gstreamer: Add object_lock method to gst::Object

See https://gitlab.freedesktop.org/gstreamer/gstreamer-rs/-/issues/439

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer-rs/-/merge_requests/1212>

gstreamer/src/lib.rs

@@ -252,6 +252,7 @@ pub mod functions;
 pub use crate::functions::*;
 
 mod utils;
+pub use crate::utils::ObjectLockGuard;
 
 #[cfg(any(feature = "v1_18", feature = "dox"))]
 mod gtype;

gstreamer/src/object.rs

@@ -28,6 +28,8 @@ pub trait GstObjectExtManual: 'static {
         interval: ClockTime,
         values: &mut [glib::Value],
     ) -> Result<(), glib::error::BoolError>;
+
+    fn object_lock(&self) -> crate::utils::ObjectLockGuard<Self>;
 }
 
 impl<O: IsA<crate::Object>> GstObjectExtManual for O {
@@ -118,6 +120,11 @@ impl<O: IsA<crate::Object>> GstObjectExtManual for O {
             )
         }
     }
+
+    #[inline]
+    fn object_lock(&self) -> crate::utils::ObjectLockGuard<Self> {
+        crate::utils::ObjectLockGuard::acquire(self)
+    }
 }
 
 #[cfg(test)]

gstreamer/src/utils.rs

@@ -35,3 +35,73 @@ pub trait Displayable {
 
     fn display(self) -> Self::DisplayImpl;
 }
+
+#[must_use = "if unused the object lock will immediately be released"]
+pub struct ObjectLockGuard<'a, T: ?Sized> {
+    obj: &'a T,
+    mutex: &'a mut glib::ffi::GMutex,
+}
+
+impl<'a, T> ObjectLockGuard<'a, T>
+where
+    T: glib::IsA<crate::Object> + ?Sized,
+{
+    #[inline]
+    pub fn acquire(obj: &'a T) -> ObjectLockGuard<'a, T> {
+        skip_assert_initialized!();
+        unsafe {
+            use glib::ObjectType;
+            let mutex = &mut (*obj.as_ref().as_ptr()).lock;
+            glib::ffi::g_mutex_lock(mutex);
+            Self { obj, mutex }
+        }
+    }
+}
+
+impl<T> AsRef<T> for ObjectLockGuard<'_, T> {
+    #[inline]
+    fn as_ref(&self) -> &T {
+        self.obj
+    }
+}
+
+impl<T> std::ops::Deref for ObjectLockGuard<'_, T> {
+    type Target = T;
+
+    #[inline]
+    fn deref(&self) -> &Self::Target {
+        self.obj
+    }
+}
+
+impl<T> std::fmt::Debug for ObjectLockGuard<'_, T>
+where
+    T: std::fmt::Debug,
+{
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        self.obj.fmt(f)
+    }
+}
+
+impl<T> std::cmp::PartialEq for ObjectLockGuard<'_, T>
+where
+    T: std::cmp::PartialEq,
+{
+    fn eq(&self, other: &Self) -> bool {
+        self.obj.eq(other)
+    }
+}
+
+impl<T> std::cmp::Eq for ObjectLockGuard<'_, T> where T: std::cmp::Eq {}
+
+impl<T> Drop for ObjectLockGuard<'_, T>
+where
+    T: ?Sized,
+{
+    #[inline]
+    fn drop(&mut self) {
+        unsafe {
+            glib::ffi::g_mutex_unlock(self.mutex);
+        }
+    }
+}