[core] Crash on Transform::setScale()

[tmpsantos]

Also observed when calling Map::setZoom() using padding repeatedly which internally calls Transform::setScale().

https://travis-ci.org/mapbox/mapbox-gl-native/jobs/103073819#L1353

Program received signal SIGSEGV, Segmentation fault.
std::_Function_handler<mbgl::Update (std::chrono::time_point<std::chrono::_V2::steady_clock, std::chrono::duration<long, std::ratio<1l, 1000000000l> > >), mbgl::Transform::startTransition(mbgl::CameraOptions const&, mbgl::AnimationOptions const&, std::function<mbgl::Update (double)>, std::chrono::duration<long, std::ratio<1l, 1000000000l> > const&)::{lambda(std::chrono::time_point<std::chrono::_V2::steady_clock, std::chrono::duration<long, std::ratio<1l, 1000000000l> > >)#1}>::_M_invoke(std::_Any_data const&, std::chrono::time_point<std::chrono::_V2::steady_clock, std::chrono::duration<long, std::ratio<1l, 1000000000l> > >) () at /usr/include/c++/4.9/functional:2275
2275        if (_M_manager)
Thread 1 (Thread 0x2aaaaaaf2580 (LWP 12797)):
#0  std::_Function_handler<mbgl::Update (std::chrono::time_point<std::chrono::_V2::steady_clock, std::chrono::duration<long, std::ratio<1l, 1000000000l> > >), mbgl::Transform::startTransition(mbgl::CameraOptions const&, mbgl::AnimationOptions const&, std::function<mbgl::Update (double)>, std::chrono::duration<long, std::ratio<1l, 1000000000l> > const&)::{lambda(std::chrono::time_point<std::chrono::_V2::steady_clock, std::chrono::duration<long, std::ratio<1l, 1000000000l> > >)#1}>::_M_invoke(std::_Any_data const&, std::chrono::time_point<std::chrono::_V2::steady_clock, std::chrono::duration<long, std::ratio<1l, 1000000000l> > >) () at /usr/include/c++/4.9/functional:2275
#1  0x00000000005df9d4 in mbgl::Transform::startTransition(mbgl::CameraOptions const&, mbgl::AnimationOptions const&, std::function<mbgl::Update (double)>, std::chrono::duration<long, std::ratio<1l, 1000000000l> > const&) () at /usr/include/c++/4.9/functional:2439
#2  0x00000000005e0351 in mbgl::Transform::easeTo(mbgl::CameraOptions const&, mbgl::AnimationOptions const&) () at ../../src/mbgl/map/transform.cpp:145
#3  0x00000000005e0cbe in mbgl::Transform::setScale(double, mbgl::vec2<double> const&, std::chrono::duration<long, std::ratio<1l, 1000000000l> > const&) () at ../../src/mbgl/map/transform.cpp:416
#4  0x00000000004c7d9b in Transform_InvalidScale_Test::TestBody() () at ../../test/miscellaneous/transform.cpp:16
#5  0x00000000006e68a3 in void testing::internal::HandleSehExceptionsInMethodIfSupported<testing::Test, void>(testing::Test*, void (testing::Test::*)(), char const*) ()

/cc @1ec5

[tmpsantos]

The backtrace is not very helpful because lambdas. Manually keeping track of function calls I found out that the crash has something to do with recursion.

The usually looks like:

void mbgl::Transform::setScale(double, const PrecisionPoint&, const Duration&) {
    void mbgl::Transform::easeTo(const mbgl::CameraOptions&, const mbgl::AnimationOptions&) {
    }
}

But when it crashes, what I get is:

void mbgl::Transform::setScale(double, const PrecisionPoint&, const Duration&) {
    void mbgl::Transform::easeTo(const mbgl::CameraOptions&, const mbgl::AnimationOptions&) {
        void mbgl::Transform::setLatLng(const mbgl::LatLng&, const mbgl::EdgeInsets&, const Duration&) {
            void mbgl::Transform::easeTo(const mbgl::CameraOptions&, const mbgl::AnimationOptions&) {
            }
        }
        void mbgl::Transform::setLatLng(const mbgl::LatLng&, const mbgl::EdgeInsets&, const Duration&) {
            void mbgl::Transform::easeTo(const mbgl::CameraOptions&, const mbgl::AnimationOptions&) {
            }
        }
        void mbgl::Transform::setLatLng(const mbgl::LatLng&, const mbgl::EdgeInsets&, const Duration&) {
            void mbgl::Transform::easeTo(const mbgl::CameraOptions&, const mbgl::AnimationOptions&) {
            }
        }
        void mbgl::Transform::setLatLng(const mbgl::LatLng&, const mbgl::EdgeInsets&, const Duration&) {
            void mbgl::Transform::easeTo(const mbgl::CameraOptions&, const mbgl::AnimationOptions&) {
            }
        }
        CRASH!

So easeTo is calling setLatLng which call easeTo again. Possibly invalidating the state set by setScale.

[tmpsantos]

The issue lies on calling view.notifyMapChange(isAnimated ? MapChangeRegionDidChangeAnimated : MapChangeRegionDidChange); that depending on what the client is doing, can cause the recursion.

[1ec5]

As a rule, MGLMapView responds to these notifications by calling out to the main thread asynchronously, avoiding any recursion. Maybe we can put in a guard of some sort to fail sooner instead of crashing this way.

[tmpsantos]

As a rule, MGLMapView responds to these notifications by calling out to the main thread asynchronously, avoiding any recursion. Maybe we can put in a guard of some sort to fail sooner instead of crashing this way.

The problem of responding this async is that if you wanna paint things on top of the map in sync with the transform, you are always going to be one frame behind.

[tmpsantos]

Closing as it was mostly an API misuse from my side.

[1ec5]

What explains the failure on Travis, then? Has that crash appeared since?

[tmpsantos]

What explains the failure on Travis, then? Has that crash appeared since?

I've not seen this one on Travis again.

I ran the utests literally thousand times trying to reproduce without success. We can re-open if we ever see it again.