1 /*
   2  * Copyright (c) 2001, 2010, 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_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.inline.hpp"
  28 #include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepThread.hpp"
  29 #include "memory/genCollectedHeap.hpp"
  30 #include "oops/instanceRefKlass.hpp"
  31 #include "oops/oop.inline.hpp"
  32 #include "runtime/init.hpp"
  33 #include "runtime/interfaceSupport.hpp"
  34 #include "runtime/java.hpp"
  35 #include "runtime/javaCalls.hpp"
  36 #include "runtime/mutexLocker.hpp"
  37 #include "runtime/os.hpp"
  38 #include "runtime/vmThread.hpp"
  39 
  40 // ======= Concurrent Mark Sweep Thread ========
  41 
  42 // The CMS thread is created when Concurrent Mark Sweep is used in the
  43 // older of two generations in a generational memory system.
  44 
  45 ConcurrentMarkSweepThread*
  46      ConcurrentMarkSweepThread::_cmst     = NULL;
  47 CMSCollector* ConcurrentMarkSweepThread::_collector = NULL;
  48 bool ConcurrentMarkSweepThread::_should_terminate = false;
  49 int  ConcurrentMarkSweepThread::_CMS_flag         = CMS_nil;
  50 
  51 volatile jint ConcurrentMarkSweepThread::_pending_yields      = 0;
  52 volatile jint ConcurrentMarkSweepThread::_pending_decrements  = 0;
  53 
  54 volatile bool ConcurrentMarkSweepThread::_icms_enabled   = false;
  55 volatile bool ConcurrentMarkSweepThread::_should_run     = false;
  56 // When icms is enabled, the icms thread is stopped until explicitly
  57 // started.
  58 volatile bool ConcurrentMarkSweepThread::_should_stop    = true;
  59 
  60 SurrogateLockerThread*
  61      ConcurrentMarkSweepThread::_slt = NULL;
  62 SurrogateLockerThread::SLT_msg_type
  63      ConcurrentMarkSweepThread::_sltBuffer = SurrogateLockerThread::empty;
  64 Monitor*
  65      ConcurrentMarkSweepThread::_sltMonitor = NULL;
  66 
  67 ConcurrentMarkSweepThread::ConcurrentMarkSweepThread(CMSCollector* collector)
  68   : ConcurrentGCThread() {
  69   assert(UseConcMarkSweepGC,  "UseConcMarkSweepGC should be set");
  70   assert(_cmst == NULL, "CMS thread already created");
  71   _cmst = this;
  72   assert(_collector == NULL, "Collector already set");
  73   _collector = collector;
  74 
  75   set_name("Concurrent Mark-Sweep GC Thread");
  76 
  77   if (os::create_thread(this, os::cgc_thread)) {
  78     // XXX: need to set this to low priority
  79     // unless "agressive mode" set; priority
  80     // should be just less than that of VMThread.
  81     os::set_priority(this, NearMaxPriority);
  82     if (!DisableStartThread) {
  83       os::start_thread(this);
  84     }
  85   }
  86   _sltMonitor = SLT_lock;
  87   set_icms_enabled(CMSIncrementalMode);
  88 }
  89 
  90 void ConcurrentMarkSweepThread::run() {
  91   assert(this == cmst(), "just checking");
  92 
  93   this->record_stack_base_and_size();
  94   this->initialize_thread_local_storage();
  95   this->set_active_handles(JNIHandleBlock::allocate_block());
  96   // From this time Thread::current() should be working.
  97   assert(this == Thread::current(), "just checking");
  98   if (BindCMSThreadToCPU && !os::bind_to_processor(CPUForCMSThread)) {
  99     warning("Couldn't bind CMS thread to processor %u", CPUForCMSThread);
 100   }
 101   // Wait until Universe::is_fully_initialized()
 102   {
 103     CMSLoopCountWarn loopX("CMS::run", "waiting for "
 104                            "Universe::is_fully_initialized()", 2);
 105     MutexLockerEx x(CGC_lock, true);
 106     set_CMS_flag(CMS_cms_wants_token);
 107     // Wait until Universe is initialized and all initialization is completed.
 108     while (!is_init_completed() && !Universe::is_fully_initialized() &&
 109            !_should_terminate) {
 110       CGC_lock->wait(true, 200);
 111       loopX.tick();
 112     }
 113     // Wait until the surrogate locker thread that will do
 114     // pending list locking on our behalf has been created.
 115     // We cannot start the SLT thread ourselves since we need
 116     // to be a JavaThread to do so.
 117     CMSLoopCountWarn loopY("CMS::run", "waiting for SLT installation", 2);
 118     while (_slt == NULL && !_should_terminate) {
 119       CGC_lock->wait(true, 200);
 120       loopY.tick();
 121     }
 122     clear_CMS_flag(CMS_cms_wants_token);
 123   }
 124 
 125   while (!_should_terminate) {
 126     sleepBeforeNextCycle();
 127     if (_should_terminate) break;
 128     _collector->collect_in_background(false);  // !clear_all_soft_refs
 129   }
 130   assert(_should_terminate, "just checking");
 131   // Check that the state of any protocol for synchronization
 132   // between background (CMS) and foreground collector is "clean"
 133   // (i.e. will not potentially block the foreground collector,
 134   // requiring action by us).
 135   verify_ok_to_terminate();
 136   // Signal that it is terminated
 137   {
 138     MutexLockerEx mu(Terminator_lock,
 139                      Mutex::_no_safepoint_check_flag);
 140     assert(_cmst == this, "Weird!");
 141     _cmst = NULL;
 142     Terminator_lock->notify();
 143   }
 144 
 145   // Thread destructor usually does this..
 146   ThreadLocalStorage::set_thread(NULL);
 147 }
 148 
 149 #ifndef PRODUCT
 150 void ConcurrentMarkSweepThread::verify_ok_to_terminate() const {
 151   assert(!(CGC_lock->owned_by_self() || cms_thread_has_cms_token() ||
 152            cms_thread_wants_cms_token()),
 153          "Must renounce all worldly possessions and desires for nirvana");
 154   _collector->verify_ok_to_terminate();
 155 }
 156 #endif
 157 
 158 // create and start a new ConcurrentMarkSweep Thread for given CMS generation
 159 ConcurrentMarkSweepThread* ConcurrentMarkSweepThread::start(CMSCollector* collector) {
 160   if (!_should_terminate) {
 161     assert(cmst() == NULL, "start() called twice?");
 162     ConcurrentMarkSweepThread* th = new ConcurrentMarkSweepThread(collector);
 163     assert(cmst() == th, "Where did the just-created CMS thread go?");
 164     return th;
 165   }
 166   return NULL;
 167 }
 168 
 169 void ConcurrentMarkSweepThread::stop() {
 170   if (CMSIncrementalMode) {
 171     // Disable incremental mode and wake up the thread so it notices the change.
 172     disable_icms();
 173     start_icms();
 174   }
 175   // it is ok to take late safepoints here, if needed
 176   {
 177     MutexLockerEx x(Terminator_lock);
 178     _should_terminate = true;
 179   }
 180   { // Now post a notify on CGC_lock so as to nudge
 181     // CMS thread(s) that might be slumbering in
 182     // sleepBeforeNextCycle.
 183     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
 184     CGC_lock->notify_all();
 185   }
 186   { // Now wait until (all) CMS thread(s) have exited
 187     MutexLockerEx x(Terminator_lock);
 188     while(cmst() != NULL) {
 189       Terminator_lock->wait();
 190     }
 191   }
 192 }
 193 
 194 void ConcurrentMarkSweepThread::threads_do(ThreadClosure* tc) {
 195   assert(tc != NULL, "Null ThreadClosure");
 196   if (_cmst != NULL) {
 197     tc->do_thread(_cmst);
 198   }
 199   assert(Universe::is_fully_initialized(),
 200          "Called too early, make sure heap is fully initialized");
 201   if (_collector != NULL) {
 202     AbstractWorkGang* gang = _collector->conc_workers();
 203     if (gang != NULL) {
 204       gang->threads_do(tc);
 205     }
 206   }
 207 }
 208 
 209 void ConcurrentMarkSweepThread::print_on(outputStream* st) const {
 210   st->print("\"%s\" ", name());
 211   Thread::print_on(st);
 212   st->cr();
 213 }
 214 
 215 void ConcurrentMarkSweepThread::print_all_on(outputStream* st) {
 216   if (_cmst != NULL) {
 217     _cmst->print_on(st);
 218   }
 219   if (_collector != NULL) {
 220     AbstractWorkGang* gang = _collector->conc_workers();
 221     if (gang != NULL) {
 222       gang->print_worker_threads_on(st);
 223     }
 224   }
 225 }
 226 
 227 void ConcurrentMarkSweepThread::synchronize(bool is_cms_thread) {
 228   assert(UseConcMarkSweepGC, "just checking");
 229 
 230   MutexLockerEx x(CGC_lock,
 231                   Mutex::_no_safepoint_check_flag);
 232   if (!is_cms_thread) {
 233     assert(Thread::current()->is_VM_thread(), "Not a VM thread");
 234     CMSSynchronousYieldRequest yr;
 235     while (CMS_flag_is_set(CMS_cms_has_token)) {
 236       // indicate that we want to get the token
 237       set_CMS_flag(CMS_vm_wants_token);
 238       CGC_lock->wait(true);
 239     }
 240     // claim the token and proceed
 241     clear_CMS_flag(CMS_vm_wants_token);
 242     set_CMS_flag(CMS_vm_has_token);
 243   } else {
 244     assert(Thread::current()->is_ConcurrentGC_thread(),
 245            "Not a CMS thread");
 246     // The following barrier assumes there's only one CMS thread.
 247     // This will need to be modified is there are more CMS threads than one.
 248     while (CMS_flag_is_set(CMS_vm_has_token | CMS_vm_wants_token)) {
 249       set_CMS_flag(CMS_cms_wants_token);
 250       CGC_lock->wait(true);
 251     }
 252     // claim the token
 253     clear_CMS_flag(CMS_cms_wants_token);
 254     set_CMS_flag(CMS_cms_has_token);
 255   }
 256 }
 257 
 258 void ConcurrentMarkSweepThread::desynchronize(bool is_cms_thread) {
 259   assert(UseConcMarkSweepGC, "just checking");
 260 
 261   MutexLockerEx x(CGC_lock,
 262                   Mutex::_no_safepoint_check_flag);
 263   if (!is_cms_thread) {
 264     assert(Thread::current()->is_VM_thread(), "Not a VM thread");
 265     assert(CMS_flag_is_set(CMS_vm_has_token), "just checking");
 266     clear_CMS_flag(CMS_vm_has_token);
 267     if (CMS_flag_is_set(CMS_cms_wants_token)) {
 268       // wake-up a waiting CMS thread
 269       CGC_lock->notify();
 270     }
 271     assert(!CMS_flag_is_set(CMS_vm_has_token | CMS_vm_wants_token),
 272            "Should have been cleared");
 273   } else {
 274     assert(Thread::current()->is_ConcurrentGC_thread(),
 275            "Not a CMS thread");
 276     assert(CMS_flag_is_set(CMS_cms_has_token), "just checking");
 277     clear_CMS_flag(CMS_cms_has_token);
 278     if (CMS_flag_is_set(CMS_vm_wants_token)) {
 279       // wake-up a waiting VM thread
 280       CGC_lock->notify();
 281     }
 282     assert(!CMS_flag_is_set(CMS_cms_has_token | CMS_cms_wants_token),
 283            "Should have been cleared");
 284   }
 285 }
 286 
 287 // Wait until the next synchronous GC, a concurrent full gc request,
 288 // or a timeout, whichever is earlier.
 289 void ConcurrentMarkSweepThread::wait_on_cms_lock(long t_millis) {
 290   MutexLockerEx x(CGC_lock,
 291                   Mutex::_no_safepoint_check_flag);
 292   if (_should_terminate || _collector->_full_gc_requested) {
 293     return;
 294   }
 295   set_CMS_flag(CMS_cms_wants_token);   // to provoke notifies
 296   CGC_lock->wait(Mutex::_no_safepoint_check_flag, t_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 void ConcurrentMarkSweepThread::sleepBeforeNextCycle() {
 303   while (!_should_terminate) {
 304     if (CMSIncrementalMode) {
 305       icms_wait();
 306       return;
 307     } else {
 308       // Wait until the next synchronous GC, a concurrent full gc
 309       // request or a timeout, whichever is earlier.
 310       wait_on_cms_lock(CMSWaitDuration);
 311     }
 312     // Check if we should start a CMS collection cycle
 313     if (_collector->shouldConcurrentCollect()) {
 314       return;
 315     }
 316     // .. collection criterion not yet met, let's go back
 317     // and wait some more
 318   }
 319 }
 320 
 321 // Incremental CMS
 322 void ConcurrentMarkSweepThread::start_icms() {
 323   assert(UseConcMarkSweepGC && CMSIncrementalMode, "just checking");
 324   MutexLockerEx x(iCMS_lock, Mutex::_no_safepoint_check_flag);
 325   trace_state("start_icms");
 326   _should_run = true;
 327   iCMS_lock->notify_all();
 328 }
 329 
 330 void ConcurrentMarkSweepThread::stop_icms() {
 331   assert(UseConcMarkSweepGC && CMSIncrementalMode, "just checking");
 332   MutexLockerEx x(iCMS_lock, Mutex::_no_safepoint_check_flag);
 333   if (!_should_stop) {
 334     trace_state("stop_icms");
 335     _should_stop = true;
 336     _should_run = false;
 337     asynchronous_yield_request();
 338     iCMS_lock->notify_all();
 339   }
 340 }
 341 
 342 void ConcurrentMarkSweepThread::icms_wait() {
 343   assert(UseConcMarkSweepGC && CMSIncrementalMode, "just checking");
 344   if (_should_stop && icms_enabled()) {
 345     MutexLockerEx x(iCMS_lock, Mutex::_no_safepoint_check_flag);
 346     trace_state("pause_icms");
 347     _collector->stats().stop_cms_timer();
 348     while(!_should_run && icms_enabled()) {
 349       iCMS_lock->wait(Mutex::_no_safepoint_check_flag);
 350     }
 351     _collector->stats().start_cms_timer();
 352     _should_stop = false;
 353     trace_state("pause_icms end");
 354   }
 355 }
 356 
 357 // Note: this method, although exported by the ConcurrentMarkSweepThread,
 358 // which is a non-JavaThread, can only be called by a JavaThread.
 359 // Currently this is done at vm creation time (post-vm-init) by the
 360 // main/Primordial (Java)Thread.
 361 // XXX Consider changing this in the future to allow the CMS thread
 362 // itself to create this thread?
 363 void ConcurrentMarkSweepThread::makeSurrogateLockerThread(TRAPS) {
 364   assert(UseConcMarkSweepGC, "SLT thread needed only for CMS GC");
 365   assert(_slt == NULL, "SLT already created");
 366   _slt = SurrogateLockerThread::make(THREAD);
 367 }