Move SDL joystick scanning off the main thread#7491
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Setting SDL_HINT_JOYSTICK_THREAD=1 before SDL_InitSubSystem(SDL_INIT_JOYSTICK) tells SDL2 to run joystick polling and HID device-detection on a dedicated background thread, rather than processing them inline inside SDL_PollEvent on the main thread. Without this hint, every WM_DEVICECHANGE broadcast (which Windows sends when *any* HID device wakes, sleeps, or pulses the USB bus) causes SDL to walk every HID device class via SetupAPI / cfgmgr32 from inside SDL_PollEvent, stalling the frame loop for multiple seconds on machines with many HID peripherals - especially wireless Logitech mice and keyboards that periodically pulse the bus. Diagnosed via ProcMon stack capture on one affected user's machine, with the slow frame's call chain ending in SDL2.dll -> SETUPAPI.dll -> cfgmgr32.dll -> kernel registry queries against HKLM\System\CurrentControlSet\Enum\HID\*. With the hint enabled, that work happens on SDL's own thread and the main thread just dequeues already-collected events.
notimaginative
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Jun 1, 2026
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Should be fine, assuming that it resolves the reported problem. I don't believe there is any real downside with this for us whether it solves the problem or not.
I should note as well that this is the default setting for SDL3.
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Well according to Joe it does not actually solve the problem. It still looks like a good thing to do though. |
wookieejedi
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Jun 1, 2026
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Setting SDL_HINT_JOYSTICK_THREAD=1 before SDL_InitSubSystem(SDL_INIT_JOYSTICK) tells SDL2 to run joystick polling and HID device-detection on a dedicated background thread, rather than processing them inline inside SDL_PollEvent on the main thread.
Without this hint, every WM_DEVICECHANGE broadcast (which Windows sends when any HID device wakes, sleeps, or pulses the USB bus) causes SDL to walk every HID device class via SetupAPI / cfgmgr32 from inside SDL_PollEvent, stalling the frame loop for multiple seconds on machines with many HID peripherals - especially wireless Logitech mice and keyboards that periodically pulse the bus. Diagnosed via ProcMon stack capture on one affected user's machine, with the slow frame's call chain ending in SDL2.dll -> SETUPAPI.dll -> cfgmgr32.dll -> kernel registry queries against HKLM\System\CurrentControlSet\Enum\HID*.
With the hint enabled, that work happens on SDL's own thread and the main thread just dequeues already-collected events.
In draft pending confirmation via test.