rusticl: add a safe abstraction to execute a DeleteContextCB

Reviewed-by: Karol Herbst <kherbst@redhat.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/25669>

src/gallium/frontends/rusticl/api/types.rs

@@ -1,4 +1,6 @@
 use crate::api::icd::CLResult;
+use crate::api::icd::ReferenceCountedAPIPointer;
+use crate::core::context::Context;
 
 use rusticl_opencl_gen::*;
 
@@ -110,6 +112,15 @@ cl_callback!(
     }
 );
 
+impl DeleteContextCB {
+    pub fn call(self, ctx: &Context) {
+        let cl = cl_context::from_ptr(ctx);
+        // SAFETY: `cl` must have pointed to an OpenCL context, which is where we just got it from.
+        // All other requirements are covered by this callback's type invariants.
+        unsafe { (self.func)(cl, self.data) };
+    }
+}
+
 cl_callback!(
     EventCB(FuncEventCB) {
         event: cl_event,

src/gallium/frontends/rusticl/core/context.rs

@@ -203,12 +203,11 @@ impl Context {
 
 impl Drop for Context {
     fn drop(&mut self) {
-        let cl = cl_context::from_ptr(self);
         self.dtors
             .lock()
             .unwrap()
-            .iter()
+            .drain(..)
             .rev()
-            .for_each(|cb| unsafe { (cb.func)(cl, cb.data) });
+            .for_each(|cb| cb.call(self));
     }
 }