Mercurial > hg > graal-compiler
annotate src/share/vm/runtime/biasedLocking.cpp @ 58:7ee622712fcf
6666698: EnableBiasedLocking with BiasedLockingStartupDelay can block Watcher thread
Summary: Enqueue VM_EnableBiasedLocking operation asynchronously
Reviewed-by: never, xlu, kbr, acorn
| author | sbohne |
|---|---|
| date | Tue, 04 Mar 2008 09:44:24 -0500 |
| parents | a61af66fc99e |
| children | 6e085831cad7 |
| rev | line source |
|---|---|
| 0 | 1 |
| 2 /* | |
| 3 * Copyright 2005-2007 Sun Microsystems, Inc. All Rights Reserved. | |
| 4 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. | |
| 5 * | |
| 6 * This code is free software; you can redistribute it and/or modify it | |
| 7 * under the terms of the GNU General Public License version 2 only, as | |
| 8 * published by the Free Software Foundation. | |
| 9 * | |
| 10 * This code is distributed in the hope that it will be useful, but WITHOUT | |
| 11 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or | |
| 12 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License | |
| 13 * version 2 for more details (a copy is included in the LICENSE file that | |
| 14 * accompanied this code). | |
| 15 * | |
| 16 * You should have received a copy of the GNU General Public License version | |
| 17 * 2 along with this work; if not, write to the Free Software Foundation, | |
| 18 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. | |
| 19 * | |
| 20 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara, | |
| 21 * CA 95054 USA or visit www.sun.com if you need additional information or | |
| 22 * have any questions. | |
| 23 * | |
| 24 */ | |
| 25 | |
| 26 # include "incls/_precompiled.incl" | |
| 27 # include "incls/_biasedLocking.cpp.incl" | |
| 28 | |
| 29 static bool _biased_locking_enabled = false; | |
| 30 BiasedLockingCounters BiasedLocking::_counters; | |
| 31 | |
| 32 static GrowableArray<Handle>* _preserved_oop_stack = NULL; | |
| 33 static GrowableArray<markOop>* _preserved_mark_stack = NULL; | |
| 34 | |
| 35 static void enable_biased_locking(klassOop k) { | |
| 36 Klass::cast(k)->set_prototype_header(markOopDesc::biased_locking_prototype()); | |
| 37 } | |
| 38 | |
| 39 class VM_EnableBiasedLocking: public VM_Operation { | |
| 40 public: | |
|
58
7ee622712fcf
6666698: EnableBiasedLocking with BiasedLockingStartupDelay can block Watcher thread
sbohne
parents:
0
diff
changeset
|
41 VM_EnableBiasedLocking() {} |
|
7ee622712fcf
6666698: EnableBiasedLocking with BiasedLockingStartupDelay can block Watcher thread
sbohne
parents:
0
diff
changeset
|
42 VMOp_Type type() const { return VMOp_EnableBiasedLocking; } |
|
7ee622712fcf
6666698: EnableBiasedLocking with BiasedLockingStartupDelay can block Watcher thread
sbohne
parents:
0
diff
changeset
|
43 Mode evaluation_mode() const { return _async_safepoint; } |
|
7ee622712fcf
6666698: EnableBiasedLocking with BiasedLockingStartupDelay can block Watcher thread
sbohne
parents:
0
diff
changeset
|
44 bool is_cheap_allocated() const { return true; } |
|
7ee622712fcf
6666698: EnableBiasedLocking with BiasedLockingStartupDelay can block Watcher thread
sbohne
parents:
0
diff
changeset
|
45 |
| 0 | 46 void doit() { |
| 47 // Iterate the system dictionary enabling biased locking for all | |
| 48 // currently loaded classes | |
| 49 SystemDictionary::classes_do(enable_biased_locking); | |
| 50 // Indicate that future instances should enable it as well | |
| 51 _biased_locking_enabled = true; | |
| 52 | |
| 53 if (TraceBiasedLocking) { | |
| 54 tty->print_cr("Biased locking enabled"); | |
| 55 } | |
| 56 } | |
| 57 | |
| 58 bool allow_nested_vm_operations() const { return false; } | |
| 59 }; | |
| 60 | |
| 61 | |
| 62 // One-shot PeriodicTask subclass for enabling biased locking | |
| 63 class EnableBiasedLockingTask : public PeriodicTask { | |
| 64 public: | |
| 65 EnableBiasedLockingTask(size_t interval_time) : PeriodicTask(interval_time) {} | |
| 66 | |
| 67 virtual void task() { | |
|
58
7ee622712fcf
6666698: EnableBiasedLocking with BiasedLockingStartupDelay can block Watcher thread
sbohne
parents:
0
diff
changeset
|
68 // Use async VM operation to avoid blocking the Watcher thread. |
|
7ee622712fcf
6666698: EnableBiasedLocking with BiasedLockingStartupDelay can block Watcher thread
sbohne
parents:
0
diff
changeset
|
69 // VM Thread will free C heap storage. |
|
7ee622712fcf
6666698: EnableBiasedLocking with BiasedLockingStartupDelay can block Watcher thread
sbohne
parents:
0
diff
changeset
|
70 VM_EnableBiasedLocking *op = new VM_EnableBiasedLocking(); |
|
7ee622712fcf
6666698: EnableBiasedLocking with BiasedLockingStartupDelay can block Watcher thread
sbohne
parents:
0
diff
changeset
|
71 VMThread::execute(op); |
| 0 | 72 |
| 73 // Reclaim our storage and disenroll ourself | |
| 74 delete this; | |
| 75 } | |
| 76 }; | |
| 77 | |
| 78 | |
| 79 void BiasedLocking::init() { | |
| 80 // If biased locking is enabled, schedule a task to fire a few | |
| 81 // seconds into the run which turns on biased locking for all | |
| 82 // currently loaded classes as well as future ones. This is a | |
| 83 // workaround for startup time regressions due to a large number of | |
| 84 // safepoints being taken during VM startup for bias revocation. | |
| 85 // Ideally we would have a lower cost for individual bias revocation | |
| 86 // and not need a mechanism like this. | |
| 87 if (UseBiasedLocking) { | |
| 88 if (BiasedLockingStartupDelay > 0) { | |
| 89 EnableBiasedLockingTask* task = new EnableBiasedLockingTask(BiasedLockingStartupDelay); | |
| 90 task->enroll(); | |
| 91 } else { | |
| 92 VM_EnableBiasedLocking op; | |
| 93 VMThread::execute(&op); | |
| 94 } | |
| 95 } | |
| 96 } | |
| 97 | |
| 98 | |
| 99 bool BiasedLocking::enabled() { | |
| 100 return _biased_locking_enabled; | |
| 101 } | |
| 102 | |
| 103 // Returns MonitorInfos for all objects locked on this thread in youngest to oldest order | |
| 104 static GrowableArray<MonitorInfo*>* get_or_compute_monitor_info(JavaThread* thread) { | |
| 105 GrowableArray<MonitorInfo*>* info = thread->cached_monitor_info(); | |
| 106 if (info != NULL) { | |
| 107 return info; | |
| 108 } | |
| 109 | |
| 110 info = new GrowableArray<MonitorInfo*>(); | |
| 111 | |
| 112 // It's possible for the thread to not have any Java frames on it, | |
| 113 // i.e., if it's the main thread and it's already returned from main() | |
| 114 if (thread->has_last_Java_frame()) { | |
| 115 RegisterMap rm(thread); | |
| 116 for (javaVFrame* vf = thread->last_java_vframe(&rm); vf != NULL; vf = vf->java_sender()) { | |
| 117 GrowableArray<MonitorInfo*> *monitors = vf->monitors(); | |
| 118 if (monitors != NULL) { | |
| 119 int len = monitors->length(); | |
| 120 // Walk monitors youngest to oldest | |
| 121 for (int i = len - 1; i >= 0; i--) { | |
| 122 MonitorInfo* mon_info = monitors->at(i); | |
| 123 oop owner = mon_info->owner(); | |
| 124 if (owner != NULL) { | |
| 125 info->append(mon_info); | |
| 126 } | |
| 127 } | |
| 128 } | |
| 129 } | |
| 130 } | |
| 131 | |
| 132 thread->set_cached_monitor_info(info); | |
| 133 return info; | |
| 134 } | |
| 135 | |
| 136 | |
| 137 static BiasedLocking::Condition revoke_bias(oop obj, bool allow_rebias, bool is_bulk, JavaThread* requesting_thread) { | |
| 138 markOop mark = obj->mark(); | |
| 139 if (!mark->has_bias_pattern()) { | |
| 140 if (TraceBiasedLocking) { | |
| 141 ResourceMark rm; | |
| 142 tty->print_cr(" (Skipping revocation of object of type %s because it's no longer biased)", | |
| 143 Klass::cast(obj->klass())->external_name()); | |
| 144 } | |
| 145 return BiasedLocking::NOT_BIASED; | |
| 146 } | |
| 147 | |
| 148 int age = mark->age(); | |
| 149 markOop biased_prototype = markOopDesc::biased_locking_prototype()->set_age(age); | |
| 150 markOop unbiased_prototype = markOopDesc::prototype()->set_age(age); | |
| 151 | |
| 152 if (TraceBiasedLocking && (Verbose || !is_bulk)) { | |
| 153 ResourceMark rm; | |
| 154 tty->print_cr("Revoking bias of object " INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s , prototype header " INTPTR_FORMAT " , allow rebias %d , requesting thread " INTPTR_FORMAT, | |
| 155 (intptr_t) obj, (intptr_t) mark, Klass::cast(obj->klass())->external_name(), (intptr_t) Klass::cast(obj->klass())->prototype_header(), (allow_rebias ? 1 : 0), (intptr_t) requesting_thread); | |
| 156 } | |
| 157 | |
| 158 JavaThread* biased_thread = mark->biased_locker(); | |
| 159 if (biased_thread == NULL) { | |
| 160 // Object is anonymously biased. We can get here if, for | |
| 161 // example, we revoke the bias due to an identity hash code | |
| 162 // being computed for an object. | |
| 163 if (!allow_rebias) { | |
| 164 obj->set_mark(unbiased_prototype); | |
| 165 } | |
| 166 if (TraceBiasedLocking && (Verbose || !is_bulk)) { | |
| 167 tty->print_cr(" Revoked bias of anonymously-biased object"); | |
| 168 } | |
| 169 return BiasedLocking::BIAS_REVOKED; | |
| 170 } | |
| 171 | |
| 172 // Handle case where the thread toward which the object was biased has exited | |
| 173 bool thread_is_alive = false; | |
| 174 if (requesting_thread == biased_thread) { | |
| 175 thread_is_alive = true; | |
| 176 } else { | |
| 177 for (JavaThread* cur_thread = Threads::first(); cur_thread != NULL; cur_thread = cur_thread->next()) { | |
| 178 if (cur_thread == biased_thread) { | |
| 179 thread_is_alive = true; | |
| 180 break; | |
| 181 } | |
| 182 } | |
| 183 } | |
| 184 if (!thread_is_alive) { | |
| 185 if (allow_rebias) { | |
| 186 obj->set_mark(biased_prototype); | |
| 187 } else { | |
| 188 obj->set_mark(unbiased_prototype); | |
| 189 } | |
| 190 if (TraceBiasedLocking && (Verbose || !is_bulk)) { | |
| 191 tty->print_cr(" Revoked bias of object biased toward dead thread"); | |
| 192 } | |
| 193 return BiasedLocking::BIAS_REVOKED; | |
| 194 } | |
| 195 | |
| 196 // Thread owning bias is alive. | |
| 197 // Check to see whether it currently owns the lock and, if so, | |
| 198 // write down the needed displaced headers to the thread's stack. | |
| 199 // Otherwise, restore the object's header either to the unlocked | |
| 200 // or unbiased state. | |
| 201 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(biased_thread); | |
| 202 BasicLock* highest_lock = NULL; | |
| 203 for (int i = 0; i < cached_monitor_info->length(); i++) { | |
| 204 MonitorInfo* mon_info = cached_monitor_info->at(i); | |
| 205 if (mon_info->owner() == obj) { | |
| 206 if (TraceBiasedLocking && Verbose) { | |
| 207 tty->print_cr(" mon_info->owner (" PTR_FORMAT ") == obj (" PTR_FORMAT ")", | |
| 208 (intptr_t) mon_info->owner(), | |
| 209 (intptr_t) obj); | |
| 210 } | |
| 211 // Assume recursive case and fix up highest lock later | |
| 212 markOop mark = markOopDesc::encode((BasicLock*) NULL); | |
| 213 highest_lock = mon_info->lock(); | |
| 214 highest_lock->set_displaced_header(mark); | |
| 215 } else { | |
| 216 if (TraceBiasedLocking && Verbose) { | |
| 217 tty->print_cr(" mon_info->owner (" PTR_FORMAT ") != obj (" PTR_FORMAT ")", | |
| 218 (intptr_t) mon_info->owner(), | |
| 219 (intptr_t) obj); | |
| 220 } | |
| 221 } | |
| 222 } | |
| 223 if (highest_lock != NULL) { | |
| 224 // Fix up highest lock to contain displaced header and point | |
| 225 // object at it | |
| 226 highest_lock->set_displaced_header(unbiased_prototype); | |
| 227 // Reset object header to point to displaced mark | |
| 228 obj->set_mark(markOopDesc::encode(highest_lock)); | |
| 229 assert(!obj->mark()->has_bias_pattern(), "illegal mark state: stack lock used bias bit"); | |
| 230 if (TraceBiasedLocking && (Verbose || !is_bulk)) { | |
| 231 tty->print_cr(" Revoked bias of currently-locked object"); | |
| 232 } | |
| 233 } else { | |
| 234 if (TraceBiasedLocking && (Verbose || !is_bulk)) { | |
| 235 tty->print_cr(" Revoked bias of currently-unlocked object"); | |
| 236 } | |
| 237 if (allow_rebias) { | |
| 238 obj->set_mark(biased_prototype); | |
| 239 } else { | |
| 240 // Store the unlocked value into the object's header. | |
| 241 obj->set_mark(unbiased_prototype); | |
| 242 } | |
| 243 } | |
| 244 | |
| 245 return BiasedLocking::BIAS_REVOKED; | |
| 246 } | |
| 247 | |
| 248 | |
| 249 enum HeuristicsResult { | |
| 250 HR_NOT_BIASED = 1, | |
| 251 HR_SINGLE_REVOKE = 2, | |
| 252 HR_BULK_REBIAS = 3, | |
| 253 HR_BULK_REVOKE = 4 | |
| 254 }; | |
| 255 | |
| 256 | |
| 257 static HeuristicsResult update_heuristics(oop o, bool allow_rebias) { | |
| 258 markOop mark = o->mark(); | |
| 259 if (!mark->has_bias_pattern()) { | |
| 260 return HR_NOT_BIASED; | |
| 261 } | |
| 262 | |
| 263 // Heuristics to attempt to throttle the number of revocations. | |
| 264 // Stages: | |
| 265 // 1. Revoke the biases of all objects in the heap of this type, | |
| 266 // but allow rebiasing of those objects if unlocked. | |
| 267 // 2. Revoke the biases of all objects in the heap of this type | |
| 268 // and don't allow rebiasing of these objects. Disable | |
| 269 // allocation of objects of that type with the bias bit set. | |
| 270 Klass* k = o->blueprint(); | |
| 271 jlong cur_time = os::javaTimeMillis(); | |
| 272 jlong last_bulk_revocation_time = k->last_biased_lock_bulk_revocation_time(); | |
| 273 int revocation_count = k->biased_lock_revocation_count(); | |
| 274 if ((revocation_count >= BiasedLockingBulkRebiasThreshold) && | |
| 275 (revocation_count < BiasedLockingBulkRevokeThreshold) && | |
| 276 (last_bulk_revocation_time != 0) && | |
| 277 (cur_time - last_bulk_revocation_time >= BiasedLockingDecayTime)) { | |
| 278 // This is the first revocation we've seen in a while of an | |
| 279 // object of this type since the last time we performed a bulk | |
| 280 // rebiasing operation. The application is allocating objects in | |
| 281 // bulk which are biased toward a thread and then handing them | |
| 282 // off to another thread. We can cope with this allocation | |
| 283 // pattern via the bulk rebiasing mechanism so we reset the | |
| 284 // klass's revocation count rather than allow it to increase | |
| 285 // monotonically. If we see the need to perform another bulk | |
| 286 // rebias operation later, we will, and if subsequently we see | |
| 287 // many more revocation operations in a short period of time we | |
| 288 // will completely disable biasing for this type. | |
| 289 k->set_biased_lock_revocation_count(0); | |
| 290 revocation_count = 0; | |
| 291 } | |
| 292 | |
| 293 // Make revocation count saturate just beyond BiasedLockingBulkRevokeThreshold | |
| 294 if (revocation_count <= BiasedLockingBulkRevokeThreshold) { | |
| 295 revocation_count = k->atomic_incr_biased_lock_revocation_count(); | |
| 296 } | |
| 297 | |
| 298 if (revocation_count == BiasedLockingBulkRevokeThreshold) { | |
| 299 return HR_BULK_REVOKE; | |
| 300 } | |
| 301 | |
| 302 if (revocation_count == BiasedLockingBulkRebiasThreshold) { | |
| 303 return HR_BULK_REBIAS; | |
| 304 } | |
| 305 | |
| 306 return HR_SINGLE_REVOKE; | |
| 307 } | |
| 308 | |
| 309 | |
| 310 static BiasedLocking::Condition bulk_revoke_or_rebias_at_safepoint(oop o, | |
| 311 bool bulk_rebias, | |
| 312 bool attempt_rebias_of_object, | |
| 313 JavaThread* requesting_thread) { | |
| 314 assert(SafepointSynchronize::is_at_safepoint(), "must be done at safepoint"); | |
| 315 | |
| 316 if (TraceBiasedLocking) { | |
| 317 tty->print_cr("* Beginning bulk revocation (kind == %s) because of object " | |
| 318 INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s", | |
| 319 (bulk_rebias ? "rebias" : "revoke"), | |
| 320 (intptr_t) o, (intptr_t) o->mark(), Klass::cast(o->klass())->external_name()); | |
| 321 } | |
| 322 | |
| 323 jlong cur_time = os::javaTimeMillis(); | |
| 324 o->blueprint()->set_last_biased_lock_bulk_revocation_time(cur_time); | |
| 325 | |
| 326 | |
| 327 klassOop k_o = o->klass(); | |
| 328 Klass* klass = Klass::cast(k_o); | |
| 329 | |
| 330 if (bulk_rebias) { | |
| 331 // Use the epoch in the klass of the object to implicitly revoke | |
| 332 // all biases of objects of this data type and force them to be | |
| 333 // reacquired. However, we also need to walk the stacks of all | |
| 334 // threads and update the headers of lightweight locked objects | |
| 335 // with biases to have the current epoch. | |
| 336 | |
| 337 // If the prototype header doesn't have the bias pattern, don't | |
| 338 // try to update the epoch -- assume another VM operation came in | |
| 339 // and reset the header to the unbiased state, which will | |
| 340 // implicitly cause all existing biases to be revoked | |
| 341 if (klass->prototype_header()->has_bias_pattern()) { | |
| 342 int prev_epoch = klass->prototype_header()->bias_epoch(); | |
| 343 klass->set_prototype_header(klass->prototype_header()->incr_bias_epoch()); | |
| 344 int cur_epoch = klass->prototype_header()->bias_epoch(); | |
| 345 | |
| 346 // Now walk all threads' stacks and adjust epochs of any biased | |
| 347 // and locked objects of this data type we encounter | |
| 348 for (JavaThread* thr = Threads::first(); thr != NULL; thr = thr->next()) { | |
| 349 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr); | |
| 350 for (int i = 0; i < cached_monitor_info->length(); i++) { | |
| 351 MonitorInfo* mon_info = cached_monitor_info->at(i); | |
| 352 oop owner = mon_info->owner(); | |
| 353 markOop mark = owner->mark(); | |
| 354 if ((owner->klass() == k_o) && mark->has_bias_pattern()) { | |
| 355 // We might have encountered this object already in the case of recursive locking | |
| 356 assert(mark->bias_epoch() == prev_epoch || mark->bias_epoch() == cur_epoch, "error in bias epoch adjustment"); | |
| 357 owner->set_mark(mark->set_bias_epoch(cur_epoch)); | |
| 358 } | |
| 359 } | |
| 360 } | |
| 361 } | |
| 362 | |
| 363 // At this point we're done. All we have to do is potentially | |
| 364 // adjust the header of the given object to revoke its bias. | |
| 365 revoke_bias(o, attempt_rebias_of_object && klass->prototype_header()->has_bias_pattern(), true, requesting_thread); | |
| 366 } else { | |
| 367 if (TraceBiasedLocking) { | |
| 368 ResourceMark rm; | |
| 369 tty->print_cr("* Disabling biased locking for type %s", klass->external_name()); | |
| 370 } | |
| 371 | |
| 372 // Disable biased locking for this data type. Not only will this | |
| 373 // cause future instances to not be biased, but existing biased | |
| 374 // instances will notice that this implicitly caused their biases | |
| 375 // to be revoked. | |
| 376 klass->set_prototype_header(markOopDesc::prototype()); | |
| 377 | |
| 378 // Now walk all threads' stacks and forcibly revoke the biases of | |
| 379 // any locked and biased objects of this data type we encounter. | |
| 380 for (JavaThread* thr = Threads::first(); thr != NULL; thr = thr->next()) { | |
| 381 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr); | |
| 382 for (int i = 0; i < cached_monitor_info->length(); i++) { | |
| 383 MonitorInfo* mon_info = cached_monitor_info->at(i); | |
| 384 oop owner = mon_info->owner(); | |
| 385 markOop mark = owner->mark(); | |
| 386 if ((owner->klass() == k_o) && mark->has_bias_pattern()) { | |
| 387 revoke_bias(owner, false, true, requesting_thread); | |
| 388 } | |
| 389 } | |
| 390 } | |
| 391 | |
| 392 // Must force the bias of the passed object to be forcibly revoked | |
| 393 // as well to ensure guarantees to callers | |
| 394 revoke_bias(o, false, true, requesting_thread); | |
| 395 } | |
| 396 | |
| 397 if (TraceBiasedLocking) { | |
| 398 tty->print_cr("* Ending bulk revocation"); | |
| 399 } | |
| 400 | |
| 401 BiasedLocking::Condition status_code = BiasedLocking::BIAS_REVOKED; | |
| 402 | |
| 403 if (attempt_rebias_of_object && | |
| 404 o->mark()->has_bias_pattern() && | |
| 405 klass->prototype_header()->has_bias_pattern()) { | |
| 406 markOop new_mark = markOopDesc::encode(requesting_thread, o->mark()->age(), | |
| 407 klass->prototype_header()->bias_epoch()); | |
| 408 o->set_mark(new_mark); | |
| 409 status_code = BiasedLocking::BIAS_REVOKED_AND_REBIASED; | |
| 410 if (TraceBiasedLocking) { | |
| 411 tty->print_cr(" Rebiased object toward thread " INTPTR_FORMAT, (intptr_t) requesting_thread); | |
| 412 } | |
| 413 } | |
| 414 | |
| 415 assert(!o->mark()->has_bias_pattern() || | |
| 416 (attempt_rebias_of_object && (o->mark()->biased_locker() == requesting_thread)), | |
| 417 "bug in bulk bias revocation"); | |
| 418 | |
| 419 return status_code; | |
| 420 } | |
| 421 | |
| 422 | |
| 423 static void clean_up_cached_monitor_info() { | |
| 424 // Walk the thread list clearing out the cached monitors | |
| 425 for (JavaThread* thr = Threads::first(); thr != NULL; thr = thr->next()) { | |
| 426 thr->set_cached_monitor_info(NULL); | |
| 427 } | |
| 428 } | |
| 429 | |
| 430 | |
| 431 class VM_RevokeBias : public VM_Operation { | |
| 432 protected: | |
| 433 Handle* _obj; | |
| 434 GrowableArray<Handle>* _objs; | |
| 435 JavaThread* _requesting_thread; | |
| 436 BiasedLocking::Condition _status_code; | |
| 437 | |
| 438 public: | |
| 439 VM_RevokeBias(Handle* obj, JavaThread* requesting_thread) | |
| 440 : _obj(obj) | |
| 441 , _objs(NULL) | |
| 442 , _requesting_thread(requesting_thread) | |
| 443 , _status_code(BiasedLocking::NOT_BIASED) {} | |
| 444 | |
| 445 VM_RevokeBias(GrowableArray<Handle>* objs, JavaThread* requesting_thread) | |
| 446 : _obj(NULL) | |
| 447 , _objs(objs) | |
| 448 , _requesting_thread(requesting_thread) | |
| 449 , _status_code(BiasedLocking::NOT_BIASED) {} | |
| 450 | |
| 451 virtual VMOp_Type type() const { return VMOp_RevokeBias; } | |
| 452 | |
| 453 virtual bool doit_prologue() { | |
| 454 // Verify that there is actual work to do since the callers just | |
| 455 // give us locked object(s). If we don't find any biased objects | |
| 456 // there is nothing to do and we avoid a safepoint. | |
| 457 if (_obj != NULL) { | |
| 458 markOop mark = (*_obj)()->mark(); | |
| 459 if (mark->has_bias_pattern()) { | |
| 460 return true; | |
| 461 } | |
| 462 } else { | |
| 463 for ( int i = 0 ; i < _objs->length(); i++ ) { | |
| 464 markOop mark = (_objs->at(i))()->mark(); | |
| 465 if (mark->has_bias_pattern()) { | |
| 466 return true; | |
| 467 } | |
| 468 } | |
| 469 } | |
| 470 return false; | |
| 471 } | |
| 472 | |
| 473 virtual void doit() { | |
| 474 if (_obj != NULL) { | |
| 475 if (TraceBiasedLocking) { | |
| 476 tty->print_cr("Revoking bias with potentially per-thread safepoint:"); | |
| 477 } | |
| 478 _status_code = revoke_bias((*_obj)(), false, false, _requesting_thread); | |
| 479 clean_up_cached_monitor_info(); | |
| 480 return; | |
| 481 } else { | |
| 482 if (TraceBiasedLocking) { | |
| 483 tty->print_cr("Revoking bias with global safepoint:"); | |
| 484 } | |
| 485 BiasedLocking::revoke_at_safepoint(_objs); | |
| 486 } | |
| 487 } | |
| 488 | |
| 489 BiasedLocking::Condition status_code() const { | |
| 490 return _status_code; | |
| 491 } | |
| 492 }; | |
| 493 | |
| 494 | |
| 495 class VM_BulkRevokeBias : public VM_RevokeBias { | |
| 496 private: | |
| 497 bool _bulk_rebias; | |
| 498 bool _attempt_rebias_of_object; | |
| 499 | |
| 500 public: | |
| 501 VM_BulkRevokeBias(Handle* obj, JavaThread* requesting_thread, | |
| 502 bool bulk_rebias, | |
| 503 bool attempt_rebias_of_object) | |
| 504 : VM_RevokeBias(obj, requesting_thread) | |
| 505 , _bulk_rebias(bulk_rebias) | |
| 506 , _attempt_rebias_of_object(attempt_rebias_of_object) {} | |
| 507 | |
| 508 virtual VMOp_Type type() const { return VMOp_BulkRevokeBias; } | |
| 509 virtual bool doit_prologue() { return true; } | |
| 510 | |
| 511 virtual void doit() { | |
| 512 _status_code = bulk_revoke_or_rebias_at_safepoint((*_obj)(), _bulk_rebias, _attempt_rebias_of_object, _requesting_thread); | |
| 513 clean_up_cached_monitor_info(); | |
| 514 } | |
| 515 }; | |
| 516 | |
| 517 | |
| 518 BiasedLocking::Condition BiasedLocking::revoke_and_rebias(Handle obj, bool attempt_rebias, TRAPS) { | |
| 519 assert(!SafepointSynchronize::is_at_safepoint(), "must not be called while at safepoint"); | |
| 520 | |
| 521 // We can revoke the biases of anonymously-biased objects | |
| 522 // efficiently enough that we should not cause these revocations to | |
| 523 // update the heuristics because doing so may cause unwanted bulk | |
| 524 // revocations (which are expensive) to occur. | |
| 525 markOop mark = obj->mark(); | |
| 526 if (mark->is_biased_anonymously() && !attempt_rebias) { | |
| 527 // We are probably trying to revoke the bias of this object due to | |
| 528 // an identity hash code computation. Try to revoke the bias | |
| 529 // without a safepoint. This is possible if we can successfully | |
| 530 // compare-and-exchange an unbiased header into the mark word of | |
| 531 // the object, meaning that no other thread has raced to acquire | |
| 532 // the bias of the object. | |
| 533 markOop biased_value = mark; | |
| 534 markOop unbiased_prototype = markOopDesc::prototype()->set_age(mark->age()); | |
| 535 markOop res_mark = (markOop) Atomic::cmpxchg_ptr(unbiased_prototype, obj->mark_addr(), mark); | |
| 536 if (res_mark == biased_value) { | |
| 537 return BIAS_REVOKED; | |
| 538 } | |
| 539 } else if (mark->has_bias_pattern()) { | |
| 540 Klass* k = Klass::cast(obj->klass()); | |
| 541 markOop prototype_header = k->prototype_header(); | |
| 542 if (!prototype_header->has_bias_pattern()) { | |
| 543 // This object has a stale bias from before the bulk revocation | |
| 544 // for this data type occurred. It's pointless to update the | |
| 545 // heuristics at this point so simply update the header with a | |
| 546 // CAS. If we fail this race, the object's bias has been revoked | |
| 547 // by another thread so we simply return and let the caller deal | |
| 548 // with it. | |
| 549 markOop biased_value = mark; | |
| 550 markOop res_mark = (markOop) Atomic::cmpxchg_ptr(prototype_header, obj->mark_addr(), mark); | |
| 551 assert(!(*(obj->mark_addr()))->has_bias_pattern(), "even if we raced, should still be revoked"); | |
| 552 return BIAS_REVOKED; | |
| 553 } else if (prototype_header->bias_epoch() != mark->bias_epoch()) { | |
| 554 // The epoch of this biasing has expired indicating that the | |
| 555 // object is effectively unbiased. Depending on whether we need | |
| 556 // to rebias or revoke the bias of this object we can do it | |
| 557 // efficiently enough with a CAS that we shouldn't update the | |
| 558 // heuristics. This is normally done in the assembly code but we | |
| 559 // can reach this point due to various points in the runtime | |
| 560 // needing to revoke biases. | |
| 561 if (attempt_rebias) { | |
| 562 assert(THREAD->is_Java_thread(), ""); | |
| 563 markOop biased_value = mark; | |
| 564 markOop rebiased_prototype = markOopDesc::encode((JavaThread*) THREAD, mark->age(), prototype_header->bias_epoch()); | |
| 565 markOop res_mark = (markOop) Atomic::cmpxchg_ptr(rebiased_prototype, obj->mark_addr(), mark); | |
| 566 if (res_mark == biased_value) { | |
| 567 return BIAS_REVOKED_AND_REBIASED; | |
| 568 } | |
| 569 } else { | |
| 570 markOop biased_value = mark; | |
| 571 markOop unbiased_prototype = markOopDesc::prototype()->set_age(mark->age()); | |
| 572 markOop res_mark = (markOop) Atomic::cmpxchg_ptr(unbiased_prototype, obj->mark_addr(), mark); | |
| 573 if (res_mark == biased_value) { | |
| 574 return BIAS_REVOKED; | |
| 575 } | |
| 576 } | |
| 577 } | |
| 578 } | |
| 579 | |
| 580 HeuristicsResult heuristics = update_heuristics(obj(), attempt_rebias); | |
| 581 if (heuristics == HR_NOT_BIASED) { | |
| 582 return NOT_BIASED; | |
| 583 } else if (heuristics == HR_SINGLE_REVOKE) { | |
| 584 if (mark->biased_locker() == THREAD) { | |
| 585 // A thread is trying to revoke the bias of an object biased | |
| 586 // toward it, again likely due to an identity hash code | |
| 587 // computation. We can again avoid a safepoint in this case | |
| 588 // since we are only going to walk our own stack. There are no | |
| 589 // races with revocations occurring in other threads because we | |
| 590 // reach no safepoints in the revocation path. | |
| 591 ResourceMark rm; | |
| 592 if (TraceBiasedLocking) { | |
| 593 tty->print_cr("Revoking bias by walking my own stack:"); | |
| 594 } | |
| 595 BiasedLocking::Condition cond = revoke_bias(obj(), false, false, (JavaThread*) THREAD); | |
| 596 ((JavaThread*) THREAD)->set_cached_monitor_info(NULL); | |
| 597 assert(cond == BIAS_REVOKED, "why not?"); | |
| 598 return cond; | |
| 599 } else { | |
| 600 VM_RevokeBias revoke(&obj, (JavaThread*) THREAD); | |
| 601 VMThread::execute(&revoke); | |
| 602 return revoke.status_code(); | |
| 603 } | |
| 604 } | |
| 605 | |
| 606 assert((heuristics == HR_BULK_REVOKE) || | |
| 607 (heuristics == HR_BULK_REBIAS), "?"); | |
| 608 VM_BulkRevokeBias bulk_revoke(&obj, (JavaThread*) THREAD, | |
| 609 (heuristics == HR_BULK_REBIAS), | |
| 610 attempt_rebias); | |
| 611 VMThread::execute(&bulk_revoke); | |
| 612 return bulk_revoke.status_code(); | |
| 613 } | |
| 614 | |
| 615 | |
| 616 void BiasedLocking::revoke(GrowableArray<Handle>* objs) { | |
| 617 assert(!SafepointSynchronize::is_at_safepoint(), "must not be called while at safepoint"); | |
| 618 if (objs->length() == 0) { | |
| 619 return; | |
| 620 } | |
| 621 VM_RevokeBias revoke(objs, JavaThread::current()); | |
| 622 VMThread::execute(&revoke); | |
| 623 } | |
| 624 | |
| 625 | |
| 626 void BiasedLocking::revoke_at_safepoint(Handle h_obj) { | |
| 627 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint"); | |
| 628 oop obj = h_obj(); | |
| 629 HeuristicsResult heuristics = update_heuristics(obj, false); | |
| 630 if (heuristics == HR_SINGLE_REVOKE) { | |
| 631 revoke_bias(obj, false, false, NULL); | |
| 632 } else if ((heuristics == HR_BULK_REBIAS) || | |
| 633 (heuristics == HR_BULK_REVOKE)) { | |
| 634 bulk_revoke_or_rebias_at_safepoint(obj, (heuristics == HR_BULK_REBIAS), false, NULL); | |
| 635 } | |
| 636 clean_up_cached_monitor_info(); | |
| 637 } | |
| 638 | |
| 639 | |
| 640 void BiasedLocking::revoke_at_safepoint(GrowableArray<Handle>* objs) { | |
| 641 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint"); | |
| 642 int len = objs->length(); | |
| 643 for (int i = 0; i < len; i++) { | |
| 644 oop obj = (objs->at(i))(); | |
| 645 HeuristicsResult heuristics = update_heuristics(obj, false); | |
| 646 if (heuristics == HR_SINGLE_REVOKE) { | |
| 647 revoke_bias(obj, false, false, NULL); | |
| 648 } else if ((heuristics == HR_BULK_REBIAS) || | |
| 649 (heuristics == HR_BULK_REVOKE)) { | |
| 650 bulk_revoke_or_rebias_at_safepoint(obj, (heuristics == HR_BULK_REBIAS), false, NULL); | |
| 651 } | |
| 652 } | |
| 653 clean_up_cached_monitor_info(); | |
| 654 } | |
| 655 | |
| 656 | |
| 657 void BiasedLocking::preserve_marks() { | |
| 658 if (!UseBiasedLocking) | |
| 659 return; | |
| 660 | |
| 661 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint"); | |
| 662 | |
| 663 assert(_preserved_oop_stack == NULL, "double initialization"); | |
| 664 assert(_preserved_mark_stack == NULL, "double initialization"); | |
| 665 | |
| 666 // In order to reduce the number of mark words preserved during GC | |
| 667 // due to the presence of biased locking, we reinitialize most mark | |
| 668 // words to the class's prototype during GC -- even those which have | |
| 669 // a currently valid bias owner. One important situation where we | |
| 670 // must not clobber a bias is when a biased object is currently | |
| 671 // locked. To handle this case we iterate over the currently-locked | |
| 672 // monitors in a prepass and, if they are biased, preserve their | |
| 673 // mark words here. This should be a relatively small set of objects | |
| 674 // especially compared to the number of objects in the heap. | |
| 675 _preserved_mark_stack = new (ResourceObj::C_HEAP) GrowableArray<markOop>(10, true); | |
| 676 _preserved_oop_stack = new (ResourceObj::C_HEAP) GrowableArray<Handle>(10, true); | |
| 677 | |
| 678 ResourceMark rm; | |
| 679 Thread* cur = Thread::current(); | |
| 680 for (JavaThread* thread = Threads::first(); thread != NULL; thread = thread->next()) { | |
| 681 if (thread->has_last_Java_frame()) { | |
| 682 RegisterMap rm(thread); | |
| 683 for (javaVFrame* vf = thread->last_java_vframe(&rm); vf != NULL; vf = vf->java_sender()) { | |
| 684 GrowableArray<MonitorInfo*> *monitors = vf->monitors(); | |
| 685 if (monitors != NULL) { | |
| 686 int len = monitors->length(); | |
| 687 // Walk monitors youngest to oldest | |
| 688 for (int i = len - 1; i >= 0; i--) { | |
| 689 MonitorInfo* mon_info = monitors->at(i); | |
| 690 oop owner = mon_info->owner(); | |
| 691 if (owner != NULL) { | |
| 692 markOop mark = owner->mark(); | |
| 693 if (mark->has_bias_pattern()) { | |
| 694 _preserved_oop_stack->push(Handle(cur, owner)); | |
| 695 _preserved_mark_stack->push(mark); | |
| 696 } | |
| 697 } | |
| 698 } | |
| 699 } | |
| 700 } | |
| 701 } | |
| 702 } | |
| 703 } | |
| 704 | |
| 705 | |
| 706 void BiasedLocking::restore_marks() { | |
| 707 if (!UseBiasedLocking) | |
| 708 return; | |
| 709 | |
| 710 assert(_preserved_oop_stack != NULL, "double free"); | |
| 711 assert(_preserved_mark_stack != NULL, "double free"); | |
| 712 | |
| 713 int len = _preserved_oop_stack->length(); | |
| 714 for (int i = 0; i < len; i++) { | |
| 715 Handle owner = _preserved_oop_stack->at(i); | |
| 716 markOop mark = _preserved_mark_stack->at(i); | |
| 717 owner->set_mark(mark); | |
| 718 } | |
| 719 | |
| 720 delete _preserved_oop_stack; | |
| 721 _preserved_oop_stack = NULL; | |
| 722 delete _preserved_mark_stack; | |
| 723 _preserved_mark_stack = NULL; | |
| 724 } | |
| 725 | |
| 726 | |
| 727 int* BiasedLocking::total_entry_count_addr() { return _counters.total_entry_count_addr(); } | |
| 728 int* BiasedLocking::biased_lock_entry_count_addr() { return _counters.biased_lock_entry_count_addr(); } | |
| 729 int* BiasedLocking::anonymously_biased_lock_entry_count_addr() { return _counters.anonymously_biased_lock_entry_count_addr(); } | |
| 730 int* BiasedLocking::rebiased_lock_entry_count_addr() { return _counters.rebiased_lock_entry_count_addr(); } | |
| 731 int* BiasedLocking::revoked_lock_entry_count_addr() { return _counters.revoked_lock_entry_count_addr(); } | |
| 732 int* BiasedLocking::fast_path_entry_count_addr() { return _counters.fast_path_entry_count_addr(); } | |
| 733 int* BiasedLocking::slow_path_entry_count_addr() { return _counters.slow_path_entry_count_addr(); } | |
| 734 | |
| 735 | |
| 736 // BiasedLockingCounters | |
| 737 | |
| 738 int BiasedLockingCounters::slow_path_entry_count() { | |
| 739 if (_slow_path_entry_count != 0) { | |
| 740 return _slow_path_entry_count; | |
| 741 } | |
| 742 int sum = _biased_lock_entry_count + _anonymously_biased_lock_entry_count + | |
| 743 _rebiased_lock_entry_count + _revoked_lock_entry_count + | |
| 744 _fast_path_entry_count; | |
| 745 | |
| 746 return _total_entry_count - sum; | |
| 747 } | |
| 748 | |
| 749 void BiasedLockingCounters::print_on(outputStream* st) { | |
| 750 tty->print_cr("# total entries: %d", _total_entry_count); | |
| 751 tty->print_cr("# biased lock entries: %d", _biased_lock_entry_count); | |
| 752 tty->print_cr("# anonymously biased lock entries: %d", _anonymously_biased_lock_entry_count); | |
| 753 tty->print_cr("# rebiased lock entries: %d", _rebiased_lock_entry_count); | |
| 754 tty->print_cr("# revoked lock entries: %d", _revoked_lock_entry_count); | |
| 755 tty->print_cr("# fast path lock entries: %d", _fast_path_entry_count); | |
| 756 tty->print_cr("# slow path lock entries: %d", slow_path_entry_count()); | |
| 757 } |