Mercurial > hg > graal-compiler
diff src/share/vm/oops/markOop.hpp @ 0:a61af66fc99e jdk7-b24
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author | duke |
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date | Sat, 01 Dec 2007 00:00:00 +0000 |
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children | d8b3ef7ee3e5 |
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--- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/src/share/vm/oops/markOop.hpp Sat Dec 01 00:00:00 2007 +0000 @@ -0,0 +1,360 @@ +/* + * 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(); } +};