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hotspot/src/share/vm/runtime/vmThread.cpp

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+/*
+ * Copyright 1998-2007 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/_vmThread.cpp.incl"
+
+// Dummy VM operation to act as first element in our circular double-linked list
+class VM_Dummy: public VM_Operation {
+  VMOp_Type type() const { return VMOp_Dummy; }
+  void  doit() {};
+};
+
+VMOperationQueue::VMOperationQueue() {
+  // The queue is a circular doubled-linked list, which always contains
+  // one element (i.e., one element means empty).
+  for(int i = 0; i < nof_priorities; i++) {
+    _queue_length[i] = 0;
+    _queue_counter = 0;
+    _queue[i] = new VM_Dummy();
+    _queue[i]->set_next(_queue[i]);
+    _queue[i]->set_prev(_queue[i]);
+  }
+  _drain_list = NULL;
+}
+
+
+bool VMOperationQueue::queue_empty(int prio) {
+  // It is empty if there is exactly one element
+  bool empty = (_queue[prio] == _queue[prio]->next());
+  assert( (_queue_length[prio] == 0 && empty) ||
+          (_queue_length[prio] > 0  && !empty), "sanity check");
+  return _queue_length[prio] == 0;
+}
+
+// Inserts an element to the right of the q element
+void VMOperationQueue::insert(VM_Operation* q, VM_Operation* n) {
+  assert(q->next()->prev() == q && q->prev()->next() == q, "sanity check");
+  n->set_prev(q);
+  n->set_next(q->next());
+  q->next()->set_prev(n);
+  q->set_next(n);
+}
+
+void VMOperationQueue::queue_add_front(int prio, VM_Operation *op) {
+  _queue_length[prio]++;
+  insert(_queue[prio]->next(), op);
+}
+
+void VMOperationQueue::queue_add_back(int prio, VM_Operation *op) {
+  _queue_length[prio]++;
+  insert(_queue[prio]->prev(), op);
+}
+
+
+void VMOperationQueue::unlink(VM_Operation* q) {
+  assert(q->next()->prev() == q && q->prev()->next() == q, "sanity check");
+  q->prev()->set_next(q->next());
+  q->next()->set_prev(q->prev());
+}
+
+VM_Operation* VMOperationQueue::queue_remove_front(int prio) {
+  if (queue_empty(prio)) return NULL;
+  assert(_queue_length[prio] >= 0, "sanity check");
+  _queue_length[prio]--;
+  VM_Operation* r = _queue[prio]->next();
+  assert(r != _queue[prio], "cannot remove base element");
+  unlink(r);
+  return r;
+}
+
+VM_Operation* VMOperationQueue::queue_drain(int prio) {
+  if (queue_empty(prio)) return NULL;
+  DEBUG_ONLY(int length = _queue_length[prio];);
+  assert(length >= 0, "sanity check");
+  _queue_length[prio] = 0;
+  VM_Operation* r = _queue[prio]->next();
+  assert(r != _queue[prio], "cannot remove base element");
+  // remove links to base element from head and tail
+  r->set_prev(NULL);
+  _queue[prio]->prev()->set_next(NULL);
+  // restore queue to empty state
+  _queue[prio]->set_next(_queue[prio]);
+  _queue[prio]->set_prev(_queue[prio]);
+  assert(queue_empty(prio), "drain corrupted queue")
+#ifdef DEBUG
+  int len = 0;
+  VM_Operation* cur;
+  for(cur = r; cur != NULL; cur=cur->next()) len++;
+  assert(len == length, "drain lost some ops");
+#endif
+  return r;
+}
+
+void VMOperationQueue::queue_oops_do(int queue, OopClosure* f) {
+  VM_Operation* cur = _queue[queue];
+  cur = cur->next();
+  while (cur != _queue[queue]) {
+    cur->oops_do(f);
+    cur = cur->next();
+  }
+}
+
+void VMOperationQueue::drain_list_oops_do(OopClosure* f) {
+  VM_Operation* cur = _drain_list;
+  while (cur != NULL) {
+    cur->oops_do(f);
+    cur = cur->next();
+  }
+}
+
+//-----------------------------------------------------------------
+// High-level interface
+bool VMOperationQueue::add(VM_Operation *op) {
+  // Encapsulates VM queue policy. Currently, that
+  // only involves putting them on the right list
+  if (op->evaluate_at_safepoint()) {
+    queue_add_back(SafepointPriority, op);
+    return true;
+  }
+
+  queue_add_back(MediumPriority, op);
+  return true;
+}
+
+VM_Operation* VMOperationQueue::remove_next() {
+  // Assuming VMOperation queue is two-level priority queue. If there are
+  // more than two priorities, we need a different scheduling algorithm.
+  assert(SafepointPriority == 0 && MediumPriority == 1 && nof_priorities == 2,
+         "current algorithm does not work");
+
+  // simple counter based scheduling to prevent starvation of lower priority
+  // queue. -- see 4390175
+  int high_prio, low_prio;
+  if (_queue_counter++ < 10) {
+      high_prio = SafepointPriority;
+      low_prio  = MediumPriority;
+  } else {
+      _queue_counter = 0;
+      high_prio = MediumPriority;
+      low_prio  = SafepointPriority;
+  }
+
+  return queue_remove_front(queue_empty(high_prio) ? low_prio : high_prio);
+}
+
+void VMOperationQueue::oops_do(OopClosure* f) {
+  for(int i = 0; i < nof_priorities; i++) {
+    queue_oops_do(i, f);
+  }
+  drain_list_oops_do(f);
+}
+
+
+//------------------------------------------------------------------------------------------------------------------
+// Implementation of VMThread stuff
+
+bool                VMThread::_should_terminate   = false;
+bool              VMThread::_terminated         = false;
+Monitor*          VMThread::_terminate_lock     = NULL;
+VMThread*         VMThread::_vm_thread          = NULL;
+VM_Operation*     VMThread::_cur_vm_operation   = NULL;
+VMOperationQueue* VMThread::_vm_queue           = NULL;
+PerfCounter*      VMThread::_perf_accumulated_vm_operation_time = NULL;
+
+
+void VMThread::create() {
+  assert(vm_thread() == NULL, "we can only allocate one VMThread");
+  _vm_thread = new VMThread();
+
+  // Create VM operation queue
+  _vm_queue = new VMOperationQueue();
+  guarantee(_vm_queue != NULL, "just checking");
+
+  _terminate_lock = new Monitor(Mutex::safepoint, "VMThread::_terminate_lock", true);
+
+  if (UsePerfData) {
+    // jvmstat performance counters
+    Thread* THREAD = Thread::current();
+    _perf_accumulated_vm_operation_time =
+                 PerfDataManager::create_counter(SUN_THREADS, "vmOperationTime",
+                                                 PerfData::U_Ticks, CHECK);
+  }
+}
+
+
+VMThread::VMThread() : Thread() {
+  // nothing to do
+}
+
+void VMThread::destroy() {
+  if (_vm_thread != NULL) {
+    delete _vm_thread;
+    _vm_thread = NULL;      // VM thread is gone
+  }
+}
+
+void VMThread::run() {
+  assert(this == vm_thread(), "check");
+
+  this->initialize_thread_local_storage();
+  this->record_stack_base_and_size();
+  // Notify_lock wait checks on active_handles() to rewait in
+  // case of spurious wakeup, it should wait on the last
+  // value set prior to the notify
+  this->set_active_handles(JNIHandleBlock::allocate_block());
+
+  {
+    MutexLocker ml(Notify_lock);
+    Notify_lock->notify();
+  }
+  // Notify_lock is destroyed by Threads::create_vm()
+
+  int prio = (VMThreadPriority == -1)
+    ? os::java_to_os_priority[NearMaxPriority]
+    : VMThreadPriority;
+  // Note that I cannot call os::set_priority because it expects Java
+  // priorities and I am *explicitly* using OS priorities so that it's
+  // possible to set the VM thread priority higher than any Java thread.
+  os::set_native_priority( this, prio );
+
+  // Wait for VM_Operations until termination
+  this->loop();
+
+  // Note the intention to exit before safepointing.
+  // 6295565  This has the effect of waiting for any large tty
+  // outputs to finish.
+  if (xtty != NULL) {
+    ttyLocker ttyl;
+    xtty->begin_elem("destroy_vm");
+    xtty->stamp();
+    xtty->end_elem();
+    assert(should_terminate(), "termination flag must be set");
+  }
+
+  // 4526887 let VM thread exit at Safepoint
+  SafepointSynchronize::begin();
+
+  if (VerifyBeforeExit) {
+    HandleMark hm(VMThread::vm_thread());
+    // Among other things, this ensures that Eden top is correct.
+    Universe::heap()->prepare_for_verify();
+    os::check_heap();
+    Universe::verify(true, true); // Silent verification to not polute normal output
+  }
+
+  CompileBroker::set_should_block();
+
+  // wait for threads (compiler threads or daemon threads) in the
+  // _thread_in_native state to block.
+  VM_Exit::wait_for_threads_in_native_to_block();
+
+  // signal other threads that VM process is gone
+  {
+    // Note: we must have the _no_safepoint_check_flag. Mutex::lock() allows
+    // VM thread to enter any lock at Safepoint as long as its _owner is NULL.
+    // If that happens after _terminate_lock->wait() has unset _owner
+    // but before it actually drops the lock and waits, the notification below
+    // may get lost and we will have a hang. To avoid this, we need to use
+    // Mutex::lock_without_safepoint_check().
+    MutexLockerEx ml(_terminate_lock, Mutex::_no_safepoint_check_flag);
+    _terminated = true;
+    _terminate_lock->notify();
+  }
+
+  // Deletion must be done synchronously by the JNI DestroyJavaVM thread
+  // so that the VMThread deletion completes before the main thread frees
+  // up the CodeHeap.
+
+}
+
+
+// Notify the VMThread that the last non-daemon JavaThread has terminated,
+// and wait until operation is performed.
+void VMThread::wait_for_vm_thread_exit() {
+  { MutexLocker mu(VMOperationQueue_lock);
+    _should_terminate = true;
+    VMOperationQueue_lock->notify();
+  }
+
+  // Note: VM thread leaves at Safepoint. We are not stopped by Safepoint
+  // because this thread has been removed from the threads list. But anything
+  // that could get blocked by Safepoint should not be used after this point,
+  // otherwise we will hang, since there is no one can end the safepoint.
+
+  // Wait until VM thread is terminated
+  // Note: it should be OK to use Terminator_lock here. But this is called
+  // at a very delicate time (VM shutdown) and we are operating in non- VM
+  // thread at Safepoint. It's safer to not share lock with other threads.
+  { MutexLockerEx ml(_terminate_lock, Mutex::_no_safepoint_check_flag);
+    while(!VMThread::is_terminated()) {
+        _terminate_lock->wait(Mutex::_no_safepoint_check_flag);
+    }
+  }
+}
+
+void VMThread::print_on(outputStream* st) const {
+  st->print("\"%s\" ", name());
+  Thread::print_on(st);
+  st->cr();
+}
+
+void VMThread::evaluate_operation(VM_Operation* op) {
+  ResourceMark rm;
+
+  {
+    PerfTraceTime vm_op_timer(perf_accumulated_vm_operation_time());
+    op->evaluate();
+  }
+
+  // Last access of info in _cur_vm_operation!
+  bool c_heap_allocated = op->is_cheap_allocated();
+
+  // Mark as completed
+  if (!op->evaluate_concurrently()) {
+    op->calling_thread()->increment_vm_operation_completed_count();
+  }
+  // It is unsafe to access the _cur_vm_operation after the 'increment_vm_operation_completed_count' call,
+  // since if it is stack allocated the calling thread might have deallocated
+  if (c_heap_allocated) {
+    delete _cur_vm_operation;
+  }
+}
+
+
+void VMThread::loop() {
+  assert(_cur_vm_operation == NULL, "no current one should be executing");
+
+  while(true) {
+    VM_Operation* safepoint_ops = NULL;
+    //
+    // Wait for VM operation
+    //
+    // use no_safepoint_check to get lock without attempting to "sneak"
+    { MutexLockerEx mu_queue(VMOperationQueue_lock,
+                             Mutex::_no_safepoint_check_flag);
+
+      // Look for new operation
+      assert(_cur_vm_operation == NULL, "no current one should be executing");
+      _cur_vm_operation = _vm_queue->remove_next();
+
+      // Stall time tracking code
+      if (PrintVMQWaitTime && _cur_vm_operation != NULL &&
+          !_cur_vm_operation->evaluate_concurrently()) {
+        long stall = os::javaTimeMillis() - _cur_vm_operation->timestamp();
+        if (stall > 0)
+          tty->print_cr("%s stall: %Ld",  _cur_vm_operation->name(), stall);
+      }
+
+      while (!should_terminate() && _cur_vm_operation == NULL) {
+        // wait with a timeout to guarantee safepoints at regular intervals
+        bool timedout =
+          VMOperationQueue_lock->wait(Mutex::_no_safepoint_check_flag,
+                                      GuaranteedSafepointInterval);
+
+        // Support for self destruction
+        if ((SelfDestructTimer != 0) && !is_error_reported() &&
+            (os::elapsedTime() > SelfDestructTimer * 60)) {
+          tty->print_cr("VM self-destructed");
+          exit(-1);
+        }
+
+        if (timedout && (SafepointALot ||
+                         SafepointSynchronize::is_cleanup_needed())) {
+          MutexUnlockerEx mul(VMOperationQueue_lock,
+                              Mutex::_no_safepoint_check_flag);
+          // Force a safepoint since we have not had one for at least
+          // 'GuaranteedSafepointInterval' milliseconds.  This will run all
+          // the clean-up processing that needs to be done regularly at a
+          // safepoint
+          SafepointSynchronize::begin();
+          #ifdef ASSERT
+            if (GCALotAtAllSafepoints) InterfaceSupport::check_gc_alot();
+          #endif
+          SafepointSynchronize::end();
+        }
+        _cur_vm_operation = _vm_queue->remove_next();
+
+        // If we are at a safepoint we will evaluate all the operations that
+        // follow that also require a safepoint
+        if (_cur_vm_operation != NULL &&
+            _cur_vm_operation->evaluate_at_safepoint()) {
+          safepoint_ops = _vm_queue->drain_at_safepoint_priority();
+        }
+      }
+
+      if (should_terminate()) break;
+    } // Release mu_queue_lock
+
+    //
+    // Execute VM operation
+    //
+    { HandleMark hm(VMThread::vm_thread());
+
+      EventMark em("Executing VM operation: %s", vm_operation()->name());
+      assert(_cur_vm_operation != NULL, "we should have found an operation to execute");
+
+      // Give the VM thread an extra quantum.  Jobs tend to be bursty and this
+      // helps the VM thread to finish up the job.
+      // FIXME: When this is enabled and there are many threads, this can degrade
+      // performance significantly.
+      if( VMThreadHintNoPreempt )
+        os::hint_no_preempt();
+
+      // If we are at a safepoint we will evaluate all the operations that
+      // follow that also require a safepoint
+      if (_cur_vm_operation->evaluate_at_safepoint()) {
+
+        if (PrintGCApplicationConcurrentTime) {
+           gclog_or_tty->print_cr("Application time: %3.7f seconds",
+                                  RuntimeService::last_application_time_sec());
+        }
+
+        _vm_queue->set_drain_list(safepoint_ops); // ensure ops can be scanned
+
+        SafepointSynchronize::begin();
+        evaluate_operation(_cur_vm_operation);
+        // now process all queued safepoint ops, iteratively draining
+        // the queue until there are none left
+        do {
+          _cur_vm_operation = safepoint_ops;
+          if (_cur_vm_operation != NULL) {
+            do {
+              // evaluate_operation deletes the op object so we have
+              // to grab the next op now
+              VM_Operation* next = _cur_vm_operation->next();
+              _vm_queue->set_drain_list(next);
+              evaluate_operation(_cur_vm_operation);
+              _cur_vm_operation = next;
+              if (PrintSafepointStatistics) {
+                SafepointSynchronize::inc_vmop_coalesced_count();
+              }
+            } while (_cur_vm_operation != NULL);
+          }
+          // There is a chance that a thread enqueued a safepoint op
+          // since we released the op-queue lock and initiated the safepoint.
+          // So we drain the queue again if there is anything there, as an
+          // optimization to try and reduce the number of safepoints.
+          // As the safepoint synchronizes us with JavaThreads we will see
+          // any enqueue made by a JavaThread, but the peek will not
+          // necessarily detect a concurrent enqueue by a GC thread, but
+          // that simply means the op will wait for the next major cycle of the
+          // VMThread - just as it would if the GC thread lost the race for
+          // the lock.
+          if (_vm_queue->peek_at_safepoint_priority()) {
+            // must hold lock while draining queue
+            MutexLockerEx mu_queue(VMOperationQueue_lock,
+                                     Mutex::_no_safepoint_check_flag);
+            safepoint_ops = _vm_queue->drain_at_safepoint_priority();
+          } else {
+            safepoint_ops = NULL;
+          }
+        } while(safepoint_ops != NULL);
+
+        _vm_queue->set_drain_list(NULL);
+
+        // Complete safepoint synchronization
+        SafepointSynchronize::end();
+
+        if (PrintGCApplicationStoppedTime) {
+          gclog_or_tty->print_cr("Total time for which application threads "
+                                 "were stopped: %3.7f seconds",
+                                 RuntimeService::last_safepoint_time_sec());
+        }
+
+      } else {  // not a safepoint operation
+        if (TraceLongCompiles) {
+          elapsedTimer t;
+          t.start();
+          evaluate_operation(_cur_vm_operation);
+          t.stop();
+          double secs = t.seconds();
+          if (secs * 1e3 > LongCompileThreshold) {
+            // XXX - _cur_vm_operation should not be accessed after
+            // the completed count has been incremented; the waiting
+            // thread may have already freed this memory.
+            tty->print_cr("vm %s: %3.7f secs]", _cur_vm_operation->name(), secs);
+          }
+        } else {
+          evaluate_operation(_cur_vm_operation);
+        }
+
+        _cur_vm_operation = NULL;
+      }
+    }
+
+    //
+    //  Notify (potential) waiting Java thread(s) - lock without safepoint
+    //  check so that sneaking is not possible
+    { MutexLockerEx mu(VMOperationRequest_lock,
+                       Mutex::_no_safepoint_check_flag);
+      VMOperationRequest_lock->notify_all();
+    }
+
+    //
+    // We want to make sure that we get to a safepoint regularly.
+    //
+    if (SafepointALot || SafepointSynchronize::is_cleanup_needed()) {
+      long interval          = SafepointSynchronize::last_non_safepoint_interval();
+      bool max_time_exceeded = GuaranteedSafepointInterval != 0 && (interval > GuaranteedSafepointInterval);
+      if (SafepointALot || max_time_exceeded) {
+        HandleMark hm(VMThread::vm_thread());
+        SafepointSynchronize::begin();
+        SafepointSynchronize::end();
+      }
+    }
+  }
+}
+
+void VMThread::execute(VM_Operation* op) {
+  Thread* t = Thread::current();
+
+  if (!t->is_VM_thread()) {
+    // JavaThread or WatcherThread
+    t->check_for_valid_safepoint_state(true);
+
+    // New request from Java thread, evaluate prologue
+    if (!op->doit_prologue()) {
+      return;   // op was cancelled
+    }
+
+    // Setup VM_operations for execution
+    op->set_calling_thread(t, Thread::get_priority(t));
+
+    // It does not make sense to execute the epilogue, if the VM operation object is getting
+    // deallocated by the VM thread.
+    bool concurrent     = op->evaluate_concurrently();
+    bool execute_epilog = !op->is_cheap_allocated();
+    assert(!concurrent || op->is_cheap_allocated(), "concurrent => cheap_allocated");
+
+    // Get ticket number for non-concurrent VM operations
+    int ticket = 0;
+    if (!concurrent) {
+      ticket = t->vm_operation_ticket();
+    }
+
+    // Add VM operation to list of waiting threads. We are guaranteed not to block while holding the
+    // VMOperationQueue_lock, so we can block without a safepoint check. This allows vm operation requests
+    // to be queued up during a safepoint synchronization.
+    {
+      VMOperationQueue_lock->lock_without_safepoint_check();
+      bool ok = _vm_queue->add(op);
+      op->set_timestamp(os::javaTimeMillis());
+      VMOperationQueue_lock->notify();
+      VMOperationQueue_lock->unlock();
+      // VM_Operation got skipped
+      if (!ok) {
+        assert(concurrent, "can only skip concurrent tasks");
+        if (op->is_cheap_allocated()) delete op;
+        return;
+      }
+    }
+
+    if (!concurrent) {
+      // Wait for completion of request (non-concurrent)
+      // Note: only a JavaThread triggers the safepoint check when locking
+      MutexLocker mu(VMOperationRequest_lock);
+      while(t->vm_operation_completed_count() < ticket) {
+        VMOperationRequest_lock->wait(!t->is_Java_thread());
+      }
+    }
+
+    if (execute_epilog) {
+      op->doit_epilogue();
+    }
+  } else {
+    // invoked by VM thread; usually nested VM operation
+    assert(t->is_VM_thread(), "must be a VM thread");
+    VM_Operation* prev_vm_operation = vm_operation();
+    if (prev_vm_operation != NULL) {
+      // Check the VM operation allows nested VM operation. This normally not the case, e.g., the compiler
+      // does not allow nested scavenges or compiles.
+      if (!prev_vm_operation->allow_nested_vm_operations()) {
+        fatal2("Nested VM operation %s requested by operation %s", op->name(), vm_operation()->name());
+      }
+      op->set_calling_thread(prev_vm_operation->calling_thread(), prev_vm_operation->priority());
+    }
+
+    EventMark em("Executing %s VM operation: %s", prev_vm_operation ? "nested" : "", op->name());
+
+    // Release all internal handles after operation is evaluated
+    HandleMark hm(t);
+    _cur_vm_operation = op;
+
+    if (op->evaluate_at_safepoint() && !SafepointSynchronize::is_at_safepoint()) {
+      SafepointSynchronize::begin();
+      op->evaluate();
+      SafepointSynchronize::end();
+    } else {
+      op->evaluate();
+    }
+
+    // Free memory if needed
+    if (op->is_cheap_allocated()) delete op;
+
+    _cur_vm_operation = prev_vm_operation;
+  }
+}
+
+
+void VMThread::oops_do(OopClosure* f) {
+  Thread::oops_do(f);
+  _vm_queue->oops_do(f);
+}
+
+//------------------------------------------------------------------------------------------------------------------
+#ifndef PRODUCT
+
+void VMOperationQueue::verify_queue(int prio) {
+  // Check that list is correctly linked
+  int length = _queue_length[prio];
+  VM_Operation *cur = _queue[prio];
+  int i;
+
+  // Check forward links
+  for(i = 0; i < length; i++) {
+    cur = cur->next();
+    assert(cur != _queue[prio], "list to short (forward)");
+  }
+  assert(cur->next() == _queue[prio], "list to long (forward)");
+
+  // Check backwards links
+  cur = _queue[prio];
+  for(i = 0; i < length; i++) {
+    cur = cur->prev();
+    assert(cur != _queue[prio], "list to short (backwards)");
+  }
+  assert(cur->prev() == _queue[prio], "list to long (backwards)");
+}
+
+#endif
+
+void VMThread::verify() {
+  oops_do(&VerifyOopClosure::verify_oop);
+}