1 /*
   2  * Copyright (c) 2001, 2016, 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/systemDictionary.hpp"
  27 #include "gc/cms/concurrentMarkSweepGeneration.inline.hpp"
  28 #include "gc/cms/concurrentMarkSweepThread.hpp"
  29 #include "gc/shared/gcId.hpp"
  30 #include "gc/shared/genCollectedHeap.hpp"
  31 #include "oops/instanceRefKlass.hpp"
  32 #include "oops/oop.inline.hpp"
  33 #include "runtime/init.hpp"
  34 #include "runtime/interfaceSupport.hpp"
  35 #include "runtime/java.hpp"
  36 #include "runtime/javaCalls.hpp"
  37 #include "runtime/mutexLocker.hpp"
  38 #include "runtime/os.hpp"
  39 #include "runtime/vmThread.hpp"
  40 
  41 // ======= Concurrent Mark Sweep Thread ========
  42 
  43 ConcurrentMarkSweepThread* ConcurrentMarkSweepThread::_cmst = NULL;
  44 CMSCollector* ConcurrentMarkSweepThread::_collector         = NULL;
  45 int  ConcurrentMarkSweepThread::_CMS_flag                   = CMS_nil;
  46 
  47 volatile jint ConcurrentMarkSweepThread::_pending_yields    = 0;
  48 
  49 SurrogateLockerThread* ConcurrentMarkSweepThread::_slt      = NULL;
  50 SurrogateLockerThread::SLT_msg_type
  51      ConcurrentMarkSweepThread::_sltBuffer = SurrogateLockerThread::empty;
  52 Monitor* ConcurrentMarkSweepThread::_sltMonitor             = NULL;
  53 
  54 ConcurrentMarkSweepThread::ConcurrentMarkSweepThread(CMSCollector* collector)
  55   : ConcurrentGCThread() {
  56   assert(UseConcMarkSweepGC,  "UseConcMarkSweepGC should be set");
  57   assert(_cmst == NULL, "CMS thread already created");
  58   _cmst = this;
  59   assert(_collector == NULL, "Collector already set");
  60   _collector = collector;
  61 
  62   set_name("CMS Main Thread");
  63 
  64   // An old comment here said: "Priority should be just less
  65   // than that of VMThread".  Since the VMThread runs at
  66   // NearMaxPriority, the old comment was inaccurate, but
  67   // changing the default priority to NearMaxPriority-1
  68   // could change current behavior, so the default of
  69   // NearMaxPriority stays in place.
  70   //
  71   // Note that there's a possibility of the VMThread
  72   // starving if UseCriticalCMSThreadPriority is on.
  73   // That won't happen on Solaris for various reasons,
  74   // but may well happen on non-Solaris platforms.
  75   create_and_start(UseCriticalCMSThreadPriority ? CriticalPriority : NearMaxPriority);
  76 
  77   _sltMonitor = SLT_lock;
  78 }
  79 
  80 void ConcurrentMarkSweepThread::run_service() {
  81   assert(this == cmst(), "just checking");
  82 
  83   if (BindCMSThreadToCPU && !os::bind_to_processor(CPUForCMSThread)) {
  84     warning("Couldn't bind CMS thread to processor " UINTX_FORMAT, CPUForCMSThread);
  85   }
  86 
  87   {
  88     MutexLockerEx x(CGC_lock, true);
  89     set_CMS_flag(CMS_cms_wants_token);
  90     assert(is_init_completed() && Universe::is_fully_initialized(), "ConcurrentGCThread::run() should have waited for this.");
  91 
  92     // Wait until the surrogate locker thread that will do
  93     // pending list locking on our behalf has been created.
  94     // We cannot start the SLT thread ourselves since we need
  95     // to be a JavaThread to do so.
  96     CMSLoopCountWarn loopY("CMS::run", "waiting for SLT installation", 2);
  97     while (_slt == NULL && !should_terminate()) {
  98       CGC_lock->wait(true, 200);
  99       loopY.tick();
 100     }
 101     clear_CMS_flag(CMS_cms_wants_token);
 102   }
 103 
 104   while (!should_terminate()) {
 105     sleepBeforeNextCycle();
 106     if (should_terminate()) break;
 107     GCIdMark gc_id_mark;
 108     GCCause::Cause cause = _collector->_full_gc_requested ?
 109       _collector->_full_gc_cause : GCCause::_cms_concurrent_mark;
 110     _collector->collect_in_background(cause);
 111   }
 112 
 113   // Check that the state of any protocol for synchronization
 114   // between background (CMS) and foreground collector is "clean"
 115   // (i.e. will not potentially block the foreground collector,
 116   // requiring action by us).
 117   verify_ok_to_terminate();
 118 }
 119 
 120 #ifndef PRODUCT
 121 void ConcurrentMarkSweepThread::verify_ok_to_terminate() const {
 122   assert(!(CGC_lock->owned_by_self() || cms_thread_has_cms_token() ||
 123            cms_thread_wants_cms_token()),
 124          "Must renounce all worldly possessions and desires for nirvana");
 125   _collector->verify_ok_to_terminate();
 126 }
 127 #endif
 128 
 129 // create and start a new ConcurrentMarkSweep Thread for given CMS generation
 130 ConcurrentMarkSweepThread* ConcurrentMarkSweepThread::start(CMSCollector* collector) {
 131   guarantee(_cmst == NULL, "start() called twice!");
 132   ConcurrentMarkSweepThread* th = new ConcurrentMarkSweepThread(collector);
 133   assert(_cmst == th, "Where did the just-created CMS thread go?");
 134   return th;
 135 }
 136 
 137 void ConcurrentMarkSweepThread::stop_all() {
 138   assert(_cmst != NULL, "stop_all should be called after initialization");
 139   _cmst->stop();
 140 }
 141 
 142 void ConcurrentMarkSweepThread::stop_service() {
 143   // Now post a notify on CGC_lock so as to nudge
 144   // CMS thread(s) that might be slumbering in
 145   // sleepBeforeNextCycle.
 146   MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
 147   CGC_lock->notify_all();
 148 }
 149 
 150 void ConcurrentMarkSweepThread::threads_do(ThreadClosure* tc) {
 151   assert(tc != NULL, "Null ThreadClosure");
 152   if (cmst() != NULL && !cmst()->has_terminated()) {
 153     tc->do_thread(cmst());
 154   }
 155   assert(Universe::is_fully_initialized(),
 156          "Called too early, make sure heap is fully initialized");
 157   if (_collector != NULL) {
 158     AbstractWorkGang* gang = _collector->conc_workers();
 159     if (gang != NULL) {
 160       gang->threads_do(tc);
 161     }
 162   }
 163 }
 164 
 165 void ConcurrentMarkSweepThread::print_all_on(outputStream* st) {
 166   if (cmst() != NULL && !cmst()->has_terminated()) {
 167     cmst()->print_on(st);
 168     st->cr();
 169   }
 170   if (_collector != NULL) {
 171     AbstractWorkGang* gang = _collector->conc_workers();
 172     if (gang != NULL) {
 173       gang->print_worker_threads_on(st);
 174     }
 175   }
 176 }
 177 
 178 void ConcurrentMarkSweepThread::synchronize(bool is_cms_thread) {
 179   assert(UseConcMarkSweepGC, "just checking");
 180 
 181   MutexLockerEx x(CGC_lock,
 182                   Mutex::_no_safepoint_check_flag);
 183   if (!is_cms_thread) {
 184     assert(Thread::current()->is_VM_thread(), "Not a VM thread");
 185     CMSSynchronousYieldRequest yr;
 186     while (CMS_flag_is_set(CMS_cms_has_token)) {
 187       // indicate that we want to get the token
 188       set_CMS_flag(CMS_vm_wants_token);
 189       CGC_lock->wait(true);
 190     }
 191     // claim the token and proceed
 192     clear_CMS_flag(CMS_vm_wants_token);
 193     set_CMS_flag(CMS_vm_has_token);
 194   } else {
 195     assert(Thread::current()->is_ConcurrentGC_thread(),
 196            "Not a CMS thread");
 197     // The following barrier assumes there's only one CMS thread.
 198     // This will need to be modified is there are more CMS threads than one.
 199     while (CMS_flag_is_set(CMS_vm_has_token | CMS_vm_wants_token)) {
 200       set_CMS_flag(CMS_cms_wants_token);
 201       CGC_lock->wait(true);
 202     }
 203     // claim the token
 204     clear_CMS_flag(CMS_cms_wants_token);
 205     set_CMS_flag(CMS_cms_has_token);
 206   }
 207 }
 208 
 209 void ConcurrentMarkSweepThread::desynchronize(bool is_cms_thread) {
 210   assert(UseConcMarkSweepGC, "just checking");
 211 
 212   MutexLockerEx x(CGC_lock,
 213                   Mutex::_no_safepoint_check_flag);
 214   if (!is_cms_thread) {
 215     assert(Thread::current()->is_VM_thread(), "Not a VM thread");
 216     assert(CMS_flag_is_set(CMS_vm_has_token), "just checking");
 217     clear_CMS_flag(CMS_vm_has_token);
 218     if (CMS_flag_is_set(CMS_cms_wants_token)) {
 219       // wake-up a waiting CMS thread
 220       CGC_lock->notify();
 221     }
 222     assert(!CMS_flag_is_set(CMS_vm_has_token | CMS_vm_wants_token),
 223            "Should have been cleared");
 224   } else {
 225     assert(Thread::current()->is_ConcurrentGC_thread(),
 226            "Not a CMS thread");
 227     assert(CMS_flag_is_set(CMS_cms_has_token), "just checking");
 228     clear_CMS_flag(CMS_cms_has_token);
 229     if (CMS_flag_is_set(CMS_vm_wants_token)) {
 230       // wake-up a waiting VM thread
 231       CGC_lock->notify();
 232     }
 233     assert(!CMS_flag_is_set(CMS_cms_has_token | CMS_cms_wants_token),
 234            "Should have been cleared");
 235   }
 236 }
 237 
 238 // Wait until any cms_lock event
 239 void ConcurrentMarkSweepThread::wait_on_cms_lock(long t_millis) {
 240   MutexLockerEx x(CGC_lock,
 241                   Mutex::_no_safepoint_check_flag);
 242   if (should_terminate() || _collector->_full_gc_requested) {
 243     return;
 244   }
 245   set_CMS_flag(CMS_cms_wants_token);   // to provoke notifies
 246   CGC_lock->wait(Mutex::_no_safepoint_check_flag, t_millis);
 247   clear_CMS_flag(CMS_cms_wants_token);
 248   assert(!CMS_flag_is_set(CMS_cms_has_token | CMS_cms_wants_token),
 249          "Should not be set");
 250 }
 251 
 252 // Wait until the next synchronous GC, a concurrent full gc request,
 253 // or a timeout, whichever is earlier.
 254 void ConcurrentMarkSweepThread::wait_on_cms_lock_for_scavenge(long t_millis) {
 255   // Wait time in millis or 0 value representing infinite wait for a scavenge
 256   assert(t_millis >= 0, "Wait time for scavenge should be 0 or positive");
 257 
 258   GenCollectedHeap* gch = GenCollectedHeap::heap();
 259   double start_time_secs = os::elapsedTime();
 260   double end_time_secs = start_time_secs + (t_millis / ((double) MILLIUNITS));
 261 
 262   // Total collections count before waiting loop
 263   unsigned int before_count;
 264   {
 265     MutexLockerEx hl(Heap_lock, Mutex::_no_safepoint_check_flag);
 266     before_count = gch->total_collections();
 267   }
 268 
 269   unsigned int loop_count = 0;
 270 
 271   while(!should_terminate()) {
 272     double now_time = os::elapsedTime();
 273     long wait_time_millis;
 274 
 275     if(t_millis != 0) {
 276       // New wait limit
 277       wait_time_millis = (long) ((end_time_secs - now_time) * MILLIUNITS);
 278       if(wait_time_millis <= 0) {
 279         // Wait time is over
 280         break;
 281       }
 282     } else {
 283       // No wait limit, wait if necessary forever
 284       wait_time_millis = 0;
 285     }
 286 
 287     // Wait until the next event or the remaining timeout
 288     {
 289       MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
 290 
 291       if (should_terminate() || _collector->_full_gc_requested) {
 292         return;
 293       }
 294       set_CMS_flag(CMS_cms_wants_token);   // to provoke notifies
 295       assert(t_millis == 0 || wait_time_millis > 0, "Sanity");
 296       CGC_lock->wait(Mutex::_no_safepoint_check_flag, wait_time_millis);
 297       clear_CMS_flag(CMS_cms_wants_token);
 298       assert(!CMS_flag_is_set(CMS_cms_has_token | CMS_cms_wants_token),
 299              "Should not be set");
 300     }
 301 
 302     // Extra wait time check before entering the heap lock to get the collection count
 303     if(t_millis != 0 && os::elapsedTime() >= end_time_secs) {
 304       // Wait time is over
 305       break;
 306     }
 307 
 308     // Total collections count after the event
 309     unsigned int after_count;
 310     {
 311       MutexLockerEx hl(Heap_lock, Mutex::_no_safepoint_check_flag);
 312       after_count = gch->total_collections();
 313     }
 314 
 315     if(before_count != after_count) {
 316       // There was a collection - success
 317       break;
 318     }
 319 
 320     // Too many loops warning
 321     if(++loop_count == 0) {
 322       warning("wait_on_cms_lock_for_scavenge() has looped %u times", loop_count - 1);
 323     }
 324   }
 325 }
 326 
 327 void ConcurrentMarkSweepThread::sleepBeforeNextCycle() {
 328   while (!should_terminate()) {
 329     if(CMSWaitDuration >= 0) {
 330       // Wait until the next synchronous GC, a concurrent full gc
 331       // request or a timeout, whichever is earlier.
 332       wait_on_cms_lock_for_scavenge(CMSWaitDuration);
 333     } else {
 334       // Wait until any cms_lock event or check interval not to call shouldConcurrentCollect permanently
 335       wait_on_cms_lock(CMSCheckInterval);
 336     }
 337     // Check if we should start a CMS collection cycle
 338     if (_collector->shouldConcurrentCollect()) {
 339       return;
 340     }
 341     // .. collection criterion not yet met, let's go back
 342     // and wait some more
 343   }
 344 }
 345 
 346 // Note: this method, although exported by the ConcurrentMarkSweepThread,
 347 // which is a non-JavaThread, can only be called by a JavaThread.
 348 // Currently this is done at vm creation time (post-vm-init) by the
 349 // main/Primordial (Java)Thread.
 350 // XXX Consider changing this in the future to allow the CMS thread
 351 // itself to create this thread?
 352 void ConcurrentMarkSweepThread::makeSurrogateLockerThread(TRAPS) {
 353   assert(UseConcMarkSweepGC, "SLT thread needed only for CMS GC");
 354   assert(_slt == NULL, "SLT already created");
 355   _slt = SurrogateLockerThread::make(THREAD);
 356 }