/*
* Copyright 2001-2007 Sun Microsystems, Inc. All Rights Reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
* CA 95054 USA or visit www.sun.com if you need additional information or
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*/
// ReferenceProcessor class encapsulates the per-"collector" processing
// of "weak" references for GC. The interface is useful for supporting
// a generational abstraction, in particular when there are multiple
// generations that are being independently collected -- possibly
// concurrently and/or incrementally. Note, however, that the
// ReferenceProcessor class abstracts away from a generational setting
// by using only a heap interval (called "span" below), thus allowing
// its use in a straightforward manner in a general, non-generational
// setting.
//
// The basic idea is that each ReferenceProcessor object concerns
// itself with ("weak") reference processing in a specific "span"
// of the heap of interest to a specific collector. Currently,
// the span is a convex interval of the heap, but, efficiency
// apart, there seems to be no reason it couldn't be extended
// (with appropriate modifications) to any "non-convex interval".
// forward references
class ReferencePolicy;
class AbstractRefProcTaskExecutor;
class DiscoveredList;
class ReferenceProcessor : public CHeapObj {
protected:
// End of list marker
static oop _sentinelRef;
MemRegion _span; // (right-open) interval of heap
// subject to wkref discovery
bool _discovering_refs; // true when discovery enabled
bool _discovery_is_atomic; // if discovery is atomic wrt
// other collectors in configuration
bool _discovery_is_mt; // true if reference discovery is MT.
// If true, setting "next" field of a discovered refs list requires
// write barrier(s). (Must be true if used in a collector in which
// elements of a discovered list may be moved during discovery: for
// example, a collector like Garbage-First that moves objects during a
// long-term concurrent marking phase that does weak reference
// discovery.)
bool _discovered_list_needs_barrier;
BarrierSet* _bs; // Cached copy of BarrierSet.
bool _enqueuing_is_done; // true if all weak references enqueued
bool _processing_is_mt; // true during phases when
// reference processing is MT.
int _next_id; // round-robin counter in
// support of work distribution
// For collectors that do not keep GC marking information
// in the object header, this field holds a closure that
// helps the reference processor determine the reachability
// of an oop (the field is currently initialized to NULL for
// all collectors but the CMS collector).
BoolObjectClosure* _is_alive_non_header;
// The discovered ref lists themselves
// The MT'ness degree of the queues below
int _num_q;
// Arrays of lists of oops, one per thread
DiscoveredList* _discoveredSoftRefs;
DiscoveredList* _discoveredWeakRefs;
DiscoveredList* _discoveredFinalRefs;
DiscoveredList* _discoveredPhantomRefs;
public:
int num_q() { return _num_q; }
DiscoveredList* discovered_soft_refs() { return _discoveredSoftRefs; }
static oop sentinel_ref() { return _sentinelRef; }
static oop* adr_sentinel_ref() { return &_sentinelRef; }
public:
// Process references with a certain reachability level.
void process_discovered_reflist(DiscoveredList refs_lists[],
ReferencePolicy* policy,
bool clear_referent,
BoolObjectClosure* is_alive,
OopClosure* keep_alive,
VoidClosure* complete_gc,
AbstractRefProcTaskExecutor* task_executor);
void process_phaseJNI(BoolObjectClosure* is_alive,
OopClosure* keep_alive,
VoidClosure* complete_gc);
// Work methods used by the method process_discovered_reflist
// Phase1: keep alive all those referents that are otherwise
// dead but which must be kept alive by policy (and their closure).
void process_phase1(DiscoveredList& refs_list,
ReferencePolicy* policy,
BoolObjectClosure* is_alive,
OopClosure* keep_alive,
VoidClosure* complete_gc);
// Phase2: remove all those references whose referents are
// reachable.
inline void process_phase2(DiscoveredList& refs_list,
BoolObjectClosure* is_alive,
OopClosure* keep_alive,
VoidClosure* complete_gc) {
if (discovery_is_atomic()) {
// complete_gc is ignored in this case for this phase
pp2_work(refs_list, is_alive, keep_alive);
} else {
assert(complete_gc != NULL, "Error");
pp2_work_concurrent_discovery(refs_list, is_alive,
keep_alive, complete_gc);
}
}
// Work methods in support of process_phase2
void pp2_work(DiscoveredList& refs_list,
BoolObjectClosure* is_alive,
OopClosure* keep_alive);
void pp2_work_concurrent_discovery(
DiscoveredList& refs_list,
BoolObjectClosure* is_alive,
OopClosure* keep_alive,
VoidClosure* complete_gc);
// Phase3: process the referents by either clearing them
// or keeping them alive (and their closure)
void process_phase3(DiscoveredList& refs_list,
bool clear_referent,
BoolObjectClosure* is_alive,
OopClosure* keep_alive,
VoidClosure* complete_gc);
// Enqueue references with a certain reachability level
void enqueue_discovered_reflist(DiscoveredList& refs_list, HeapWord* pending_list_addr);
// "Preclean" all the discovered reference lists
// by removing references with strongly reachable referents.
// The first argument is a predicate on an oop that indicates
// its (strong) reachability and the second is a closure that
// may be used to incrementalize or abort the precleaning process.
// The caller is responsible for taking care of potential
// interference with concurrent operations on these lists
// (or predicates involved) by other threads. Currently
// only used by the CMS collector.
void preclean_discovered_references(BoolObjectClosure* is_alive,
OopClosure* keep_alive,
VoidClosure* complete_gc,
YieldClosure* yield);
// Delete entries in the discovered lists that have
// either a null referent or are not active. Such
// Reference objects can result from the clearing
// or enqueueing of Reference objects concurrent
// with their discovery by a (concurrent) collector.
// For a definition of "active" see java.lang.ref.Reference;
// Refs are born active, become inactive when enqueued,
// and never become active again. The state of being
// active is encoded as follows: A Ref is active
// if and only if its "next" field is NULL.
void clean_up_discovered_references();
void clean_up_discovered_reflist(DiscoveredList& refs_list);
// Returns the name of the discovered reference list
// occupying the i / _num_q slot.
const char* list_name(int i);
void enqueue_discovered_reflists(HeapWord* pending_list_addr, AbstractRefProcTaskExecutor* task_executor);
protected:
// "Preclean" the given discovered reference list
// by removing references with strongly reachable referents.
// Currently used in support of CMS only.
void preclean_discovered_reflist(DiscoveredList& refs_list,
BoolObjectClosure* is_alive,
OopClosure* keep_alive,
VoidClosure* complete_gc,
YieldClosure* yield);
int next_id() {
int id = _next_id;
if (++_next_id == _num_q) {
_next_id = 0;
}
return id;
}
DiscoveredList* get_discovered_list(ReferenceType rt);
inline void add_to_discovered_list_mt(DiscoveredList& refs_list, oop obj,
HeapWord* discovered_addr);
void verify_ok_to_handle_reflists() PRODUCT_RETURN;
void abandon_partial_discovered_list(DiscoveredList& refs_list);
// Calculate the number of jni handles.
unsigned int count_jni_refs();
// Balances reference queues.
void balance_queues(DiscoveredList ref_lists[]);
// Update (advance) the soft ref master clock field.
void update_soft_ref_master_clock();
public:
// constructor
ReferenceProcessor():
_span((HeapWord*)NULL, (HeapWord*)NULL),
_discoveredSoftRefs(NULL), _discoveredWeakRefs(NULL),
_discoveredFinalRefs(NULL), _discoveredPhantomRefs(NULL),
_discovering_refs(false),
_discovery_is_atomic(true),
_enqueuing_is_done(false),
_discovery_is_mt(false),
_discovered_list_needs_barrier(false),
_bs(NULL),
_is_alive_non_header(NULL),
_num_q(0),
_processing_is_mt(false),
_next_id(0)
{}
ReferenceProcessor(MemRegion span, bool atomic_discovery,
bool mt_discovery,
int mt_degree = 1,
bool mt_processing = false,
bool discovered_list_needs_barrier = false);
// Allocates and initializes a reference processor.
static ReferenceProcessor* create_ref_processor(
MemRegion span,
bool atomic_discovery,
bool mt_discovery,
BoolObjectClosure* is_alive_non_header = NULL,
int parallel_gc_threads = 1,
bool mt_processing = false,
bool discovered_list_needs_barrier = false);
// RefDiscoveryPolicy values
enum {
ReferenceBasedDiscovery = 0,
ReferentBasedDiscovery = 1
};
static void init_statics();
public:
// get and set "is_alive_non_header" field
BoolObjectClosure* is_alive_non_header() {
return _is_alive_non_header;
}
void set_is_alive_non_header(BoolObjectClosure* is_alive_non_header) {
_is_alive_non_header = is_alive_non_header;
}
// get and set span
MemRegion span() { return _span; }
void set_span(MemRegion span) { _span = span; }
// start and stop weak ref discovery
void enable_discovery() { _discovering_refs = true; }
void disable_discovery() { _discovering_refs = false; }
bool discovery_enabled() { return _discovering_refs; }
// whether discovery is atomic wrt other collectors
bool discovery_is_atomic() const { return _discovery_is_atomic; }
void set_atomic_discovery(bool atomic) { _discovery_is_atomic = atomic; }
// whether discovery is done by multiple threads same-old-timeously
bool discovery_is_mt() const { return _discovery_is_mt; }
void set_mt_discovery(bool mt) { _discovery_is_mt = mt; }
// Whether we are in a phase when _processing_ is MT.
bool processing_is_mt() const { return _processing_is_mt; }
void set_mt_processing(bool mt) { _processing_is_mt = mt; }
// whether all enqueuing of weak references is complete
bool enqueuing_is_done() { return _enqueuing_is_done; }
void set_enqueuing_is_done(bool v) { _enqueuing_is_done = v; }
// iterate over oops
void weak_oops_do(OopClosure* f); // weak roots
static void oops_do(OopClosure* f); // strong root(s)
// Discover a Reference object, using appropriate discovery criteria
bool discover_reference(oop obj, ReferenceType rt);
// Process references found during GC (called by the garbage collector)
void process_discovered_references(ReferencePolicy* policy,
BoolObjectClosure* is_alive,
OopClosure* keep_alive,
VoidClosure* complete_gc,
AbstractRefProcTaskExecutor* task_executor);
public:
// Enqueue references at end of GC (called by the garbage collector)
bool enqueue_discovered_references(AbstractRefProcTaskExecutor* task_executor = NULL);
// If a discovery is in process that is being superceded, abandon it: all
// the discovered lists will be empty, and all the objects on them will
// have NULL discovered fields. Must be called only at a safepoint.
void abandon_partial_discovery();
// debugging
void verify_no_references_recorded() PRODUCT_RETURN;
static void verify();
// clear the discovered lists (unlinking each entry).
void clear_discovered_references() PRODUCT_RETURN;
};
// A utility class to disable reference discovery in
// the scope which contains it, for given ReferenceProcessor.
class NoRefDiscovery: StackObj {
private:
ReferenceProcessor* _rp;
bool _was_discovering_refs;
public:
NoRefDiscovery(ReferenceProcessor* rp) : _rp(rp) {
if (_was_discovering_refs = _rp->discovery_enabled()) {
_rp->disable_discovery();
}
}
~NoRefDiscovery() {
if (_was_discovering_refs) {
_rp->enable_discovery();
}
}
};
// A utility class to temporarily mutate the span of the
// given ReferenceProcessor in the scope that contains it.
class ReferenceProcessorSpanMutator: StackObj {
private:
ReferenceProcessor* _rp;
MemRegion _saved_span;
public:
ReferenceProcessorSpanMutator(ReferenceProcessor* rp,
MemRegion span):
_rp(rp) {
_saved_span = _rp->span();
_rp->set_span(span);
}
~ReferenceProcessorSpanMutator() {
_rp->set_span(_saved_span);
}
};
// A utility class to temporarily change the MT'ness of
// reference discovery for the given ReferenceProcessor
// in the scope that contains it.
class ReferenceProcessorMTMutator: StackObj {
private:
ReferenceProcessor* _rp;
bool _saved_mt;
public:
ReferenceProcessorMTMutator(ReferenceProcessor* rp,
bool mt):
_rp(rp) {
_saved_mt = _rp->discovery_is_mt();
_rp->set_mt_discovery(mt);
}
~ReferenceProcessorMTMutator() {
_rp->set_mt_discovery(_saved_mt);
}
};
// A utility class to temporarily change the disposition
// of the "is_alive_non_header" closure field of the
// given ReferenceProcessor in the scope that contains it.
class ReferenceProcessorIsAliveMutator: StackObj {
private:
ReferenceProcessor* _rp;
BoolObjectClosure* _saved_cl;
public:
ReferenceProcessorIsAliveMutator(ReferenceProcessor* rp,
BoolObjectClosure* cl):
_rp(rp) {
_saved_cl = _rp->is_alive_non_header();
_rp->set_is_alive_non_header(cl);
}
~ReferenceProcessorIsAliveMutator() {
_rp->set_is_alive_non_header(_saved_cl);
}
};
// A utility class to temporarily change the disposition
// of the "discovery_is_atomic" field of the
// given ReferenceProcessor in the scope that contains it.
class ReferenceProcessorAtomicMutator: StackObj {
private:
ReferenceProcessor* _rp;
bool _saved_atomic_discovery;
public:
ReferenceProcessorAtomicMutator(ReferenceProcessor* rp,
bool atomic):
_rp(rp) {
_saved_atomic_discovery = _rp->discovery_is_atomic();
_rp->set_atomic_discovery(atomic);
}
~ReferenceProcessorAtomicMutator() {
_rp->set_atomic_discovery(_saved_atomic_discovery);
}
};
// A utility class to temporarily change the MT processing
// disposition of the given ReferenceProcessor instance
// in the scope that contains it.
class ReferenceProcessorMTProcMutator: StackObj {
private:
ReferenceProcessor* _rp;
bool _saved_mt;
public:
ReferenceProcessorMTProcMutator(ReferenceProcessor* rp,
bool mt):
_rp(rp) {
_saved_mt = _rp->processing_is_mt();
_rp->set_mt_processing(mt);
}
~ReferenceProcessorMTProcMutator() {
_rp->set_mt_processing(_saved_mt);
}
};
// This class is an interface used to implement task execution for the
// reference processing.
class AbstractRefProcTaskExecutor {
public:
// Abstract tasks to execute.
class ProcessTask;
class EnqueueTask;
// Executes a task using worker threads.
virtual void execute(ProcessTask& task) = 0;
virtual void execute(EnqueueTask& task) = 0;
// Switch to single threaded mode.
virtual void set_single_threaded_mode() { };
};
// Abstract reference processing task to execute.
class AbstractRefProcTaskExecutor::ProcessTask {
protected:
ProcessTask(ReferenceProcessor& ref_processor,
DiscoveredList refs_lists[],
bool marks_oops_alive)
: _ref_processor(ref_processor),
_refs_lists(refs_lists),
_marks_oops_alive(marks_oops_alive)
{ }
public:
virtual void work(unsigned int work_id, BoolObjectClosure& is_alive,
OopClosure& keep_alive,
VoidClosure& complete_gc) = 0;
// Returns true if a task marks some oops as alive.
bool marks_oops_alive() const
{ return _marks_oops_alive; }
protected:
ReferenceProcessor& _ref_processor;
DiscoveredList* _refs_lists;
const bool _marks_oops_alive;
};
// Abstract reference processing task to execute.
class AbstractRefProcTaskExecutor::EnqueueTask {
protected:
EnqueueTask(ReferenceProcessor& ref_processor,
DiscoveredList refs_lists[],
HeapWord* pending_list_addr,
oop sentinel_ref,
int n_queues)
: _ref_processor(ref_processor),
_refs_lists(refs_lists),
_pending_list_addr(pending_list_addr),
_sentinel_ref(sentinel_ref),
_n_queues(n_queues)
{ }
public:
virtual void work(unsigned int work_id) = 0;
protected:
ReferenceProcessor& _ref_processor;
DiscoveredList* _refs_lists;
HeapWord* _pending_list_addr;
oop _sentinel_ref;
int _n_queues;
};