Move subclassing infrastructure into the main bindings

And port Element bindings to the new infrastructure.

Gir_Gst.toml

@@ -312,6 +312,7 @@ status = "generate"
 
 [[object]]
 name = "Gst.Element"
+subclassing = true
 status = "generate"
     [[object.function]]
     name = "make_from_uri"

gstreamer/Cargo.toml

@@ -47,6 +47,7 @@ dox = ["gstreamer-sys/dox", "glib/dox", "futures", "ser_de"]
 futures = ["futures-core-preview"]
 ser_de = ["num-rational/serde", "serde", "serde_bytes", "serde_derive"]
 default-features = []
+subclassing = ["glib/subclassing"]
 
 [badges]
 gitlab = { repository = "https://gitlab.freedesktop.org/gstreamer/gstreamer-rs", branch = "master" }

gstreamer/src/auto/element.rs

@@ -33,8 +33,10 @@ use std::mem;
 use std::mem::transmute;
 use std::ptr;
 
+use ElementClass;
+
 glib_wrapper! {
-    pub struct Element(Object<ffi::GstElement, ffi::GstElementClass>): Object;
+    pub struct Element(Object<ffi::GstElement, ffi::GstElementClass, ElementClass>): Object;
 
     match fn {
         get_type => || ffi::gst_element_get_type(),

gstreamer/src/element.rs

@@ -16,7 +16,7 @@ use glib::translate::FromGlibPtrBorrow;
 use glib::translate::{
     from_glib, from_glib_full, from_glib_none, FromGlib, FromGlibPtrContainer, ToGlib, ToGlibPtr,
 };
-use glib::IsA;
+use glib::{IsA, IsClassFor};
 use miniobject::MiniObject;
 use Event;
 use Format;
@@ -29,6 +29,7 @@ use SpecificFormattedValue;
 
 use std::ffi::CStr;
 use std::mem;
+use std::ops;
 
 use libc;
 
@@ -92,6 +93,8 @@ impl FromGlib<libc::c_ulong> for NotifyWatchId {
 }
 
 pub trait ElementExtManual {
+    fn get_element_class(&self) -> &ElementClass;
+
     fn query(&self, query: &mut QueryRef) -> bool;
 
     fn send_event(&self, event: Event) -> bool;
@@ -192,6 +195,14 @@ pub trait ElementExtManual {
 }
 
 impl<O: IsA<Element>> ElementExtManual for O {
+    fn get_element_class(&self) -> &ElementClass {
+        unsafe {
+            let klass = (*(self.to_glib_none().0 as *mut gobject_ffi::GTypeInstance)).g_class
+                as *const ElementClass;
+            &*klass
+        }
+    }
+
     fn query(&self, query: &mut QueryRef) -> bool {
         unsafe {
             from_glib(ffi::gst_element_query(
@@ -211,41 +222,15 @@ impl<O: IsA<Element>> ElementExtManual for O {
     }
 
     fn get_metadata<'a>(&self, key: &str) -> Option<&'a str> {
-        unsafe {
+        self.get_element_class().get_metadata(key)
-            let klass = (*(self.to_glib_none().0 as *mut gobject_ffi::GTypeInstance)).g_class
-                as *mut ffi::GstElementClass;
-
-            let ptr = ffi::gst_element_class_get_metadata(klass, key.to_glib_none().0);
-
-            if ptr.is_null() {
-                None
-            } else {
-                Some(CStr::from_ptr(ptr).to_str().unwrap())
-            }
-        }
     }
 
     fn get_pad_template(&self, name: &str) -> Option<PadTemplate> {
-        unsafe {
+        self.get_element_class().get_pad_template(name)
-            let klass = (*(self.to_glib_none().0 as *mut gobject_ffi::GTypeInstance)).g_class
-                as *mut ffi::GstElementClass;
-
-            from_glib_none(ffi::gst_element_class_get_pad_template(
-                klass,
-                name.to_glib_none().0,
-            ))
-        }
     }
 
     fn get_pad_template_list(&self) -> Vec<PadTemplate> {
-        unsafe {
+        self.get_element_class().get_pad_template_list()
-            let klass = (*(self.to_glib_none().0 as *mut gobject_ffi::GTypeInstance)).g_class
-                as *mut ffi::GstElementClass;
-
-            FromGlibPtrContainer::from_glib_none(ffi::gst_element_class_get_pad_template_list(
-                klass,
-            ))
-        }
     }
 
     fn message_full<T: ::MessageErrorDomain>(
@@ -614,6 +599,67 @@ impl<O: IsA<Element>> ElementExtManual for O {
     }
 }
 
+#[repr(C)]
+pub struct ElementClass(ffi::GstElementClass);
+
+unsafe impl IsClassFor for ElementClass {
+    type Instance = ::Element;
+}
+
+unsafe impl Send for ElementClass {}
+unsafe impl Sync for ElementClass {}
+
+impl ops::Deref for ElementClass {
+    type Target = glib::ObjectClass;
+
+    fn deref(&self) -> &Self::Target {
+        self.upcast_ref()
+    }
+}
+
+impl ops::DerefMut for ElementClass {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        self.upcast_ref_mut()
+    }
+}
+
+impl ElementClass {
+    pub fn get_metadata<'a>(&self, key: &str) -> Option<&'a str> {
+        unsafe {
+            let klass = self as *const _ as *const ffi::GstElementClass;
+
+            let ptr = ffi::gst_element_class_get_metadata(klass as *mut _, key.to_glib_none().0);
+
+            if ptr.is_null() {
+                None
+            } else {
+                Some(CStr::from_ptr(ptr).to_str().unwrap())
+            }
+        }
+    }
+
+    pub fn get_pad_template(&self, name: &str) -> Option<PadTemplate> {
+        unsafe {
+            let klass = self as *const _ as *const ffi::GstElementClass;
+
+            from_glib_none(ffi::gst_element_class_get_pad_template(
+                klass as *mut _,
+                name.to_glib_none().0,
+            ))
+        }
+    }
+
+    pub fn get_pad_template_list(&self) -> Vec<PadTemplate> {
+        unsafe {
+            let klass = self as *const _ as *const ffi::GstElementClass;
+
+            FromGlibPtrContainer::from_glib_none(ffi::gst_element_class_get_pad_template_list(
+                klass as *mut _,
+            ))
+        }
+    }
+}
+
 lazy_static! {
     pub static ref ELEMENT_METADATA_AUTHOR: &'static str = unsafe {
         CStr::from_ptr(ffi::GST_ELEMENT_METADATA_AUTHOR)

gstreamer/src/lib.rs

@@ -16,12 +16,17 @@ extern crate cfg_if;
 extern crate lazy_static;
 extern crate libc;
 
-extern crate glib_sys as glib_ffi;
+// Re-exported for the subclass gst_plugin_define! macro
-extern crate gobject_sys as gobject_ffi;
+#[doc(hidden)]
-extern crate gstreamer_sys as ffi;
+pub extern crate glib_sys as glib_ffi;
+#[doc(hidden)]
+pub extern crate gobject_sys as gobject_ffi;
+#[doc(hidden)]
+pub extern crate gstreamer_sys as ffi;
 
 #[macro_use]
-extern crate glib;
+#[doc(hidden)]
+pub extern crate glib;
 
 extern crate num_rational;
 
@@ -143,6 +148,7 @@ pub use promise::*;
 mod bin;
 mod bus;
 mod element;
+pub use element::ElementClass;
 
 // OS dependent Bus extensions (also import the other plateform mod for doc)
 #[cfg(any(feature = "v1_14", feature = "dox"))]
@@ -330,3 +336,7 @@ pub mod prelude {
 }
 
 mod utils;
+
+#[macro_use]
+#[cfg(feature = "subclassing")]
+pub mod subclass;

gstreamer/src/subclass/element.rs

@@ -0,0 +1,365 @@
+// Copyright (C) 2017,2018 Sebastian Dröge <sebastian@centricular.com>
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use libc;
+
+use ffi;
+use glib_ffi;
+
+use super::prelude::*;
+use glib;
+use glib::prelude::*;
+use glib::subclass::prelude::*;
+use glib::translate::*;
+use prelude::*;
+
+use Element;
+use ElementClass;
+use Event;
+use PadTemplate;
+use QueryRef;
+use StateChange;
+use StateChangeReturn;
+
+pub trait ElementImpl: ObjectImpl + Send + Sync + 'static {
+    fn change_state(&self, element: &::Element, transition: StateChange) -> StateChangeReturn {
+        self.parent_change_state(element, transition)
+    }
+
+    fn request_new_pad(
+        &self,
+        _element: &::Element,
+        _templ: &::PadTemplate,
+        _name: Option<String>,
+        _caps: Option<&::CapsRef>,
+    ) -> Option<::Pad> {
+        None
+    }
+
+    fn release_pad(&self, _element: &::Element, _pad: &::Pad) {}
+
+    fn send_event(&self, element: &::Element, event: Event) -> bool {
+        self.parent_send_event(element, event)
+    }
+
+    fn query(&self, element: &::Element, query: &mut QueryRef) -> bool {
+        self.parent_query(element, query)
+    }
+
+    fn set_context(&self, element: &::Element, context: &::Context) {
+        self.parent_set_context(element, context)
+    }
+
+    fn parent_change_state(
+        &self,
+        element: &::Element,
+        transition: StateChange,
+    ) -> StateChangeReturn {
+        unsafe {
+            let data = self.get_type_data();
+            let parent_class = data.as_ref().get_parent_class() as *mut ffi::GstElementClass;
+
+            (*parent_class)
+                .change_state
+                .map(|f| from_glib(f(element.to_glib_none().0, transition.to_glib())))
+                .unwrap_or(::StateChangeReturn::Success)
+        }
+    }
+
+    fn parent_send_event(&self, element: &::Element, event: Event) -> bool {
+        unsafe {
+            let data = self.get_type_data();
+            let parent_class = data.as_ref().get_parent_class() as *mut ffi::GstElementClass;
+
+            (*parent_class)
+                .send_event
+                .map(|f| from_glib(f(element.to_glib_none().0, event.into_ptr())))
+                .unwrap_or(false)
+        }
+    }
+
+    fn parent_query(&self, element: &::Element, query: &mut QueryRef) -> bool {
+        unsafe {
+            let data = self.get_type_data();
+            let parent_class = data.as_ref().get_parent_class() as *mut ffi::GstElementClass;
+
+            (*parent_class)
+                .query
+                .map(|f| from_glib(f(element.to_glib_none().0, query.as_mut_ptr())))
+                .unwrap_or(false)
+        }
+    }
+
+    fn parent_set_context(&self, element: &::Element, context: &::Context) {
+        unsafe {
+            let data = self.get_type_data();
+            let parent_class = data.as_ref().get_parent_class() as *mut ffi::GstElementClass;
+
+            (*parent_class)
+                .set_context
+                .map(|f| f(element.to_glib_none().0, context.to_glib_none().0))
+                .unwrap_or(())
+        }
+    }
+}
+
+pub trait ElementImplExt {
+    fn catch_panic<
+        R,
+        F: FnOnce(&Self) -> R,
+        G: FnOnce() -> R,
+        P: IsA<::Element> + IsA<glib::Object> + glib::value::SetValue,
+    >(
+        &self,
+        element: &P,
+        fallback: G,
+        f: F,
+    ) -> R;
+
+    fn catch_panic_pad_function<R, F: FnOnce(&Self, &::Element) -> R, G: FnOnce() -> R>(
+        parent: &Option<::Object>,
+        fallback: G,
+        f: F,
+    ) -> R;
+}
+
+impl<T: ElementImpl + ObjectSubclass> ElementImplExt for T
+where
+    T::Instance: PanicPoison,
+{
+    fn catch_panic<
+        R,
+        F: FnOnce(&Self) -> R,
+        G: FnOnce() -> R,
+        P: IsA<::Element> + IsA<glib::Object> + glib::value::SetValue,
+    >(
+        &self,
+        element: &P,
+        fallback: G,
+        f: F,
+    ) -> R {
+        unsafe {
+            assert!(element.get_type().is_a(&T::static_type()));
+            let ptr: *mut ffi::GstElement = element.to_glib_none().0;
+            let instance = &*(ptr as *mut T::Instance);
+            let imp = instance.get_impl();
+
+            gst_panic_to_error!(element, &instance.panicked(), fallback(), { f(&imp) })
+        }
+    }
+
+    fn catch_panic_pad_function<R, F: FnOnce(&Self, &::Element) -> R, G: FnOnce() -> R>(
+        parent: &Option<::Object>,
+        fallback: G,
+        f: F,
+    ) -> R {
+        unsafe {
+            let wrap = parent
+                .as_ref()
+                .unwrap()
+                .downcast_ref::<::Element>()
+                .unwrap();
+            assert!(wrap.get_type().is_a(&T::static_type()));
+            let ptr: *mut ffi::GstElement = wrap.to_glib_none().0;
+            let instance = &*(ptr as *mut T::Instance);
+            let imp = instance.get_impl();
+
+            gst_panic_to_error!(wrap, &instance.panicked(), fallback(), { f(&imp, &wrap) })
+        }
+    }
+}
+
+pub unsafe trait ElementClassSubclassExt: Sized + 'static {
+    fn add_pad_template(&mut self, pad_template: PadTemplate) {
+        unsafe {
+            ffi::gst_element_class_add_pad_template(
+                self as *const Self as *mut ffi::GstElementClass,
+                pad_template.to_glib_none().0,
+            );
+        }
+    }
+
+    fn set_metadata(
+        &mut self,
+        long_name: &str,
+        classification: &str,
+        description: &str,
+        author: &str,
+    ) {
+        unsafe {
+            ffi::gst_element_class_set_metadata(
+                self as *const Self as *mut ffi::GstElementClass,
+                long_name.to_glib_none().0,
+                classification.to_glib_none().0,
+                description.to_glib_none().0,
+                author.to_glib_none().0,
+            );
+        }
+    }
+}
+
+unsafe impl ElementClassSubclassExt for ElementClass {}
+
+unsafe impl<T: ObjectSubclass + ElementImpl> IsSubclassable<T> for ElementClass
+where
+    <T as ObjectSubclass>::Instance: PanicPoison,
+{
+    fn override_vfuncs(&mut self) {
+        <glib::ObjectClass as IsSubclassable<T>>::override_vfuncs(self);
+
+        unsafe {
+            let klass = &mut *(self as *const Self as *mut ffi::GstElementClass);
+            klass.change_state = Some(element_change_state::<T>);
+            klass.request_new_pad = Some(element_request_new_pad::<T>);
+            klass.release_pad = Some(element_release_pad::<T>);
+            klass.send_event = Some(element_send_event::<T>);
+            klass.query = Some(element_query::<T>);
+            klass.set_context = Some(element_set_context::<T>);
+        }
+    }
+}
+
+unsafe extern "C" fn element_change_state<T: ObjectSubclass>(
+    ptr: *mut ffi::GstElement,
+    transition: ffi::GstStateChange,
+) -> ffi::GstStateChangeReturn
+where
+    T: ElementImpl,
+    T::Instance: PanicPoison,
+{
+    glib_floating_reference_guard!(ptr);
+    let instance = &*(ptr as *mut T::Instance);
+    let imp = instance.get_impl();
+    let wrap: Element = from_glib_borrow(ptr);
+
+    // *Never* fail downwards state changes, this causes bugs in GStreamer
+    // and leads to crashes and deadlocks.
+    let transition = from_glib(transition);
+    let fallback = match transition {
+        StateChange::PlayingToPaused | StateChange::PausedToReady | StateChange::ReadyToNull => {
+            StateChangeReturn::Success
+        }
+        _ => StateChangeReturn::Failure,
+    };
+
+    gst_panic_to_error!(&wrap, &instance.panicked(), fallback, {
+        imp.change_state(&wrap, transition)
+    })
+    .to_glib()
+}
+
+unsafe extern "C" fn element_request_new_pad<T: ObjectSubclass>(
+    ptr: *mut ffi::GstElement,
+    templ: *mut ffi::GstPadTemplate,
+    name: *const libc::c_char,
+    caps: *const ffi::GstCaps,
+) -> *mut ffi::GstPad
+where
+    T: ElementImpl,
+    T::Instance: PanicPoison,
+{
+    glib_floating_reference_guard!(ptr);
+    let instance = &*(ptr as *mut T::Instance);
+    let imp = instance.get_impl();
+    let wrap: Element = from_glib_borrow(ptr);
+
+    let caps = if caps.is_null() {
+        None
+    } else {
+        Some(::CapsRef::from_ptr(caps))
+    };
+
+    // XXX: This is effectively unsafe but the best we can do
+    // See https://bugzilla.gnome.org/show_bug.cgi?id=791193
+    let pad = gst_panic_to_error!(&wrap, &instance.panicked(), None, {
+        imp.request_new_pad(&wrap, &from_glib_borrow(templ), from_glib_none(name), caps)
+    });
+
+    // Ensure that the pad is owned by the element now, if a pad was returned
+    if let Some(ref pad) = pad {
+        assert_eq!(
+            pad.get_parent(),
+            Some(::Object::from_glib_borrow(ptr as *mut ffi::GstObject))
+        );
+    }
+
+    pad.to_glib_none().0
+}
+
+unsafe extern "C" fn element_release_pad<T: ObjectSubclass>(
+    ptr: *mut ffi::GstElement,
+    pad: *mut ffi::GstPad,
+) where
+    T: ElementImpl,
+    T::Instance: PanicPoison,
+{
+    glib_floating_reference_guard!(ptr);
+    let instance = &*(ptr as *mut T::Instance);
+    let imp = instance.get_impl();
+    let wrap: Element = from_glib_borrow(ptr);
+
+    gst_panic_to_error!(&wrap, &instance.panicked(), (), {
+        imp.release_pad(&wrap, &from_glib_borrow(pad))
+    })
+}
+
+unsafe extern "C" fn element_send_event<T: ObjectSubclass>(
+    ptr: *mut ffi::GstElement,
+    event: *mut ffi::GstEvent,
+) -> glib_ffi::gboolean
+where
+    T: ElementImpl,
+    T::Instance: PanicPoison,
+{
+    glib_floating_reference_guard!(ptr);
+    let instance = &*(ptr as *mut T::Instance);
+    let imp = instance.get_impl();
+    let wrap: Element = from_glib_borrow(ptr);
+
+    gst_panic_to_error!(&wrap, &instance.panicked(), false, {
+        imp.send_event(&wrap, from_glib_full(event))
+    })
+    .to_glib()
+}
+
+unsafe extern "C" fn element_query<T: ObjectSubclass>(
+    ptr: *mut ffi::GstElement,
+    query: *mut ffi::GstQuery,
+) -> glib_ffi::gboolean
+where
+    T: ElementImpl,
+    T::Instance: PanicPoison,
+{
+    glib_floating_reference_guard!(ptr);
+    let instance = &*(ptr as *mut T::Instance);
+    let imp = instance.get_impl();
+    let wrap: Element = from_glib_borrow(ptr);
+    let query = QueryRef::from_mut_ptr(query);
+
+    gst_panic_to_error!(&wrap, &instance.panicked(), false, {
+        imp.query(&wrap, query)
+    })
+    .to_glib()
+}
+
+unsafe extern "C" fn element_set_context<T: ObjectSubclass>(
+    ptr: *mut ffi::GstElement,
+    context: *mut ffi::GstContext,
+) where
+    T: ElementImpl,
+    T::Instance: PanicPoison,
+{
+    glib_floating_reference_guard!(ptr);
+    let instance = &*(ptr as *mut T::Instance);
+    let imp = instance.get_impl();
+    let wrap: Element = from_glib_borrow(ptr);
+
+    gst_panic_to_error!(&wrap, &instance.panicked(), (), {
+        imp.set_context(&wrap, &from_glib_borrow(context))
+    })
+}

gstreamer/src/subclass/error.rs

@@ -0,0 +1,93 @@
+// Copyright (C) 2016-2018 Sebastian Dröge <sebastian@centricular.com>
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use std::error::Error;
+use std::fmt::Error as FmtError;
+use std::fmt::{Display, Formatter};
+
+use ErrorMessage;
+use FlowReturn;
+
+#[macro_export]
+macro_rules! gst_panic_to_error(
+    ($element:expr, $panicked:expr, $ret:expr, $code:block) => {{
+        use std::panic::{self, AssertUnwindSafe};
+        use std::sync::atomic::Ordering;
+        use $crate::ElementExtManual;
+
+        if $panicked.load(Ordering::Relaxed) {
+            $element.post_error_message(&gst_error_msg!($crate::LibraryError::Failed, ["Panicked"]));
+            $ret
+        } else {
+            let result = panic::catch_unwind(AssertUnwindSafe(|| $code));
+
+            match result {
+                Ok(result) => result,
+                Err(err) => {
+                    $panicked.store(true, Ordering::Relaxed);
+                    if let Some(cause) = err.downcast_ref::<&str>() {
+                        $element.post_error_message(&gst_error_msg!($crate::LibraryError::Failed, ["Panicked: {}", cause]));
+                    } else if let Some(cause) = err.downcast_ref::<String>() {
+                        $element.post_error_message(&gst_error_msg!($crate::LibraryError::Failed, ["Panicked: {}", cause]));
+                    } else {
+                        $element.post_error_message(&gst_error_msg!($crate::LibraryError::Failed, ["Panicked"]));
+                    }
+                    $ret
+                }
+            }
+        }
+    }};
+);
+
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub enum FlowError {
+    Flushing,
+    Eos,
+    NotNegotiated(ErrorMessage),
+    Error(ErrorMessage),
+}
+
+impl From<FlowError> for FlowReturn {
+    fn from(err: FlowError) -> Self {
+        FlowReturn::from(&err)
+    }
+}
+
+impl<'a> From<&'a FlowError> for FlowReturn {
+    fn from(err: &FlowError) -> FlowReturn {
+        match *err {
+            FlowError::Flushing => FlowReturn::Flushing,
+            FlowError::Eos => FlowReturn::Eos,
+            FlowError::NotNegotiated(..) => FlowReturn::NotNegotiated,
+            FlowError::Error(..) => FlowReturn::Error,
+        }
+    }
+}
+
+impl Display for FlowError {
+    fn fmt(&self, f: &mut Formatter) -> Result<(), FmtError> {
+        match *self {
+            FlowError::Flushing | FlowError::Eos => f.write_str(self.description()),
+            FlowError::NotNegotiated(ref m) => {
+                f.write_fmt(format_args!("{}: {}", self.description(), m))
+            }
+            FlowError::Error(ref m) => f.write_fmt(format_args!("{}: {}", self.description(), m)),
+        }
+    }
+}
+
+impl Error for FlowError {
+    fn description(&self) -> &str {
+        match *self {
+            FlowError::Flushing => "Flushing",
+            FlowError::Eos => "Eos",
+            FlowError::NotNegotiated(..) => "Not Negotiated",
+            FlowError::Error(..) => "Error",
+        }
+    }
+}

gstreamer/src/subclass/mod.rs

@@ -0,0 +1,46 @@
+// Copyright (C) 2016-2018 Sebastian Dröge <sebastian@centricular.com>
+//               2016 Luis de Bethencourt <luisbg@osg.samsung.com>
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+#![cfg_attr(feature = "cargo-clippy", allow(cast_ptr_alignment))]
+
+#[macro_use]
+pub mod error;
+#[macro_use]
+pub mod plugin;
+
+pub mod element;
+
+pub mod prelude {
+    pub use super::element::{ElementClassSubclassExt, ElementImpl, ElementImplExt};
+    pub use super::PanicPoison;
+    pub use glib::subclass::prelude::*;
+}
+
+use self::prelude::*;
+use glib;
+use std::sync::atomic::AtomicBool;
+
+#[repr(C)]
+pub struct ElementInstanceStruct<T: ObjectSubclass> {
+    parent: <T::ParentType as glib::wrapper::Wrapper>::GlibType,
+    panicked: AtomicBool,
+}
+
+unsafe impl<T: ObjectSubclass> InstanceStruct for ElementInstanceStruct<T> {
+    type Type = T;
+}
+
+pub trait PanicPoison {
+    fn panicked(&self) -> &AtomicBool;
+}
+
+impl<T: ObjectSubclass> PanicPoison for ElementInstanceStruct<T> {
+    fn panicked(&self) -> &AtomicBool {
+        &self.panicked
+    }
+}

gstreamer/src/subclass/plugin.rs

@@ -0,0 +1,92 @@
+// Copyright (C) 2016-2018 Sebastian Dröge <sebastian@centricular.com>
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#[macro_export]
+macro_rules! gst_plugin_define(
+    ($name:expr, $description:expr, $plugin_init:ident,
+     $version:expr, $license:expr, $source:expr,
+     $package:expr, $origin:expr, $release_datetime:expr) => {
+        pub mod plugin_desc {
+            use $crate::glib::translate::{from_glib_borrow, ToGlib, from_glib};
+
+            const MAJOR_VERSION: i32 = 1;
+            const MINOR_VERSION: i32 = 8;
+
+            // Not using c_char here because it requires the libc crate
+            #[allow(non_camel_case_types)]
+            type c_char = i8;
+
+            #[repr(C)]
+            pub struct GstPluginDesc($crate::ffi::GstPluginDesc);
+            unsafe impl Sync for GstPluginDesc {}
+
+            #[no_mangle]
+            #[allow(non_upper_case_globals)]
+            pub static gst_plugin_desc: GstPluginDesc = GstPluginDesc($crate::ffi::GstPluginDesc {
+                major_version: MAJOR_VERSION,
+                minor_version: MINOR_VERSION,
+                name: $name as *const u8 as *const c_char,
+                description: $description as *const u8 as *const c_char,
+                plugin_init: Some(plugin_init_trampoline),
+                version: $version as *const u8 as *const c_char,
+                license: $license as *const u8 as *const c_char,
+                source: $source as *const u8 as *const c_char,
+                package: $package as *const u8 as *const c_char,
+                origin: $origin as *const u8 as *const c_char,
+                release_datetime: $release_datetime as *const u8 as *const c_char,
+                _gst_reserved: [0 as $crate::glib_ffi::gpointer; 4],
+            });
+
+            pub fn plugin_register_static() -> bool {
+                unsafe {
+                    from_glib($crate::ffi::gst_plugin_register_static(
+                        MAJOR_VERSION,
+                        MINOR_VERSION,
+                        $name as *const u8 as *const c_char,
+                        $description as *const u8 as *const c_char,
+                        Some(plugin_init_trampoline),
+                        $version as *const u8 as *const c_char,
+                        $license as *const u8 as *const c_char,
+                        $source as *const u8 as *const c_char,
+                        $package as *const u8 as *const c_char,
+                        $origin as *const u8 as *const c_char,
+                    ))
+                }
+            }
+
+            unsafe extern "C" fn plugin_init_trampoline(plugin: *mut $crate::ffi::GstPlugin) -> $crate::glib_ffi::gboolean {
+                use std::panic::{self, AssertUnwindSafe};
+
+                let panic_result = panic::catch_unwind(AssertUnwindSafe(|| super::$plugin_init(&from_glib_borrow(plugin))));
+                match panic_result {
+                    Ok(register_result) => match register_result {
+                        Ok(_) => $crate::glib_ffi::GTRUE,
+                        Err(err) => {
+                            let cat = $crate::DebugCategory::get("GST_PLUGIN_LOADING").unwrap();
+                            gst_error!(cat, "Failed to register plugin: {}", err);
+                            $crate::glib_ffi::GFALSE
+                        }
+                    }
+                    Err(err) => {
+                        let cat = $crate::DebugCategory::get("GST_PLUGIN_LOADING").unwrap();
+                        if let Some(cause) = err.downcast_ref::<&str>() {
+                            gst_error!(cat, "Failed to initialize plugin due to panic: {}", cause);
+                        } else if let Some(cause) = err.downcast_ref::<String>() {
+                            gst_error!(cat, "Failed to initialize plugin due to panic: {}", cause);
+                        } else {
+                            gst_error!(cat, "Failed to initialize plugin due to panic");
+                        }
+
+                        $crate::glib_ffi::GFALSE
+                    }
+                }
+            }
+        }
+        pub use plugin_desc::plugin_register_static;
+    };
+);