Tkinter - Memory Leak With Canvas

I have a Python script that handles Modbus communications. One feature I added was a 'graph' that shows the response times along with a color coded line that indicates if the respo

Solution 1:

The underlying tk canvas doesn't reuse or recycle object identifiers. Whenever you create a new object, a new identifier is generated. The memory of these objects is never reclaimed.

Note: this is memory inside the embedded tcl interpreter, rather than memory managed by python.

The solution is to reconfigure old, no longer used elements rather than deleting them and creating new ones.

Solution 2:

Here's the code with no memory leak. The original source of the leak was me deleting the old line then creating a new one. This solution moves the first the line to the end then change's its attributes as necessary. I had a second 'leak' in my example code where I was picking a random color each time which lead to the number of colors used eating up a lot of memory. This code just prints green lines but the length will be random.

import tkinter
from tkinter import Tk, Frame, Canvas, ALL
import random

defRGB(r, g, b):
    return'#{:02x}{:02x}{:02x}'.format(r, g, b)

classMainUI:
    def__init__(self, master):
        self.master = master
        self.lineList = []
        self.xPos = 0

        self.maxLine = 122

        self.responseIndex = 0 


        self.responseWidth = 100
        self.responseTimeCanvas = Canvas(self.master, height=self.responseWidth)
        self.responseTimeCanvas.pack()

        self.UpdateResponseTimeGraph()

    defUpdateResponseTimeGraph(self):
        self.lineLength   = random.randint(10,99)

        iflen(self.lineList) >= self.maxLine:
            self.lineLength = random.randint(5,95)
            self.responseTimeCanvas.coords(self.lineList[self.responseIndex % self.maxLine], self.xPos, self.responseWidth, self.xPos + 4, self.responseWidth-self.lineLength)

            self.responseTimeCanvas.itemconfig(self.lineList[self.responseIndex % self.maxLine], fill=RGB(100, 255, 100))
        else:
            self.lineList.append(self.responseTimeCanvas.create_rectangle(self.xPos, self.responseWidth, self.xPos + 4, self.responseWidth-self.lineLength, 
                                                fill=RGB(100, 255, 100), outline=''))


        self.xPos += 5#will cause the next line to start 5 pixels later. 
        self.responseIndex += 1

        self.responseTimeCanvas.config(scrollregion=self.responseTimeCanvas.bbox(ALL))

        self.responseTimeCanvas.xview_moveto(1.0) #move to the end of the canvas which is scrollable.



        self.responseTimeCanvas.after(10, self.UpdateResponseTimeGraph)


mw = Tk()
mainUI = MainUI(mw)
mw.mainloop()