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hotspot/src/share/vm/gc_implementation/concurrentMarkSweep/concurrentMarkSweepThread.cpp

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+/*
+ * Copyright 2001-2006 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.
+ *
+ */
+
+# include "incls/_precompiled.incl"
+# include "incls/_concurrentMarkSweepThread.cpp.incl"
+
+// ======= Concurrent Mark Sweep Thread ========
+
+// The CMS thread is created when Concurrent Mark Sweep is used in the
+// older of two generations in a generational memory system.
+
+ConcurrentMarkSweepThread*
+     ConcurrentMarkSweepThread::_cmst     = NULL;
+CMSCollector* ConcurrentMarkSweepThread::_collector = NULL;
+bool ConcurrentMarkSweepThread::_should_terminate = false;
+int  ConcurrentMarkSweepThread::_CMS_flag         = CMS_nil;
+
+volatile jint ConcurrentMarkSweepThread::_pending_yields      = 0;
+volatile jint ConcurrentMarkSweepThread::_pending_decrements  = 0;
+
+volatile bool ConcurrentMarkSweepThread::_icms_enabled   = false;
+volatile bool ConcurrentMarkSweepThread::_should_run     = false;
+// When icms is enabled, the icms thread is stopped until explicitly
+// started.
+volatile bool ConcurrentMarkSweepThread::_should_stop    = true;
+
+SurrogateLockerThread*
+     ConcurrentMarkSweepThread::_slt = NULL;
+SurrogateLockerThread::SLT_msg_type
+     ConcurrentMarkSweepThread::_sltBuffer = SurrogateLockerThread::empty;
+Monitor*
+     ConcurrentMarkSweepThread::_sltMonitor = NULL;
+
+ConcurrentMarkSweepThread::ConcurrentMarkSweepThread(CMSCollector* collector)
+  : ConcurrentGCThread() {
+  assert(UseConcMarkSweepGC,  "UseConcMarkSweepGC should be set");
+  assert(_cmst == NULL, "CMS thread already created");
+  _cmst = this;
+  assert(_collector == NULL, "Collector already set");
+  _collector = collector;
+
+  set_name("Concurrent Mark-Sweep GC Thread");
+
+  if (os::create_thread(this, os::cgc_thread)) {
+    // XXX: need to set this to low priority
+    // unless "agressive mode" set; priority
+    // should be just less than that of VMThread.
+    os::set_priority(this, NearMaxPriority);
+    if (!DisableStartThread) {
+      os::start_thread(this);
+    }
+  }
+  _sltMonitor = SLT_lock;
+  set_icms_enabled(CMSIncrementalMode);
+}
+
+void ConcurrentMarkSweepThread::run() {
+  assert(this == cmst(), "just checking");
+
+  this->record_stack_base_and_size();
+  this->initialize_thread_local_storage();
+  this->set_active_handles(JNIHandleBlock::allocate_block());
+  // From this time Thread::current() should be working.
+  assert(this == Thread::current(), "just checking");
+  if (BindCMSThreadToCPU && !os::bind_to_processor(CPUForCMSThread)) {
+    warning("Couldn't bind CMS thread to processor %u", CPUForCMSThread);
+  }
+  // Wait until Universe::is_fully_initialized()
+  {
+    CMSLoopCountWarn loopX("CMS::run", "waiting for "
+                           "Universe::is_fully_initialized()", 2);
+    MutexLockerEx x(CGC_lock, true);
+    set_CMS_flag(CMS_cms_wants_token);
+    // Wait until Universe is initialized and all initialization is completed.
+    while (!is_init_completed() && !Universe::is_fully_initialized() &&
+           !_should_terminate) {
+      CGC_lock->wait(true, 200);
+      loopX.tick();
+    }
+    // Wait until the surrogate locker thread that will do
+    // pending list locking on our behalf has been created.
+    // We cannot start the SLT thread ourselves since we need
+    // to be a JavaThread to do so.
+    CMSLoopCountWarn loopY("CMS::run", "waiting for SLT installation", 2);
+    while (_slt == NULL && !_should_terminate) {
+      CGC_lock->wait(true, 200);
+      loopY.tick();
+    }
+    clear_CMS_flag(CMS_cms_wants_token);
+  }
+
+  while (!_should_terminate) {
+    sleepBeforeNextCycle();
+    if (_should_terminate) break;
+    _collector->collect_in_background(false);  // !clear_all_soft_refs
+  }
+  assert(_should_terminate, "just checking");
+  // Check that the state of any protocol for synchronization
+  // between background (CMS) and foreground collector is "clean"
+  // (i.e. will not potentially block the foreground collector,
+  // requiring action by us).
+  verify_ok_to_terminate();
+  // Signal that it is terminated
+  {
+    MutexLockerEx mu(Terminator_lock,
+                     Mutex::_no_safepoint_check_flag);
+    assert(_cmst == this, "Weird!");
+    _cmst = NULL;
+    Terminator_lock->notify();
+  }
+
+  // Thread destructor usually does this..
+  ThreadLocalStorage::set_thread(NULL);
+}
+
+#ifndef PRODUCT
+void ConcurrentMarkSweepThread::verify_ok_to_terminate() const {
+  assert(!(CGC_lock->owned_by_self() || cms_thread_has_cms_token() ||
+           cms_thread_wants_cms_token()),
+         "Must renounce all worldly possessions and desires for nirvana");
+  _collector->verify_ok_to_terminate();
+}
+#endif
+
+// create and start a new ConcurrentMarkSweep Thread for given CMS generation
+ConcurrentMarkSweepThread* ConcurrentMarkSweepThread::start(CMSCollector* collector) {
+  if (!_should_terminate) {
+    assert(cmst() == NULL, "start() called twice?");
+    ConcurrentMarkSweepThread* th = new ConcurrentMarkSweepThread(collector);
+    assert(cmst() == th, "Where did the just-created CMS thread go?");
+    return th;
+  }
+  return NULL;
+}
+
+void ConcurrentMarkSweepThread::stop() {
+  if (CMSIncrementalMode) {
+    // Disable incremental mode and wake up the thread so it notices the change.
+    disable_icms();
+    start_icms();
+  }
+  // it is ok to take late safepoints here, if needed
+  {
+    MutexLockerEx x(Terminator_lock);
+    _should_terminate = true;
+  }
+  { // Now post a notify on CGC_lock so as to nudge
+    // CMS thread(s) that might be slumbering in
+    // sleepBeforeNextCycle.
+    MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
+    CGC_lock->notify_all();
+  }
+  { // Now wait until (all) CMS thread(s) have exited
+    MutexLockerEx x(Terminator_lock);
+    while(cmst() != NULL) {
+      Terminator_lock->wait();
+    }
+  }
+}
+
+void ConcurrentMarkSweepThread::threads_do(ThreadClosure* tc) {
+  assert(tc != NULL, "Null ThreadClosure");
+  if (_cmst != NULL) {
+    tc->do_thread(_cmst);
+  }
+  assert(Universe::is_fully_initialized(),
+         "Called too early, make sure heap is fully initialized");
+  if (_collector != NULL) {
+    AbstractWorkGang* gang = _collector->conc_workers();
+    if (gang != NULL) {
+      gang->threads_do(tc);
+    }
+  }
+}
+
+void ConcurrentMarkSweepThread::print_on(outputStream* st) const {
+  st->print("\"%s\" ", name());
+  Thread::print_on(st);
+  st->cr();
+}
+
+void ConcurrentMarkSweepThread::print_all_on(outputStream* st) {
+  if (_cmst != NULL) {
+    _cmst->print_on(st);
+  }
+  if (_collector != NULL) {
+    AbstractWorkGang* gang = _collector->conc_workers();
+    if (gang != NULL) {
+      gang->print_worker_threads_on(st);
+    }
+  }
+}
+
+void ConcurrentMarkSweepThread::synchronize(bool is_cms_thread) {
+  assert(UseConcMarkSweepGC, "just checking");
+
+  MutexLockerEx x(CGC_lock,
+                  Mutex::_no_safepoint_check_flag);
+  if (!is_cms_thread) {
+    assert(Thread::current()->is_VM_thread(), "Not a VM thread");
+    CMSSynchronousYieldRequest yr;
+    while (CMS_flag_is_set(CMS_cms_has_token)) {
+      // indicate that we want to get the token
+      set_CMS_flag(CMS_vm_wants_token);
+      CGC_lock->wait(true);
+    }
+    // claim the token and proceed
+    clear_CMS_flag(CMS_vm_wants_token);
+    set_CMS_flag(CMS_vm_has_token);
+  } else {
+    assert(Thread::current()->is_ConcurrentGC_thread(),
+           "Not a CMS thread");
+    // The following barrier assumes there's only one CMS thread.
+    // This will need to be modified is there are more CMS threads than one.
+    while (CMS_flag_is_set(CMS_vm_has_token | CMS_vm_wants_token)) {
+      set_CMS_flag(CMS_cms_wants_token);
+      CGC_lock->wait(true);
+    }
+    // claim the token
+    clear_CMS_flag(CMS_cms_wants_token);
+    set_CMS_flag(CMS_cms_has_token);
+  }
+}
+
+void ConcurrentMarkSweepThread::desynchronize(bool is_cms_thread) {
+  assert(UseConcMarkSweepGC, "just checking");
+
+  MutexLockerEx x(CGC_lock,
+                  Mutex::_no_safepoint_check_flag);
+  if (!is_cms_thread) {
+    assert(Thread::current()->is_VM_thread(), "Not a VM thread");
+    assert(CMS_flag_is_set(CMS_vm_has_token), "just checking");
+    clear_CMS_flag(CMS_vm_has_token);
+    if (CMS_flag_is_set(CMS_cms_wants_token)) {
+      // wake-up a waiting CMS thread
+      CGC_lock->notify();
+    }
+    assert(!CMS_flag_is_set(CMS_vm_has_token | CMS_vm_wants_token),
+           "Should have been cleared");
+  } else {
+    assert(Thread::current()->is_ConcurrentGC_thread(),
+           "Not a CMS thread");
+    assert(CMS_flag_is_set(CMS_cms_has_token), "just checking");
+    clear_CMS_flag(CMS_cms_has_token);
+    if (CMS_flag_is_set(CMS_vm_wants_token)) {
+      // wake-up a waiting VM thread
+      CGC_lock->notify();
+    }
+    assert(!CMS_flag_is_set(CMS_cms_has_token | CMS_cms_wants_token),
+           "Should have been cleared");
+  }
+}
+
+// Wait until the next synchronous GC or a timeout, whichever is earlier.
+void ConcurrentMarkSweepThread::wait_on_cms_lock(long t) {
+  MutexLockerEx x(CGC_lock,
+                  Mutex::_no_safepoint_check_flag);
+  set_CMS_flag(CMS_cms_wants_token);   // to provoke notifies
+  CGC_lock->wait(Mutex::_no_safepoint_check_flag, t);
+  clear_CMS_flag(CMS_cms_wants_token);
+  assert(!CMS_flag_is_set(CMS_cms_has_token | CMS_cms_wants_token),
+         "Should not be set");
+}
+
+void ConcurrentMarkSweepThread::sleepBeforeNextCycle() {
+  while (!_should_terminate) {
+    if (CMSIncrementalMode) {
+      icms_wait();
+      return;
+    } else {
+      // Wait until the next synchronous GC or a timeout, whichever is earlier
+      wait_on_cms_lock(CMSWaitDuration);
+    }
+    // Check if we should start a CMS collection cycle
+    if (_collector->shouldConcurrentCollect()) {
+      return;
+    }
+    // .. collection criterion not yet met, let's go back
+    // and wait some more
+  }
+}
+
+// Incremental CMS
+void ConcurrentMarkSweepThread::start_icms() {
+  assert(UseConcMarkSweepGC && CMSIncrementalMode, "just checking");
+  MutexLockerEx x(iCMS_lock, Mutex::_no_safepoint_check_flag);
+  trace_state("start_icms");
+  _should_run = true;
+  iCMS_lock->notify_all();
+}
+
+void ConcurrentMarkSweepThread::stop_icms() {
+  assert(UseConcMarkSweepGC && CMSIncrementalMode, "just checking");
+  MutexLockerEx x(iCMS_lock, Mutex::_no_safepoint_check_flag);
+  if (!_should_stop) {
+    trace_state("stop_icms");
+    _should_stop = true;
+    _should_run = false;
+    asynchronous_yield_request();
+    iCMS_lock->notify_all();
+  }
+}
+
+void ConcurrentMarkSweepThread::icms_wait() {
+  assert(UseConcMarkSweepGC && CMSIncrementalMode, "just checking");
+  if (_should_stop && icms_enabled()) {
+    MutexLockerEx x(iCMS_lock, Mutex::_no_safepoint_check_flag);
+    trace_state("pause_icms");
+    _collector->stats().stop_cms_timer();
+    while(!_should_run && icms_enabled()) {
+      iCMS_lock->wait(Mutex::_no_safepoint_check_flag);
+    }
+    _collector->stats().start_cms_timer();
+    _should_stop = false;
+    trace_state("pause_icms end");
+  }
+}
+
+// Note: this method, although exported by the ConcurrentMarkSweepThread,
+// which is a non-JavaThread, can only be called by a JavaThread.
+// Currently this is done at vm creation time (post-vm-init) by the
+// main/Primordial (Java)Thread.
+// XXX Consider changing this in the future to allow the CMS thread
+// itself to create this thread?
+void ConcurrentMarkSweepThread::makeSurrogateLockerThread(TRAPS) {
+  assert(UseConcMarkSweepGC, "SLT thread needed only for CMS GC");
+  assert(_slt == NULL, "SLT already created");
+  _slt = SurrogateLockerThread::make(THREAD);
+}