1 /*

     2  * Copyright (c) 2014, 2015, Oracle and/or its affiliates. All rights reserved.

     3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

     4  *

     5  * This code is free software; you can redistribute it and/or modify it

     6  * under the terms of the GNU General Public License version 2 only, as

     7  * published by the Free Software Foundation.

     8  *

     9  * This code is distributed in the hope that it will be useful, but WITHOUT

    10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

    11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

    12  * version 2 for more details (a copy is included in the LICENSE file that

    13  * accompanied this code).

    14  *

    15  * You should have received a copy of the GNU General Public License version

    16  * 2 along with this work; if not, write to the Free Software Foundation,

    17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

    18  *

    19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

    20  * or visit www.oracle.com if you need additional information or have any

    21  * questions.

    22  *

    23  */

    24 

    25 #include "precompiled.hpp"

    26 #include "classfile/javaClasses.inline.hpp"

    27 #include "gc/g1/g1CollectedHeap.inline.hpp"

    28 #include "gc/g1/g1GCPhaseTimes.hpp"

    29 #include "gc/g1/g1StringDedup.hpp"

    30 #include "gc/g1/g1StringDedupQueue.hpp"

    31 #include "gc/g1/g1StringDedupStat.hpp"

    32 #include "gc/g1/g1StringDedupTable.hpp"

    33 #include "gc/g1/g1StringDedupThread.hpp"

    34 #include "runtime/atomic.inline.hpp"

    35 

    36 bool G1StringDedup::_enabled = false;

    37 

    38 void G1StringDedup::initialize() {

    39   assert(UseG1GC, "String deduplication only available with G1");

    40   if (UseStringDeduplication) {

    41     _enabled = true;

    42     G1StringDedupQueue::create();

    43     G1StringDedupTable::create();

    44     G1StringDedupThread::create();

    45   }

    46 }

    47 

    48 void G1StringDedup::stop() {

    49   assert(is_enabled(), "String deduplication not enabled");

    50   G1StringDedupThread::stop();

    51 }

    52 

    53 bool G1StringDedup::is_candidate_from_mark(oop obj) {

    54   if (java_lang_String::is_instance_inlined(obj)) {

    55     bool from_young = G1CollectedHeap::heap()->heap_region_containing_raw(obj)->is_young();

    56     if (from_young && obj->age() < StringDeduplicationAgeThreshold) {

    57       // Candidate found. String is being evacuated from young to old but has not

    58       // reached the deduplication age threshold, i.e. has not previously been a

    59       // candidate during its life in the young generation.

    60       return true;

    61     }

    62   }

    63 

    64   // Not a candidate

    65   return false;

    66 }

    67 

    68 void G1StringDedup::enqueue_from_mark(oop java_string) {

    69   assert(is_enabled(), "String deduplication not enabled");

    70   if (is_candidate_from_mark(java_string)) {

    71     G1StringDedupQueue::push(0 /* worker_id */, java_string);

    72   }

    73 }

    74 

    75 bool G1StringDedup::is_candidate_from_evacuation(bool from_young, bool to_young, oop obj) {

    76   if (from_young && java_lang_String::is_instance_inlined(obj)) {

    77     if (to_young && obj->age() == StringDeduplicationAgeThreshold) {

    78       // Candidate found. String is being evacuated from young to young and just

    79       // reached the deduplication age threshold.

    80       return true;

    81     }

    82     if (!to_young && obj->age() < StringDeduplicationAgeThreshold) {

    83       // Candidate found. String is being evacuated from young to old but has not

    84       // reached the deduplication age threshold, i.e. has not previously been a

    85       // candidate during its life in the young generation.

    86       return true;

    87     }

    88   }

    89 

    90   // Not a candidate

    91   return false;

    92 }

    93 

    94 void G1StringDedup::enqueue_from_evacuation(bool from_young, bool to_young, uint worker_id, oop java_string) {

    95   assert(is_enabled(), "String deduplication not enabled");

    96   if (is_candidate_from_evacuation(from_young, to_young, java_string)) {

    97     G1StringDedupQueue::push(worker_id, java_string);

    98   }

    99 }

   100 

   101 void G1StringDedup::deduplicate(oop java_string) {

   102   assert(is_enabled(), "String deduplication not enabled");

   103   G1StringDedupStat dummy; // Statistics from this path is never used

   104   G1StringDedupTable::deduplicate(java_string, dummy);

   105 }

   106 

   107 void G1StringDedup::oops_do(OopClosure* keep_alive) {

   108   assert(is_enabled(), "String deduplication not enabled");

   109   unlink_or_oops_do(NULL, keep_alive, true /* allow_resize_and_rehash */);

   110 }

   111 

   112 void G1StringDedup::unlink(BoolObjectClosure* is_alive) {

   113   assert(is_enabled(), "String deduplication not enabled");

   114   // Don't allow a potential resize or rehash during unlink, as the unlink

   115   // operation itself might remove enough entries to invalidate such a decision.

   116   unlink_or_oops_do(is_alive, NULL, false /* allow_resize_and_rehash */);

   117 }

   118 

   119 //

   120 // Task for parallel unlink_or_oops_do() operation on the deduplication queue

   121 // and table.

   122 //

   123 class G1StringDedupUnlinkOrOopsDoTask : public AbstractGangTask {

   124 private:

   125   G1StringDedupUnlinkOrOopsDoClosure _cl;

   126   G1GCPhaseTimes* _phase_times;

   127 

   128 public:

   129   G1StringDedupUnlinkOrOopsDoTask(BoolObjectClosure* is_alive,

   130                                   OopClosure* keep_alive,

   131                                   bool allow_resize_and_rehash,

   132                                   G1GCPhaseTimes* phase_times) :

   133     AbstractGangTask("G1StringDedupUnlinkOrOopsDoTask"),

   134     _cl(is_alive, keep_alive, allow_resize_and_rehash), _phase_times(phase_times) { }

   135 

   136   virtual void work(uint worker_id) {

   137     {

   138       G1GCParPhaseTimesTracker x(_phase_times, G1GCPhaseTimes::StringDedupQueueFixup, worker_id);

   139       G1StringDedupQueue::unlink_or_oops_do(&_cl);

   140     }

   141     {

   142       G1GCParPhaseTimesTracker x(_phase_times, G1GCPhaseTimes::StringDedupTableFixup, worker_id);

   143       G1StringDedupTable::unlink_or_oops_do(&_cl, worker_id);

   144     }

   145   }

   146 };

   147 

   148 void G1StringDedup::unlink_or_oops_do(BoolObjectClosure* is_alive,

   149                                       OopClosure* keep_alive,

   150                                       bool allow_resize_and_rehash,

   151                                       G1GCPhaseTimes* phase_times) {

   152   assert(is_enabled(), "String deduplication not enabled");

   153 

   154   G1StringDedupUnlinkOrOopsDoTask task(is_alive, keep_alive, allow_resize_and_rehash, phase_times);

   155   G1CollectedHeap* g1h = G1CollectedHeap::heap();

   156   g1h->set_par_threads();

   157   g1h->workers()->run_task(&task);

   158   g1h->set_par_threads(0);

   159 }

   160 

   161 void G1StringDedup::threads_do(ThreadClosure* tc) {

   162   assert(is_enabled(), "String deduplication not enabled");

   163   tc->do_thread(G1StringDedupThread::thread());

   164 }

   165 

   166 void G1StringDedup::print_worker_threads_on(outputStream* st) {

   167   assert(is_enabled(), "String deduplication not enabled");

   168   G1StringDedupThread::thread()->print_on(st);

   169   st->cr();

   170 }

   171 

   172 void G1StringDedup::verify() {

   173   assert(is_enabled(), "String deduplication not enabled");

   174   G1StringDedupQueue::verify();

   175   G1StringDedupTable::verify();

   176 }

   177 

   178 G1StringDedupUnlinkOrOopsDoClosure::G1StringDedupUnlinkOrOopsDoClosure(BoolObjectClosure* is_alive,

   179                                                                        OopClosure* keep_alive,

   180                                                                        bool allow_resize_and_rehash) :

   181   _is_alive(is_alive),

   182   _keep_alive(keep_alive),

   183   _resized_table(NULL),

   184   _rehashed_table(NULL),

   185   _next_queue(0),

   186   _next_bucket(0) {

   187   if (allow_resize_and_rehash) {

   188     // If both resize and rehash is needed, only do resize. Rehash of

   189     // the table will eventually happen if the situation persists.

   190     _resized_table = G1StringDedupTable::prepare_resize();

   191     if (!is_resizing()) {

   192       _rehashed_table = G1StringDedupTable::prepare_rehash();

   193     }

   194   }

   195 }

   196 

   197 G1StringDedupUnlinkOrOopsDoClosure::~G1StringDedupUnlinkOrOopsDoClosure() {

   198   assert(!is_resizing() || !is_rehashing(), "Can not both resize and rehash");

   199   if (is_resizing()) {

   200     G1StringDedupTable::finish_resize(_resized_table);

   201   } else if (is_rehashing()) {

   202     G1StringDedupTable::finish_rehash(_rehashed_table);

   203   }

   204 }

   205 

   206 // Atomically claims the next available queue for exclusive access by

   207 // the current thread. Returns the queue number of the claimed queue.

   208 size_t G1StringDedupUnlinkOrOopsDoClosure::claim_queue() {

   209   return (size_t)Atomic::add_ptr(1, &_next_queue) - 1;

   210 }

   211 

   212 // Atomically claims the next available table partition for exclusive

   213 // access by the current thread. Returns the table bucket number where

   214 // the claimed partition starts.

   215 size_t G1StringDedupUnlinkOrOopsDoClosure::claim_table_partition(size_t partition_size) {

   216   return (size_t)Atomic::add_ptr(partition_size, &_next_bucket) - partition_size;

   217 }