Segmentation fault on huge physics lag

[Astralcircle]

Took your example from #47, tested on the latest dev build (main gmod branch).

Desktop.2025.08.23.-.16.55.47.01.mp4

Start params: -game garrysmod -tickrate 33 +gamemode sandbox +map gm_construct -maxplayers 32 -usegh -holylib_startdisabled -holylib_enable_networking 1 -holylib_enable_physenv 1 -holylib_enable_precachefix 1 -debug

For some reason, if i suddenly put a lot of entities in one point, it will cause a segmentation fault.
This does not happen until the code from #47 is run

[RaphaelIT7]

Could you possibly send the debug.log file? 👀

[Astralcircle]

Could you possibly send the debug.log file? 👀

There's nothing useful in it

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CRASH: Sat Aug 23 17:05:20 +03 2025
Start Line: ./srcds_linux -game garrysmod -tickrate 33 +gamemode sandbox +map gm_construct -maxplayers 32 -usegh -holylib_startdisabled -holylib_enable_networking 1 -holylib_enable_physenv 1 -holylib_enable_precachefix 1 -debug
End of Source crash report
----------------------------------------------

[RaphaelIT7]

It seems like the entire physics engine is killing itself because of the SetCollisionGroup call...
This is going to be a fun one

[Astralcircle]

It seems like the entire physics engine is killing itself because of the SetCollisionGroup call... This is going to be a fun one

It crashes even if i don't change the collision group, but it seems like it's harder to achieve then

[RaphaelIT7]

It seems to be related to RecheckCollisionFilter which is called by both SetCollisionGroup and EnableMotion

[RaphaelIT7]

Should also be noted that I can reproduce this crash in HolyLib's ivp build which makes it easier to debug xd

[Astralcircle]

great! i hope you can fix this before prerelease 😫

[RaphaelIT7]

It seems to be specifically when IVP_U_Min_List::add triggers the OnPhysicsLag call and IVP_SkipSimulation is returned.

great! i hope you can fix this before prerelease 😫

I'll think that I can get this fixed today/it should be fixed before the prerelease

[RaphaelIT7]

I think I might have a guess. The example changes the collision rules of all physics objects, though IVP_U_Min_List::add can trigger the hook in the middle of IVP_Mindist_Manager::recheck_ov_element and changing collision rules causes a call to IVP_Mindist_Manager::recheck_ov_element so the issue probably is that it calls recheck_ov_element while recheck_ov_element is being called for the physics object.

[RaphaelIT7]

My comment predicted this...

It seems to work stable with this:

physenv.SetLagThreshold(50)

hook.Add("HolyLib:OnPhysicsLag", "Test", function(delta, phys1, ent1, phys2, ent2, callerFunc)
    local mainEnv = physenv.GetActiveEnvironmentByIndex(0)
    local simulating = mainEnv:IsInSimulation()
    print("Tiggered OnPhysicsLag!", mainEnv, simulating, callerFunc)
    --if callerFunc == "IVP_Mindist_Minimize_Solver::p_minimize_PP" then return physenv.IVP_Die end
            
    mainEnv:SetInSimulation(false)
    for _, v in ipairs(ents.GetAll()) do
        local phys = v:GetPhysicsObject()
	
        if phys:IsValid() and phys != phys1 and phys != phys2 then -- Never modify the currently used physObjects!
            if phys:IsPenetrating() then
                v:SetCollisionGroup(COLLISION_GROUP_WORLD)
            end

            phys:EnableMotion(false)
        end
    end
    mainEnv:SetInSimulation(simulating)

    return physenv.IVP_SkipSimulation
end)

when the callerFunc is IVP_Mindist_Minimize_Solver::p_minimize_PP, it can be inside of a recheck_ov_element and if you change the collision rules as I had already described, it will cause a recheck_ov_element inside of the current recheck_ov_element and then it dies.

[RaphaelIT7]

This should be stable now:

physenv.SetLagThreshold(50)

hook.Add("HolyLib:OnPhysicsLag", "Test", function(delta, phys1, phys2, recalcPhys, callerFunc)
    local mainEnv = physenv.GetActiveEnvironmentByIndex(0)
    local simulating = mainEnv:IsInSimulation()
    print("Tiggered OnPhysicsLag!", mainEnv, simulating, callerFunc)
            
    mainEnv:SetInSimulation(false)
    for _, v in ipairs(ents.GetAll()) do
        local phys = v:GetPhysicsObject()
	
        if phys:IsValid() and phys != recalcPhys then
            if phys:IsPenetrating() then
                v:SetCollisionGroup(COLLISION_GROUP_WORLD)
            end

            phys:EnableMotion(false)
        end
    end
    mainEnv:SetInSimulation(simulating)

    return physenv.IVP_SkipSimulation
end)