Fix cuCtxPopCurrent (#519)

zluda/src/impl/context.rs

@@ -188,12 +188,25 @@ pub(crate) unsafe fn push_current_v2(ctx: CUcontext) -> CUresult {
     push_current(ctx)
 }
 
-pub(crate) unsafe fn pop_current(ctx: &mut CUcontext) -> CUresult {
+pub(crate) unsafe fn pop_current(result: Option<&mut CUcontext>) -> CUresult {
-    STACK.with(|stack| {
+    let old_ctx_and_new_device = STACK.with(|stack| {
-        if let Some((_ctx, _)) = stack.borrow_mut().pop() {
+        let mut stack = stack.borrow_mut();
-            *ctx = _ctx;
+        stack
-        }
+            .pop()
+            .map(|(ctx, _)| (ctx, stack.last().map(|(_, dev)| *dev)))
     });
+    let ctx = match old_ctx_and_new_device {
+        Some((old_ctx, new_device)) => {
+            if let Some(new_device) = new_device {
+                hipSetDevice(new_device)?;
+            }
+            old_ctx
+        }
+        None => return CUresult::ERROR_INVALID_CONTEXT,
+    };
+    if let Some(out) = result {
+        *out = ctx;
+    }
     Ok(())
 }
 
@@ -213,7 +226,7 @@ pub(crate) unsafe fn destroy_v2(ctx: CUcontext) -> CUresult {
     zluda_common::drop_checked::<Context>(ctx)
 }
 
-pub(crate) unsafe fn pop_current_v2(ctx: &mut CUcontext) -> CUresult {
+pub(crate) unsafe fn pop_current_v2(ctx: Option<&mut CUcontext>) -> CUresult {
     pop_current(ctx)
 }
 
@@ -241,3 +254,27 @@ pub(crate) unsafe fn get_api_version(
     *version = 3020;
     Ok(())
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::tests::CudaApi;
+    use cuda_macros::test_cuda;
+    use std::mem;
+
+    #[test_cuda]
+    fn empty_pop_fails(api: impl CudaApi) {
+        api.cuInit(0);
+        assert_eq!(
+            api.cuCtxPopCurrent_v2_unchecked(&mut unsafe { mem::zeroed() }),
+            CUresult::ERROR_INVALID_CONTEXT
+        );
+    }
+
+    #[test_cuda]
+    fn pop_into_null_succeeds(api: impl CudaApi) {
+        api.cuInit(0);
+        api.cuCtxCreate_v2(&mut unsafe { mem::zeroed() }, 0, 0);
+        api.cuCtxPopCurrent_v2(ptr::null_mut());
+    }
+}