361 lines
15 KiB
C++
361 lines
15 KiB
C++
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/*
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* Copyright 1997-2006 Sun Microsystems, Inc. All Rights Reserved.
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 only, as
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* published by the Free Software Foundation.
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*
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* This code is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* version 2 for more details (a copy is included in the LICENSE file that
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* accompanied this code).
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*
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* You should have received a copy of the GNU General Public License version
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* 2 along with this work; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
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* CA 95054 USA or visit www.sun.com if you need additional information or
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* have any questions.
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*
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*/
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// The markOop describes the header of an object.
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//
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// Note that the mark is not a real oop but just a word.
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// It is placed in the oop hierarchy for historical reasons.
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//
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// Bit-format of an object header (most significant first):
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//
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//
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// unused:0/25 hash:25/31 age:4 biased_lock:1 lock:2 = 32/64 bits
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//
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// - hash contains the identity hash value: largest value is
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// 31 bits, see os::random(). Also, 64-bit vm's require
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// a hash value no bigger than 32 bits because they will not
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// properly generate a mask larger than that: see library_call.cpp
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// and c1_CodePatterns_sparc.cpp.
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//
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// - the biased lock pattern is used to bias a lock toward a given
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// thread. When this pattern is set in the low three bits, the lock
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// is either biased toward a given thread or "anonymously" biased,
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// indicating that it is possible for it to be biased. When the
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// lock is biased toward a given thread, locking and unlocking can
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// be performed by that thread without using atomic operations.
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// When a lock's bias is revoked, it reverts back to the normal
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// locking scheme described below.
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//
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// Note that we are overloading the meaning of the "unlocked" state
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// of the header. Because we steal a bit from the age we can
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// guarantee that the bias pattern will never be seen for a truly
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// unlocked object.
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//
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// Note also that the biased state contains the age bits normally
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// contained in the object header. Large increases in scavenge
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// times were seen when these bits were absent and an arbitrary age
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// assigned to all biased objects, because they tended to consume a
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// significant fraction of the eden semispaces and were not
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// promoted promptly, causing an increase in the amount of copying
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// performed. The runtime system aligns all JavaThread* pointers to
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// a very large value (currently 128 bytes) to make room for the
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// age bits when biased locking is enabled.
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//
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// [JavaThread* | epoch | age | 1 | 01] lock is biased toward given thread
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// [0 | epoch | age | 1 | 01] lock is anonymously biased
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//
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// - the two lock bits are used to describe three states: locked/unlocked and monitor.
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//
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// [ptr | 00] locked ptr points to real header on stack
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// [header | 0 | 01] unlocked regular object header
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// [ptr | 10] monitor inflated lock (header is wapped out)
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// [ptr | 11] marked used by markSweep to mark an object
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// not valid at any other time
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//
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// We assume that stack/thread pointers have the lowest two bits cleared.
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class BasicLock;
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class ObjectMonitor;
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class JavaThread;
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class markOopDesc: public oopDesc {
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private:
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// Conversion
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uintptr_t value() const { return (uintptr_t) this; }
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public:
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// Constants
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enum { age_bits = 4,
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lock_bits = 2,
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biased_lock_bits = 1,
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max_hash_bits = BitsPerOop - age_bits - lock_bits - biased_lock_bits,
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hash_bits = max_hash_bits > 31 ? 31 : max_hash_bits,
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epoch_bits = 2
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};
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// The biased locking code currently requires that the age bits be
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// contiguous to the lock bits. Class data sharing would prefer the
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// hash bits to be lower down to provide more random hash codes for
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// shared read-only symbolOop objects, because these objects' mark
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// words are set to their own address with marked_value in the lock
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// bit, and using lower bits would make their identity hash values
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// more random. However, the performance decision was made in favor
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// of the biased locking code.
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enum { lock_shift = 0,
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biased_lock_shift = lock_bits,
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age_shift = lock_bits + biased_lock_bits,
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hash_shift = lock_bits + biased_lock_bits + age_bits,
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epoch_shift = hash_shift
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};
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enum { lock_mask = right_n_bits(lock_bits),
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lock_mask_in_place = lock_mask << lock_shift,
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biased_lock_mask = right_n_bits(lock_bits + biased_lock_bits),
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biased_lock_mask_in_place= biased_lock_mask << lock_shift,
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biased_lock_bit_in_place = 1 << biased_lock_shift,
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age_mask = right_n_bits(age_bits),
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age_mask_in_place = age_mask << age_shift,
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epoch_mask = right_n_bits(epoch_bits),
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epoch_mask_in_place = epoch_mask << epoch_shift
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#ifndef _WIN64
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,hash_mask = right_n_bits(hash_bits),
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hash_mask_in_place = (address_word)hash_mask << hash_shift
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#endif
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};
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// Alignment of JavaThread pointers encoded in object header required by biased locking
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enum { biased_lock_alignment = 2 << (epoch_shift + epoch_bits)
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};
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#ifdef _WIN64
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// These values are too big for Win64
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const static uintptr_t hash_mask = right_n_bits(hash_bits);
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const static uintptr_t hash_mask_in_place =
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(address_word)hash_mask << hash_shift;
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#endif
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enum { locked_value = 0,
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unlocked_value = 1,
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monitor_value = 2,
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marked_value = 3,
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biased_lock_pattern = 5
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};
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enum { no_hash = 0 }; // no hash value assigned
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enum { no_hash_in_place = (address_word)no_hash << hash_shift,
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no_lock_in_place = unlocked_value
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};
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enum { max_age = age_mask };
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enum { max_bias_epoch = epoch_mask };
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// Biased Locking accessors.
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// These must be checked by all code which calls into the
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// ObjectSynchronizer and other code. The biasing is not understood
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// by the lower-level CAS-based locking code, although the runtime
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// fixes up biased locks to be compatible with it when a bias is
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// revoked.
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bool has_bias_pattern() const {
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return (mask_bits(value(), biased_lock_mask_in_place) == biased_lock_pattern);
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}
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JavaThread* biased_locker() const {
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assert(has_bias_pattern(), "should not call this otherwise");
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return (JavaThread*) ((intptr_t) (mask_bits(value(), ~(biased_lock_mask_in_place | age_mask_in_place | epoch_mask_in_place))));
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}
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// Indicates that the mark has the bias bit set but that it has not
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// yet been biased toward a particular thread
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bool is_biased_anonymously() const {
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return (has_bias_pattern() && (biased_locker() == NULL));
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}
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// Indicates epoch in which this bias was acquired. If the epoch
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// changes due to too many bias revocations occurring, the biases
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// from the previous epochs are all considered invalid.
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int bias_epoch() const {
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assert(has_bias_pattern(), "should not call this otherwise");
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return (mask_bits(value(), epoch_mask_in_place) >> epoch_shift);
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}
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markOop set_bias_epoch(int epoch) {
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assert(has_bias_pattern(), "should not call this otherwise");
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assert((epoch & (~epoch_mask)) == 0, "epoch overflow");
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return markOop(mask_bits(value(), ~epoch_mask_in_place) | (epoch << epoch_shift));
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}
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markOop incr_bias_epoch() {
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return set_bias_epoch((1 + bias_epoch()) & epoch_mask);
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}
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// Prototype mark for initialization
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static markOop biased_locking_prototype() {
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return markOop( biased_lock_pattern );
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}
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// lock accessors (note that these assume lock_shift == 0)
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bool is_locked() const {
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return (mask_bits(value(), lock_mask_in_place) != unlocked_value);
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}
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bool is_unlocked() const {
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return (mask_bits(value(), biased_lock_mask_in_place) == unlocked_value);
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}
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bool is_marked() const {
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return (mask_bits(value(), lock_mask_in_place) == marked_value);
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}
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bool is_neutral() const { return (mask_bits(value(), biased_lock_mask_in_place) == unlocked_value); }
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// Special temporary state of the markOop while being inflated.
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// Code that looks at mark outside a lock need to take this into account.
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bool is_being_inflated() const { return (value() == 0); }
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// Distinguished markword value - used when inflating over
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// an existing stacklock. 0 indicates the markword is "BUSY".
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// Lockword mutators that use a LD...CAS idiom should always
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// check for and avoid overwriting a 0 value installed by some
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// other thread. (They should spin or block instead. The 0 value
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// is transient and *should* be short-lived).
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static markOop INFLATING() { return (markOop) 0; } // inflate-in-progress
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// Should this header be preserved during GC?
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bool must_be_preserved(oop obj_containing_mark) const {
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if (!UseBiasedLocking)
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return (!is_unlocked() || !has_no_hash());
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return must_be_preserved_with_bias(obj_containing_mark);
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}
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inline bool must_be_preserved_with_bias(oop obj_containing_mark) const;
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// Should this header (including its age bits) be preserved in the
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// case of a promotion failure during scavenge?
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// Note that we special case this situation. We want to avoid
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// calling BiasedLocking::preserve_marks()/restore_marks() (which
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// decrease the number of mark words that need to be preserved
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// during GC) during each scavenge. During scavenges in which there
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// is no promotion failure, we actually don't need to call the above
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// routines at all, since we don't mutate and re-initialize the
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// marks of promoted objects using init_mark(). However, during
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// scavenges which result in promotion failure, we do re-initialize
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// the mark words of objects, meaning that we should have called
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// these mark word preservation routines. Currently there's no good
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// place in which to call them in any of the scavengers (although
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// guarded by appropriate locks we could make one), but the
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// observation is that promotion failures are quite rare and
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// reducing the number of mark words preserved during them isn't a
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// high priority.
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bool must_be_preserved_for_promotion_failure(oop obj_containing_mark) const {
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if (!UseBiasedLocking)
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return (this != prototype());
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return must_be_preserved_with_bias_for_promotion_failure(obj_containing_mark);
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}
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inline bool must_be_preserved_with_bias_for_promotion_failure(oop obj_containing_mark) const;
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// Should this header be preserved during a scavenge where CMS is
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// the old generation?
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// (This is basically the same body as must_be_preserved_for_promotion_failure(),
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// but takes the klassOop as argument instead)
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bool must_be_preserved_for_cms_scavenge(klassOop klass_of_obj_containing_mark) const {
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if (!UseBiasedLocking)
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return (this != prototype());
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return must_be_preserved_with_bias_for_cms_scavenge(klass_of_obj_containing_mark);
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}
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inline bool must_be_preserved_with_bias_for_cms_scavenge(klassOop klass_of_obj_containing_mark) const;
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// WARNING: The following routines are used EXCLUSIVELY by
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// synchronization functions. They are not really gc safe.
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// They must get updated if markOop layout get changed.
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markOop set_unlocked() const {
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return markOop(value() | unlocked_value);
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}
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bool has_locker() const {
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return ((value() & lock_mask_in_place) == locked_value);
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}
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BasicLock* locker() const {
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assert(has_locker(), "check");
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return (BasicLock*) value();
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}
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bool has_monitor() const {
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return ((value() & monitor_value) != 0);
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}
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ObjectMonitor* monitor() const {
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assert(has_monitor(), "check");
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// Use xor instead of &~ to provide one extra tag-bit check.
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return (ObjectMonitor*) (value() ^ monitor_value);
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}
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bool has_displaced_mark_helper() const {
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return ((value() & unlocked_value) == 0);
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}
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markOop displaced_mark_helper() const {
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assert(has_displaced_mark_helper(), "check");
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intptr_t ptr = (value() & ~monitor_value);
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return *(markOop*)ptr;
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}
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void set_displaced_mark_helper(markOop m) const {
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assert(has_displaced_mark_helper(), "check");
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intptr_t ptr = (value() & ~monitor_value);
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*(markOop*)ptr = m;
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}
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markOop copy_set_hash(intptr_t hash) const {
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intptr_t tmp = value() & (~hash_mask_in_place);
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tmp |= ((hash & hash_mask) << hash_shift);
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return (markOop)tmp;
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}
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// it is only used to be stored into BasicLock as the
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// indicator that the lock is using heavyweight monitor
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static markOop unused_mark() {
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return (markOop) marked_value;
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}
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// the following two functions create the markOop to be
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// stored into object header, it encodes monitor info
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static markOop encode(BasicLock* lock) {
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return (markOop) lock;
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}
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static markOop encode(ObjectMonitor* monitor) {
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intptr_t tmp = (intptr_t) monitor;
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return (markOop) (tmp | monitor_value);
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}
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static markOop encode(JavaThread* thread, int age, int bias_epoch) {
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intptr_t tmp = (intptr_t) thread;
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assert(UseBiasedLocking && ((tmp & (epoch_mask_in_place | age_mask_in_place | biased_lock_mask_in_place)) == 0), "misaligned JavaThread pointer");
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assert(age <= max_age, "age too large");
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assert(bias_epoch <= max_bias_epoch, "bias epoch too large");
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return (markOop) (tmp | (bias_epoch << epoch_shift) | (age << age_shift) | biased_lock_pattern);
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}
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// used to encode pointers during GC
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markOop clear_lock_bits() { return markOop(value() & ~lock_mask_in_place); }
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// age operations
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markOop set_marked() { return markOop((value() & ~lock_mask_in_place) | marked_value); }
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int age() const { return mask_bits(value() >> age_shift, age_mask); }
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markOop set_age(int v) const {
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assert((v & ~age_mask) == 0, "shouldn't overflow age field");
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return markOop((value() & ~age_mask_in_place) | (((intptr_t)v & age_mask) << age_shift));
|
||
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|
}
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||
|
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markOop incr_age() const { return age() == max_age ? markOop(this) : set_age(age() + 1); }
|
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||
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// hash operations
|
||
|
|
intptr_t hash() const {
|
||
|
|
return mask_bits(value() >> hash_shift, hash_mask);
|
||
|
|
}
|
||
|
|
|
||
|
|
bool has_no_hash() const {
|
||
|
|
return hash() == no_hash;
|
||
|
|
}
|
||
|
|
|
||
|
|
// Prototype mark for initialization
|
||
|
|
static markOop prototype() {
|
||
|
|
return markOop( no_hash_in_place | no_lock_in_place );
|
||
|
|
}
|
||
|
|
|
||
|
|
// Helper function for restoration of unmarked mark oops during GC
|
||
|
|
static inline markOop prototype_for_object(oop obj);
|
||
|
|
|
||
|
|
// Debugging
|
||
|
|
void print_on(outputStream* st) const;
|
||
|
|
|
||
|
|
// Prepare address of oop for placement into mark
|
||
|
|
inline static markOop encode_pointer_as_mark(void* p) { return markOop(p)->set_marked(); }
|
||
|
|
|
||
|
|
// Recover address of oop from encoded form used in mark
|
||
|
|
inline void* decode_pointer() { if (UseBiasedLocking && has_bias_pattern()) return NULL; return clear_lock_bits(); }
|
||
|
|
};
|