| /* |
| * Copyright 1997-2006 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 |
| * have any questions. |
| * |
| */ |
| |
| // The markOop describes the header of an object. |
| // |
| // Note that the mark is not a real oop but just a word. |
| // It is placed in the oop hierarchy for historical reasons. |
| // |
| // Bit-format of an object header (most significant first): |
| // |
| // |
| // unused:0/25 hash:25/31 age:4 biased_lock:1 lock:2 = 32/64 bits |
| // |
| // - 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) to make room for the |
| // age bits when biased locking is enabled. |
| // |
| // [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 markOopDesc: public oopDesc { |
| private: |
| // Conversion |
| uintptr_t value() const { return (uintptr_t) this; } |
| |
| public: |
| // Constants |
| enum { age_bits = 4, |
| lock_bits = 2, |
| biased_lock_bits = 1, |
| max_hash_bits = BitsPerOop - age_bits - lock_bits - biased_lock_bits, |
| hash_bits = max_hash_bits > 31 ? 31 : max_hash_bits, |
| epoch_bits = 2 |
| }; |
| |
| // The biased locking code currently requires that the age bits be |
| // contiguous to the lock bits. Class data sharing would prefer the |
| // hash bits to be lower down to provide more random hash codes for |
| // shared read-only symbolOop objects, because these objects' mark |
| // words are set to their own address with marked_value in the lock |
| // bit, and using lower bits would make their identity hash values |
| // more random. However, the performance decision was made in favor |
| // of the biased locking code. |
| |
| enum { lock_shift = 0, |
| biased_lock_shift = lock_bits, |
| age_shift = lock_bits + biased_lock_bits, |
| hash_shift = lock_bits + biased_lock_bits + age_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 |
| #ifndef _WIN64 |
| ,hash_mask = right_n_bits(hash_bits), |
| hash_mask_in_place = (address_word)hash_mask << hash_shift |
| #endif |
| }; |
| |
| // Alignment of JavaThread pointers encoded in object header required by biased locking |
| enum { biased_lock_alignment = 2 << (epoch_shift + epoch_bits) |
| }; |
| |
| #ifdef _WIN64 |
| // These values are too big for Win64 |
| const static uintptr_t hash_mask = right_n_bits(hash_bits); |
| const static uintptr_t hash_mask_in_place = |
| (address_word)hash_mask << hash_shift; |
| #endif |
| |
| 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 }; |
| |
| // 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); |
| } |
| markOop set_bias_epoch(int epoch) { |
| assert(has_bias_pattern(), "should not call this otherwise"); |
| assert((epoch & (~epoch_mask)) == 0, "epoch overflow"); |
| return markOop(mask_bits(value(), ~epoch_mask_in_place) | (epoch << epoch_shift)); |
| } |
| markOop incr_bias_epoch() { |
| return set_bias_epoch((1 + bias_epoch()) & epoch_mask); |
| } |
| // Prototype mark for initialization |
| static markOop biased_locking_prototype() { |
| return markOop( 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 markOop 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 markOop INFLATING() { return (markOop) 0; } // inflate-in-progress |
| |
| // Should this header be preserved during GC? |
| bool must_be_preserved(oop obj_containing_mark) const { |
| if (!UseBiasedLocking) |
| return (!is_unlocked() || !has_no_hash()); |
| return must_be_preserved_with_bias(obj_containing_mark); |
| } |
| 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. |
| bool must_be_preserved_for_promotion_failure(oop obj_containing_mark) const { |
| if (!UseBiasedLocking) |
| return (this != prototype()); |
| return must_be_preserved_with_bias_for_promotion_failure(obj_containing_mark); |
| } |
| 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 klassOop as argument instead) |
| bool must_be_preserved_for_cms_scavenge(klassOop klass_of_obj_containing_mark) const { |
| if (!UseBiasedLocking) |
| return (this != prototype()); |
| return must_be_preserved_with_bias_for_cms_scavenge(klass_of_obj_containing_mark); |
| } |
| inline bool must_be_preserved_with_bias_for_cms_scavenge(klassOop 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 markOop layout get changed. |
| markOop set_unlocked() const { |
| return markOop(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); |
| } |
| markOop displaced_mark_helper() const { |
| assert(has_displaced_mark_helper(), "check"); |
| intptr_t ptr = (value() & ~monitor_value); |
| return *(markOop*)ptr; |
| } |
| void set_displaced_mark_helper(markOop m) const { |
| assert(has_displaced_mark_helper(), "check"); |
| intptr_t ptr = (value() & ~monitor_value); |
| *(markOop*)ptr = m; |
| } |
| markOop copy_set_hash(intptr_t hash) const { |
| intptr_t tmp = value() & (~hash_mask_in_place); |
| tmp |= ((hash & hash_mask) << hash_shift); |
| return (markOop)tmp; |
| } |
| // it is only used to be stored into BasicLock as the |
| // indicator that the lock is using heavyweight monitor |
| static markOop unused_mark() { |
| return (markOop) marked_value; |
| } |
| // the following two functions create the markOop to be |
| // stored into object header, it encodes monitor info |
| static markOop encode(BasicLock* lock) { |
| return (markOop) lock; |
| } |
| static markOop encode(ObjectMonitor* monitor) { |
| intptr_t tmp = (intptr_t) monitor; |
| return (markOop) (tmp | monitor_value); |
| } |
| static markOop encode(JavaThread* thread, int 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 (markOop) (tmp | (bias_epoch << epoch_shift) | (age << age_shift) | biased_lock_pattern); |
| } |
| |
| // used to encode pointers during GC |
| markOop clear_lock_bits() { return markOop(value() & ~lock_mask_in_place); } |
| |
| // age operations |
| markOop set_marked() { return markOop((value() & ~lock_mask_in_place) | marked_value); } |
| |
| int age() const { return mask_bits(value() >> age_shift, age_mask); } |
| markOop set_age(int v) const { |
| assert((v & ~age_mask) == 0, "shouldn't overflow age field"); |
| return markOop((value() & ~age_mask_in_place) | (((intptr_t)v & age_mask) << age_shift)); |
| } |
| markOop incr_age() const { return age() == max_age ? markOop(this) : 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 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(); } |
| }; |
