Mercurial > jdk8-mips64-public > hotspot / file revision

 /*

  * Copyright (c) 2012, 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.

  *

  */

 #include "precompiled.hpp"

 #include "oops/instanceKlass.hpp"

 #include "runtime/atomic.hpp"

 #include "runtime/interfaceSupport.hpp"

 #include "runtime/mutexLocker.hpp"

 #include "runtime/safepoint.hpp"

 #include "runtime/threadCritical.hpp"

 #include "runtime/vm_operations.hpp"

 #include "services/memPtr.hpp"

 #include "services/memReporter.hpp"

 #include "services/memTracker.hpp"

 #include "utilities/decoder.hpp"

 #include "utilities/globalDefinitions.hpp"

 bool NMT_track_callsite = false;

 // walk all 'known' threads at NMT sync point, and collect their recorders

 void SyncThreadRecorderClosure::do_thread(Thread* thread) {

   assert(SafepointSynchronize::is_at_safepoint(), "Safepoint required");

   if (thread->is_Java_thread()) {

     JavaThread* javaThread = (JavaThread*)thread;

     MemRecorder* recorder = javaThread->get_recorder();

     if (recorder != NULL) {

       MemTracker::enqueue_pending_recorder(recorder);

       javaThread->set_recorder(NULL);

     }

   }

   _thread_count ++;

 }

 MemRecorder*                    MemTracker::_global_recorder = NULL;

 MemSnapshot*                    MemTracker::_snapshot = NULL;

 MemBaseline                     MemTracker::_baseline;

 Mutex*                          MemTracker::_query_lock = NULL;

 volatile MemRecorder*           MemTracker::_merge_pending_queue = NULL;

 volatile MemRecorder*           MemTracker::_pooled_recorders = NULL;

 MemTrackWorker*                 MemTracker::_worker_thread = NULL;

 int                             MemTracker::_sync_point_skip_count = 0;

 MemTracker::NMTLevel            MemTracker::_tracking_level = MemTracker::NMT_off;

 volatile MemTracker::NMTStates  MemTracker::_state = NMT_uninited;

 MemTracker::ShutdownReason      MemTracker::_reason = NMT_shutdown_none;

 int                             MemTracker::_thread_count = 255;

 volatile jint                   MemTracker::_pooled_recorder_count = 0;

 volatile unsigned long          MemTracker::_processing_generation = 0;

 volatile bool                   MemTracker::_worker_thread_idle = false;

 volatile bool                   MemTracker::_slowdown_calling_thread = false;

 debug_only(intx                 MemTracker::_main_thread_tid = 0;)

 NOT_PRODUCT(volatile jint       MemTracker::_pending_recorder_count = 0;)

 void MemTracker::init_tracking_options(const char* option_line) {

   _tracking_level = NMT_off;

   if (strcmp(option_line, "=summary") == 0) {

     _tracking_level = NMT_summary;

   } else if (strcmp(option_line, "=detail") == 0) {

     _tracking_level = NMT_detail;

   } else if (strcmp(option_line, "=off") != 0) {

     vm_exit_during_initialization("Syntax error, expecting -XX:NativeMemoryTracking=[off|summary|detail]", NULL);

   }

 }

 // first phase of bootstrapping, when VM is still in single-threaded mode.

 void MemTracker::bootstrap_single_thread() {

   if (_tracking_level > NMT_off) {

     assert(_state == NMT_uninited, "wrong state");

     // NMT is not supported with UseMallocOnly is on. NMT can NOT

     // handle the amount of malloc data without significantly impacting

     // runtime performance when this flag is on.

     if (UseMallocOnly) {

       shutdown(NMT_use_malloc_only);

       return;

     }

     _query_lock = new (std::nothrow) Mutex(Monitor::max_nonleaf, "NMT_queryLock");

     if (_query_lock == NULL) {

       shutdown(NMT_out_of_memory);

       return;

     }

     debug_only(_main_thread_tid = os::current_thread_id();)

     _state = NMT_bootstrapping_single_thread;

     NMT_track_callsite = (_tracking_level == NMT_detail && can_walk_stack());

   }

 }

 // second phase of bootstrapping, when VM is about to or already entered multi-theaded mode.

 void MemTracker::bootstrap_multi_thread() {

   if (_tracking_level > NMT_off && _state == NMT_bootstrapping_single_thread) {

   // create nmt lock for multi-thread execution

     assert(_main_thread_tid == os::current_thread_id(), "wrong thread");

     _state = NMT_bootstrapping_multi_thread;

     NMT_track_callsite = (_tracking_level == NMT_detail && can_walk_stack());

   }

 }

 // fully start nmt

 void MemTracker::start() {

   // Native memory tracking is off from command line option

   if (_tracking_level == NMT_off || shutdown_in_progress()) return;

   assert(_main_thread_tid == os::current_thread_id(), "wrong thread");

   assert(_state == NMT_bootstrapping_multi_thread, "wrong state");

   _snapshot = new (std::nothrow)MemSnapshot();

   if (_snapshot != NULL && !_snapshot->out_of_memory()) {

     if (start_worker()) {

       _state = NMT_started;

       NMT_track_callsite = (_tracking_level == NMT_detail && can_walk_stack());

       return;

     }

   }

   // fail to start native memory tracking, shut it down

   shutdown(NMT_initialization);

 }

 /**

  * Shutting down native memory tracking.

  * We can not shutdown native memory tracking immediately, so we just

  * setup shutdown pending flag, every native memory tracking component

  * should orderly shut itself down.

  *

  * The shutdown sequences:

  *  1. MemTracker::shutdown() sets MemTracker to shutdown pending state

  *  2. Worker thread calls MemTracker::final_shutdown(), which transites

  *     MemTracker to final shutdown state.

  *  3. At sync point, MemTracker does final cleanup, before sets memory

  *     tracking level to off to complete shutdown.

  */

 void MemTracker::shutdown(ShutdownReason reason) {

   if (_tracking_level == NMT_off) return;

   if (_state <= NMT_bootstrapping_single_thread) {

     // we still in single thread mode, there is not contention

     _state = NMT_shutdown_pending;

     _reason = reason;

   } else {

     // we want to know who initialized shutdown

     if ((jint)NMT_started == Atomic::cmpxchg((jint)NMT_shutdown_pending,

                                        (jint*)&_state, (jint)NMT_started)) {

         _reason = reason;

     }

   }

 }

 // final phase of shutdown

 void MemTracker::final_shutdown() {

   // delete all pending recorders and pooled recorders

   delete_all_pending_recorders();

   delete_all_pooled_recorders();

   {

     // shared baseline and snapshot are the only objects needed to

     // create query results

     MutexLockerEx locker(_query_lock, true);

     // cleanup baseline data and snapshot

     _baseline.clear();

     delete _snapshot;

     _snapshot = NULL;

   }

   // shutdown shared decoder instance, since it is only

   // used by native memory tracking so far.

   Decoder::shutdown();

   MemTrackWorker* worker = NULL;

   {

     ThreadCritical tc;

     // can not delete worker inside the thread critical

     if (_worker_thread != NULL && Thread::current() == _worker_thread) {

       worker = _worker_thread;

       _worker_thread = NULL;

     }

   }

   if (worker != NULL) {

     delete worker;

   }

   _state = NMT_final_shutdown;

 }

 // delete all pooled recorders

 void MemTracker::delete_all_pooled_recorders() {

   // free all pooled recorders

   volatile MemRecorder* cur_head = _pooled_recorders;

   if (cur_head != NULL) {

     MemRecorder* null_ptr = NULL;

     while (cur_head != NULL && (void*)cur_head != Atomic::cmpxchg_ptr((void*)null_ptr,

       (void*)&_pooled_recorders, (void*)cur_head)) {

       cur_head = _pooled_recorders;

     }

     if (cur_head != NULL) {

       delete cur_head;

       _pooled_recorder_count = 0;

     }

   }

 }

 // delete all recorders in pending queue

 void MemTracker::delete_all_pending_recorders() {

   // free all pending recorders

   MemRecorder* pending_head = get_pending_recorders();

   if (pending_head != NULL) {

     delete pending_head;

   }

 }

 /*

  * retrieve per-thread recorder of specified thread.

  * if thread == NULL, it means global recorder

  */

 MemRecorder* MemTracker::get_thread_recorder(JavaThread* thread) {

   if (shutdown_in_progress()) return NULL;

   MemRecorder* rc;

   if (thread == NULL) {

     rc = _global_recorder;

   } else {

     rc = thread->get_recorder();

   }

   if (rc != NULL && rc->is_full()) {

     enqueue_pending_recorder(rc);

     rc = NULL;

   }

   if (rc == NULL) {

     rc = get_new_or_pooled_instance();

     if (thread == NULL) {

       _global_recorder = rc;

     } else {

       thread->set_recorder(rc);

     }

   }

   return rc;

 }

 /*

  * get a per-thread recorder from pool, or create a new one if

  * there is not one available.

  */

 MemRecorder* MemTracker::get_new_or_pooled_instance() {

    MemRecorder* cur_head = const_cast<MemRecorder*> (_pooled_recorders);

    if (cur_head == NULL) {

      MemRecorder* rec = new (std::nothrow)MemRecorder();

      if (rec == NULL || rec->out_of_memory()) {

        shutdown(NMT_out_of_memory);

        if (rec != NULL) {

          delete rec;

          rec = NULL;

        }

      }

      return rec;

    } else {

      MemRecorder* next_head = cur_head->next();

      if ((void*)cur_head != Atomic::cmpxchg_ptr((void*)next_head, (void*)&_pooled_recorders,

        (void*)cur_head)) {

        return get_new_or_pooled_instance();

      }

      cur_head->set_next(NULL);

      Atomic::dec(&_pooled_recorder_count);

      cur_head->set_generation();

      return cur_head;

   }

 }

 /*

  * retrieve all recorders in pending queue, and empty the queue

  */

 MemRecorder* MemTracker::get_pending_recorders() {

   MemRecorder* cur_head = const_cast<MemRecorder*>(_merge_pending_queue);

   MemRecorder* null_ptr = NULL;

   while ((void*)cur_head != Atomic::cmpxchg_ptr((void*)null_ptr, (void*)&_merge_pending_queue,

     (void*)cur_head)) {

     cur_head = const_cast<MemRecorder*>(_merge_pending_queue);

   }

   NOT_PRODUCT(Atomic::store(0, &_pending_recorder_count));

   return cur_head;

 }

 /*

  * release a recorder to recorder pool.

  */

 void MemTracker::release_thread_recorder(MemRecorder* rec) {

   assert(rec != NULL, "null recorder");

   // we don't want to pool too many recorders

   rec->set_next(NULL);

   if (shutdown_in_progress() || _pooled_recorder_count > _thread_count * 2) {

     delete rec;

     return;

   }

   rec->clear();

   MemRecorder* cur_head = const_cast<MemRecorder*>(_pooled_recorders);

   rec->set_next(cur_head);

   while ((void*)cur_head != Atomic::cmpxchg_ptr((void*)rec, (void*)&_pooled_recorders,

     (void*)cur_head)) {

     cur_head = const_cast<MemRecorder*>(_pooled_recorders);

     rec->set_next(cur_head);

   }

   Atomic::inc(&_pooled_recorder_count);

 }

 /*

  * This is the most important method in whole nmt implementation.

  *

  * Create a memory record.

  * 1. When nmt is in single-threaded bootstrapping mode, no lock is needed as VM

  *    still in single thread mode.

  * 2. For all threads other than JavaThread, ThreadCritical is needed

  *    to write to recorders to global recorder.

  * 3. For JavaThreads that are not longer visible by safepoint, also

  *    need to take ThreadCritical and records are written to global

  *    recorders, since these threads are NOT walked by Threads.do_thread().

  * 4. JavaThreads that are running in native state, have to transition

  *    to VM state before writing to per-thread recorders.

  * 5. JavaThreads that are running in VM state do not need any lock and

  *    records are written to per-thread recorders.

  * 6. For a thread has yet to attach VM 'Thread', they need to take

  *    ThreadCritical to write to global recorder.

  *

  *    Important note:

  *    NO LOCK should be taken inside ThreadCritical lock !!!

  */

 void MemTracker::create_memory_record(address addr, MEMFLAGS flags,

     size_t size, address pc, Thread* thread) {

   assert(addr != NULL, "Sanity check");

   if (!shutdown_in_progress()) {

     // single thread, we just write records direct to global recorder,'

     // with any lock

     if (_state == NMT_bootstrapping_single_thread) {

       assert(_main_thread_tid == os::current_thread_id(), "wrong thread");

       thread = NULL;

     } else {

       if (thread == NULL) {

           // don't use Thread::current(), since it is possible that

           // the calling thread has yet to attach to VM 'Thread',

           // which will result assertion failure

           thread = ThreadLocalStorage::thread();

       }

     }

     if (thread != NULL) {

       // slow down all calling threads except NMT worker thread, so it

       // can catch up.

       if (_slowdown_calling_thread && thread != _worker_thread) {

         os::yield_all();

       }

       if (thread->is_Java_thread() && ((JavaThread*)thread)->is_safepoint_visible()) {

         JavaThread*      java_thread = (JavaThread*)thread;

         JavaThreadState  state = java_thread->thread_state();

         if (SafepointSynchronize::safepoint_safe(java_thread, state)) {

           // JavaThreads that are safepoint safe, can run through safepoint,

           // so ThreadCritical is needed to ensure no threads at safepoint create

           // new records while the records are being gathered and the sequence number is changing

           ThreadCritical tc;

           create_record_in_recorder(addr, flags, size, pc, java_thread);

         } else {

           create_record_in_recorder(addr, flags, size, pc, java_thread);

         }

       } else {

         // other threads, such as worker and watcher threads, etc. need to

         // take ThreadCritical to write to global recorder

         ThreadCritical tc;

         create_record_in_recorder(addr, flags, size, pc, NULL);

       }

     } else {

       if (_state == NMT_bootstrapping_single_thread) {

         // single thread, no lock needed

         create_record_in_recorder(addr, flags, size, pc, NULL);

       } else {

         // for thread has yet to attach VM 'Thread', we can not use VM mutex.

         // use native thread critical instead

         ThreadCritical tc;

         create_record_in_recorder(addr, flags, size, pc, NULL);

       }

     }

   }

 }

 // write a record to proper recorder. No lock can be taken from this method

 // down.

 void MemTracker::create_record_in_recorder(address addr, MEMFLAGS flags,

     size_t size, address pc, JavaThread* thread) {

     MemRecorder* rc = get_thread_recorder(thread);

     if (rc != NULL) {

       rc->record(addr, flags, size, pc);

     }

 }

 /**

  * enqueue a recorder to pending queue

  */

 void MemTracker::enqueue_pending_recorder(MemRecorder* rec) {

   assert(rec != NULL, "null recorder");

   // we are shutting down, so just delete it

   if (shutdown_in_progress()) {

     rec->set_next(NULL);

     delete rec;

     return;

   }

   MemRecorder* cur_head = const_cast<MemRecorder*>(_merge_pending_queue);

   rec->set_next(cur_head);

   while ((void*)cur_head != Atomic::cmpxchg_ptr((void*)rec, (void*)&_merge_pending_queue,

     (void*)cur_head)) {

     cur_head = const_cast<MemRecorder*>(_merge_pending_queue);

     rec->set_next(cur_head);

   }

   NOT_PRODUCT(Atomic::inc(&_pending_recorder_count);)

 }

 /*

  * The method is called at global safepoint

  * during it synchronization process.

  *   1. enqueue all JavaThreads' per-thread recorders

  *   2. enqueue global recorder

  *   3. retrieve all pending recorders

  *   4. reset global sequence number generator

  *   5. call worker's sync

  */

 #define MAX_SAFEPOINTS_TO_SKIP     128

 #define SAFE_SEQUENCE_THRESHOLD    30

 #define HIGH_GENERATION_THRESHOLD  60

 #define MAX_RECORDER_THREAD_RATIO  30

 void MemTracker::sync() {

   assert(_tracking_level > NMT_off, "NMT is not enabled");

   assert(SafepointSynchronize::is_at_safepoint(), "Safepoint required");

   // Some GC tests hit large number of safepoints in short period of time

   // without meaningful activities. We should prevent going to

   // sync point in these cases, which can potentially exhaust generation buffer.

   // Here is the factots to determine if we should go into sync point:

   // 1. not to overflow sequence number

   // 2. if we are in danger to overflow generation buffer

   // 3. how many safepoints we already skipped sync point

   if (_state == NMT_started) {

     // worker thread is not ready, no one can manage generation

     // buffer, so skip this safepoint

     if (_worker_thread == NULL) return;

     if (_sync_point_skip_count < MAX_SAFEPOINTS_TO_SKIP) {

       int per_seq_in_use = SequenceGenerator::peek() * 100 / max_jint;

       int per_gen_in_use = _worker_thread->generations_in_use() * 100 / MAX_GENERATIONS;

       if (per_seq_in_use < SAFE_SEQUENCE_THRESHOLD && per_gen_in_use >= HIGH_GENERATION_THRESHOLD) {

         _sync_point_skip_count ++;

         return;

       }

     }

     _sync_point_skip_count = 0;

     {

       // This method is running at safepoint, with ThreadCritical lock,

       // it should guarantee that NMT is fully sync-ed.

       ThreadCritical tc;

       SequenceGenerator::reset();

       // walk all JavaThreads to collect recorders

       SyncThreadRecorderClosure stc;

       Threads::threads_do(&stc);

       _thread_count = stc.get_thread_count();

       MemRecorder* pending_recorders = get_pending_recorders();

       if (_global_recorder != NULL) {

         _global_recorder->set_next(pending_recorders);

         pending_recorders = _global_recorder;

         _global_recorder = NULL;

       }

       // see if NMT has too many outstanding recorder instances, it usually

       // means that worker thread is lagging behind in processing them.

       if (!AutoShutdownNMT) {

         _slowdown_calling_thread = (MemRecorder::_instance_count > MAX_RECORDER_THREAD_RATIO * _thread_count);

       }

       // check _worker_thread with lock to avoid racing condition

       if (_worker_thread != NULL) {

         _worker_thread->at_sync_point(pending_recorders, InstanceKlass::number_of_instance_classes());

       }

       assert(SequenceGenerator::peek() == 1, "Should not have memory activities during sync-point");

     }

   }

   // now, it is the time to shut whole things off

   if (_state == NMT_final_shutdown) {

     // walk all JavaThreads to delete all recorders

     SyncThreadRecorderClosure stc;

     Threads::threads_do(&stc);

     // delete global recorder

     {

       ThreadCritical tc;

       if (_global_recorder != NULL) {

         delete _global_recorder;

         _global_recorder = NULL;

       }

     }

     MemRecorder* pending_recorders = get_pending_recorders();

     if (pending_recorders != NULL) {

       delete pending_recorders;

     }

     // try at a later sync point to ensure MemRecorder instance drops to zero to

     // completely shutdown NMT

     if (MemRecorder::_instance_count == 0) {

       _state = NMT_shutdown;

       _tracking_level = NMT_off;

     }

   }

 }

 /*

  * Start worker thread.

  */

 bool MemTracker::start_worker() {

   assert(_worker_thread == NULL, "Just Check");

   _worker_thread = new (std::nothrow) MemTrackWorker();

   if (_worker_thread == NULL || _worker_thread->has_error()) {

     shutdown(NMT_initialization);

     return false;

   }

   _worker_thread->start();

   return true;

 }

 /*

  * We need to collect a JavaThread's per-thread recorder

  * before it exits.

  */

 void MemTracker::thread_exiting(JavaThread* thread) {

   if (is_on()) {

     MemRecorder* rec = thread->get_recorder();

     if (rec != NULL) {

       enqueue_pending_recorder(rec);

       thread->set_recorder(NULL);

     }

   }

 }

 // baseline current memory snapshot

 bool MemTracker::baseline() {

   MutexLockerEx lock(_query_lock, true);

   MemSnapshot* snapshot = get_snapshot();

   if (snapshot != NULL) {

     return _baseline.baseline(*snapshot, false);

   }

   return false;

 }

 // print memory usage from current snapshot

 bool MemTracker::print_memory_usage(BaselineOutputer& out, size_t unit, bool summary_only) {

   MemBaseline  baseline;

   MutexLockerEx lock(_query_lock, true);

   MemSnapshot* snapshot = get_snapshot();

   if (snapshot != NULL && baseline.baseline(*snapshot, summary_only)) {

     BaselineReporter reporter(out, unit);

     reporter.report_baseline(baseline, summary_only);

     return true;

   }

   return false;

 }

 // Whitebox API for blocking until the current generation of NMT data has been merged

 bool MemTracker::wbtest_wait_for_data_merge() {

   // NMT can't be shutdown while we're holding _query_lock

   MutexLockerEx lock(_query_lock, true);

   assert(_worker_thread != NULL, "Invalid query");

   // the generation at query time, so NMT will spin till this generation is processed

   unsigned long generation_at_query_time = SequenceGenerator::current_generation();

   unsigned long current_processing_generation = _processing_generation;

   // if generation counter overflown

   bool generation_overflown = (generation_at_query_time < current_processing_generation);

   long generations_to_wrap = MAX_UNSIGNED_LONG - current_processing_generation;

   // spin

   while (!shutdown_in_progress()) {

     if (!generation_overflown) {

       if (current_processing_generation > generation_at_query_time) {

         return true;

       }

     } else {

       assert(generations_to_wrap >= 0, "Sanity check");

       long current_generations_to_wrap = MAX_UNSIGNED_LONG - current_processing_generation;

       assert(current_generations_to_wrap >= 0, "Sanity check");

       // to overflow an unsigned long should take long time, so to_wrap check should be sufficient

       if (current_generations_to_wrap > generations_to_wrap &&

           current_processing_generation > generation_at_query_time) {

         return true;

       }

     }

     // if worker thread is idle, but generation is not advancing, that means

     // there is not safepoint to let NMT advance generation, force one.

     if (_worker_thread_idle) {

       VM_ForceSafepoint vfs;

       VMThread::execute(&vfs);

     }

     MemSnapshot* snapshot = get_snapshot();

     if (snapshot == NULL) {

       return false;

     }

     snapshot->wait(1000);

     current_processing_generation = _processing_generation;

   }

   // We end up here if NMT is shutting down before our data has been merged

   return false;

 }

 // compare memory usage between current snapshot and baseline

 bool MemTracker::compare_memory_usage(BaselineOutputer& out, size_t unit, bool summary_only) {

   MutexLockerEx lock(_query_lock, true);

   if (_baseline.baselined()) {

     MemBaseline baseline;

     MemSnapshot* snapshot = get_snapshot();

     if (snapshot != NULL && baseline.baseline(*snapshot, summary_only)) {

       BaselineReporter reporter(out, unit);

       reporter.diff_baselines(baseline, _baseline, summary_only);

       return true;

     }

   }

   return false;

 }

 #ifndef PRODUCT

 void MemTracker::walk_stack(int toSkip, char* buf, int len) {

   int cur_len = 0;

   char tmp[1024];

   address pc;

   while (cur_len < len) {

     pc = os::get_caller_pc(toSkip + 1);

     if (pc != NULL && os::dll_address_to_function_name(pc, tmp, sizeof(tmp), NULL)) {

       jio_snprintf(&buf[cur_len], (len - cur_len), "%s\n", tmp);

       cur_len = (int)strlen(buf);

     } else {

       buf[cur_len] = '\0';

       break;

     }

     toSkip ++;

   }

 }

 void MemTracker::print_tracker_stats(outputStream* st) {

   st->print_cr("\nMemory Tracker Stats:");

   st->print_cr("\tMax sequence number = %d", SequenceGenerator::max_seq_num());

   st->print_cr("\tthead count = %d", _thread_count);

   st->print_cr("\tArena instance = %d", Arena::_instance_count);

   st->print_cr("\tpooled recorder count = %d", _pooled_recorder_count);

   st->print_cr("\tqueued recorder count = %d", _pending_recorder_count);

   st->print_cr("\tmemory recorder instance count = %d", MemRecorder::_instance_count);

   if (_worker_thread != NULL) {

     st->print_cr("\tWorker thread:");

     st->print_cr("\t\tSync point count = %d", _worker_thread->_sync_point_count);

     st->print_cr("\t\tpending recorder count = %d", _worker_thread->count_pending_recorders());

     st->print_cr("\t\tmerge count = %d", _worker_thread->_merge_count);

   } else {

     st->print_cr("\tWorker thread is not started");

   }

   st->print_cr(" ");

   if (_snapshot != NULL) {

     _snapshot->print_snapshot_stats(st);

   } else {

     st->print_cr("No snapshot");

   }

 }

 #endif