127 lines
5.6 KiB
HTML
127 lines
5.6 KiB
HTML
<h1>Garbage Collector Interface</h1>
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<h1>Public Interface</h1>
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<p>The public interface of the Mono GC is fairly limited, and
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its the only one that embedders should be using:
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<h3>Garbage Collector</h3>
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<h4><a name="api:mono_gc_collect">mono_gc_collect</a></h4>
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<h4><a name="api:mono_gc_collection_count">mono_gc_collection_count</a></h4>
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<h4><a name="api:mono_gc_max_generation">mono_gc_max_generation</a></h4>
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<h4><a name="api:mono_gc_get_generation">mono_gc_get_generation</a></h4>
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<h4><a name="api:mono_gc_get_heap_size">mono_gc_get_heap_size</a></h4>
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<h4><a name="api:mono_gc_get_used_size">mono_gc_get_used_size</a></h4>
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<h4><a name="api:mono_gc_walk_heap">mono_gc_walk_heap</a></h4>
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<h3>Reference Queues</h3>
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<h4><a name="api:mono_gc_reference_queue_add">mono_gc_reference_queue_add</a></h4>
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<h4><a name="api:mono_gc_reference_queue_free">mono_gc_reference_queue_free</a></h4>
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<h4><a name="api:mono_gc_reference_queue_new">mono_gc_reference_queue_new</a></h4>
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<h3>SGen Bridge</h3>
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<p>The bridge is a mechanism for SGen to let clients override
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the death of some unreachable objects. We use it in monodroid
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to do garbage collection across the Mono and Java heaps.
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<p>The client can designate some objects as "bridged", which
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means that they participate in the bridge processing step once
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SGen considers them unreachable, i.e., dead. Bridged objects
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must be registered for finalization.
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<p>When SGen is done marking, it puts together a list of all
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dead bridged objects and then does a strongly connected
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component analysis over their object graph. That graph will
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usually contain non-bridged objects, too.
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<p>The output of the SCC analysis is passed to the
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`cross_references()` callback. It is expected to set the
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`is_alive` flag on those strongly connected components that it
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wishes to be kept alive. The value of `is_alive` will be
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ignored on any SCCs which lack bridges.
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<p>In monodroid each bridged object has a corresponding Java
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mirror object. In the bridge callback it reifies the Mono
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object graph in the Java heap so that the full, combined
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object graph is now instantiated on the Java side. Then it
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triggers a Java GC, waits for it to finish, and checks which
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of the Java mirror objects are still alive. For those it sets
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the `is_alive` flag and returns from the callback.
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<p>The SCC analysis is done while the world is stopped, but
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the callback is made with the world running again. Weak links
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to bridged objects and other objects reachable from them are
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kept until the callback returns, at which point all links to
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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
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bridged objects are not nulled. This might be considered a
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bug.
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<div class="mapi-header">
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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 of 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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</div>
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<h4><a name="api:mono_gc_register_bridge_callbacks">mono_gc_register_bridge_callbacks</a></h4>
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<h4><a name="api:mono_gc_wait_for_bridge_processing">mono_gc_wait_for_bridge_processing</a></h4>
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<h3>Write Barriers</h3>
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<p>SGen is a concurrent and generational GC, features which require
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tracking changes to the state of the heap. This is achieved through
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write barriers. Whenever native code is changing the state of the
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heap by storing references into another managed object, it needs to
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do it using this write barrier API.
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<h4><a name="api:mono_gc_wbarrier_arrayref_copy">mono_gc_wbarrier_arrayref_copy</a></h4>
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<h4><a name="api:mono_gc_wbarrier_generic_nostore">mono_gc_wbarrier_generic_nostore</a></h4>
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<h4><a name="api:mono_gc_wbarrier_generic_store">mono_gc_wbarrier_generic_store</a></h4>
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<h4><a name="api:mono_gc_wbarrier_generic_store_atomic">mono_gc_wbarrier_generic_store_atomic</a></h4>
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<h4><a name="api:mono_gc_wbarrier_object_copy">mono_gc_wbarrier_object_copy</a></h4>
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<h4><a name="api:mono_gc_wbarrier_set_arrayref">mono_gc_wbarrier_set_arrayref</a></h4>
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<h4><a name="api:mono_gc_wbarrier_set_field">mono_gc_wbarrier_set_field</a></h4>
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<h4><a name="api:mono_gc_wbarrier_value_copy">mono_gc_wbarrier_value_copy</a></h4>
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