. Please CC me on replies.
Chris
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