/* * Copyright (c) 2005, 2017, 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 "logging/log.hpp" #include "memory/resourceArea.hpp" #include "oops/klass.inline.hpp" #include "oops/markOop.hpp" #include "oops/oop.inline.hpp" #include "runtime/atomic.hpp" #include "runtime/basicLock.hpp" #include "runtime/biasedLocking.hpp" #include "runtime/task.hpp" #include "runtime/threadSMR.hpp" #include "runtime/vframe.hpp" #include "runtime/vmThread.hpp" #include "runtime/vm_operations.hpp" #include "trace/tracing.hpp" static bool _biased_locking_enabled = false; BiasedLockingCounters BiasedLocking::_counters; static GrowableArray* _preserved_oop_stack = NULL; static GrowableArray* _preserved_mark_stack = NULL; static void enable_biased_locking(InstanceKlass* 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 class loader data dictionaries enabling biased locking for all // currently loaded classes. ClassLoaderDataGraph::dictionary_classes_do(enable_biased_locking); // Indicate that future instances should enable it as well _biased_locking_enabled = true; log_info(biasedlocking)("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* get_or_compute_monitor_info(JavaThread* thread) { GrowableArray* info = thread->cached_monitor_info(); if (info != NULL) { return info; } info = new GrowableArray(); // 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 *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; } // After the call, *biased_locker will be set to obj->mark()->biased_locker() if biased_locker != NULL, // AND it is a living thread. Otherwise it will not be updated, (i.e. the caller is responsible for initialization). static BiasedLocking::Condition revoke_bias(oop obj, bool allow_rebias, bool is_bulk, JavaThread* requesting_thread, JavaThread** biased_locker) { markOop mark = obj->mark(); if (!mark->has_bias_pattern()) { if (log_is_enabled(Info, biasedlocking)) { ResourceMark rm; log_info(biasedlocking)(" (Skipping revocation of object " INTPTR_FORMAT ", mark " INTPTR_FORMAT ", type %s" ", requesting thread " INTPTR_FORMAT " because it's no longer biased)", p2i((void *)obj), (intptr_t) mark, obj->klass()->external_name(), (intptr_t) requesting_thread); } 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); // Log at "info" level if not bulk, else "trace" level if (!is_bulk) { ResourceMark rm; log_info(biasedlocking)("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); } else { ResourceMark rm; log_trace(biasedlocking)("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); } // Log at "info" level if not bulk, else "trace" level if (!is_bulk) { log_info(biasedlocking)(" Revoked bias of anonymously-biased object"); } else { log_trace(biasedlocking)(" 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 (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur_thread = jtiwh.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); } // Log at "info" level if not bulk, else "trace" level if (!is_bulk) { log_info(biasedlocking)(" Revoked bias of object biased toward dead thread (" PTR_FORMAT ")", p2i(biased_thread)); } else { log_trace(biasedlocking)(" Revoked bias of object biased toward dead thread (" PTR_FORMAT ")", p2i(biased_thread)); } return BiasedLocking::BIAS_REVOKED; } // Log at "info" level if not bulk, else "trace" level if (!is_bulk) { log_info(biasedlocking)(" Revoked bias of object biased toward live thread (" PTR_FORMAT ")", p2i(biased_thread)); } else { log_trace(biasedlocking)(" Revoked bias of object biased toward live thread (" PTR_FORMAT ")", p2i(biased_thread)); } // 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* 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) { log_trace(biasedlocking)(" 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 { log_trace(biasedlocking)(" 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"); // Log at "info" level if not bulk, else "trace" level if (!is_bulk) { log_info(biasedlocking)(" Revoked bias of currently-locked object"); } else { log_trace(biasedlocking)(" Revoked bias of currently-locked object"); } } else { // Log at "info" level if not bulk, else "trace" level if (!is_bulk) { log_info(biasedlocking)(" Revoked bias of currently-unlocked object"); } else { log_trace(biasedlocking)(" 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); } } // If requested, return information on which thread held the bias if (biased_locker != NULL) { *biased_locker = biased_thread; } 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"); log_info(biasedlocking)("* 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; { JavaThreadIteratorWithHandle jtiwh; 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 = jtiwh.next(); ) { GrowableArray* 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, NULL); } else { if (log_is_enabled(Info, biasedlocking)) { ResourceMark rm; log_info(biasedlocking)("* 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 = jtiwh.next(); ) { GrowableArray* 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, NULL); } } } // 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, NULL); } } // ThreadsListHandle is destroyed here. log_info(biasedlocking)("* 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; log_info(biasedlocking)(" 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 (JavaThreadIteratorWithHandle jtiwh; JavaThread *thr = jtiwh.next(); ) { thr->set_cached_monitor_info(NULL); } } class VM_RevokeBias : public VM_Operation { protected: Handle* _obj; GrowableArray* _objs; JavaThread* _requesting_thread; BiasedLocking::Condition _status_code; traceid _biased_locker_id; public: VM_RevokeBias(Handle* obj, JavaThread* requesting_thread) : _obj(obj) , _objs(NULL) , _requesting_thread(requesting_thread) , _status_code(BiasedLocking::NOT_BIASED) , _biased_locker_id(0) {} VM_RevokeBias(GrowableArray* objs, JavaThread* requesting_thread) : _obj(NULL) , _objs(objs) , _requesting_thread(requesting_thread) , _status_code(BiasedLocking::NOT_BIASED) , _biased_locker_id(0) {} 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) { log_info(biasedlocking)("Revoking bias with potentially per-thread safepoint:"); JavaThread* biased_locker = NULL; _status_code = revoke_bias((*_obj)(), false, false, _requesting_thread, &biased_locker); if (biased_locker != NULL) { _biased_locker_id = THREAD_TRACE_ID(biased_locker); } clean_up_cached_monitor_info(); return; } else { log_info(biasedlocking)("Revoking bias with global safepoint:"); BiasedLocking::revoke_at_safepoint(_objs); } } BiasedLocking::Condition status_code() const { return _status_code; } traceid biased_locker() const { return _biased_locker_id; } }; 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 = obj->cas_set_mark(unbiased_prototype, 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 = obj->cas_set_mark(prototype_header, 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 = obj->cas_set_mark(rebiased_prototype, 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 = obj->cas_set_mark(unbiased_prototype, 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; log_info(biasedlocking)("Revoking bias by walking my own stack:"); EventBiasedLockSelfRevocation event; BiasedLocking::Condition cond = revoke_bias(obj(), false, false, (JavaThread*) THREAD, NULL); ((JavaThread*) THREAD)->set_cached_monitor_info(NULL); assert(cond == BIAS_REVOKED, "why not?"); if (event.should_commit()) { event.set_lockClass(k); event.commit(); } return cond; } else { EventBiasedLockRevocation event; VM_RevokeBias revoke(&obj, (JavaThread*) THREAD); VMThread::execute(&revoke); if (event.should_commit() && (revoke.status_code() != NOT_BIASED)) { event.set_lockClass(k); // Subtract 1 to match the id of events committed inside the safepoint event.set_safepointId(SafepointSynchronize::safepoint_counter() - 1); event.set_previousOwner(revoke.biased_locker()); event.commit(); } return revoke.status_code(); } } assert((heuristics == HR_BULK_REVOKE) || (heuristics == HR_BULK_REBIAS), "?"); EventBiasedLockClassRevocation event; VM_BulkRevokeBias bulk_revoke(&obj, (JavaThread*) THREAD, (heuristics == HR_BULK_REBIAS), attempt_rebias); VMThread::execute(&bulk_revoke); if (event.should_commit()) { event.set_revokedClass(obj->klass()); event.set_disableBiasing((heuristics != HR_BULK_REBIAS)); // Subtract 1 to match the id of events committed inside the safepoint event.set_safepointId(SafepointSynchronize::safepoint_counter() - 1); event.commit(); } return bulk_revoke.status_code(); } void BiasedLocking::revoke(GrowableArray* 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, 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* 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, 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(10, true); _preserved_oop_stack = new (ResourceObj::C_HEAP, mtInternal) GrowableArray(10, true); ResourceMark rm; Thread* cur = Thread::current(); for (JavaThreadIteratorWithHandle jtiwh; JavaThread *thread = jtiwh.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 *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()); }