1 /*
2 * Copyright (c) 1997, 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.
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.
18 *
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
21 * questions.
22 *
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
45 // The direct lock/unlock calls do not force a collection if an unlock
46 // decrements the count to zero. Avoid calling these if at all possible.
47
48 class GC_locker: public AllStatic {
49 private:
50 static volatile jint _jni_lock_count; // number of jni active instances
51 static volatile jint _lock_count; // number of other active instances
52 static volatile bool _needs_gc; // heap is filling, we need a GC
53 // note: bool is typedef'd as jint
54 static volatile bool _doing_gc; // unlock_critical() is doing a GC
55
56 // Accessors
57 static bool is_jni_active() {
58 return _jni_lock_count > 0;
59 }
60
61 static void set_needs_gc() {
62 assert(SafepointSynchronize::is_at_safepoint(),
63 "needs_gc is only set at a safepoint");
64 _needs_gc = true;
65 }
66
67 static void clear_needs_gc() {
68 assert_lock_strong(JNICritical_lock);
69 _needs_gc = false;
70 }
71
72 static void jni_lock() {
73 Atomic::inc(&_jni_lock_count);
74 CHECK_UNHANDLED_OOPS_ONLY(
75 if (CheckUnhandledOops) { Thread::current()->_gc_locked_out_count++; })
76 assert(Universe::heap() == NULL || !Universe::heap()->is_gc_active(),
77 "locking failed");
78 }
79
80 static void jni_unlock() {
81 Atomic::dec(&_jni_lock_count);
82 CHECK_UNHANDLED_OOPS_ONLY(
83 if (CheckUnhandledOops) { Thread::current()->_gc_locked_out_count--; })
84 }
85
86 static void jni_lock_slow();
87 static void jni_unlock_slow();
88
89 public:
90 // Accessors
91 static bool is_active();
92 static bool needs_gc() { return _needs_gc; }
93 // Shorthand
94 static bool is_active_and_needs_gc() { return is_active() && needs_gc();}
95
96 // Calls set_needs_gc() if is_active() is true. Returns is_active().
97 static bool check_active_before_gc();
98
99 // Stalls the caller (who should not be in a jni critical section)
100 // until needs_gc() clears. Note however that needs_gc() may be
101 // set at a subsequent safepoint and/or cleared under the
102 // JNICritical_lock, so the caller may not safely assert upon
103 // return from this method that "!needs_gc()" since that is
104 // not a stable predicate.
105 static void stall_until_clear();
106
107 // Non-structured GC locking: currently needed for JNI. Use with care!
108 static void lock();
109 static void unlock();
110
111 // The following two methods are used for JNI critical regions.
112 // If we find that we failed to perform a GC because the GC_locker
113 // was active, arrange for one as soon as possible by allowing
114 // all threads in critical regions to complete, but not allowing
115 // other critical regions to be entered. The reasons for that are:
116 // 1) a GC request won't be starved by overlapping JNI critical
117 // region activities, which can cause unnecessary OutOfMemory errors.
118 // 2) even if allocation requests can still be satisfied before GC locker
119 // becomes inactive, for example, in tenured generation possibly with
120 // heap expansion, those allocations can trigger lots of safepointing
121 // attempts (ineffective GC attempts) and require Heap_lock which
122 // slow down allocations tremendously.
123 //
124 // Note that critical regions can be nested in a single thread, so
125 // we must allow threads already in critical regions to continue.
126 //
127 // JNI critical regions are the only participants in this scheme
128 // because they are, by spec, well bounded while in a critical region.
129 //
130 // Each of the following two method is split into a fast path and a slow
131 // path. JNICritical_lock is only grabbed in the slow path.
132 // _needs_gc is initially false and every java thread will go
133 // through the fast path (which does the same thing as the slow path
134 // when _needs_gc is false). When GC happens at a safepoint,
135 // GC_locker::is_active() is checked. Since there is no safepoint in the
136 // fast path of lock_critical() and unlock_critical(), there is no race
137 // condition between the fast path and GC. After _needs_gc is set at a
138 // safepoint, every thread will go through the slow path after the safepoint.
139 // Since after a safepoint, each of the following two methods is either
140 // entered from the method entry and falls into the slow path, or is
141 // resumed from the safepoints in the method, which only exist in the slow
142 // path. So when _needs_gc is set, the slow path is always taken, till
143 // _needs_gc is cleared.
144 static void lock_critical(JavaThread* thread);
145 static void unlock_critical(JavaThread* thread);
146 };
147
148
149 // A No_GC_Verifier object can be placed in methods where one assumes that
150 // no garbage collection will occur. The destructor will verify this property
151 // unless the constructor is called with argument false (not verifygc).
152 //
153 // The check will only be done in debug mode and if verifygc true.
154
155 class No_GC_Verifier: public StackObj {
156 friend class Pause_No_GC_Verifier;
157
158 protected:
159 bool _verifygc;
160 unsigned int _old_invocations;
161
162 public:
163 #ifdef ASSERT
164 No_GC_Verifier(bool verifygc = true);
165 ~No_GC_Verifier();
166 #else
167 No_GC_Verifier(bool verifygc = true) {}
168 ~No_GC_Verifier() {}
169 #endif
170 };
171
172 // A Pause_No_GC_Verifier is used to temporarily pause the behavior
173 // of a No_GC_Verifier object. If we are not in debug mode or if the
174 // No_GC_Verifier object has a _verifygc value of false, then there
175 // is nothing to do.
176
177 class Pause_No_GC_Verifier: public StackObj {
178 private:
179 No_GC_Verifier * _ngcv;
180
181 public:
182 #ifdef ASSERT
183 Pause_No_GC_Verifier(No_GC_Verifier * ngcv);
184 ~Pause_No_GC_Verifier();
185 #else
186 Pause_No_GC_Verifier(No_GC_Verifier * ngcv) {}
187 ~Pause_No_GC_Verifier() {}
188 #endif
189 };
190
191
192 // A No_Safepoint_Verifier object will throw an assertion failure if
193 // the current thread passes a possible safepoint while this object is
194 // instantiated. A safepoint, will either be: an oop allocation, blocking
195 // on a Mutex or JavaLock, or executing a VM operation.
196 //
197 // If StrictSafepointChecks is turned off, it degrades into a No_GC_Verifier
198 //
199 class No_Safepoint_Verifier : public No_GC_Verifier {
200 friend class Pause_No_Safepoint_Verifier;
201
202 private:
203 bool _activated;
204 Thread *_thread;
205 public:
206 #ifdef ASSERT
207 No_Safepoint_Verifier(bool activated = true, bool verifygc = true ) :
208 No_GC_Verifier(verifygc),
209 _activated(activated) {
210 _thread = Thread::current();
211 if (_activated) {
212 _thread->_allow_allocation_count++;
213 _thread->_allow_safepoint_count++;
214 }
215 }
216
217 ~No_Safepoint_Verifier() {
218 if (_activated) {
219 _thread->_allow_allocation_count--;
220 _thread->_allow_safepoint_count--;
221 }
222 }
223 #else
224 No_Safepoint_Verifier(bool activated = true, bool verifygc = true) : No_GC_Verifier(verifygc){}
225 ~No_Safepoint_Verifier() {}
226 #endif
227 };
228
229 // A Pause_No_Safepoint_Verifier is used to temporarily pause the
230 // behavior of a No_Safepoint_Verifier object. If we are not in debug
231 // mode then there is nothing to do. If the No_Safepoint_Verifier
232 // object has an _activated value of false, then there is nothing to
233 // do for safepoint and allocation checking, but there may still be
234 // something to do for the underlying No_GC_Verifier object.
235
236 class Pause_No_Safepoint_Verifier : public Pause_No_GC_Verifier {
237 private:
238 No_Safepoint_Verifier * _nsv;
239
240 public:
241 #ifdef ASSERT
242 Pause_No_Safepoint_Verifier(No_Safepoint_Verifier * nsv)
243 : Pause_No_GC_Verifier(nsv) {
244
245 _nsv = nsv;
246 if (_nsv->_activated) {
247 _nsv->_thread->_allow_allocation_count--;
248 _nsv->_thread->_allow_safepoint_count--;
249 }
250 }
251
252 ~Pause_No_Safepoint_Verifier() {
253 if (_nsv->_activated) {
254 _nsv->_thread->_allow_allocation_count++;
255 _nsv->_thread->_allow_safepoint_count++;
256 }
257 }
258 #else
259 Pause_No_Safepoint_Verifier(No_Safepoint_Verifier * nsv)
260 : Pause_No_GC_Verifier(nsv) {}
261 ~Pause_No_Safepoint_Verifier() {}
262 #endif
263 };
264
265 // A SkipGCALot object is used to elide the usual effect of gc-a-lot
266 // over a section of execution by a thread. Currently, it's used only to
267 // prevent re-entrant calls to GC.
268 class SkipGCALot : public StackObj {
269 private:
270 bool _saved;
271 Thread* _t;
272
273 public:
274 #ifdef ASSERT
275 SkipGCALot(Thread* t) : _t(t) {
276 _saved = _t->skip_gcalot();
277 _t->set_skip_gcalot(true);
278 }
279
280 ~SkipGCALot() {
281 assert(_t->skip_gcalot(), "Save-restore protocol invariant");
282 _t->set_skip_gcalot(_saved);
283 }
284 #else
285 SkipGCALot(Thread* t) { }
286 ~SkipGCALot() { }
287 #endif
288 };
289
290 // JRT_LEAF currently can be called from either _thread_in_Java or
291 // _thread_in_native mode. In _thread_in_native, it is ok
292 // for another thread to trigger GC. The rest of the JRT_LEAF
293 // rules apply.
294 class JRT_Leaf_Verifier : public No_Safepoint_Verifier {
295 static bool should_verify_GC();
296 public:
297 #ifdef ASSERT
298 JRT_Leaf_Verifier();
299 ~JRT_Leaf_Verifier();
300 #else
301 JRT_Leaf_Verifier() {}
302 ~JRT_Leaf_Verifier() {}
303 #endif
304 };
305
306 // A No_Alloc_Verifier object can be placed in methods where one assumes that
307 // no allocation will occur. The destructor will verify this property
308 // unless the constructor is called with argument false (not activated).
309 //
310 // The check will only be done in debug mode and if activated.
311 // Note: this only makes sense at safepoints (otherwise, other threads may
312 // allocate concurrently.)
313
314 class No_Alloc_Verifier : public StackObj {
315 private:
316 bool _activated;
317
318 public:
319 #ifdef ASSERT
320 No_Alloc_Verifier(bool activated = true) {
321 _activated = activated;
322 if (_activated) Thread::current()->_allow_allocation_count++;
323 }
324
325 ~No_Alloc_Verifier() {
326 if (_activated) Thread::current()->_allow_allocation_count--;
327 }
328 #else
329 No_Alloc_Verifier(bool activated = true) {}
330 ~No_Alloc_Verifier() {}
331 #endif
332 };
333
334 #endif // SHARE_VM_MEMORY_GCLOCKER_HPP