-/*
+/**
+ * \file
* Copyright 2011 Novell, Inc.
*
- * Permission is hereby granted, free of charge, to any person obtaining
- * a copy of this software and associated documentation files (the
- * "Software"), to deal in the Software without restriction, including
- * without limitation the rights to use, copy, modify, merge, publish,
- * distribute, sublicense, and/or sell copies of the Software, and to
- * permit persons to whom the Software is furnished to do so, subject to
- * the following conditions:
- *
- * The above copyright notice and this permission notice shall be
- * included in all copies or substantial portions of the Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
- * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
- * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
- * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
- * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
- * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
- * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ * Licensed under the MIT license. See LICENSE file in the project root for full license information.
+ */
+
+/*
+ * The bridge is a mechanism for SGen to let clients override the death of some
+ * unreachable objects. We use it in monodroid to do garbage collection across
+ * the Mono and Java heaps.
+ *
+ * The client (Monodroid) can designate some objects as "bridged", which means
+ * that they participate in the bridge processing step once SGen considers them
+ * unreachable, i.e., dead. Bridged objects must be registered for
+ * finalization.
+ *
+ * When SGen is done marking, it puts together a list of all dead bridged
+ * objects. This is passed to the bridge processor, which does an analysis to
+ * simplify the graph: It replaces strongly-connected components with single
+ * nodes, and may remove nodes corresponding to components which do not contain
+ * bridged objects.
+ *
+ * The output of the SCC analysis is passed to the client's `cross_references()`
+ * callback. This consists of 2 arrays, an array of SCCs (MonoGCBridgeSCC),
+ * and an array of "xrefs" (edges between SCCs, MonoGCBridgeXRef). Edges are
+ * encoded as pairs of "API indices", ie indexes in the SCC array. The client
+ * is expected to set the `is_alive` flag on those strongly connected components
+ * that it wishes to be kept alive.
+ *
+ * In monodroid each bridged object has a corresponding Java mirror object. In
+ * the bridge callback it reifies the Mono object graph in the Java heap so that
+ * the full, combined object graph is now instantiated on the Java side. Then
+ * it triggers a Java GC, waits for it to finish, and checks which of the Java
+ * mirror objects are still alive. For those it sets the `is_alive` flag and
+ * returns from the callback.
+ *
+ * The SCC analysis is done while the world is stopped, but the callback is made
+ * with the world running again. Weak links to bridged objects and other
+ * objects reachable from them are kept until the callback returns, at which
+ * point all links to bridged objects that don't have `is_alive` set are nulled.
+ * Note that weak links to non-bridged objects reachable from bridged objects
+ * are not nulled. This might be considered a bug.
+ *
+ * There are three different implementations of the bridge processor, each of
+ * which implements 8 callbacks (see SgenBridgeProcessor). The implementations
+ * differ in the algorithm they use to compute the "simplified" SCC graph.
*/
#ifndef _MONO_SGEN_BRIDGE_H_
MONO_BEGIN_DECLS
enum {
- SGEN_BRIDGE_VERSION = 4
+ SGEN_BRIDGE_VERSION = 5
};
typedef enum {
typedef struct {
int bridge_version;
+ /*
+ * Tells the runtime which classes to even consider when looking for
+ * bridged objects. If subclasses are to be considered as well, the
+ * subclass check must be done in the callback.
+ */
MonoGCBridgeObjectKind (*bridge_class_kind) (MonoClass *klass);
+ /*
+ * This is only called on objects for whose classes
+ * `bridge_class_kind()` returned `XXX_BRIDGE_CLASS`.
+ */
mono_bool (*is_bridge_object) (MonoObject *object);
void (*cross_references) (int num_sccs, MonoGCBridgeSCC **sccs, int num_xrefs, MonoGCBridgeXRef *xrefs);
} MonoGCBridgeCallbacks;
+/*
+ * Note: This may be called at any time, but cannot be called concurrently
+ * with (during and on a separate thread from) sgen init. Callers are
+ * responsible for enforcing this.
+ */
MONO_API void mono_gc_register_bridge_callbacks (MonoGCBridgeCallbacks *callbacks);
MONO_API void mono_gc_wait_for_bridge_processing (void);
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