| /* |
| * Copyright (c) 2005, 2014, Oracle and/or its affiliates. All rights reserved. |
| * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
| * |
| * This code is free software; you can redistribute it and/or modify it |
| * under the terms of the GNU General Public License version 2 only, as |
| * published by the Free Software Foundation. |
| * |
| * This code is distributed in the hope that it will be useful, but WITHOUT |
| * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
| * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
| * version 2 for more details (a copy is included in the LICENSE file that |
| * accompanied this code). |
| * |
| * You should have received a copy of the GNU General Public License version |
| * 2 along with this work; if not, write to the Free Software Foundation, |
| * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
| * |
| * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
| * or visit www.oracle.com if you need additional information or have any |
| * questions. |
| * |
| */ |
| |
| #include "precompiled.hpp" |
| #include "oops/klass.inline.hpp" |
| #include "oops/markOop.hpp" |
| #include "runtime/basicLock.hpp" |
| #include "runtime/biasedLocking.hpp" |
| #include "runtime/task.hpp" |
| #include "runtime/vframe.hpp" |
| #include "runtime/vmThread.hpp" |
| #include "runtime/vm_operations.hpp" |
| |
| static bool _biased_locking_enabled = false; |
| BiasedLockingCounters BiasedLocking::_counters; |
| |
| static GrowableArray<Handle>* _preserved_oop_stack = NULL; |
| static GrowableArray<markOop>* _preserved_mark_stack = NULL; |
| |
| static void enable_biased_locking(Klass* k) { |
| k->set_prototype_header(markOopDesc::biased_locking_prototype()); |
| } |
| |
| class VM_EnableBiasedLocking: public VM_Operation { |
| private: |
| bool _is_cheap_allocated; |
| public: |
| VM_EnableBiasedLocking(bool is_cheap_allocated) { _is_cheap_allocated = is_cheap_allocated; } |
| VMOp_Type type() const { return VMOp_EnableBiasedLocking; } |
| Mode evaluation_mode() const { return _is_cheap_allocated ? _async_safepoint : _safepoint; } |
| bool is_cheap_allocated() const { return _is_cheap_allocated; } |
| |
| void doit() { |
| // Iterate the system dictionary enabling biased locking for all |
| // currently loaded classes |
| SystemDictionary::classes_do(enable_biased_locking); |
| // Indicate that future instances should enable it as well |
| _biased_locking_enabled = true; |
| |
| if (TraceBiasedLocking) { |
| tty->print_cr("Biased locking enabled"); |
| } |
| } |
| |
| bool allow_nested_vm_operations() const { return false; } |
| }; |
| |
| |
| // One-shot PeriodicTask subclass for enabling biased locking |
| class EnableBiasedLockingTask : public PeriodicTask { |
| public: |
| EnableBiasedLockingTask(size_t interval_time) : PeriodicTask(interval_time) {} |
| |
| virtual void task() { |
| // Use async VM operation to avoid blocking the Watcher thread. |
| // VM Thread will free C heap storage. |
| VM_EnableBiasedLocking *op = new VM_EnableBiasedLocking(true); |
| VMThread::execute(op); |
| |
| // Reclaim our storage and disenroll ourself |
| delete this; |
| } |
| }; |
| |
| |
| void BiasedLocking::init() { |
| // If biased locking is enabled, schedule a task to fire a few |
| // seconds into the run which turns on biased locking for all |
| // currently loaded classes as well as future ones. This is a |
| // workaround for startup time regressions due to a large number of |
| // safepoints being taken during VM startup for bias revocation. |
| // Ideally we would have a lower cost for individual bias revocation |
| // and not need a mechanism like this. |
| if (UseBiasedLocking) { |
| if (BiasedLockingStartupDelay > 0) { |
| EnableBiasedLockingTask* task = new EnableBiasedLockingTask(BiasedLockingStartupDelay); |
| task->enroll(); |
| } else { |
| VM_EnableBiasedLocking op(false); |
| VMThread::execute(&op); |
| } |
| } |
| } |
| |
| |
| bool BiasedLocking::enabled() { |
| return _biased_locking_enabled; |
| } |
| |
| // Returns MonitorInfos for all objects locked on this thread in youngest to oldest order |
| static GrowableArray<MonitorInfo*>* get_or_compute_monitor_info(JavaThread* thread) { |
| GrowableArray<MonitorInfo*>* info = thread->cached_monitor_info(); |
| if (info != NULL) { |
| return info; |
| } |
| |
| info = new GrowableArray<MonitorInfo*>(); |
| |
| // It's possible for the thread to not have any Java frames on it, |
| // i.e., if it's the main thread and it's already returned from main() |
| if (thread->has_last_Java_frame()) { |
| RegisterMap rm(thread); |
| for (javaVFrame* vf = thread->last_java_vframe(&rm); vf != NULL; vf = vf->java_sender()) { |
| GrowableArray<MonitorInfo*> *monitors = vf->monitors(); |
| if (monitors != NULL) { |
| int len = monitors->length(); |
| // Walk monitors youngest to oldest |
| for (int i = len - 1; i >= 0; i--) { |
| MonitorInfo* mon_info = monitors->at(i); |
| if (mon_info->eliminated()) continue; |
| oop owner = mon_info->owner(); |
| if (owner != NULL) { |
| info->append(mon_info); |
| } |
| } |
| } |
| } |
| } |
| |
| thread->set_cached_monitor_info(info); |
| return info; |
| } |
| |
| |
| static BiasedLocking::Condition revoke_bias(oop obj, bool allow_rebias, bool is_bulk, JavaThread* requesting_thread) { |
| markOop mark = obj->mark(); |
| if (!mark->has_bias_pattern()) { |
| if (TraceBiasedLocking) { |
| ResourceMark rm; |
| tty->print_cr(" (Skipping revocation of object of type %s because it's no longer biased)", |
| obj->klass()->external_name()); |
| } |
| return BiasedLocking::NOT_BIASED; |
| } |
| |
| uint age = mark->age(); |
| markOop biased_prototype = markOopDesc::biased_locking_prototype()->set_age(age); |
| markOop unbiased_prototype = markOopDesc::prototype()->set_age(age); |
| |
| if (TraceBiasedLocking && (Verbose || !is_bulk)) { |
| ResourceMark rm; |
| 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, |
| p2i((void *)obj), (intptr_t) mark, obj->klass()->external_name(), (intptr_t) obj->klass()->prototype_header(), (allow_rebias ? 1 : 0), (intptr_t) requesting_thread); |
| } |
| |
| JavaThread* biased_thread = mark->biased_locker(); |
| if (biased_thread == NULL) { |
| // Object is anonymously biased. We can get here if, for |
| // example, we revoke the bias due to an identity hash code |
| // being computed for an object. |
| if (!allow_rebias) { |
| obj->set_mark(unbiased_prototype); |
| } |
| if (TraceBiasedLocking && (Verbose || !is_bulk)) { |
| tty->print_cr(" Revoked bias of anonymously-biased object"); |
| } |
| return BiasedLocking::BIAS_REVOKED; |
| } |
| |
| // Handle case where the thread toward which the object was biased has exited |
| bool thread_is_alive = false; |
| if (requesting_thread == biased_thread) { |
| thread_is_alive = true; |
| } else { |
| for (JavaThread* cur_thread = Threads::first(); cur_thread != NULL; cur_thread = cur_thread->next()) { |
| if (cur_thread == biased_thread) { |
| thread_is_alive = true; |
| break; |
| } |
| } |
| } |
| if (!thread_is_alive) { |
| if (allow_rebias) { |
| obj->set_mark(biased_prototype); |
| } else { |
| obj->set_mark(unbiased_prototype); |
| } |
| if (TraceBiasedLocking && (Verbose || !is_bulk)) { |
| tty->print_cr(" Revoked bias of object biased toward dead thread"); |
| } |
| return BiasedLocking::BIAS_REVOKED; |
| } |
| |
| // Thread owning bias is alive. |
| // Check to see whether it currently owns the lock and, if so, |
| // write down the needed displaced headers to the thread's stack. |
| // Otherwise, restore the object's header either to the unlocked |
| // or unbiased state. |
| GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(biased_thread); |
| BasicLock* highest_lock = NULL; |
| for (int i = 0; i < cached_monitor_info->length(); i++) { |
| MonitorInfo* mon_info = cached_monitor_info->at(i); |
| if (mon_info->owner() == obj) { |
| if (TraceBiasedLocking && Verbose) { |
| tty->print_cr(" mon_info->owner (" PTR_FORMAT ") == obj (" PTR_FORMAT ")", |
| p2i((void *) mon_info->owner()), |
| p2i((void *) obj)); |
| } |
| // Assume recursive case and fix up highest lock later |
| markOop mark = markOopDesc::encode((BasicLock*) NULL); |
| highest_lock = mon_info->lock(); |
| highest_lock->set_displaced_header(mark); |
| } else { |
| if (TraceBiasedLocking && Verbose) { |
| tty->print_cr(" mon_info->owner (" PTR_FORMAT ") != obj (" PTR_FORMAT ")", |
| p2i((void *) mon_info->owner()), |
| p2i((void *) obj)); |
| } |
| } |
| } |
| if (highest_lock != NULL) { |
| // Fix up highest lock to contain displaced header and point |
| // object at it |
| highest_lock->set_displaced_header(unbiased_prototype); |
| // Reset object header to point to displaced mark. |
| // Must release storing the lock address for platforms without TSO |
| // ordering (e.g. ppc). |
| obj->release_set_mark(markOopDesc::encode(highest_lock)); |
| assert(!obj->mark()->has_bias_pattern(), "illegal mark state: stack lock used bias bit"); |
| if (TraceBiasedLocking && (Verbose || !is_bulk)) { |
| tty->print_cr(" Revoked bias of currently-locked object"); |
| } |
| } else { |
| if (TraceBiasedLocking && (Verbose || !is_bulk)) { |
| tty->print_cr(" Revoked bias of currently-unlocked object"); |
| } |
| if (allow_rebias) { |
| obj->set_mark(biased_prototype); |
| } else { |
| // Store the unlocked value into the object's header. |
| obj->set_mark(unbiased_prototype); |
| } |
| } |
| |
| return BiasedLocking::BIAS_REVOKED; |
| } |
| |
| |
| enum HeuristicsResult { |
| HR_NOT_BIASED = 1, |
| HR_SINGLE_REVOKE = 2, |
| HR_BULK_REBIAS = 3, |
| HR_BULK_REVOKE = 4 |
| }; |
| |
| |
| static HeuristicsResult update_heuristics(oop o, bool allow_rebias) { |
| markOop mark = o->mark(); |
| if (!mark->has_bias_pattern()) { |
| return HR_NOT_BIASED; |
| } |
| |
| // Heuristics to attempt to throttle the number of revocations. |
| // Stages: |
| // 1. Revoke the biases of all objects in the heap of this type, |
| // but allow rebiasing of those objects if unlocked. |
| // 2. Revoke the biases of all objects in the heap of this type |
| // and don't allow rebiasing of these objects. Disable |
| // allocation of objects of that type with the bias bit set. |
| Klass* k = o->klass(); |
| jlong cur_time = os::javaTimeMillis(); |
| jlong last_bulk_revocation_time = k->last_biased_lock_bulk_revocation_time(); |
| int revocation_count = k->biased_lock_revocation_count(); |
| if ((revocation_count >= BiasedLockingBulkRebiasThreshold) && |
| (revocation_count < BiasedLockingBulkRevokeThreshold) && |
| (last_bulk_revocation_time != 0) && |
| (cur_time - last_bulk_revocation_time >= BiasedLockingDecayTime)) { |
| // This is the first revocation we've seen in a while of an |
| // object of this type since the last time we performed a bulk |
| // rebiasing operation. The application is allocating objects in |
| // bulk which are biased toward a thread and then handing them |
| // off to another thread. We can cope with this allocation |
| // pattern via the bulk rebiasing mechanism so we reset the |
| // klass's revocation count rather than allow it to increase |
| // monotonically. If we see the need to perform another bulk |
| // rebias operation later, we will, and if subsequently we see |
| // many more revocation operations in a short period of time we |
| // will completely disable biasing for this type. |
| k->set_biased_lock_revocation_count(0); |
| revocation_count = 0; |
| } |
| |
| // Make revocation count saturate just beyond BiasedLockingBulkRevokeThreshold |
| if (revocation_count <= BiasedLockingBulkRevokeThreshold) { |
| revocation_count = k->atomic_incr_biased_lock_revocation_count(); |
| } |
| |
| if (revocation_count == BiasedLockingBulkRevokeThreshold) { |
| return HR_BULK_REVOKE; |
| } |
| |
| if (revocation_count == BiasedLockingBulkRebiasThreshold) { |
| return HR_BULK_REBIAS; |
| } |
| |
| return HR_SINGLE_REVOKE; |
| } |
| |
| |
| static BiasedLocking::Condition bulk_revoke_or_rebias_at_safepoint(oop o, |
| bool bulk_rebias, |
| bool attempt_rebias_of_object, |
| JavaThread* requesting_thread) { |
| assert(SafepointSynchronize::is_at_safepoint(), "must be done at safepoint"); |
| |
| if (TraceBiasedLocking) { |
| tty->print_cr("* Beginning bulk revocation (kind == %s) because of object " |
| INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s", |
| (bulk_rebias ? "rebias" : "revoke"), |
| p2i((void *) o), (intptr_t) o->mark(), o->klass()->external_name()); |
| } |
| |
| jlong cur_time = os::javaTimeMillis(); |
| o->klass()->set_last_biased_lock_bulk_revocation_time(cur_time); |
| |
| |
| Klass* k_o = o->klass(); |
| Klass* klass = k_o; |
| |
| if (bulk_rebias) { |
| // Use the epoch in the klass of the object to implicitly revoke |
| // all biases of objects of this data type and force them to be |
| // reacquired. However, we also need to walk the stacks of all |
| // threads and update the headers of lightweight locked objects |
| // with biases to have the current epoch. |
| |
| // If the prototype header doesn't have the bias pattern, don't |
| // try to update the epoch -- assume another VM operation came in |
| // and reset the header to the unbiased state, which will |
| // implicitly cause all existing biases to be revoked |
| if (klass->prototype_header()->has_bias_pattern()) { |
| int prev_epoch = klass->prototype_header()->bias_epoch(); |
| klass->set_prototype_header(klass->prototype_header()->incr_bias_epoch()); |
| int cur_epoch = klass->prototype_header()->bias_epoch(); |
| |
| // Now walk all threads' stacks and adjust epochs of any biased |
| // and locked objects of this data type we encounter |
| for (JavaThread* thr = Threads::first(); thr != NULL; thr = thr->next()) { |
| GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr); |
| for (int i = 0; i < cached_monitor_info->length(); i++) { |
| MonitorInfo* mon_info = cached_monitor_info->at(i); |
| oop owner = mon_info->owner(); |
| markOop mark = owner->mark(); |
| if ((owner->klass() == k_o) && mark->has_bias_pattern()) { |
| // We might have encountered this object already in the case of recursive locking |
| assert(mark->bias_epoch() == prev_epoch || mark->bias_epoch() == cur_epoch, "error in bias epoch adjustment"); |
| owner->set_mark(mark->set_bias_epoch(cur_epoch)); |
| } |
| } |
| } |
| } |
| |
| // At this point we're done. All we have to do is potentially |
| // adjust the header of the given object to revoke its bias. |
| revoke_bias(o, attempt_rebias_of_object && klass->prototype_header()->has_bias_pattern(), true, requesting_thread); |
| } else { |
| if (TraceBiasedLocking) { |
| ResourceMark rm; |
| tty->print_cr("* Disabling biased locking for type %s", klass->external_name()); |
| } |
| |
| // Disable biased locking for this data type. Not only will this |
| // cause future instances to not be biased, but existing biased |
| // instances will notice that this implicitly caused their biases |
| // to be revoked. |
| klass->set_prototype_header(markOopDesc::prototype()); |
| |
| // Now walk all threads' stacks and forcibly revoke the biases of |
| // any locked and biased objects of this data type we encounter. |
| for (JavaThread* thr = Threads::first(); thr != NULL; thr = thr->next()) { |
| GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr); |
| for (int i = 0; i < cached_monitor_info->length(); i++) { |
| MonitorInfo* mon_info = cached_monitor_info->at(i); |
| oop owner = mon_info->owner(); |
| markOop mark = owner->mark(); |
| if ((owner->klass() == k_o) && mark->has_bias_pattern()) { |
| revoke_bias(owner, false, true, requesting_thread); |
| } |
| } |
| } |
| |
| // Must force the bias of the passed object to be forcibly revoked |
| // as well to ensure guarantees to callers |
| revoke_bias(o, false, true, requesting_thread); |
| } |
| |
| if (TraceBiasedLocking) { |
| tty->print_cr("* Ending bulk revocation"); |
| } |
| |
| BiasedLocking::Condition status_code = BiasedLocking::BIAS_REVOKED; |
| |
| if (attempt_rebias_of_object && |
| o->mark()->has_bias_pattern() && |
| klass->prototype_header()->has_bias_pattern()) { |
| markOop new_mark = markOopDesc::encode(requesting_thread, o->mark()->age(), |
| klass->prototype_header()->bias_epoch()); |
| o->set_mark(new_mark); |
| status_code = BiasedLocking::BIAS_REVOKED_AND_REBIASED; |
| if (TraceBiasedLocking) { |
| tty->print_cr(" Rebiased object toward thread " INTPTR_FORMAT, (intptr_t) requesting_thread); |
| } |
| } |
| |
| assert(!o->mark()->has_bias_pattern() || |
| (attempt_rebias_of_object && (o->mark()->biased_locker() == requesting_thread)), |
| "bug in bulk bias revocation"); |
| |
| return status_code; |
| } |
| |
| |
| static void clean_up_cached_monitor_info() { |
| // Walk the thread list clearing out the cached monitors |
| for (JavaThread* thr = Threads::first(); thr != NULL; thr = thr->next()) { |
| thr->set_cached_monitor_info(NULL); |
| } |
| } |
| |
| |
| class VM_RevokeBias : public VM_Operation { |
| protected: |
| Handle* _obj; |
| GrowableArray<Handle>* _objs; |
| JavaThread* _requesting_thread; |
| BiasedLocking::Condition _status_code; |
| |
| public: |
| VM_RevokeBias(Handle* obj, JavaThread* requesting_thread) |
| : _obj(obj) |
| , _objs(NULL) |
| , _requesting_thread(requesting_thread) |
| , _status_code(BiasedLocking::NOT_BIASED) {} |
| |
| VM_RevokeBias(GrowableArray<Handle>* objs, JavaThread* requesting_thread) |
| : _obj(NULL) |
| , _objs(objs) |
| , _requesting_thread(requesting_thread) |
| , _status_code(BiasedLocking::NOT_BIASED) {} |
| |
| virtual VMOp_Type type() const { return VMOp_RevokeBias; } |
| |
| virtual bool doit_prologue() { |
| // Verify that there is actual work to do since the callers just |
| // give us locked object(s). If we don't find any biased objects |
| // there is nothing to do and we avoid a safepoint. |
| if (_obj != NULL) { |
| markOop mark = (*_obj)()->mark(); |
| if (mark->has_bias_pattern()) { |
| return true; |
| } |
| } else { |
| for ( int i = 0 ; i < _objs->length(); i++ ) { |
| markOop mark = (_objs->at(i))()->mark(); |
| if (mark->has_bias_pattern()) { |
| return true; |
| } |
| } |
| } |
| return false; |
| } |
| |
| virtual void doit() { |
| if (_obj != NULL) { |
| if (TraceBiasedLocking) { |
| tty->print_cr("Revoking bias with potentially per-thread safepoint:"); |
| } |
| _status_code = revoke_bias((*_obj)(), false, false, _requesting_thread); |
| clean_up_cached_monitor_info(); |
| return; |
| } else { |
| if (TraceBiasedLocking) { |
| tty->print_cr("Revoking bias with global safepoint:"); |
| } |
| BiasedLocking::revoke_at_safepoint(_objs); |
| } |
| } |
| |
| BiasedLocking::Condition status_code() const { |
| return _status_code; |
| } |
| }; |
| |
| |
| class VM_BulkRevokeBias : public VM_RevokeBias { |
| private: |
| bool _bulk_rebias; |
| bool _attempt_rebias_of_object; |
| |
| public: |
| VM_BulkRevokeBias(Handle* obj, JavaThread* requesting_thread, |
| bool bulk_rebias, |
| bool attempt_rebias_of_object) |
| : VM_RevokeBias(obj, requesting_thread) |
| , _bulk_rebias(bulk_rebias) |
| , _attempt_rebias_of_object(attempt_rebias_of_object) {} |
| |
| virtual VMOp_Type type() const { return VMOp_BulkRevokeBias; } |
| virtual bool doit_prologue() { return true; } |
| |
| virtual void doit() { |
| _status_code = bulk_revoke_or_rebias_at_safepoint((*_obj)(), _bulk_rebias, _attempt_rebias_of_object, _requesting_thread); |
| clean_up_cached_monitor_info(); |
| } |
| }; |
| |
| |
| BiasedLocking::Condition BiasedLocking::revoke_and_rebias(Handle obj, bool attempt_rebias, TRAPS) { |
| assert(!SafepointSynchronize::is_at_safepoint(), "must not be called while at safepoint"); |
| |
| // We can revoke the biases of anonymously-biased objects |
| // efficiently enough that we should not cause these revocations to |
| // update the heuristics because doing so may cause unwanted bulk |
| // revocations (which are expensive) to occur. |
| markOop mark = obj->mark(); |
| if (mark->is_biased_anonymously() && !attempt_rebias) { |
| // We are probably trying to revoke the bias of this object due to |
| // an identity hash code computation. Try to revoke the bias |
| // without a safepoint. This is possible if we can successfully |
| // compare-and-exchange an unbiased header into the mark word of |
| // the object, meaning that no other thread has raced to acquire |
| // the bias of the object. |
| markOop biased_value = mark; |
| markOop unbiased_prototype = markOopDesc::prototype()->set_age(mark->age()); |
| markOop res_mark = (markOop) Atomic::cmpxchg_ptr(unbiased_prototype, obj->mark_addr(), mark); |
| if (res_mark == biased_value) { |
| return BIAS_REVOKED; |
| } |
| } else if (mark->has_bias_pattern()) { |
| Klass* k = obj->klass(); |
| markOop prototype_header = k->prototype_header(); |
| if (!prototype_header->has_bias_pattern()) { |
| // This object has a stale bias from before the bulk revocation |
| // for this data type occurred. It's pointless to update the |
| // heuristics at this point so simply update the header with a |
| // CAS. If we fail this race, the object's bias has been revoked |
| // by another thread so we simply return and let the caller deal |
| // with it. |
| markOop biased_value = mark; |
| markOop res_mark = (markOop) Atomic::cmpxchg_ptr(prototype_header, obj->mark_addr(), mark); |
| assert(!(*(obj->mark_addr()))->has_bias_pattern(), "even if we raced, should still be revoked"); |
| return BIAS_REVOKED; |
| } else if (prototype_header->bias_epoch() != mark->bias_epoch()) { |
| // The epoch of this biasing has expired indicating that the |
| // object is effectively unbiased. Depending on whether we need |
| // to rebias or revoke the bias of this object we can do it |
| // efficiently enough with a CAS that we shouldn't update the |
| // heuristics. This is normally done in the assembly code but we |
| // can reach this point due to various points in the runtime |
| // needing to revoke biases. |
| if (attempt_rebias) { |
| assert(THREAD->is_Java_thread(), ""); |
| markOop biased_value = mark; |
| markOop rebiased_prototype = markOopDesc::encode((JavaThread*) THREAD, mark->age(), prototype_header->bias_epoch()); |
| markOop res_mark = (markOop) Atomic::cmpxchg_ptr(rebiased_prototype, obj->mark_addr(), mark); |
| if (res_mark == biased_value) { |
| return BIAS_REVOKED_AND_REBIASED; |
| } |
| } else { |
| markOop biased_value = mark; |
| markOop unbiased_prototype = markOopDesc::prototype()->set_age(mark->age()); |
| markOop res_mark = (markOop) Atomic::cmpxchg_ptr(unbiased_prototype, obj->mark_addr(), mark); |
| if (res_mark == biased_value) { |
| return BIAS_REVOKED; |
| } |
| } |
| } |
| } |
| |
| HeuristicsResult heuristics = update_heuristics(obj(), attempt_rebias); |
| if (heuristics == HR_NOT_BIASED) { |
| return NOT_BIASED; |
| } else if (heuristics == HR_SINGLE_REVOKE) { |
| Klass *k = obj->klass(); |
| markOop prototype_header = k->prototype_header(); |
| if (mark->biased_locker() == THREAD && |
| prototype_header->bias_epoch() == mark->bias_epoch()) { |
| // A thread is trying to revoke the bias of an object biased |
| // toward it, again likely due to an identity hash code |
| // computation. We can again avoid a safepoint in this case |
| // since we are only going to walk our own stack. There are no |
| // races with revocations occurring in other threads because we |
| // reach no safepoints in the revocation path. |
| // Also check the epoch because even if threads match, another thread |
| // can come in with a CAS to steal the bias of an object that has a |
| // stale epoch. |
| ResourceMark rm; |
| if (TraceBiasedLocking) { |
| tty->print_cr("Revoking bias by walking my own stack:"); |
| } |
| BiasedLocking::Condition cond = revoke_bias(obj(), false, false, (JavaThread*) THREAD); |
| ((JavaThread*) THREAD)->set_cached_monitor_info(NULL); |
| assert(cond == BIAS_REVOKED, "why not?"); |
| return cond; |
| } else { |
| VM_RevokeBias revoke(&obj, (JavaThread*) THREAD); |
| VMThread::execute(&revoke); |
| return revoke.status_code(); |
| } |
| } |
| |
| assert((heuristics == HR_BULK_REVOKE) || |
| (heuristics == HR_BULK_REBIAS), "?"); |
| VM_BulkRevokeBias bulk_revoke(&obj, (JavaThread*) THREAD, |
| (heuristics == HR_BULK_REBIAS), |
| attempt_rebias); |
| VMThread::execute(&bulk_revoke); |
| return bulk_revoke.status_code(); |
| } |
| |
| |
| void BiasedLocking::revoke(GrowableArray<Handle>* objs) { |
| assert(!SafepointSynchronize::is_at_safepoint(), "must not be called while at safepoint"); |
| if (objs->length() == 0) { |
| return; |
| } |
| VM_RevokeBias revoke(objs, JavaThread::current()); |
| VMThread::execute(&revoke); |
| } |
| |
| |
| void BiasedLocking::revoke_at_safepoint(Handle h_obj) { |
| assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint"); |
| oop obj = h_obj(); |
| HeuristicsResult heuristics = update_heuristics(obj, false); |
| if (heuristics == HR_SINGLE_REVOKE) { |
| revoke_bias(obj, false, false, NULL); |
| } else if ((heuristics == HR_BULK_REBIAS) || |
| (heuristics == HR_BULK_REVOKE)) { |
| bulk_revoke_or_rebias_at_safepoint(obj, (heuristics == HR_BULK_REBIAS), false, NULL); |
| } |
| clean_up_cached_monitor_info(); |
| } |
| |
| |
| void BiasedLocking::revoke_at_safepoint(GrowableArray<Handle>* objs) { |
| assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint"); |
| int len = objs->length(); |
| for (int i = 0; i < len; i++) { |
| oop obj = (objs->at(i))(); |
| HeuristicsResult heuristics = update_heuristics(obj, false); |
| if (heuristics == HR_SINGLE_REVOKE) { |
| revoke_bias(obj, false, false, NULL); |
| } else if ((heuristics == HR_BULK_REBIAS) || |
| (heuristics == HR_BULK_REVOKE)) { |
| bulk_revoke_or_rebias_at_safepoint(obj, (heuristics == HR_BULK_REBIAS), false, NULL); |
| } |
| } |
| clean_up_cached_monitor_info(); |
| } |
| |
| |
| void BiasedLocking::preserve_marks() { |
| if (!UseBiasedLocking) |
| return; |
| |
| assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint"); |
| |
| assert(_preserved_oop_stack == NULL, "double initialization"); |
| assert(_preserved_mark_stack == NULL, "double initialization"); |
| |
| // In order to reduce the number of mark words preserved during GC |
| // due to the presence of biased locking, we reinitialize most mark |
| // words to the class's prototype during GC -- even those which have |
| // a currently valid bias owner. One important situation where we |
| // must not clobber a bias is when a biased object is currently |
| // locked. To handle this case we iterate over the currently-locked |
| // monitors in a prepass and, if they are biased, preserve their |
| // mark words here. This should be a relatively small set of objects |
| // especially compared to the number of objects in the heap. |
| _preserved_mark_stack = new (ResourceObj::C_HEAP, mtInternal) GrowableArray<markOop>(10, true); |
| _preserved_oop_stack = new (ResourceObj::C_HEAP, mtInternal) GrowableArray<Handle>(10, true); |
| |
| ResourceMark rm; |
| Thread* cur = Thread::current(); |
| for (JavaThread* thread = Threads::first(); thread != NULL; thread = thread->next()) { |
| if (thread->has_last_Java_frame()) { |
| RegisterMap rm(thread); |
| for (javaVFrame* vf = thread->last_java_vframe(&rm); vf != NULL; vf = vf->java_sender()) { |
| GrowableArray<MonitorInfo*> *monitors = vf->monitors(); |
| if (monitors != NULL) { |
| int len = monitors->length(); |
| // Walk monitors youngest to oldest |
| for (int i = len - 1; i >= 0; i--) { |
| MonitorInfo* mon_info = monitors->at(i); |
| if (mon_info->owner_is_scalar_replaced()) continue; |
| oop owner = mon_info->owner(); |
| if (owner != NULL) { |
| markOop mark = owner->mark(); |
| if (mark->has_bias_pattern()) { |
| _preserved_oop_stack->push(Handle(cur, owner)); |
| _preserved_mark_stack->push(mark); |
| } |
| } |
| } |
| } |
| } |
| } |
| } |
| } |
| |
| |
| void BiasedLocking::restore_marks() { |
| if (!UseBiasedLocking) |
| return; |
| |
| assert(_preserved_oop_stack != NULL, "double free"); |
| assert(_preserved_mark_stack != NULL, "double free"); |
| |
| int len = _preserved_oop_stack->length(); |
| for (int i = 0; i < len; i++) { |
| Handle owner = _preserved_oop_stack->at(i); |
| markOop mark = _preserved_mark_stack->at(i); |
| owner->set_mark(mark); |
| } |
| |
| delete _preserved_oop_stack; |
| _preserved_oop_stack = NULL; |
| delete _preserved_mark_stack; |
| _preserved_mark_stack = NULL; |
| } |
| |
| |
| int* BiasedLocking::total_entry_count_addr() { return _counters.total_entry_count_addr(); } |
| int* BiasedLocking::biased_lock_entry_count_addr() { return _counters.biased_lock_entry_count_addr(); } |
| int* BiasedLocking::anonymously_biased_lock_entry_count_addr() { return _counters.anonymously_biased_lock_entry_count_addr(); } |
| int* BiasedLocking::rebiased_lock_entry_count_addr() { return _counters.rebiased_lock_entry_count_addr(); } |
| int* BiasedLocking::revoked_lock_entry_count_addr() { return _counters.revoked_lock_entry_count_addr(); } |
| int* BiasedLocking::fast_path_entry_count_addr() { return _counters.fast_path_entry_count_addr(); } |
| int* BiasedLocking::slow_path_entry_count_addr() { return _counters.slow_path_entry_count_addr(); } |
| |
| |
| // BiasedLockingCounters |
| |
| int BiasedLockingCounters::slow_path_entry_count() { |
| if (_slow_path_entry_count != 0) { |
| return _slow_path_entry_count; |
| } |
| int sum = _biased_lock_entry_count + _anonymously_biased_lock_entry_count + |
| _rebiased_lock_entry_count + _revoked_lock_entry_count + |
| _fast_path_entry_count; |
| |
| return _total_entry_count - sum; |
| } |
| |
| void BiasedLockingCounters::print_on(outputStream* st) { |
| tty->print_cr("# total entries: %d", _total_entry_count); |
| tty->print_cr("# biased lock entries: %d", _biased_lock_entry_count); |
| tty->print_cr("# anonymously biased lock entries: %d", _anonymously_biased_lock_entry_count); |
| tty->print_cr("# rebiased lock entries: %d", _rebiased_lock_entry_count); |
| tty->print_cr("# revoked lock entries: %d", _revoked_lock_entry_count); |
| tty->print_cr("# fast path lock entries: %d", _fast_path_entry_count); |
| tty->print_cr("# slow path lock entries: %d", slow_path_entry_count()); |
| } |
