3 * Copyright 2011 Novell, Inc.
5 * Licensed under the MIT license. See LICENSE file in the project root for full license information.
9 * The bridge is a mechanism for SGen to let clients override the death of some
10 * unreachable objects. We use it in monodroid to do garbage collection across
11 * the Mono and Java heaps.
13 * The client (Monodroid) can designate some objects as "bridged", which means
14 * that they participate in the bridge processing step once SGen considers them
15 * unreachable, i.e., dead. Bridged objects must be registered for
18 * When SGen is done marking, it puts together a list of all dead bridged
19 * objects. This is passed to the bridge processor, which does an analysis to
20 * simplify the graph: It replaces strongly-connected components with single
21 * nodes, and may remove nodes corresponding to components which do not contain
24 * The output of the SCC analysis is passed to the client's `cross_references()`
25 * callback. This consists of 2 arrays, an array of SCCs (MonoGCBridgeSCC),
26 * and an array of "xrefs" (edges between SCCs, MonoGCBridgeXRef). Edges are
27 * encoded as pairs of "API indices", ie indexes in the SCC array. The client
28 * is expected to set the `is_alive` flag on those strongly connected components
29 * that it wishes to be kept alive.
31 * In monodroid each bridged object has a corresponding Java mirror object. In
32 * the bridge callback it reifies the Mono object graph in the Java heap so that
33 * the full, combined object graph is now instantiated on the Java side. Then
34 * it triggers a Java GC, waits for it to finish, and checks which of the Java
35 * mirror objects are still alive. For those it sets the `is_alive` flag and
36 * returns from the callback.
38 * The SCC analysis is done while the world is stopped, but the callback is made
39 * with the world running again. Weak links to bridged objects and other
40 * objects reachable from them are kept until the callback returns, at which
41 * point all links to bridged objects that don't have `is_alive` set are nulled.
42 * Note that weak links to non-bridged objects reachable from bridged objects
43 * are not nulled. This might be considered a bug.
45 * There are three different implementations of the bridge processor, each of
46 * which implements 8 callbacks (see SgenBridgeProcessor). The implementations
47 * differ in the algorithm they use to compute the "simplified" SCC graph.
50 #ifndef _MONO_SGEN_BRIDGE_H_
51 #define _MONO_SGEN_BRIDGE_H_
53 #include <mono/utils/mono-publib.h>
58 SGEN_BRIDGE_VERSION
= 5
62 /* Instances of this class should be scanned when computing the transitive dependency among bridges. E.g. List<object>*/
63 GC_BRIDGE_TRANSPARENT_CLASS
,
64 /* Instances of this class should not be scanned when computing the transitive dependency among bridges. E.g. String*/
65 GC_BRIDGE_OPAQUE_CLASS
,
66 /* Instances of this class should be bridged and have their dependency computed. */
67 GC_BRIDGE_TRANSPARENT_BRIDGE_CLASS
,
68 /* Instances of this class should be bridged but no dependencies should not be calculated. */
69 GC_BRIDGE_OPAQUE_BRIDGE_CLASS
,
70 } MonoGCBridgeObjectKind
;
73 mono_bool is_alive
; /* to be set by the cross reference callback */
75 MonoObject
*objs
[MONO_ZERO_LEN_ARRAY
];
86 * Tells the runtime which classes to even consider when looking for
87 * bridged objects. If subclasses are to be considered as well, the
88 * subclass check must be done in the callback.
90 MonoGCBridgeObjectKind (*bridge_class_kind
) (MonoClass
*klass
);
92 * This is only called on objects for whose classes
93 * `bridge_class_kind()` returned `XXX_BRIDGE_CLASS`.
95 mono_bool (*is_bridge_object
) (MonoObject
*object
);
96 void (*cross_references
) (int num_sccs
, MonoGCBridgeSCC
**sccs
, int num_xrefs
, MonoGCBridgeXRef
*xrefs
);
97 } MonoGCBridgeCallbacks
;
100 * Note: This may be called at any time, but cannot be called concurrently
101 * with (during and on a separate thread from) sgen init. Callers are
102 * responsible for enforcing this.
104 MONO_API
void mono_gc_register_bridge_callbacks (MonoGCBridgeCallbacks
*callbacks
);
106 MONO_API
void mono_gc_wait_for_bridge_processing (void);