Do not allow a null CEGLSync to reach doOnReadable

[myQwil]

Describe your PR, what does it fix/add?

The function CEventLoopManager::doOnReadable is expecting its first parameter to be a non-null value, but CEGLSync::create can potentially return a nullptr.

If m_sync is null, and it reaches doOnReadable, Hyprland will crash.

Is there anything you want to mention? (unchecked code, possible bugs, found problems, breaking compatibility, etc.)

This is one way of addressing the problem, but there may be a better one. For example, maybe the null check should happen directly in doOnReadable. Here, I'm checking only where a null value might potentially reach the function.

Is it ready for merging, or does it need work?

It's ready for merging.

[gulafaran]

you could use the isValid to catch more cases.

    if (!m_sync->isValid()) {
        Debug::log(ERR, "onFinishRender: failed to create CEGLSync, skipping.");
        return;
    }

question is if it should call onSyncFired directly then or return?

[myQwil]

I'm not sure that'll work. CFileDescriptor::isValid() is also expecting a non-null value, plus doOnReadable already calls the isValid() function

[gulafaran]

I'm not sure that'll work. CFileDescriptor::isValid() is also expecting a non-null value, plus doOnReadable already calls the isValid() function

oh lol the CEGLSync::isValid() is rather broken indeed, if the creation fails nullptr is returned. and isValid wont work.

[myQwil]

Actually, never mind. I think the problem is m_sync->fd().duplicate(), so it never even enters the function doOnReadable. Instead, it crashes while trying to perform fd().duplicate()

[gulafaran]

Actually, never mind. I think the problem is m_sync->fd().duplicate(), so it never even enters the function doOnReadable. Instead, it crashes while trying to perform fd().duplicate()

when is this crashing?

[gulafaran]

ah renderer does this,

Hyprland/src/render/Renderer.cpp

Line 2316 in 9517d0e

if (eglSync && eglSync->isValid()) {

so do something similiar i guess?

[myQwil]

when is this crashing?

When trying to run a debug build of Hyprland, it was crashing while starting up. It has something to do with eglCreateSyncKHR failing.

[gulafaran]

when is this crashing?

I'm trying to run a debug build of Hyprland and it crashes while starting up. It has to do with eglCreateSyncKHR failing.

void CMonitorFrameScheduler::onFinishRender() {
    m_sync = CEGLSync::create(); // this destroys the old sync

    if(m_sync && m_sync->isValid()) {
        g_pEventLoopManager->doOnReadable(m_sync->fd().duplicate(), [this, mon = m_monitor] {
            if (!m_monitor) // might've gotten destroyed
                return;
            onSyncFired();
        });
    }
    else
        Debug::log(ERR, "onFinishRender: failed to create CEGLSync, skipping.");
}

now the question still remains if at the end it should just call onSyncFired() anyways.
@vaxerski

[vaxerski]

if we can't sync, we should not try to triple buffer, as it won't work. Entire pipeline should be skipped and fallback to standard frame sync should be used