/**
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* \file
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* Copyright 2011 Novell, Inc.
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*
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* Licensed under the MIT license. See LICENSE file in the project root for full license information.
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*/
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/*
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* The bridge is a mechanism for SGen to let clients override the death of some
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* unreachable objects. We use it in monodroid to do garbage collection across
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* the Mono and Java heaps.
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*
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* The client (Monodroid) can designate some objects as "bridged", which means
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* that they participate in the bridge processing step once SGen considers them
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* unreachable, i.e., dead. Bridged objects must be registered for
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* finalization.
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*
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* When SGen is done marking, it puts together a list of all dead bridged
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* objects. This is passed to the bridge processor, which does an analysis to
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* simplify the graph: It replaces strongly-connected components with single
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* nodes, and may remove nodes corresponding to components which do not contain
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* bridged objects.
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*
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* The output of the SCC analysis is passed to the client's `cross_references()`
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* callback. This consists of 2 arrays, an array of SCCs (MonoGCBridgeSCC),
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* and an array of "xrefs" (edges between SCCs, MonoGCBridgeXRef). Edges are
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* encoded as pairs of "API indices", ie indexes in the SCC array. The client
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* is expected to set the `is_alive` flag on those strongly connected components
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* that it wishes to be kept alive.
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*
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* In monodroid each bridged object has a corresponding Java mirror object. In
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* the bridge callback it reifies the Mono object graph in the Java heap so that
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* the full, combined object graph is now instantiated on the Java side. Then
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* it triggers a Java GC, waits for it to finish, and checks which of the Java
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* mirror objects are still alive. For those it sets the `is_alive` flag and
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* returns from the callback.
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*
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* The SCC analysis is done while the world is stopped, but the callback is made
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* with the world running again. Weak links to bridged objects and other
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* objects reachable from them are kept until the callback returns, at which
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* point all links to bridged objects that don't have `is_alive` set are nulled.
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* Note that weak links to non-bridged objects reachable from bridged objects
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* are not nulled. This might be considered a bug.
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*
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* There are three different implementations of the bridge processor, each of
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* which implements 8 callbacks (see SgenBridgeProcessor). The implementations
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* differ in the algorithm they use to compute the "simplified" SCC graph.
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*/
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#ifndef _MONO_SGEN_BRIDGE_H_
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#define _MONO_SGEN_BRIDGE_H_
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#include <mono/utils/mono-publib.h>
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MONO_BEGIN_DECLS
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enum {
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SGEN_BRIDGE_VERSION = 5
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};
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typedef enum {
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/* Instances of this class should be scanned when computing the transitive dependency among bridges. E.g. List<object>*/
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GC_BRIDGE_TRANSPARENT_CLASS,
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/* Instances of this class should not be scanned when computing the transitive dependency among bridges. E.g. String*/
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GC_BRIDGE_OPAQUE_CLASS,
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/* Instances of this class should be bridged and have their dependency computed. */
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GC_BRIDGE_TRANSPARENT_BRIDGE_CLASS,
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/* Instances of this class should be bridged but no dependencies should not be calculated. */
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GC_BRIDGE_OPAQUE_BRIDGE_CLASS,
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} MonoGCBridgeObjectKind;
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typedef struct {
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mono_bool is_alive; /* to be set by the cross reference callback */
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int num_objs;
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MonoObject *objs [MONO_ZERO_LEN_ARRAY];
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} MonoGCBridgeSCC;
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typedef struct {
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int src_scc_index;
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int dst_scc_index;
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} MonoGCBridgeXRef;
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typedef struct {
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int bridge_version;
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/*
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* Tells the runtime which classes to even consider when looking for
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* bridged objects. If subclasses are to be considered as well, the
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* subclass check must be done in the callback.
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*/
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MonoGCBridgeObjectKind (*bridge_class_kind) (MonoClass *klass);
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/*
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* This is only called on objects for whose classes
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* `bridge_class_kind()` returned `XXX_BRIDGE_CLASS`.
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*/
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mono_bool (*is_bridge_object) (MonoObject *object);
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void (*cross_references) (int num_sccs, MonoGCBridgeSCC **sccs, int num_xrefs, MonoGCBridgeXRef *xrefs);
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} MonoGCBridgeCallbacks;
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/*
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* Note: This may be called at any time, but cannot be called concurrently
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* with (during and on a separate thread from) sgen init. Callers are
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* responsible for enforcing this.
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*/
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MONO_API void mono_gc_register_bridge_callbacks (MonoGCBridgeCallbacks *callbacks);
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MONO_API void mono_gc_wait_for_bridge_processing (void);
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MONO_END_DECLS
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#endif
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