There are better ways to draw donuts:

There is the undocumented breakShape() function. From the source code: "This feature is in testing, do not use or rely upon its implementation"

PhiL and tf - thank you for your suggestions! I ended up not using either because:
a) I want the curve shape to be a direct representation of a plot from a data file, which is possible with PhiL's approach, but somewhat masked. I opted to maintain the curveVertex approach so that the plotting of individual data points was transparent in the code.
b) I want my code to be portable, documented, and stable (though I do love finding out about features in testing, so thank you tf!)

I ended up coming up with the following approach, which I wanted to share in case anyone else has a similar type of project:

(pseudocode):

1. float x, y;
2. int torWidth = 10;
   
3. fill(bgColor);
4. 
   
5. beginShape();
6. // Draw outer edge of donut
   
7. for (int i = 0; i < ptsInCircle; i++){
8.       //...compute r, theta...
9.       x = r*cos(theta);
10.       y = r*sin(theta);
    
11.       curveVertex(x,y);
12. }
13. // trace inner edge of donut, in OPPOSITE direction
    
14. for (int i = ptsInCircle-1; i >= 0 ; i--){
15.       //...compute r, theta...
16.       x = (r-torWidth)*cos(theta);
17.       y = (r-torWidth)*sin(theta);
18.       curveVertex(x,y);
19. }
20. endShape();