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