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25 * The bridge is a mechanism for SGen to let clients override the death of some
26 * unreachable objects. We use it in monodroid to do garbage collection across
27 * the Mono and Java heaps.
29 * The client can designate some objects as "bridged", which means that they
30 * participate in the bridge processing step once SGen considers them
31 * unreachable, i.e., dead. Bridged objects must be registered for
34 * When SGen is done marking, it puts together a list of all dead bridged
35 * objects and then does a strongly connected component analysis over their
36 * object graph. That graph will usually contain non-bridged objects, too.
38 * The output of the SCC analysis is passed to the `cross_references()`
39 * callback. It is expected to set the `is_alive` flag on those strongly
40 * connected components that it wishes to be kept alive. Only bridged objects
41 * will be reported to the callback, i.e., non-bridged objects are removed from
44 * In monodroid each bridged object has a corresponding Java mirror object. In
45 * the bridge callback it reifies the Mono object graph in the Java heap so that
46 * the full, combined object graph is now instantiated on the Java side. Then
47 * it triggers a Java GC, waits for it to finish, and checks which of the Java
48 * mirror objects are still alive. For those it sets the `is_alive` flag and
49 * returns from the callback.
51 * The SCC analysis is done while the world is stopped, but the callback is made
52 * with the world running again. Weak links to bridged objects and other
53 * objects reachable from them are kept until the callback returns, at which
54 * point all links to bridged objects that don't have `is_alive` set are nulled.
55 * Note that weak links to non-bridged objects reachable from bridged objects
56 * are not nulled. This might be considered a bug.
59 #ifndef _MONO_SGEN_BRIDGE_H_
60 #define _MONO_SGEN_BRIDGE_H_
62 #include <mono/utils/mono-publib.h>
67 SGEN_BRIDGE_VERSION = 4
71 /* Instances of this class should be scanned when computing the transitive dependency among bridges. E.g. List<object>*/
72 GC_BRIDGE_TRANSPARENT_CLASS,
73 /* Instances of this class should not be scanned when computing the transitive dependency among bridges. E.g. String*/
74 GC_BRIDGE_OPAQUE_CLASS,
75 /* Instances of this class should be bridged and have their dependency computed. */
76 GC_BRIDGE_TRANSPARENT_BRIDGE_CLASS,
77 /* Instances of this class should be bridged but no dependencies should not be calculated. */
78 GC_BRIDGE_OPAQUE_BRIDGE_CLASS,
79 } MonoGCBridgeObjectKind;
82 mono_bool is_alive; /* to be set by the cross reference callback */
84 MonoObject *objs [MONO_ZERO_LEN_ARRAY];
95 * Tells the runtime which classes to even consider when looking for
96 * bridged objects. If subclasses are to be considered as well, the
97 * subclass check must be done in the callback.
99 MonoGCBridgeObjectKind (*bridge_class_kind) (MonoClass *klass);
101 * This is only called on objects for whose classes
102 * `bridge_class_kind()` returned `XXX_BRIDGE_CLASS`.
104 mono_bool (*is_bridge_object) (MonoObject *object);
105 void (*cross_references) (int num_sccs, MonoGCBridgeSCC **sccs, int num_xrefs, MonoGCBridgeXRef *xrefs);
106 } MonoGCBridgeCallbacks;
108 MONO_API void mono_gc_register_bridge_callbacks (MonoGCBridgeCallbacks *callbacks);
110 MONO_API void mono_gc_wait_for_bridge_processing (void);