Ximagesink segfault on element.name() (custom rust tracer)

Plugin and library development
1

Summary

When using ximagesink in a pipeline, element.name().as_str() panics on its child GstVideoSink.

Minimal Reproduction Steps

Impl a custom tracer that registers element_post_message_pre and prints the element name that posted the message

use gst::glib;
use gst::prelude::*;
use gst::subclass::prelude::*;
use once_cell::sync::Lazy;

glib::wrapper! {
    pub struct TestTracer(ObjectSubclass<TestTracerImp>) @extends gst::Tracer, gst::Object;
}

pub fn register(plugin: &gst::Plugin) -> Result<(), glib::BoolError> {
    gst::Tracer::register(Some(plugin), "test-tracer", TestTracer::static_type())
}

static CAT: Lazy<gst::DebugCategory> =
    Lazy::new(|| gst::DebugCategory::new("test-tracer", gst::DebugColorFlags::empty(), Some("")));

#[derive(Default)]
pub struct TestTracerImp {}

#[glib::object_subclass]
impl ObjectSubclass for TestTracerImp {
    const NAME: &'static str = "GstTestTracer";
    type Type = TestTracer;
    type ParentType = gst::Tracer;
}

impl ObjectImpl for TestTracerImp {
    fn constructed(&self) {
        self.parent_constructed();
        self.register_hook(TracerHook::ElementPostMessagePre);
    }
}

impl GstObjectImpl for TestTracerImp {}

impl TracerImpl for TestTracerImp {
    fn element_post_message_pre(&self, _ts: u64, element: &gst::Element, message: &gst::Message) {
        println!("element class name = {}", element.class().type_().name());
        println!("element name = {}", element.name().as_str()); // panics here
    }
}

compile and run:

RUST_BACKTRACE=full GST_TRACERS=test-tracer gst-launch-1.0 -v videotestsrc ! queue ! ximagesink

You will notice that println!("element class name = {}", element.class().type_().name()); will print: element class name = GstVideoSink. And then it will panic on this line: println!("element name = {}", element.name().as_str());

stdout and backtrace:

element class name = GstVideoSink
thread '<unnamed>' panicked at /home/jaydenelliott/.cargo/git/checkouts/gtk-rs-core-7be42ca38bd6361c/8922643/glib/src/gstring.rs:1917:9:
assertion failed: !ptr.is_null()
stack backtrace:
   0:     0x7ae2268042e6 - std::backtrace_rs::backtrace::libunwind::trace::hbee8a7973eeb6c93
                               at /rustc/07dca489ac2d933c78d3c5158e3f43beefeb02ce/library/std/src/../../backtrace/src/backtrace/libunwind.rs:104:5
   1:     0x7ae2268042e6 - std::backtrace_rs::backtrace::trace_unsynchronized::hc8ac75eea3aa6899
                               at /rustc/07dca489ac2d933c78d3c5158e3f43beefeb02ce/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   2:     0x7ae2268042e6 - std::sys_common::backtrace::_print_fmt::hc7f3e3b5298b1083
                               at /rustc/07dca489ac2d933c78d3c5158e3f43beefeb02ce/library/std/src/sys_common/backtrace.rs:68:5
   3:     0x7ae2268042e6 - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::hbb235daedd7c6190
                               at /rustc/07dca489ac2d933c78d3c5158e3f43beefeb02ce/library/std/src/sys_common/backtrace.rs:44:22
   4:     0x7ae226822e50 - core::fmt::rt::Argument::fmt::h76c38a80d925a410
                               at /rustc/07dca489ac2d933c78d3c5158e3f43beefeb02ce/library/core/src/fmt/rt.rs:142:9
   5:     0x7ae226822e50 - core::fmt::write::h3ed6aeaa977c8e45
                               at /rustc/07dca489ac2d933c78d3c5158e3f43beefeb02ce/library/core/src/fmt/mod.rs:1120:17
   6:     0x7ae22680274f - std::io::Write::write_fmt::h78b18af5775fedb5
                               at /rustc/07dca489ac2d933c78d3c5158e3f43beefeb02ce/library/std/src/io/mod.rs:1810:15
   7:     0x7ae2268040c4 - std::sys_common::backtrace::_print::h5d645a07e0fcfdbb
                               at /rustc/07dca489ac2d933c78d3c5158e3f43beefeb02ce/library/std/src/sys_common/backtrace.rs:47:5
   8:     0x7ae2268040c4 - std::sys_common::backtrace::print::h85035a511aafe7a8
                               at /rustc/07dca489ac2d933c78d3c5158e3f43beefeb02ce/library/std/src/sys_common/backtrace.rs:34:9
   9:     0x7ae226805437 - std::panicking::default_hook::{{closure}}::hcce8cea212785a25
  10:     0x7ae226805199 - std::panicking::default_hook::hf5fcb0f213fe709a
                               at /rustc/07dca489ac2d933c78d3c5158e3f43beefeb02ce/library/std/src/panicking.rs:292:9
  11:     0x7ae2268058c8 - std::panicking::rust_panic_with_hook::h095fccf1dc9379ee
                               at /rustc/07dca489ac2d933c78d3c5158e3f43beefeb02ce/library/std/src/panicking.rs:779:13
  12:     0x7ae226805769 - std::panicking::begin_panic_handler::{{closure}}::h032ba12139b353db
                               at /rustc/07dca489ac2d933c78d3c5158e3f43beefeb02ce/library/std/src/panicking.rs:649:13
  13:     0x7ae2268047e6 - std::sys_common::backtrace::__rust_end_short_backtrace::h9259bc2ff8fd0f76
                               at /rustc/07dca489ac2d933c78d3c5158e3f43beefeb02ce/library/std/src/sys_common/backtrace.rs:171:18
  14:     0x7ae226805500 - rust_begin_unwind
                               at /rustc/07dca489ac2d933c78d3c5158e3f43beefeb02ce/library/std/src/panicking.rs:645:5
  15:     0x7ae2267c3e95 - core::panicking::panic_fmt::h784f20a50eaab275
                               at /rustc/07dca489ac2d933c78d3c5158e3f43beefeb02ce/library/core/src/panicking.rs:72:14
  16:     0x7ae2267c3f53 - core::panicking::panic::hb837a5ebbbe5b188
                               at /rustc/07dca489ac2d933c78d3c5158e3f43beefeb02ce/library/core/src/panicking.rs:144:5
  17:     0x7ae2267dcba5 - <glib::gstring::GString as glib::translate::FromGlibPtrFull<*mut u8>>::from_glib_full::h1b8b04581948e288
                               at /home/jaydenelliott/.cargo/git/checkouts/gtk-rs-core-7be42ca38bd6361c/8922643/glib/src/gstring.rs:1917:9
  18:     0x7ae2267dabb6 - glib::translate::from_glib_full::ha7644b08b41f2461
                               at /home/jaydenelliott/.cargo/git/checkouts/gtk-rs-core-7be42ca38bd6361c/8922643/glib/src/translate.rs:1634:5
  19:     0x7ae2267dcc57 - <glib::gstring::GString as glib::translate::FromGlibPtrFull<*mut i8>>::from_glib_full::he05ade9901dd6ad3
                               at /home/jaydenelliott/.cargo/git/checkouts/gtk-rs-core-7be42ca38bd6361c/8922643/glib/src/gstring.rs:1933:9
  20:     0x7ae2267dabd6 - glib::translate::from_glib_full::hb4d083adabcca2cc
                               at /home/jaydenelliott/.cargo/git/checkouts/gtk-rs-core-7be42ca38bd6361c/8922643/glib/src/translate.rs:1634:5
  21:     0x7ae2267c4ab4 - gstreamer::auto::object::GstObjectExt::name::hdd347312df1b3e93
                               at /home/jaydenelliott/.cargo/git/checkouts/gstreamer-rs-79e52a2d27eb91a3/7433ea7/gstreamer/src/auto/object.rs:115:18
  22:     0x7ae2267cc2ca - <gstrstutorial::test_tracer::TestTracerImp as gstreamer::subclass::tracer::TracerImpl>::element_post_message_pre::hfffa73505a7ce453
                               at /home/jaydenelliott/Repos/temp-rs/src/test_tracer.rs:39:39
  23:     0x7ae2267c7719 - <T as gstreamer::subclass::tracer::TracerImplExt>::register_hook::callback::h56ab9e5e023f5a41
                               at /home/jaydenelliott/.cargo/git/checkouts/gstreamer-rs-79e52a2d27eb91a3/7433ea7/gstreamer/src/subclass/tracer.rs:184:9
  24:     0x7ae226fcf823 - gst_element_post_message
  25:     0x7ae22617a8de - <unknown>
  26:     0x7ae226e0405b - g_type_create_instance
  27:     0x7ae226de9b11 - <unknown>
  28:     0x7ae226deb0c7 - g_object_new_with_properties
  29:     0x7ae226fda2d5 - gst_element_factory_create_with_properties
  30:     0x7ae226fa2332 - <unknown>
  31:     0x7ae227054f48 - gst_parse_launch_full
  32:     0x7ae22705614b - gst_parse_launchv_full
  33:     0x625de4b58705 - <unknown>
  34:     0x7ae226c0acd0 - <unknown>
  35:     0x7ae226c0ad8a - __libc_start_main
  36:     0x625de4b56055 - <unknown>
  37:                0x0 - <unknown>
fatal runtime error: failed to initiate panic, error 5
[1]    347064 IOT instruction (core dumped)  RUST_BACKTRACE=full GST_TRACERS=test-tracer gst-launch-1.0 -v videotestsrc !

Setup

gst-launch-1.0 --version                           
gst-launch-1.0 version 1.24.1
GStreamer 1.24.1
https://www.archlinux.org/

Any help would be appreciated

2

When your TestTracer processes the first message, the element which posted this message is still being initialized and its name is not assigned yet. The gst::Object::name() accessor builds a GString assuming the underlying C string is not NULL, which is acceptable in most cases. As a workaround, you could use:

    println!(
        "element name {:?}",
        element.property::<Option<glib::GString>>("name")
    );
1 Like
3

It sounds like you’re running into this bug: Avoid setting state, posting message or sending query when constructing objects (#2794) · Issues · GStreamer / gstreamer · GitLab

Since you’re using GStreamer 1.24, you could also check if the GstObject CONSTRUCTED flag is set.

1 Like