jdk-sandbox: comparison src/hotspot/share/oops/markWord.hpp

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+/*
+* 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"
+// 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
+enum { age_bits                 = 4,
+lock_bits                = 2,
+biased_lock_bits         = 1,
+max_hash_bits            = BitsPerWord - age_bits - lock_bits - biased_lock_bits,
+hash_bits                = max_hash_bits > 31 ? 31 : max_hash_bits,
+cms_bits                 = LP64_ONLY(1) NOT_LP64(0),
+epoch_bits               = 2
+};
+// The biased locking code currently requires that the age bits be
+// contiguous to the lock bits.
+enum { lock_shift               = 0,
+biased_lock_shift        = lock_bits,
+age_shift                = lock_bits + biased_lock_bits,
+cms_shift                = age_shift + age_bits,
+hash_shift               = cms_shift + cms_bits,
+epoch_shift              = hash_shift
+};
+enum { lock_mask                = right_n_bits(lock_bits),
+lock_mask_in_place       = lock_mask << lock_shift,
+biased_lock_mask         = right_n_bits(lock_bits + biased_lock_bits),
+biased_lock_mask_in_place= biased_lock_mask << lock_shift,
+biased_lock_bit_in_place = 1 << biased_lock_shift,
+age_mask                 = right_n_bits(age_bits),
+age_mask_in_place        = age_mask << age_shift,
+epoch_mask               = right_n_bits(epoch_bits),
+epoch_mask_in_place      = epoch_mask << epoch_shift,
+cms_mask                 = right_n_bits(cms_bits),
+cms_mask_in_place        = cms_mask << cms_shift
+};
+const static uintptr_t hash_mask = right_n_bits(hash_bits);
+const static uintptr_t hash_mask_in_place = hash_mask << hash_shift;
+// Alignment of JavaThread pointers encoded in object header required by biased locking
+enum { biased_lock_alignment    = 2 << (epoch_shift + epoch_bits)
+};
+enum { locked_value             = 0,
+unlocked_value           = 1,
+monitor_value            = 2,
+marked_value             = 3,
+biased_lock_pattern      = 5
+};
+enum { no_hash                  = 0 };  // no hash value assigned
+enum { no_hash_in_place         = (address_word)no_hash << hash_shift,
+no_lock_in_place         = unlocked_value
+};
+enum { max_age                  = age_mask };
+enum { 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*) ((intptr_t) (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?
+inline bool must_be_preserved(oop obj_containing_mark) const;
+inline bool must_be_preserved_with_bias(oop obj_containing_mark) 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.
+inline bool must_be_preserved_for_promotion_failure(oop obj_containing_mark) const;
+inline bool must_be_preserved_with_bias_for_promotion_failure(oop obj_containing_mark) 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;
+inline bool must_be_preserved_with_bias_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");
+intptr_t ptr = (value() & ~monitor_value);
+return *(markWord*)ptr;
+}
+void set_displaced_mark_helper(markWord m) const {
+assert(has_displaced_mark_helper(), "check");
+intptr_t ptr = (value() & ~monitor_value);
+((markWord*)ptr)->_value = m._value;
+}
+markWord copy_set_hash(intptr_t hash) const {
+intptr_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) {
+intptr_t tmp = (intptr_t) monitor;
+return markWord(tmp | monitor_value);
+}
+static markWord encode(JavaThread* thread, uint age, int bias_epoch) {
+intptr_t tmp = (intptr_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) | (((uintptr_t)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_object(oop obj);
+// 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(((intptr_t)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(((intptr_t)cms_free_prototype().value() & ~size_mask_in_place) |
+(((intptr_t)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

changeset 57811	947252a54b98
parent 57777	90ead0febf56
child 57812	9bb28ccc6106