If subprocess is disabled, what sort of issues can happen?

[Ali Anwar]

From the README: "Disabling this option makes performance much better, but it may cause problems in some cases."

What sort of issues have you run into when calling mss in the same process?
In-process performance is substantially better, but I'm curious to know what sort of issues can arise.

[ponty]

There are different issues with different backends.
MSS doesn't support multiple X displays, so this will crash:

import mss
from pyvirtualdisplay import Display

with Display():
    sct = mss.mss()
    img = sct.grab((10, 20, 30, 40))
    print(img)
with Display():
    sct = mss.mss()
    img = sct.grab((10, 20, 30, 40))
    print(img)

Test is in double_disp.py

mss code:

    def _get_display(self, disp=None):
        """
        Retrieve a thread-safe display from XOpenDisplay().
        In multithreading, if the thread who creates *display* is dead, *display* will
        no longer be valid to grab the screen. The *display* attribute is replaced
        with *_display_dict* to maintain the *display* values in multithreading.
        Since the current thread and main thread are always alive, reuse their
        *display* value first.
        """
        cur_thread, main_thread = threading.current_thread(), threading.main_thread()
        display = MSS._display_dict.get(cur_thread) or MSS._display_dict.get(
            main_thread
        )
        if not display:
            display = MSS._display_dict[cur_thread] = self.xlib.XOpenDisplay(disp)
        return display

The problem is that it reuses the display.

[Ali Anwar]

Got it. I'll be sure to keep that in mind as I use multiple displays.
For my use case, I'll try to limit it to a single display and use mss, because it is so fast.
Thanks!