1 /*
2 * Copyright (c) 1997, 2012, 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.
8 *
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
20 * or visit www.oracle.com if you need additional information or have any
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23 */
24
25 #ifndef SHARE_VM_MEMORY_GCLOCKER_HPP
26 #define SHARE_VM_MEMORY_GCLOCKER_HPP
27
28 #include "gc_interface/collectedHeap.hpp"
29 #include "memory/genCollectedHeap.hpp"
30 #include "memory/universe.hpp"
31 #include "oops/oop.hpp"
32 #ifdef TARGET_OS_FAMILY_linux
33 # include "os_linux.inline.hpp"
34 # include "thread_linux.inline.hpp"
35 #endif
36 #ifdef TARGET_OS_FAMILY_solaris
37 # include "os_solaris.inline.hpp"
38 # include "thread_solaris.inline.hpp"
39 #endif
40 #ifdef TARGET_OS_FAMILY_windows
41 # include "os_windows.inline.hpp"
42 # include "thread_windows.inline.hpp"
43 #endif
44 #ifdef TARGET_OS_FAMILY_bsd
45 # include "os_bsd.inline.hpp"
46 # include "thread_bsd.inline.hpp"
47 #endif
48
49 // The direct lock/unlock calls do not force a collection if an unlock
50 // decrements the count to zero. Avoid calling these if at all possible.
51
52 class GC_locker: public AllStatic {
53 private:
54 // The _jni_lock_count keeps track of the number of threads that are
55 // currently in a critical region. It's only kept up to date when
56 // _needs_gc is true. The current value is computed during
57 // safepointing and decremented during the slow path of GC_locker
58 // unlocking.
59 static volatile jint _jni_lock_count; // number of jni active instances.
60
61 static volatile jint _lock_count; // number of other active instances
62 static volatile bool _needs_gc; // heap is filling, we need a GC
63 // note: bool is typedef'd as jint
64 static volatile bool _doing_gc; // unlock_critical() is doing a GC
65
66 #ifdef ASSERT
67 // This lock count is updated for all operations and is used to
68 // validate the jni_lock_count that is computed during safepoints.
69 static volatile jint _debug_jni_lock_count;
70 #endif
71
72 // Accessors
73 static bool is_jni_active() {
74 assert(_needs_gc, "only valid when _needs_gc is set");
75 return _jni_lock_count > 0;
76 }
77
78 // At a safepoint, visit all threads and count the number of active
79 // critical sections. This is used to ensure that all active
80 // critical sections are exited before a new one is started.
81 static void verify_critical_count() NOT_DEBUG_RETURN;
82
83 static void jni_lock(JavaThread* thread);
84 static void jni_unlock(JavaThread* thread);
85
86 public:
87 // Accessors
88 static bool is_active();
89 static bool needs_gc() { return _needs_gc; }
90
91 // Shorthand
92 static bool is_active_and_needs_gc() { return needs_gc() && is_active(); }
93
94 // In debug mode track the locking state at all times
95 static void increment_debug_jni_lock_count() {
96 #ifdef ASSERT
97 assert(_debug_jni_lock_count >= 0, "bad value");
98 Atomic::inc(&_debug_jni_lock_count);
99 #endif
100 }
101 static void decrement_debug_jni_lock_count() {
102 #ifdef ASSERT
103 assert(_debug_jni_lock_count > 0, "bad value");
104 Atomic::dec(&_debug_jni_lock_count);
105 #endif
106 }
107
108 // Set the current lock count
109 static void set_jni_lock_count(int count) {
110 _jni_lock_count = count;
111 verify_critical_count();
112 }
113
114 // Sets _needs_gc if is_active() is true. Returns is_active().
115 static bool check_active_before_gc();
116
117 // Stalls the caller (who should not be in a jni critical section)
118 // until needs_gc() clears. Note however that needs_gc() may be
119 // set at a subsequent safepoint and/or cleared under the
120 // JNICritical_lock, so the caller may not safely assert upon
121 // return from this method that "!needs_gc()" since that is
122 // not a stable predicate.
123 static void stall_until_clear();
124
125 // Non-structured GC locking: currently needed for JNI. Use with care!
126 static void lock();
127 static void unlock();
128
129 // The following two methods are used for JNI critical regions.
130 // If we find that we failed to perform a GC because the GC_locker
131 // was active, arrange for one as soon as possible by allowing
132 // all threads in critical regions to complete, but not allowing
133 // other critical regions to be entered. The reasons for that are:
134 // 1) a GC request won't be starved by overlapping JNI critical
135 // region activities, which can cause unnecessary OutOfMemory errors.
136 // 2) even if allocation requests can still be satisfied before GC locker
137 // becomes inactive, for example, in tenured generation possibly with
138 // heap expansion, those allocations can trigger lots of safepointing
139 // attempts (ineffective GC attempts) and require Heap_lock which
140 // slow down allocations tremendously.
141 //
142 // Note that critical regions can be nested in a single thread, so
143 // we must allow threads already in critical regions to continue.
144 //
145 // JNI critical regions are the only participants in this scheme
146 // because they are, by spec, well bounded while in a critical region.
147 //
148 // Each of the following two method is split into a fast path and a
149 // slow path. JNICritical_lock is only grabbed in the slow path.
150 // _needs_gc is initially false and every java thread will go
151 // through the fast path, which simply increments or decrements the
152 // current thread's critical count. When GC happens at a safepoint,
153 // GC_locker::is_active() is checked. Since there is no safepoint in
154 // the fast path of lock_critical() and unlock_critical(), there is
155 // no race condition between the fast path and GC. After _needs_gc
156 // is set at a safepoint, every thread will go through the slow path
157 // after the safepoint. Since after a safepoint, each of the
158 // following two methods is either entered from the method entry and
159 // falls into the slow path, or is resumed from the safepoints in
160 // the method, which only exist in the slow path. So when _needs_gc
161 // is set, the slow path is always taken, till _needs_gc is cleared.
162 static void lock_critical(JavaThread* thread);
163 static void unlock_critical(JavaThread* thread);
164
165 static address needs_gc_address() { return (address) &_needs_gc; }
166 };
167
168
169 // A No_GC_Verifier object can be placed in methods where one assumes that
170 // no garbage collection will occur. The destructor will verify this property
171 // unless the constructor is called with argument false (not verifygc).
172 //
173 // The check will only be done in debug mode and if verifygc true.
174
175 class No_GC_Verifier: public StackObj {
176 friend class Pause_No_GC_Verifier;
177
178 protected:
179 bool _verifygc;
180 unsigned int _old_invocations;
181
182 public:
183 #ifdef ASSERT
184 No_GC_Verifier(bool verifygc = true);
185 ~No_GC_Verifier();
186 #else
187 No_GC_Verifier(bool verifygc = true) {}
188 ~No_GC_Verifier() {}
189 #endif
190 };
191
192 // A Pause_No_GC_Verifier is used to temporarily pause the behavior
193 // of a No_GC_Verifier object. If we are not in debug mode or if the
194 // No_GC_Verifier object has a _verifygc value of false, then there
195 // is nothing to do.
196
197 class Pause_No_GC_Verifier: public StackObj {
198 private:
199 No_GC_Verifier * _ngcv;
200
201 public:
202 #ifdef ASSERT
203 Pause_No_GC_Verifier(No_GC_Verifier * ngcv);
204 ~Pause_No_GC_Verifier();
205 #else
206 Pause_No_GC_Verifier(No_GC_Verifier * ngcv) {}
207 ~Pause_No_GC_Verifier() {}
208 #endif
209 };
210
211
212 // A No_Safepoint_Verifier object will throw an assertion failure if
213 // the current thread passes a possible safepoint while this object is
214 // instantiated. A safepoint, will either be: an oop allocation, blocking
215 // on a Mutex or JavaLock, or executing a VM operation.
216 //
217 // If StrictSafepointChecks is turned off, it degrades into a No_GC_Verifier
218 //
219 class No_Safepoint_Verifier : public No_GC_Verifier {
220 friend class Pause_No_Safepoint_Verifier;
221
222 private:
223 bool _activated;
224 Thread *_thread;
225 public:
226 #ifdef ASSERT
227 No_Safepoint_Verifier(bool activated = true, bool verifygc = true ) :
228 No_GC_Verifier(verifygc),
229 _activated(activated) {
230 _thread = Thread::current();
231 if (_activated) {
232 _thread->_allow_allocation_count++;
233 _thread->_allow_safepoint_count++;
234 }
235 }
236
237 ~No_Safepoint_Verifier() {
238 if (_activated) {
239 _thread->_allow_allocation_count--;
240 _thread->_allow_safepoint_count--;
241 }
242 }
243 #else
244 No_Safepoint_Verifier(bool activated = true, bool verifygc = true) : No_GC_Verifier(verifygc){}
245 ~No_Safepoint_Verifier() {}
246 #endif
247 };
248
249 // A Pause_No_Safepoint_Verifier is used to temporarily pause the
250 // behavior of a No_Safepoint_Verifier object. If we are not in debug
251 // mode then there is nothing to do. If the No_Safepoint_Verifier
252 // object has an _activated value of false, then there is nothing to
253 // do for safepoint and allocation checking, but there may still be
254 // something to do for the underlying No_GC_Verifier object.
255
256 class Pause_No_Safepoint_Verifier : public Pause_No_GC_Verifier {
257 private:
258 No_Safepoint_Verifier * _nsv;
259
260 public:
261 #ifdef ASSERT
262 Pause_No_Safepoint_Verifier(No_Safepoint_Verifier * nsv)
263 : Pause_No_GC_Verifier(nsv) {
264
265 _nsv = nsv;
266 if (_nsv->_activated) {
267 _nsv->_thread->_allow_allocation_count--;
268 _nsv->_thread->_allow_safepoint_count--;
269 }
270 }
271
272 ~Pause_No_Safepoint_Verifier() {
273 if (_nsv->_activated) {
274 _nsv->_thread->_allow_allocation_count++;
275 _nsv->_thread->_allow_safepoint_count++;
276 }
277 }
278 #else
279 Pause_No_Safepoint_Verifier(No_Safepoint_Verifier * nsv)
280 : Pause_No_GC_Verifier(nsv) {}
281 ~Pause_No_Safepoint_Verifier() {}
282 #endif
283 };
284
285 // A SkipGCALot object is used to elide the usual effect of gc-a-lot
286 // over a section of execution by a thread. Currently, it's used only to
287 // prevent re-entrant calls to GC.
288 class SkipGCALot : public StackObj {
289 private:
290 bool _saved;
291 Thread* _t;
292
293 public:
294 #ifdef ASSERT
295 SkipGCALot(Thread* t) : _t(t) {
296 _saved = _t->skip_gcalot();
297 _t->set_skip_gcalot(true);
298 }
299
300 ~SkipGCALot() {
301 assert(_t->skip_gcalot(), "Save-restore protocol invariant");
302 _t->set_skip_gcalot(_saved);
303 }
304 #else
305 SkipGCALot(Thread* t) { }
306 ~SkipGCALot() { }
307 #endif
308 };
309
310 // JRT_LEAF currently can be called from either _thread_in_Java or
311 // _thread_in_native mode. In _thread_in_native, it is ok
312 // for another thread to trigger GC. The rest of the JRT_LEAF
313 // rules apply.
314 class JRT_Leaf_Verifier : public No_Safepoint_Verifier {
315 static bool should_verify_GC();
316 public:
317 #ifdef ASSERT
318 JRT_Leaf_Verifier();
319 ~JRT_Leaf_Verifier();
320 #else
321 JRT_Leaf_Verifier() {}
322 ~JRT_Leaf_Verifier() {}
323 #endif
324 };
325
326 // A No_Alloc_Verifier object can be placed in methods where one assumes that
327 // no allocation will occur. The destructor will verify this property
328 // unless the constructor is called with argument false (not activated).
329 //
330 // The check will only be done in debug mode and if activated.
331 // Note: this only makes sense at safepoints (otherwise, other threads may
332 // allocate concurrently.)
333
334 class No_Alloc_Verifier : public StackObj {
335 private:
336 bool _activated;
337
338 public:
339 #ifdef ASSERT
340 No_Alloc_Verifier(bool activated = true) {
341 _activated = activated;
342 if (_activated) Thread::current()->_allow_allocation_count++;
343 }
344
345 ~No_Alloc_Verifier() {
346 if (_activated) Thread::current()->_allow_allocation_count--;
347 }
348 #else
349 No_Alloc_Verifier(bool activated = true) {}
350 ~No_Alloc_Verifier() {}
351 #endif
352 };
353
354 #endif // SHARE_VM_MEMORY_GCLOCKER_HPP