Dart: fix race condition between garbage collection of finalizable ob…

…jects and native function calls (#1633)

----- Motivation -----
If the generated class is not marked with 'Finalizable' interface,
then, when methods are invoked on its object, the object can be
garbage collected in the middle of method execution.

For instance let's take a look at the following example from functional
tests:

'AsyncClass().asyncVoid(false)'

1. AsyncClass object is created and its lifetime is tied with the native
    finalizer, which deletes shared_ptr (this.handle) that owns resources.
2. Then, inside 'asyncVoid(false)' we use only 'this.handle' member to
    pass the opaque handle to the native function. For garbage collector
    after the handle is passed 'this' object is no longer used by anybody.
    Therefore, it is not needed – can be finalized.
3. If the garbage collection kicks in before the native call, then the
    'AsyncClass' object is garbage collected, its finalizer is run and therefore,
    the resources on C++ side are deleted. It causes the segmentation fault.

We have a race condition between the garbage collection and execution
of native functions.

The consequences can be dramatic -- the finalizer registered for
the object may be executed before the native function call inside
the member methods. The finalizers delete C++ resources tied with
the object. This can lead to segmentation fault.

----- Solution -----
The 'Finalizable' interface is a viable solution proposed by Dart:FFI
documentation. It ensures, that 'this' object outlives the whole method
call -- it guarantees, that the native function call finishes before the
finalizer is run.

Signed-off-by: Patryk Wrobel <183546751+pwrobeldev@users.noreply.github.com>

.github/workflows/functional-tests.yml

@@ -257,7 +257,7 @@ jobs:
       - name: Install Dart SDK
         run: |
           DART_RELEASE_CHANNEL=stable
-          DART_VERSION=2.12.0
+          DART_VERSION=2.18.1
           wget -nv https://storage.googleapis.com/dart-archive/channels/${DART_RELEASE_CHANNEL}/release/${DART_VERSION}/linux_packages/dart_${DART_VERSION}-1_amd64.deb
           sudo apt -y install ./dart_${DART_VERSION}-1_amd64.deb
       - name: Build and run functional tests
@@ -373,7 +373,7 @@ jobs:
       - name: Install Dart SDK
         run: |
           DART_RELEASE_CHANNEL=stable
-          DART_VERSION=2.12.0
+          DART_VERSION=2.18.1
           wget -nv https://storage.googleapis.com/dart-archive/channels/${DART_RELEASE_CHANNEL}/release/${DART_VERSION}/linux_packages/dart_${DART_VERSION}-1_amd64.deb
           sudo apt -y install ./dart_${DART_VERSION}-1_amd64.deb
       - name: Build and run functional tests

CHANGELOG.md

@@ -1,5 +1,9 @@
 # Gluecodium project Release Notes
 
+## Unreleased
+### Bug fixes:
+ * Dart: fixed race condition between garbage collector (which could trigger finalizer) and native method calls in finalizable classes.
+
 ## 13.10.0
 Release date 2024-11-28
 ### Features:

gluecodium/src/main/resources/templates/dart/DartClass.mustache

@@ -1,6 +1,6 @@
 {{!!
   !
-  ! Copyright (C) 2016-2019 HERE Europe B.V.
+  ! Copyright (C) 2016-2024 HERE Europe B.V.
   !
   ! Licensed under the Apache License, Version 2.0 (the "License");
   ! you may not use this file except in compliance with the License.
@@ -20,7 +20,7 @@
   !}}
 {{>dart/DartDocumentation}}{{>dart/DartAttributes}}
 abstract class {{resolveName}}{{!!
-}}{{#if this.parents}} implements {{#this.parents}}{{resolveName}}{{#if iter.hasNext}}, {{/if}}{{/this.parents}}{{/if}} {
+}} implements {{#if this.parents}}{{#this.parents}}{{resolveName}}, {{/this.parents}}{{/if}}Finalizable {
 {{#set parent=this container=this}}{{#constructors}}
 {{prefixPartial "dart/DartFunctionDocs" "  "}}
   factory {{resolveName parent}}{{>dart/DartConstructorName}}({{!!

gluecodium/src/main/resources/templates/dart/DartInterface.mustache

@@ -1,6 +1,6 @@
 {{!!
   !
-  ! Copyright (C) 2016-2020 HERE Europe B.V.
+  ! Copyright (C) 2016-2024 HERE Europe B.V.
   !
   ! Licensed under the Apache License, Version 2.0 (the "License");
   ! you may not use this file except in compliance with the License.
@@ -20,7 +20,7 @@
   !}}
 {{>dart/DartDocumentation}}{{>dart/DartAttributes}}
 abstract class {{resolveName}}{{!!
-}}{{#if this.parents}} implements {{#this.parents}}{{resolveName}}{{#if iter.hasNext}}, {{/if}}{{/this.parents}}{{/if}} {
+}} implements {{#if this.parents}}{{#this.parents}}{{resolveName}}, {{/this.parents}}{{/if}}Finalizable {
 {{#if inheritedFunctions functions inheritedProperties properties logic="or"}}
 {{prefixPartial "dart/DartDocumentation" "  "}}
   factory {{resolveName}}(

gluecodium/src/main/resources/templates/dart/DartLambda.mustache

@@ -1,6 +1,6 @@
 {{!!
   !
-  ! Copyright (C) 2016-2020 HERE Europe B.V.
+  ! Copyright (C) 2016-2024 HERE Europe B.V.
   !
   ! Licensed under the Apache License, Version 2.0 (the "License");
   ! you may not use this file except in compliance with the License.
@@ -42,7 +42,7 @@ final _{{resolveName "Ffi"}}CreateProxy = __lib.catchArgumentError(() => __lib.n
     Pointer<Void> Function(int, int, Object, Pointer)
   >('{{libraryName}}_{{resolveName "FfiSnakeCase"}}_create_proxy'));
 
-class {{resolveName}}$Impl {
+class {{resolveName}}$Impl implements Finalizable {
   final Pointer<Void> handle;
   {{resolveName}}$Impl(this.handle);
 

gluecodium/src/main/resources/templates/dart/DartLazyList.mustache

@@ -1,6 +1,6 @@
 {{!!
   !
-  ! Copyright (C) 2016-2021 HERE Europe B.V.
+  ! Copyright (C) 2016-2024 HERE Europe B.V.
   !
   ! Licensed under the Apache License, Version 2.0 (the "License");
   ! you may not use this file except in compliance with the License.
@@ -41,7 +41,7 @@ class _LazyIterator<E> implements Iterator<E> {
 }
 
 /// @nodoc
-class LazyList<E> extends Iterable<E> implements List<E> {
+class LazyList<E> extends Iterable<E> implements List<E>, Finalizable {
   static final _cannotModify = "Cannot modify an unmodifiable list";
 
   final Pointer<Void> handle;