author | trims |
Thu, 27 May 2010 19:08:38 -0700 | |
changeset 5547 | f4b087cbb361 |
parent 1 | 489c9b5090e2 |
child 7397 | 5b173b4ca846 |
permissions | -rw-r--r-- |
1 | 1 |
/* |
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* Copyright (c) 2003, 2007, Oracle and/or its affiliates. All rights reserved. |
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
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* |
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* This code is free software; you can redistribute it and/or modify it |
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* under the terms of the GNU General Public License version 2 only, as |
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* published by the Free Software Foundation. |
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* |
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* This code is distributed in the hope that it will be useful, but WITHOUT |
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
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* version 2 for more details (a copy is included in the LICENSE file that |
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* accompanied this code). |
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* |
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* You should have received a copy of the GNU General Public License version |
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* 2 along with this work; if not, write to the Free Software Foundation, |
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
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* |
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
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* or visit www.oracle.com if you need additional information or have any |
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* questions. |
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* |
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*/ |
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// Low Memory Detection Support |
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// Two memory alarms in the JDK (we called them sensors). |
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// - Heap memory sensor |
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// - Non-heap memory sensor |
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// When the VM detects if the memory usage of a memory pool has reached |
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// or exceeded its threshold, it will trigger the sensor for the type |
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// of the memory pool (heap or nonheap or both). |
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// |
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// If threshold == -1, no low memory detection is supported and |
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// the threshold value is not allowed to be changed. |
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// If threshold == 0, no low memory detection is performed for |
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// that memory pool. The threshold can be set to any non-negative |
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// value. |
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// |
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// The default threshold of the Hotspot memory pools are: |
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// Eden space -1 |
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// Survivor space 1 -1 |
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// Survivor space 2 -1 |
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// Old generation 0 |
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// Perm generation 0 |
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// CodeCache 0 |
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// |
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// For heap memory, detection will be performed when GC finishes |
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// and also in the slow path allocation. |
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// For Code cache, detection will be performed in the allocation |
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// and deallocation. |
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// |
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// May need to deal with hysteresis effect. |
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// |
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||
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class LowMemoryDetectorThread; |
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class OopClosure; |
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class MemoryPool; |
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class ThresholdSupport : public CHeapObj { |
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private: |
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bool _support_high_threshold; |
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bool _support_low_threshold; |
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size_t _high_threshold; |
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size_t _low_threshold; |
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public: |
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ThresholdSupport(bool support_high, bool support_low) { |
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_support_high_threshold = support_high; |
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_support_low_threshold = support_low; |
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_high_threshold = 0; |
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_low_threshold= 0; |
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} |
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size_t high_threshold() const { return _high_threshold; } |
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size_t low_threshold() const { return _low_threshold; } |
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bool is_high_threshold_supported() { return _support_high_threshold; } |
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bool is_low_threshold_supported() { return _support_low_threshold; } |
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bool is_high_threshold_crossed(MemoryUsage usage) { |
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if (_support_high_threshold && _high_threshold > 0) { |
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return (usage.used() >= _high_threshold); |
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} |
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return false; |
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} |
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bool is_low_threshold_crossed(MemoryUsage usage) { |
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if (_support_low_threshold && _low_threshold > 0) { |
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return (usage.used() < _low_threshold); |
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} |
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return false; |
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} |
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size_t set_high_threshold(size_t new_threshold) { |
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assert(_support_high_threshold, "can only be set if supported"); |
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assert(new_threshold >= _low_threshold, "new_threshold must be >= _low_threshold"); |
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size_t prev = _high_threshold; |
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_high_threshold = new_threshold; |
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return prev; |
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} |
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size_t set_low_threshold(size_t new_threshold) { |
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assert(_support_low_threshold, "can only be set if supported"); |
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assert(new_threshold <= _high_threshold, "new_threshold must be <= _high_threshold"); |
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size_t prev = _low_threshold; |
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_low_threshold = new_threshold; |
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return prev; |
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} |
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}; |
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class SensorInfo : public CHeapObj { |
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private: |
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instanceOop _sensor_obj; |
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bool _sensor_on; |
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size_t _sensor_count; |
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// before the actual sensor on flag and sensor count are set |
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// we maintain the number of pending triggers and clears. |
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// _pending_trigger_count means the number of pending triggers |
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// and the sensor count should be incremented by the same number. |
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int _pending_trigger_count; |
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// _pending_clear_count takes precedence if it's > 0 which |
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// indicates the resulting sensor will be off |
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// Sensor trigger requests will reset this clear count to |
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// indicate the resulting flag should be on. |
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int _pending_clear_count; |
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MemoryUsage _usage; |
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void clear(int count, TRAPS); |
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void trigger(int count, TRAPS); |
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public: |
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SensorInfo(); |
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void set_sensor(instanceOop sensor) { |
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assert(_sensor_obj == NULL, "Should be set only once"); |
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_sensor_obj = sensor; |
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} |
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bool has_pending_requests() { |
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return (_pending_trigger_count > 0 || _pending_clear_count > 0); |
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} |
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int pending_trigger_count() { return _pending_trigger_count; } |
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int pending_clear_count() { return _pending_clear_count; } |
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// When this method is used, the memory usage is monitored |
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// as a gauge attribute. High and low thresholds are designed |
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// to provide a hysteresis mechanism to avoid repeated triggering |
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// of notifications when the attribute value makes small oscillations |
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// around the high or low threshold value. |
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// |
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// The sensor will be triggered if: |
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// (1) the usage is crossing above the high threshold and |
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// the sensor is currently off and no pending |
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// trigger requests; or |
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// (2) the usage is crossing above the high threshold and |
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// the sensor will be off (i.e. sensor is currently on |
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// and has pending clear requests). |
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// |
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// Subsequent crossings of the high threshold value do not cause |
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// any triggers unless the usage becomes less than the low threshold. |
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// |
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// The sensor will be cleared if: |
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// (1) the usage is crossing below the low threshold and |
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// the sensor is currently on and no pending |
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// clear requests; or |
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// (2) the usage is crossing below the low threshold and |
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// the sensor will be on (i.e. sensor is currently off |
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// and has pending trigger requests). |
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// |
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// Subsequent crossings of the low threshold value do not cause |
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// any clears unless the usage becomes greater than or equal |
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// to the high threshold. |
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// |
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// If the current level is between high and low threhsold, no change. |
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// |
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void set_gauge_sensor_level(MemoryUsage usage, ThresholdSupport* high_low_threshold); |
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// When this method is used, the memory usage is monitored as a |
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// simple counter attribute. The sensor will be triggered |
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// whenever the usage is crossing the threshold to keep track |
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// of the number of times the VM detects such a condition occurs. |
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// |
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// The sensor will be triggered if: |
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// - the usage is crossing above the high threshold regardless |
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// of the current sensor state. |
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// |
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// The sensor will be cleared if: |
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// (1) the usage is crossing below the low threshold and |
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// the sensor is currently on; or |
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// (2) the usage is crossing below the low threshold and |
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// the sensor will be on (i.e. sensor is currently off |
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// and has pending trigger requests). |
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// |
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void set_counter_sensor_level(MemoryUsage usage, ThresholdSupport* counter_threshold); |
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void process_pending_requests(TRAPS); |
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void oops_do(OopClosure* f); |
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#ifndef PRODUCT |
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// printing on default output stream; |
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void print(); |
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#endif // PRODUCT |
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}; |
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class LowMemoryDetector : public AllStatic { |
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friend class LowMemoryDetectorDisabler; |
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private: |
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// true if any collected heap has low memory detection enabled |
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static volatile bool _enabled_for_collected_pools; |
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// > 0 if temporary disabed |
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static volatile jint _disabled_count; |
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static LowMemoryDetectorThread* _detector_thread; |
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static void low_memory_detector_thread_entry(JavaThread* thread, TRAPS); |
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static void check_memory_usage(); |
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static bool has_pending_requests(); |
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static bool temporary_disabled() { return _disabled_count > 0; } |
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static void disable() { Atomic::inc(&_disabled_count); } |
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static void enable() { Atomic::dec(&_disabled_count); } |
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public: |
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static void initialize(); |
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static void detect_low_memory(); |
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static void detect_low_memory(MemoryPool* pool); |
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static void detect_after_gc_memory(MemoryPool* pool); |
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static bool is_enabled(MemoryPool* pool) { |
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// low memory detection is enabled for collected memory pools |
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// iff one of the collected memory pool has a sensor and the |
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// threshold set non-zero |
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if (pool->usage_sensor() == NULL) { |
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return false; |
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} else { |
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ThresholdSupport* threshold_support = pool->usage_threshold(); |
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return (threshold_support->is_high_threshold_supported() ? |
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(threshold_support->high_threshold() > 0) : false); |
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} |
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} |
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// indicates if low memory detection is enabled for any collected |
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// memory pools |
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static inline bool is_enabled_for_collected_pools() { |
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return !temporary_disabled() && _enabled_for_collected_pools; |
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} |
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// recompute enabled flag |
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static void recompute_enabled_for_collected_pools(); |
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// low memory detection for collected memory pools. |
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static inline void detect_low_memory_for_collected_pools() { |
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// no-op if low memory detection not enabled |
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if (!is_enabled_for_collected_pools()) { |
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return; |
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} |
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int num_memory_pools = MemoryService::num_memory_pools(); |
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for (int i=0; i<num_memory_pools; i++) { |
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MemoryPool* pool = MemoryService::get_memory_pool(i); |
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// if low memory detection is enabled then check if the |
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// current used exceeds the high threshold |
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if (pool->is_collected_pool() && is_enabled(pool)) { |
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size_t used = pool->used_in_bytes(); |
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size_t high = pool->usage_threshold()->high_threshold(); |
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if (used > high) { |
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detect_low_memory(pool); |
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} |
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} |
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} |
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} |
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}; |
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class LowMemoryDetectorDisabler: public StackObj { |
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public: |
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LowMemoryDetectorDisabler() |
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{ |
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LowMemoryDetector::disable(); |
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} |
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~LowMemoryDetectorDisabler() |
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{ |
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assert(LowMemoryDetector::temporary_disabled(), "should be disabled!"); |
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LowMemoryDetector::enable(); |
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} |
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}; |