--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/src/hotspot/share/oops/markWord.hpp Thu Oct 17 20:53:35 2019 +0100
@@ -0,0 +1,426 @@
+/*
+ * Copyright (c) 1997, 2019, Oracle and/or its affiliates. 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ *
+ */
+
+#ifndef SHARE_OOPS_MARKWORD_HPP
+#define SHARE_OOPS_MARKWORD_HPP
+
+#include "metaprogramming/integralConstant.hpp"
+#include "metaprogramming/primitiveConversions.hpp"
+#include "oops/oopsHierarchy.hpp"
+#include "runtime/globals.hpp"
+
+// The markWord describes the header of an object.
+//
+// Bit-format of an object header (most significant first, big endian layout below):
+//
+// 32 bits:
+// --------
+// hash:25 ------------>| age:4 biased_lock:1 lock:2 (normal object)
+// JavaThread*:23 epoch:2 age:4 biased_lock:1 lock:2 (biased object)
+// size:32 ------------------------------------------>| (CMS free block)
+// PromotedObject*:29 ---------->| promo_bits:3 ----->| (CMS promoted object)
+//
+// 64 bits:
+// --------
+// unused:25 hash:31 -->| unused:1 age:4 biased_lock:1 lock:2 (normal object)
+// JavaThread*:54 epoch:2 unused:1 age:4 biased_lock:1 lock:2 (biased object)
+// PromotedObject*:61 --------------------->| promo_bits:3 ----->| (CMS promoted object)
+// size:64 ----------------------------------------------------->| (CMS free block)
+//
+// unused:25 hash:31 -->| cms_free:1 age:4 biased_lock:1 lock:2 (COOPs && normal object)
+// JavaThread*:54 epoch:2 cms_free:1 age:4 biased_lock:1 lock:2 (COOPs && biased object)
+// narrowOop:32 unused:24 cms_free:1 unused:4 promo_bits:3 ----->| (COOPs && CMS promoted object)
+// unused:21 size:35 -->| cms_free:1 unused:7 ------------------>| (COOPs && CMS free block)
+//
+// - hash contains the identity hash value: largest value is
+// 31 bits, see os::random(). Also, 64-bit vm's require
+// a hash value no bigger than 32 bits because they will not
+// properly generate a mask larger than that: see library_call.cpp
+// and c1_CodePatterns_sparc.cpp.
+//
+// - the biased lock pattern is used to bias a lock toward a given
+// thread. When this pattern is set in the low three bits, the lock
+// is either biased toward a given thread or "anonymously" biased,
+// indicating that it is possible for it to be biased. When the
+// lock is biased toward a given thread, locking and unlocking can
+// be performed by that thread without using atomic operations.
+// When a lock's bias is revoked, it reverts back to the normal
+// locking scheme described below.
+//
+// Note that we are overloading the meaning of the "unlocked" state
+// of the header. Because we steal a bit from the age we can
+// guarantee that the bias pattern will never be seen for a truly
+// unlocked object.
+//
+// Note also that the biased state contains the age bits normally
+// contained in the object header. Large increases in scavenge
+// times were seen when these bits were absent and an arbitrary age
+// assigned to all biased objects, because they tended to consume a
+// significant fraction of the eden semispaces and were not
+// promoted promptly, causing an increase in the amount of copying
+// performed. The runtime system aligns all JavaThread* pointers to
+// a very large value (currently 128 bytes (32bVM) or 256 bytes (64bVM))
+// to make room for the age bits & the epoch bits (used in support of
+// biased locking), and for the CMS "freeness" bit in the 64bVM (+COOPs).
+//
+// [JavaThread* | epoch | age | 1 | 01] lock is biased toward given thread
+// [0 | epoch | age | 1 | 01] lock is anonymously biased
+//
+// - the two lock bits are used to describe three states: locked/unlocked and monitor.
+//
+// [ptr | 00] locked ptr points to real header on stack
+// [header | 0 | 01] unlocked regular object header
+// [ptr | 10] monitor inflated lock (header is wapped out)
+// [ptr | 11] marked used by markSweep to mark an object
+// not valid at any other time
+//
+// We assume that stack/thread pointers have the lowest two bits cleared.
+
+class BasicLock;
+class ObjectMonitor;
+class JavaThread;
+
+class markWord {
+ private:
+ uintptr_t _value;
+
+ public:
+ explicit markWord(uintptr_t value) : _value(value) {}
+
+ markWord() { /* uninitialized */}
+
+ // It is critical for performance that this class be trivially
+ // destructable, copyable, and assignable.
+
+ static markWord from_pointer(void* ptr) {
+ return markWord((uintptr_t)ptr);
+ }
+ void* to_pointer() const {
+ return (void*)_value;
+ }
+
+ bool operator==(const markWord& other) const {
+ return _value == other._value;
+ }
+ bool operator!=(const markWord& other) const {
+ return !operator==(other);
+ }
+
+ // Conversion
+ uintptr_t value() const { return _value; }
+
+ // Constants
+ static const int age_bits = 4;
+ static const int lock_bits = 2;
+ static const int biased_lock_bits = 1;
+ static const int max_hash_bits = BitsPerWord - age_bits - lock_bits - biased_lock_bits;
+ static const int hash_bits = max_hash_bits > 31 ? 31 : max_hash_bits;
+ static const int cms_bits = LP64_ONLY(1) NOT_LP64(0);
+ static const int epoch_bits = 2;
+
+ // The biased locking code currently requires that the age bits be
+ // contiguous to the lock bits.
+ static const int lock_shift = 0;
+ static const int biased_lock_shift = lock_bits;
+ static const int age_shift = lock_bits + biased_lock_bits;
+ static const int cms_shift = age_shift + age_bits;
+ static const int hash_shift = cms_shift + cms_bits;
+ static const int epoch_shift = hash_shift;
+
+ static const uintptr_t lock_mask = right_n_bits(lock_bits);
+ static const uintptr_t lock_mask_in_place = lock_mask << lock_shift;
+ static const uintptr_t biased_lock_mask = right_n_bits(lock_bits + biased_lock_bits);
+ static const uintptr_t biased_lock_mask_in_place= biased_lock_mask << lock_shift;
+ static const uintptr_t biased_lock_bit_in_place = 1 << biased_lock_shift;
+ static const uintptr_t age_mask = right_n_bits(age_bits);
+ static const uintptr_t age_mask_in_place = age_mask << age_shift;
+ static const uintptr_t epoch_mask = right_n_bits(epoch_bits);
+ static const uintptr_t epoch_mask_in_place = epoch_mask << epoch_shift;
+ static const uintptr_t cms_mask = right_n_bits(cms_bits);
+ static const uintptr_t cms_mask_in_place = cms_mask << cms_shift;
+
+ static const uintptr_t hash_mask = right_n_bits(hash_bits);
+ static const uintptr_t hash_mask_in_place = hash_mask << hash_shift;
+
+ // Alignment of JavaThread pointers encoded in object header required by biased locking
+ static const size_t biased_lock_alignment = 2 << (epoch_shift + epoch_bits);
+
+ static const uintptr_t locked_value = 0;
+ static const uintptr_t unlocked_value = 1;
+ static const uintptr_t monitor_value = 2;
+ static const uintptr_t marked_value = 3;
+ static const uintptr_t biased_lock_pattern = 5;
+
+ static const uintptr_t no_hash = 0 ; // no hash value assigned
+ static const uintptr_t no_hash_in_place = (address_word)no_hash << hash_shift;
+ static const uintptr_t no_lock_in_place = unlocked_value;
+
+ static const uint max_age = age_mask;
+
+ static const int max_bias_epoch = epoch_mask;
+
+ // Creates a markWord with all bits set to zero.
+ static markWord zero() { return markWord(uintptr_t(0)); }
+
+ // Biased Locking accessors.
+ // These must be checked by all code which calls into the
+ // ObjectSynchronizer and other code. The biasing is not understood
+ // by the lower-level CAS-based locking code, although the runtime
+ // fixes up biased locks to be compatible with it when a bias is
+ // revoked.
+ bool has_bias_pattern() const {
+ return (mask_bits(value(), biased_lock_mask_in_place) == biased_lock_pattern);
+ }
+ JavaThread* biased_locker() const {
+ assert(has_bias_pattern(), "should not call this otherwise");
+ return (JavaThread*) mask_bits(value(), ~(biased_lock_mask_in_place | age_mask_in_place | epoch_mask_in_place));
+ }
+ // Indicates that the mark has the bias bit set but that it has not
+ // yet been biased toward a particular thread
+ bool is_biased_anonymously() const {
+ return (has_bias_pattern() && (biased_locker() == NULL));
+ }
+ // Indicates epoch in which this bias was acquired. If the epoch
+ // changes due to too many bias revocations occurring, the biases
+ // from the previous epochs are all considered invalid.
+ int bias_epoch() const {
+ assert(has_bias_pattern(), "should not call this otherwise");
+ return (mask_bits(value(), epoch_mask_in_place) >> epoch_shift);
+ }
+ markWord set_bias_epoch(int epoch) {
+ assert(has_bias_pattern(), "should not call this otherwise");
+ assert((epoch & (~epoch_mask)) == 0, "epoch overflow");
+ return markWord(mask_bits(value(), ~epoch_mask_in_place) | (epoch << epoch_shift));
+ }
+ markWord incr_bias_epoch() {
+ return set_bias_epoch((1 + bias_epoch()) & epoch_mask);
+ }
+ // Prototype mark for initialization
+ static markWord biased_locking_prototype() {
+ return markWord( biased_lock_pattern );
+ }
+
+ // lock accessors (note that these assume lock_shift == 0)
+ bool is_locked() const {
+ return (mask_bits(value(), lock_mask_in_place) != unlocked_value);
+ }
+ bool is_unlocked() const {
+ return (mask_bits(value(), biased_lock_mask_in_place) == unlocked_value);
+ }
+ bool is_marked() const {
+ return (mask_bits(value(), lock_mask_in_place) == marked_value);
+ }
+ bool is_neutral() const { return (mask_bits(value(), biased_lock_mask_in_place) == unlocked_value); }
+
+ // Special temporary state of the markWord while being inflated.
+ // Code that looks at mark outside a lock need to take this into account.
+ bool is_being_inflated() const { return (value() == 0); }
+
+ // Distinguished markword value - used when inflating over
+ // an existing stacklock. 0 indicates the markword is "BUSY".
+ // Lockword mutators that use a LD...CAS idiom should always
+ // check for and avoid overwriting a 0 value installed by some
+ // other thread. (They should spin or block instead. The 0 value
+ // is transient and *should* be short-lived).
+ static markWord INFLATING() { return zero(); } // inflate-in-progress
+
+ // Should this header be preserved during GC?
+ template <typename KlassProxy>
+ inline bool must_be_preserved(KlassProxy klass) const;
+
+ // Should this header (including its age bits) be preserved in the
+ // case of a promotion failure during scavenge?
+ // Note that we special case this situation. We want to avoid
+ // calling BiasedLocking::preserve_marks()/restore_marks() (which
+ // decrease the number of mark words that need to be preserved
+ // during GC) during each scavenge. During scavenges in which there
+ // is no promotion failure, we actually don't need to call the above
+ // routines at all, since we don't mutate and re-initialize the
+ // marks of promoted objects using init_mark(). However, during
+ // scavenges which result in promotion failure, we do re-initialize
+ // the mark words of objects, meaning that we should have called
+ // these mark word preservation routines. Currently there's no good
+ // place in which to call them in any of the scavengers (although
+ // guarded by appropriate locks we could make one), but the
+ // observation is that promotion failures are quite rare and
+ // reducing the number of mark words preserved during them isn't a
+ // high priority.
+ template <typename KlassProxy>
+ inline bool must_be_preserved_for_promotion_failure(KlassProxy klass) const;
+
+ // Should this header be preserved during a scavenge where CMS is
+ // the old generation?
+ // (This is basically the same body as must_be_preserved_for_promotion_failure(),
+ // but takes the Klass* as argument instead)
+ inline bool must_be_preserved_for_cms_scavenge(Klass* klass_of_obj_containing_mark) const;
+
+ // WARNING: The following routines are used EXCLUSIVELY by
+ // synchronization functions. They are not really gc safe.
+ // They must get updated if markWord layout get changed.
+ markWord set_unlocked() const {
+ return markWord(value() | unlocked_value);
+ }
+ bool has_locker() const {
+ return ((value() & lock_mask_in_place) == locked_value);
+ }
+ BasicLock* locker() const {
+ assert(has_locker(), "check");
+ return (BasicLock*) value();
+ }
+ bool has_monitor() const {
+ return ((value() & monitor_value) != 0);
+ }
+ ObjectMonitor* monitor() const {
+ assert(has_monitor(), "check");
+ // Use xor instead of &~ to provide one extra tag-bit check.
+ return (ObjectMonitor*) (value() ^ monitor_value);
+ }
+ bool has_displaced_mark_helper() const {
+ return ((value() & unlocked_value) == 0);
+ }
+ markWord displaced_mark_helper() const {
+ assert(has_displaced_mark_helper(), "check");
+ uintptr_t ptr = (value() & ~monitor_value);
+ return *(markWord*)ptr;
+ }
+ void set_displaced_mark_helper(markWord m) const {
+ assert(has_displaced_mark_helper(), "check");
+ uintptr_t ptr = (value() & ~monitor_value);
+ ((markWord*)ptr)->_value = m._value;
+ }
+ markWord copy_set_hash(intptr_t hash) const {
+ uintptr_t tmp = value() & (~hash_mask_in_place);
+ tmp |= ((hash & hash_mask) << hash_shift);
+ return markWord(tmp);
+ }
+ // it is only used to be stored into BasicLock as the
+ // indicator that the lock is using heavyweight monitor
+ static markWord unused_mark() {
+ return markWord(marked_value);
+ }
+ // the following two functions create the markWord to be
+ // stored into object header, it encodes monitor info
+ static markWord encode(BasicLock* lock) {
+ return from_pointer(lock);
+ }
+ static markWord encode(ObjectMonitor* monitor) {
+ uintptr_t tmp = (uintptr_t) monitor;
+ return markWord(tmp | monitor_value);
+ }
+ static markWord encode(JavaThread* thread, uint age, int bias_epoch) {
+ uintptr_t tmp = (uintptr_t) thread;
+ assert(UseBiasedLocking && ((tmp & (epoch_mask_in_place | age_mask_in_place | biased_lock_mask_in_place)) == 0), "misaligned JavaThread pointer");
+ assert(age <= max_age, "age too large");
+ assert(bias_epoch <= max_bias_epoch, "bias epoch too large");
+ return markWord(tmp | (bias_epoch << epoch_shift) | (age << age_shift) | biased_lock_pattern);
+ }
+
+ // used to encode pointers during GC
+ markWord clear_lock_bits() { return markWord(value() & ~lock_mask_in_place); }
+
+ // age operations
+ markWord set_marked() { return markWord((value() & ~lock_mask_in_place) | marked_value); }
+ markWord set_unmarked() { return markWord((value() & ~lock_mask_in_place) | unlocked_value); }
+
+ uint age() const { return mask_bits(value() >> age_shift, age_mask); }
+ markWord set_age(uint v) const {
+ assert((v & ~age_mask) == 0, "shouldn't overflow age field");
+ return markWord((value() & ~age_mask_in_place) | ((v & age_mask) << age_shift));
+ }
+ markWord incr_age() const { return age() == max_age ? markWord(_value) : set_age(age() + 1); }
+
+ // 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 markWord prototype() {
+ return markWord( no_hash_in_place | no_lock_in_place );
+ }
+
+ // Helper function for restoration of unmarked mark oops during GC
+ static inline markWord prototype_for_klass(const Klass* klass);
+
+ // Debugging
+ void print_on(outputStream* st) const;
+
+ // Prepare address of oop for placement into mark
+ inline static markWord encode_pointer_as_mark(void* p) { return from_pointer(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 (void*)clear_lock_bits().value(); }
+
+ // These markWords indicate cms free chunk blocks and not objects.
+ // In 64 bit, the markWord is set to distinguish them from oops.
+ // These are defined in 32 bit mode for vmStructs.
+ const static uintptr_t cms_free_chunk_pattern = 0x1;
+
+ // Constants for the size field.
+ enum { size_shift = cms_shift + cms_bits,
+ size_bits = 35 // need for compressed oops 32G
+ };
+ // These values are too big for Win64
+ const static uintptr_t size_mask = LP64_ONLY(right_n_bits(size_bits))
+ NOT_LP64(0);
+ const static uintptr_t size_mask_in_place =
+ (address_word)size_mask << size_shift;
+
+#ifdef _LP64
+ static markWord cms_free_prototype() {
+ return markWord((prototype().value() & ~cms_mask_in_place) |
+ ((cms_free_chunk_pattern & cms_mask) << cms_shift));
+ }
+ uintptr_t cms_encoding() const {
+ return mask_bits(value() >> cms_shift, cms_mask);
+ }
+ bool is_cms_free_chunk() const {
+ return is_neutral() &&
+ (cms_encoding() & cms_free_chunk_pattern) == cms_free_chunk_pattern;
+ }
+
+ size_t get_size() const { return (size_t)(value() >> size_shift); }
+ static markWord set_size_and_free(size_t size) {
+ assert((size & ~size_mask) == 0, "shouldn't overflow size field");
+ return markWord((cms_free_prototype().value() & ~size_mask_in_place) |
+ ((size & size_mask) << size_shift));
+ }
+#endif // _LP64
+};
+
+// Support atomic operations.
+template<>
+struct PrimitiveConversions::Translate<markWord> : public TrueType {
+ typedef markWord Value;
+ typedef uintptr_t Decayed;
+
+ static Decayed decay(const Value& x) { return x.value(); }
+ static Value recover(Decayed x) { return Value(x); }
+};
+
+#endif // SHARE_OOPS_MARKWORD_HPP