--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/share/vm/services/lowMemoryDetector.cpp	Sat Dec 01 00:00:00 2007 +0000
@@ -0,0 +1,422 @@
+/*
+ * Copyright 2003-2007 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/_lowMemoryDetector.cpp.incl"
+
+LowMemoryDetectorThread* LowMemoryDetector::_detector_thread = NULL;
+volatile bool LowMemoryDetector::_enabled_for_collected_pools = false;
+volatile jint LowMemoryDetector::_disabled_count = 0;
+
+void LowMemoryDetector::initialize() {
+  EXCEPTION_MARK;
+
+  instanceKlassHandle klass (THREAD,  SystemDictionary::thread_klass());
+  instanceHandle thread_oop = klass->allocate_instance_handle(CHECK);
+
+  const char thread_name[] = "Low Memory Detector";
+  Handle string = java_lang_String::create_from_str(thread_name, CHECK);
+
+  // Initialize thread_oop to put it into the system threadGroup
+  Handle thread_group (THREAD, Universe::system_thread_group());
+  JavaValue result(T_VOID);
+  JavaCalls::call_special(&result, thread_oop,
+                          klass,
+                          vmSymbolHandles::object_initializer_name(),
+                          vmSymbolHandles::threadgroup_string_void_signature(),
+                          thread_group,
+                          string,
+                          CHECK);
+
+  {
+    MutexLocker mu(Threads_lock);
+    _detector_thread = new LowMemoryDetectorThread(&low_memory_detector_thread_entry);
+
+    // At this point it may be possible that no osthread was created for the
+    // JavaThread due to lack of memory. We would have to throw an exception
+    // in that case. However, since this must work and we do not allow
+    // exceptions anyway, check and abort if this fails.
+    if (_detector_thread == NULL || _detector_thread->osthread() == NULL) {
+      vm_exit_during_initialization("java.lang.OutOfMemoryError",
+                                    "unable to create new native thread");
+    }
+
+    java_lang_Thread::set_thread(thread_oop(), _detector_thread);
+    java_lang_Thread::set_priority(thread_oop(), NearMaxPriority);
+    java_lang_Thread::set_daemon(thread_oop());
+    _detector_thread->set_threadObj(thread_oop());
+
+    Threads::add(_detector_thread);
+    Thread::start(_detector_thread);
+  }
+}
+
+bool LowMemoryDetector::has_pending_requests() {
+  assert(LowMemory_lock->owned_by_self(), "Must own LowMemory_lock");
+  bool has_requests = false;
+  int num_memory_pools = MemoryService::num_memory_pools();
+  for (int i = 0; i < num_memory_pools; i++) {
+    MemoryPool* pool = MemoryService::get_memory_pool(i);
+    SensorInfo* sensor = pool->usage_sensor();
+    if (sensor != NULL) {
+      has_requests = has_requests || sensor->has_pending_requests();
+    }
+
+    SensorInfo* gc_sensor = pool->gc_usage_sensor();
+    if (gc_sensor != NULL) {
+      has_requests = has_requests || gc_sensor->has_pending_requests();
+    }
+  }
+  return has_requests;
+}
+
+void LowMemoryDetector::low_memory_detector_thread_entry(JavaThread* jt, TRAPS) {
+  while (true) {
+    bool   sensors_changed = false;
+
+    {
+      // _no_safepoint_check_flag is used here as LowMemory_lock is a
+      // special lock and the VMThread may acquire this lock at safepoint.
+      // Need state transition ThreadBlockInVM so that this thread
+      // will be handled by safepoint correctly when this thread is
+      // notified at a safepoint.
+
+      // This ThreadBlockInVM object is not also considered to be
+      // suspend-equivalent because LowMemoryDetector threads are
+      // not visible to external suspension.
+
+      ThreadBlockInVM tbivm(jt);
+
+      MutexLockerEx ml(LowMemory_lock, Mutex::_no_safepoint_check_flag);
+      while (!(sensors_changed = has_pending_requests())) {
+        // wait until one of the sensors has pending requests
+        LowMemory_lock->wait(Mutex::_no_safepoint_check_flag);
+      }
+    }
+
+    {
+      ResourceMark rm(THREAD);
+      HandleMark hm(THREAD);
+
+      // No need to hold LowMemory_lock to call out to Java
+      int num_memory_pools = MemoryService::num_memory_pools();
+      for (int i = 0; i < num_memory_pools; i++) {
+        MemoryPool* pool = MemoryService::get_memory_pool(i);
+        SensorInfo* sensor = pool->usage_sensor();
+        SensorInfo* gc_sensor = pool->gc_usage_sensor();
+        if (sensor != NULL && sensor->has_pending_requests()) {
+          sensor->process_pending_requests(CHECK);
+        }
+        if (gc_sensor != NULL && gc_sensor->has_pending_requests()) {
+          gc_sensor->process_pending_requests(CHECK);
+        }
+      }
+    }
+  }
+}
+
+// This method could be called from any Java threads
+// and also VMThread.
+void LowMemoryDetector::detect_low_memory() {
+  MutexLockerEx ml(LowMemory_lock, Mutex::_no_safepoint_check_flag);
+
+  bool has_pending_requests = false;
+  int num_memory_pools = MemoryService::num_memory_pools();
+  for (int i = 0; i < num_memory_pools; i++) {
+    MemoryPool* pool = MemoryService::get_memory_pool(i);
+    SensorInfo* sensor = pool->usage_sensor();
+    if (sensor != NULL &&
+        pool->usage_threshold()->is_high_threshold_supported() &&
+        pool->usage_threshold()->high_threshold() != 0) {
+      MemoryUsage usage = pool->get_memory_usage();
+      sensor->set_gauge_sensor_level(usage,
+                                     pool->usage_threshold());
+      has_pending_requests = has_pending_requests || sensor->has_pending_requests();
+    }
+  }
+
+  if (has_pending_requests) {
+    LowMemory_lock->notify_all();
+  }
+}
+
+// This method could be called from any Java threads
+// and also VMThread.
+void LowMemoryDetector::detect_low_memory(MemoryPool* pool) {
+  SensorInfo* sensor = pool->usage_sensor();
+  if (sensor == NULL ||
+      !pool->usage_threshold()->is_high_threshold_supported() ||
+      pool->usage_threshold()->high_threshold() == 0) {
+    return;
+  }
+
+  {
+    MutexLockerEx ml(LowMemory_lock, Mutex::_no_safepoint_check_flag);
+
+    MemoryUsage usage = pool->get_memory_usage();
+    sensor->set_gauge_sensor_level(usage,
+                                   pool->usage_threshold());
+    if (sensor->has_pending_requests()) {
+      // notify sensor state update
+      LowMemory_lock->notify_all();
+    }
+  }
+}
+
+// Only called by VMThread at GC time
+void LowMemoryDetector::detect_after_gc_memory(MemoryPool* pool) {
+  SensorInfo* sensor = pool->gc_usage_sensor();
+  if (sensor == NULL ||
+      !pool->gc_usage_threshold()->is_high_threshold_supported() ||
+      pool->gc_usage_threshold()->high_threshold() == 0) {
+    return;
+  }
+
+  {
+    MutexLockerEx ml(LowMemory_lock, Mutex::_no_safepoint_check_flag);
+
+    MemoryUsage usage = pool->get_last_collection_usage();
+    sensor->set_counter_sensor_level(usage, pool->gc_usage_threshold());
+
+    if (sensor->has_pending_requests()) {
+      // notify sensor state update
+      LowMemory_lock->notify_all();
+    }
+  }
+}
+
+// recompute enabled flag
+void LowMemoryDetector::recompute_enabled_for_collected_pools() {
+  bool enabled = false;
+  int num_memory_pools = MemoryService::num_memory_pools();
+  for (int i=0; i<num_memory_pools; i++) {
+    MemoryPool* pool = MemoryService::get_memory_pool(i);
+    if (pool->is_collected_pool() && is_enabled(pool)) {
+      enabled = true;
+      break;
+    }
+  }
+  _enabled_for_collected_pools = enabled;
+}
+
+SensorInfo::SensorInfo() {
+  _sensor_obj = NULL;
+  _sensor_on = false;
+  _sensor_count = 0;
+  _pending_trigger_count = 0;
+  _pending_clear_count = 0;
+}
+
+// When this method is used, the memory usage is monitored
+// as a gauge attribute.  Sensor notifications (trigger or
+// clear) is only emitted at the first time it crosses
+// a threshold.
+//
+// High and low thresholds are designed to provide a
+// hysteresis mechanism to avoid repeated triggering
+// of notifications when the attribute value makes small oscillations
+// around the high or low threshold value.
+//
+// The sensor will be triggered if:
+//  (1) the usage is crossing above the high threshold and
+//      the sensor is currently off and no pending
+//      trigger requests; or
+//  (2) the usage is crossing above the high threshold and
+//      the sensor will be off (i.e. sensor is currently on
+//      and has pending clear requests).
+//
+// Subsequent crossings of the high threshold value do not cause
+// any triggers unless the usage becomes less than the low threshold.
+//
+// The sensor will be cleared if:
+//  (1) the usage is crossing below the low threshold and
+//      the sensor is currently on and no pending
+//      clear requests; or
+//  (2) the usage is crossing below the low threshold and
+//      the sensor will be on (i.e. sensor is currently off
+//      and has pending trigger requests).
+//
+// Subsequent crossings of the low threshold value do not cause
+// any clears unless the usage becomes greater than or equal
+// to the high threshold.
+//
+// If the current level is between high and low threhsold, no change.
+//
+void SensorInfo::set_gauge_sensor_level(MemoryUsage usage, ThresholdSupport* high_low_threshold) {
+  assert(high_low_threshold->is_high_threshold_supported(), "just checking");
+
+  bool is_over_high = high_low_threshold->is_high_threshold_crossed(usage);
+  bool is_below_low = high_low_threshold->is_low_threshold_crossed(usage);
+
+  assert(!(is_over_high && is_below_low), "Can't be both true");
+
+  if (is_over_high &&
+        ((!_sensor_on && _pending_trigger_count == 0) ||
+         _pending_clear_count > 0)) {
+    // low memory detected and need to increment the trigger pending count
+    // if the sensor is off or will be off due to _pending_clear_ > 0
+    // Request to trigger the sensor
+    _pending_trigger_count++;
+    _usage = usage;
+
+    if (_pending_clear_count > 0) {
+      // non-zero pending clear requests indicates that there are
+      // pending requests to clear this sensor.
+      // This trigger request needs to clear this clear count
+      // since the resulting sensor flag should be on.
+      _pending_clear_count = 0;
+    }
+  } else if (is_below_low &&
+               ((_sensor_on && _pending_clear_count == 0) ||
+                (_pending_trigger_count > 0 && _pending_clear_count == 0))) {
+    // memory usage returns below the threshold
+    // Request to clear the sensor if the sensor is on or will be on due to
+    // _pending_trigger_count > 0 and also no clear request
+    _pending_clear_count++;
+  }
+}
+
+// When this method is used, the memory usage is monitored as a
+// simple counter attribute.  The sensor will be triggered
+// whenever the usage is crossing the threshold to keep track
+// of the number of times the VM detects such a condition occurs.
+//
+// High and low thresholds are designed to provide a
+// hysteresis mechanism to avoid repeated triggering
+// of notifications when the attribute value makes small oscillations
+// around the high or low threshold value.
+//
+// The sensor will be triggered if:
+//   - the usage is crossing above the high threshold regardless
+//     of the current sensor state.
+//
+// The sensor will be cleared if:
+//  (1) the usage is crossing below the low threshold and
+//      the sensor is currently on; or
+//  (2) the usage is crossing below the low threshold and
+//      the sensor will be on (i.e. sensor is currently off
+//      and has pending trigger requests).
+void SensorInfo::set_counter_sensor_level(MemoryUsage usage, ThresholdSupport* counter_threshold) {
+  assert(counter_threshold->is_high_threshold_supported(), "just checking");
+
+  bool is_over_high = counter_threshold->is_high_threshold_crossed(usage);
+  bool is_below_low = counter_threshold->is_low_threshold_crossed(usage);
+
+  assert(!(is_over_high && is_below_low), "Can't be both true");
+
+  if (is_over_high) {
+    _pending_trigger_count++;
+    _usage = usage;
+    _pending_clear_count = 0;
+  } else if (is_below_low && (_sensor_on || _pending_trigger_count > 0)) {
+    _pending_clear_count++;
+  }
+}
+
+void SensorInfo::oops_do(OopClosure* f) {
+  f->do_oop((oop*) &_sensor_obj);
+}
+
+void SensorInfo::process_pending_requests(TRAPS) {
+  if (!has_pending_requests()) {
+    return;
+  }
+
+  int pending_count = pending_trigger_count();
+  if (pending_clear_count() > 0) {
+    clear(pending_count, CHECK);
+  } else {
+    trigger(pending_count, CHECK);
+  }
+
+}
+
+void SensorInfo::trigger(int count, TRAPS) {
+  assert(count <= _pending_trigger_count, "just checking");
+
+  if (_sensor_obj != NULL) {
+    klassOop k = Management::sun_management_Sensor_klass(CHECK);
+    instanceKlassHandle sensorKlass (THREAD, k);
+    Handle sensor_h(THREAD, _sensor_obj);
+    Handle usage_h = MemoryService::create_MemoryUsage_obj(_usage, CHECK);
+
+    JavaValue result(T_VOID);
+    JavaCallArguments args(sensor_h);
+    args.push_int((int) count);
+    args.push_oop(usage_h);
+
+    JavaCalls::call_virtual(&result,
+                            sensorKlass,
+                            vmSymbolHandles::trigger_name(),
+                            vmSymbolHandles::trigger_method_signature(),
+                            &args,
+                            CHECK);
+  }
+
+  {
+    // Holds LowMemory_lock and update the sensor state
+    MutexLockerEx ml(LowMemory_lock, Mutex::_no_safepoint_check_flag);
+    _sensor_on = true;
+    _sensor_count += count;
+    _pending_trigger_count = _pending_trigger_count - count;
+  }
+}
+
+void SensorInfo::clear(int count, TRAPS) {
+  if (_sensor_obj != NULL) {
+    klassOop k = Management::sun_management_Sensor_klass(CHECK);
+    instanceKlassHandle sensorKlass (THREAD, k);
+    Handle sensor(THREAD, _sensor_obj);
+
+    JavaValue result(T_VOID);
+    JavaCallArguments args(sensor);
+    args.push_int((int) count);
+    JavaCalls::call_virtual(&result,
+                            sensorKlass,
+                            vmSymbolHandles::clear_name(),
+                            vmSymbolHandles::int_void_signature(),
+                            &args,
+                            CHECK);
+  }
+
+  {
+    // Holds LowMemory_lock and update the sensor state
+    MutexLockerEx ml(LowMemory_lock, Mutex::_no_safepoint_check_flag);
+    _sensor_on = false;
+    _pending_clear_count = 0;
+    _pending_trigger_count = _pending_trigger_count - count;
+  }
+}
+
+//--------------------------------------------------------------
+// Non-product code
+
+#ifndef PRODUCT
+void SensorInfo::print() {
+  tty->print_cr("%s count = %ld pending_triggers = %ld pending_clears = %ld",
+                (_sensor_on ? "on" : "off"),
+                _sensor_count, _pending_trigger_count, _pending_clear_count);
+}
+
+#endif // PRODUCT