Fri, 14 Jan 2011 13:47:53 -0500
6811367: Fix code in HeapDumper::dump_heap() to avoid buffer overrun
Summary: Check buffer size before using and use dynamic buffer sizes for subsequent calls.
Reviewed-by: kamg, dholmes
1 /*
2 * Copyright (c) 2003, 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.
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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.
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19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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23 */
25 #include "precompiled.hpp"
26 #include "classfile/systemDictionary.hpp"
27 #include "classfile/vmSymbols.hpp"
28 #include "oops/oop.inline.hpp"
29 #include "runtime/interfaceSupport.hpp"
30 #include "runtime/java.hpp"
31 #include "runtime/javaCalls.hpp"
32 #include "runtime/mutex.hpp"
33 #include "runtime/mutexLocker.hpp"
34 #include "services/lowMemoryDetector.hpp"
35 #include "services/management.hpp"
37 LowMemoryDetectorThread* LowMemoryDetector::_detector_thread = NULL;
38 volatile bool LowMemoryDetector::_enabled_for_collected_pools = false;
39 volatile jint LowMemoryDetector::_disabled_count = 0;
41 void LowMemoryDetector::initialize() {
42 EXCEPTION_MARK;
44 instanceKlassHandle klass (THREAD, SystemDictionary::Thread_klass());
45 instanceHandle thread_oop = klass->allocate_instance_handle(CHECK);
47 const char thread_name[] = "Low Memory Detector";
48 Handle string = java_lang_String::create_from_str(thread_name, CHECK);
50 // Initialize thread_oop to put it into the system threadGroup
51 Handle thread_group (THREAD, Universe::system_thread_group());
52 JavaValue result(T_VOID);
53 JavaCalls::call_special(&result, thread_oop,
54 klass,
55 vmSymbolHandles::object_initializer_name(),
56 vmSymbolHandles::threadgroup_string_void_signature(),
57 thread_group,
58 string,
59 CHECK);
61 {
62 MutexLocker mu(Threads_lock);
63 _detector_thread = new LowMemoryDetectorThread(&low_memory_detector_thread_entry);
65 // At this point it may be possible that no osthread was created for the
66 // JavaThread due to lack of memory. We would have to throw an exception
67 // in that case. However, since this must work and we do not allow
68 // exceptions anyway, check and abort if this fails.
69 if (_detector_thread == NULL || _detector_thread->osthread() == NULL) {
70 vm_exit_during_initialization("java.lang.OutOfMemoryError",
71 "unable to create new native thread");
72 }
74 java_lang_Thread::set_thread(thread_oop(), _detector_thread);
75 java_lang_Thread::set_priority(thread_oop(), NearMaxPriority);
76 java_lang_Thread::set_daemon(thread_oop());
77 _detector_thread->set_threadObj(thread_oop());
79 Threads::add(_detector_thread);
80 Thread::start(_detector_thread);
81 }
82 }
84 bool LowMemoryDetector::has_pending_requests() {
85 assert(LowMemory_lock->owned_by_self(), "Must own LowMemory_lock");
86 bool has_requests = false;
87 int num_memory_pools = MemoryService::num_memory_pools();
88 for (int i = 0; i < num_memory_pools; i++) {
89 MemoryPool* pool = MemoryService::get_memory_pool(i);
90 SensorInfo* sensor = pool->usage_sensor();
91 if (sensor != NULL) {
92 has_requests = has_requests || sensor->has_pending_requests();
93 }
95 SensorInfo* gc_sensor = pool->gc_usage_sensor();
96 if (gc_sensor != NULL) {
97 has_requests = has_requests || gc_sensor->has_pending_requests();
98 }
99 }
100 return has_requests;
101 }
103 void LowMemoryDetector::low_memory_detector_thread_entry(JavaThread* jt, TRAPS) {
104 while (true) {
105 bool sensors_changed = false;
107 {
108 // _no_safepoint_check_flag is used here as LowMemory_lock is a
109 // special lock and the VMThread may acquire this lock at safepoint.
110 // Need state transition ThreadBlockInVM so that this thread
111 // will be handled by safepoint correctly when this thread is
112 // notified at a safepoint.
114 // This ThreadBlockInVM object is not also considered to be
115 // suspend-equivalent because LowMemoryDetector threads are
116 // not visible to external suspension.
118 ThreadBlockInVM tbivm(jt);
120 MutexLockerEx ml(LowMemory_lock, Mutex::_no_safepoint_check_flag);
121 while (!(sensors_changed = has_pending_requests())) {
122 // wait until one of the sensors has pending requests
123 LowMemory_lock->wait(Mutex::_no_safepoint_check_flag);
124 }
125 }
127 {
128 ResourceMark rm(THREAD);
129 HandleMark hm(THREAD);
131 // No need to hold LowMemory_lock to call out to Java
132 int num_memory_pools = MemoryService::num_memory_pools();
133 for (int i = 0; i < num_memory_pools; i++) {
134 MemoryPool* pool = MemoryService::get_memory_pool(i);
135 SensorInfo* sensor = pool->usage_sensor();
136 SensorInfo* gc_sensor = pool->gc_usage_sensor();
137 if (sensor != NULL && sensor->has_pending_requests()) {
138 sensor->process_pending_requests(CHECK);
139 }
140 if (gc_sensor != NULL && gc_sensor->has_pending_requests()) {
141 gc_sensor->process_pending_requests(CHECK);
142 }
143 }
144 }
145 }
146 }
148 // This method could be called from any Java threads
149 // and also VMThread.
150 void LowMemoryDetector::detect_low_memory() {
151 MutexLockerEx ml(LowMemory_lock, Mutex::_no_safepoint_check_flag);
153 bool has_pending_requests = false;
154 int num_memory_pools = MemoryService::num_memory_pools();
155 for (int i = 0; i < num_memory_pools; i++) {
156 MemoryPool* pool = MemoryService::get_memory_pool(i);
157 SensorInfo* sensor = pool->usage_sensor();
158 if (sensor != NULL &&
159 pool->usage_threshold()->is_high_threshold_supported() &&
160 pool->usage_threshold()->high_threshold() != 0) {
161 MemoryUsage usage = pool->get_memory_usage();
162 sensor->set_gauge_sensor_level(usage,
163 pool->usage_threshold());
164 has_pending_requests = has_pending_requests || sensor->has_pending_requests();
165 }
166 }
168 if (has_pending_requests) {
169 LowMemory_lock->notify_all();
170 }
171 }
173 // This method could be called from any Java threads
174 // and also VMThread.
175 void LowMemoryDetector::detect_low_memory(MemoryPool* pool) {
176 SensorInfo* sensor = pool->usage_sensor();
177 if (sensor == NULL ||
178 !pool->usage_threshold()->is_high_threshold_supported() ||
179 pool->usage_threshold()->high_threshold() == 0) {
180 return;
181 }
183 {
184 MutexLockerEx ml(LowMemory_lock, Mutex::_no_safepoint_check_flag);
186 MemoryUsage usage = pool->get_memory_usage();
187 sensor->set_gauge_sensor_level(usage,
188 pool->usage_threshold());
189 if (sensor->has_pending_requests()) {
190 // notify sensor state update
191 LowMemory_lock->notify_all();
192 }
193 }
194 }
196 // Only called by VMThread at GC time
197 void LowMemoryDetector::detect_after_gc_memory(MemoryPool* pool) {
198 SensorInfo* sensor = pool->gc_usage_sensor();
199 if (sensor == NULL ||
200 !pool->gc_usage_threshold()->is_high_threshold_supported() ||
201 pool->gc_usage_threshold()->high_threshold() == 0) {
202 return;
203 }
205 {
206 MutexLockerEx ml(LowMemory_lock, Mutex::_no_safepoint_check_flag);
208 MemoryUsage usage = pool->get_last_collection_usage();
209 sensor->set_counter_sensor_level(usage, pool->gc_usage_threshold());
211 if (sensor->has_pending_requests()) {
212 // notify sensor state update
213 LowMemory_lock->notify_all();
214 }
215 }
216 }
218 // recompute enabled flag
219 void LowMemoryDetector::recompute_enabled_for_collected_pools() {
220 bool enabled = false;
221 int num_memory_pools = MemoryService::num_memory_pools();
222 for (int i=0; i<num_memory_pools; i++) {
223 MemoryPool* pool = MemoryService::get_memory_pool(i);
224 if (pool->is_collected_pool() && is_enabled(pool)) {
225 enabled = true;
226 break;
227 }
228 }
229 _enabled_for_collected_pools = enabled;
230 }
232 SensorInfo::SensorInfo() {
233 _sensor_obj = NULL;
234 _sensor_on = false;
235 _sensor_count = 0;
236 _pending_trigger_count = 0;
237 _pending_clear_count = 0;
238 }
240 // When this method is used, the memory usage is monitored
241 // as a gauge attribute. Sensor notifications (trigger or
242 // clear) is only emitted at the first time it crosses
243 // a threshold.
244 //
245 // High and low thresholds are designed to provide a
246 // hysteresis mechanism to avoid repeated triggering
247 // of notifications when the attribute value makes small oscillations
248 // around the high or low threshold value.
249 //
250 // The sensor will be triggered if:
251 // (1) the usage is crossing above the high threshold and
252 // the sensor is currently off and no pending
253 // trigger requests; or
254 // (2) the usage is crossing above the high threshold and
255 // the sensor will be off (i.e. sensor is currently on
256 // and has pending clear requests).
257 //
258 // Subsequent crossings of the high threshold value do not cause
259 // any triggers unless the usage becomes less than the low threshold.
260 //
261 // The sensor will be cleared if:
262 // (1) the usage is crossing below the low threshold and
263 // the sensor is currently on and no pending
264 // clear requests; or
265 // (2) the usage is crossing below the low threshold and
266 // the sensor will be on (i.e. sensor is currently off
267 // and has pending trigger requests).
268 //
269 // Subsequent crossings of the low threshold value do not cause
270 // any clears unless the usage becomes greater than or equal
271 // to the high threshold.
272 //
273 // If the current level is between high and low threhsold, no change.
274 //
275 void SensorInfo::set_gauge_sensor_level(MemoryUsage usage, ThresholdSupport* high_low_threshold) {
276 assert(high_low_threshold->is_high_threshold_supported(), "just checking");
278 bool is_over_high = high_low_threshold->is_high_threshold_crossed(usage);
279 bool is_below_low = high_low_threshold->is_low_threshold_crossed(usage);
281 assert(!(is_over_high && is_below_low), "Can't be both true");
283 if (is_over_high &&
284 ((!_sensor_on && _pending_trigger_count == 0) ||
285 _pending_clear_count > 0)) {
286 // low memory detected and need to increment the trigger pending count
287 // if the sensor is off or will be off due to _pending_clear_ > 0
288 // Request to trigger the sensor
289 _pending_trigger_count++;
290 _usage = usage;
292 if (_pending_clear_count > 0) {
293 // non-zero pending clear requests indicates that there are
294 // pending requests to clear this sensor.
295 // This trigger request needs to clear this clear count
296 // since the resulting sensor flag should be on.
297 _pending_clear_count = 0;
298 }
299 } else if (is_below_low &&
300 ((_sensor_on && _pending_clear_count == 0) ||
301 (_pending_trigger_count > 0 && _pending_clear_count == 0))) {
302 // memory usage returns below the threshold
303 // Request to clear the sensor if the sensor is on or will be on due to
304 // _pending_trigger_count > 0 and also no clear request
305 _pending_clear_count++;
306 }
307 }
309 // When this method is used, the memory usage is monitored as a
310 // simple counter attribute. The sensor will be triggered
311 // whenever the usage is crossing the threshold to keep track
312 // of the number of times the VM detects such a condition occurs.
313 //
314 // High and low thresholds are designed to provide a
315 // hysteresis mechanism to avoid repeated triggering
316 // of notifications when the attribute value makes small oscillations
317 // around the high or low threshold value.
318 //
319 // The sensor will be triggered if:
320 // - the usage is crossing above the high threshold regardless
321 // of the current sensor state.
322 //
323 // The sensor will be cleared if:
324 // (1) the usage is crossing below the low threshold and
325 // the sensor is currently on; or
326 // (2) the usage is crossing below the low threshold and
327 // the sensor will be on (i.e. sensor is currently off
328 // and has pending trigger requests).
329 void SensorInfo::set_counter_sensor_level(MemoryUsage usage, ThresholdSupport* counter_threshold) {
330 assert(counter_threshold->is_high_threshold_supported(), "just checking");
332 bool is_over_high = counter_threshold->is_high_threshold_crossed(usage);
333 bool is_below_low = counter_threshold->is_low_threshold_crossed(usage);
335 assert(!(is_over_high && is_below_low), "Can't be both true");
337 if (is_over_high) {
338 _pending_trigger_count++;
339 _usage = usage;
340 _pending_clear_count = 0;
341 } else if (is_below_low && (_sensor_on || _pending_trigger_count > 0)) {
342 _pending_clear_count++;
343 }
344 }
346 void SensorInfo::oops_do(OopClosure* f) {
347 f->do_oop((oop*) &_sensor_obj);
348 }
350 void SensorInfo::process_pending_requests(TRAPS) {
351 if (!has_pending_requests()) {
352 return;
353 }
355 int pending_count = pending_trigger_count();
356 if (pending_clear_count() > 0) {
357 clear(pending_count, CHECK);
358 } else {
359 trigger(pending_count, CHECK);
360 }
362 }
364 void SensorInfo::trigger(int count, TRAPS) {
365 assert(count <= _pending_trigger_count, "just checking");
367 if (_sensor_obj != NULL) {
368 klassOop k = Management::sun_management_Sensor_klass(CHECK);
369 instanceKlassHandle sensorKlass (THREAD, k);
370 Handle sensor_h(THREAD, _sensor_obj);
371 Handle usage_h = MemoryService::create_MemoryUsage_obj(_usage, CHECK);
373 JavaValue result(T_VOID);
374 JavaCallArguments args(sensor_h);
375 args.push_int((int) count);
376 args.push_oop(usage_h);
378 JavaCalls::call_virtual(&result,
379 sensorKlass,
380 vmSymbolHandles::trigger_name(),
381 vmSymbolHandles::trigger_method_signature(),
382 &args,
383 CHECK);
384 }
386 {
387 // Holds LowMemory_lock and update the sensor state
388 MutexLockerEx ml(LowMemory_lock, Mutex::_no_safepoint_check_flag);
389 _sensor_on = true;
390 _sensor_count += count;
391 _pending_trigger_count = _pending_trigger_count - count;
392 }
393 }
395 void SensorInfo::clear(int count, TRAPS) {
396 if (_sensor_obj != NULL) {
397 klassOop k = Management::sun_management_Sensor_klass(CHECK);
398 instanceKlassHandle sensorKlass (THREAD, k);
399 Handle sensor(THREAD, _sensor_obj);
401 JavaValue result(T_VOID);
402 JavaCallArguments args(sensor);
403 args.push_int((int) count);
404 JavaCalls::call_virtual(&result,
405 sensorKlass,
406 vmSymbolHandles::clear_name(),
407 vmSymbolHandles::int_void_signature(),
408 &args,
409 CHECK);
410 }
412 {
413 // Holds LowMemory_lock and update the sensor state
414 MutexLockerEx ml(LowMemory_lock, Mutex::_no_safepoint_check_flag);
415 _sensor_on = false;
416 _pending_clear_count = 0;
417 _pending_trigger_count = _pending_trigger_count - count;
418 }
419 }
421 //--------------------------------------------------------------
422 // Non-product code
424 #ifndef PRODUCT
425 void SensorInfo::print() {
426 tty->print_cr("%s count = %ld pending_triggers = %ld pending_clears = %ld",
427 (_sensor_on ? "on" : "off"),
428 _sensor_count, _pending_trigger_count, _pending_clear_count);
429 }
431 #endif // PRODUCT