jdk8-mips64-public/hotspot: src/share/vm/oops/markOop.hpp@98cb887364d3 (annotated)

src/share/vm/oops/markOop.hpp@98cb887364d3 (annotated)

src/share/vm/oops/markOop.hpp

Fri, 27 Feb 2009 13:27:09 -0800

author: twisti
date: Fri, 27 Feb 2009 13:27:09 -0800
changeset 1040: 98cb887364d3
parent 791: 1ee8caae33af
child 1901: a00b51b2dda4
permissions: -rw-r--r--

6810672: Comment typos
Summary: I have collected some typos I have found while looking at the code.
Reviewed-by: kvn, never

 /*
  * Copyright 1997-2008 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):
 //
 //  32 bits: unused:0  hash:25 age:4 biased_lock:1 lock:2
 //  64 bits: unused:24 hash:31 cms:2 age:4 biased_lock:1 lock:2
 //           unused:20 size:35 cms:2 age:4 biased_lock:1 lock:2 (if cms
 //                                                               free chunk)
 //
 //  - 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            = 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. 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,
          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
 #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?
   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 klassOop as argument instead)
   inline bool must_be_preserved_for_cms_scavenge(klassOop klass_of_obj_containing_mark) const;
   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(); }
   // see the definition in markOop.cpp for the gory details
   bool should_not_be_cached() const;
   // These markOops indicate cms free chunk blocks and not objects.
   // In 64 bit, the markOop 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 markOop cms_free_prototype() {
     return markOop(((intptr_t)prototype() & ~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 markOop set_size_and_free(size_t size) {
     assert((size & ~size_mask) == 0, "shouldn't overflow size field");
     return markOop(((intptr_t)cms_free_prototype() & ~size_mask_in_place) |
                    (((intptr_t)size & size_mask) << size_shift));
   }
 #endif // _LP64
 };

Mercurial > jdk8-mips64-public > hotspot / annotate

src/share/vm/oops/markOop.hpp@98cb887364d3 (annotated)

src/share/vm/oops/markOop.hpp