/* * Copyright (c) 2005, 2020, 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 "classfile/classLoaderDataGraph.hpp" #include "jfr/jfrEvents.hpp" #include "jfr/support/jfrThreadId.hpp" #include "logging/log.hpp" #include "memory/resourceArea.hpp" #include "oops/klass.inline.hpp" #include "oops/markWord.hpp" #include "oops/oop.inline.hpp" #include "runtime/atomic.hpp" #include "runtime/basicLock.hpp" #include "runtime/biasedLocking.hpp" #include "runtime/handles.inline.hpp" #include "runtime/handshake.hpp" #include "runtime/safepointMechanism.hpp" #include "runtime/task.hpp" #include "runtime/threadSMR.hpp" #include "runtime/vframe.hpp" #include "runtime/vmThread.hpp" #include "runtime/vmOperations.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(markWord::biased_locking_prototype()); } static void enable_biased_locking() { _biased_locking_enabled = true; log_info(biasedlocking)("Biased locking enabled"); } class VM_EnableBiasedLocking: public VM_Operation { public: VM_EnableBiasedLocking() {} VMOp_Type type() const { return VMOp_EnableBiasedLocking; } 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 enable_biased_locking(); } 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() { VM_EnableBiasedLocking op; VMThread::execute(&op); // Reclaim our storage and disenroll ourself delete this; } }; void BiasedLocking::init() { // If biased locking is enabled and BiasedLockingStartupDelay is set, // schedule a task to fire after the specified delay which turns on // biased locking for all currently loaded classes as well as future // ones. This could be a workaround for startup time regressions // due to large number of safepoints being taken during VM startup for // bias revocation. if (UseBiasedLocking) { if (BiasedLockingStartupDelay > 0) { EnableBiasedLockingTask* task = new EnableBiasedLockingTask(BiasedLockingStartupDelay); task->enroll(); } else { enable_biased_locking(); } } } bool BiasedLocking::enabled() { assert(UseBiasedLocking, "precondition"); // We check "BiasedLockingStartupDelay == 0" here to cover the // possibility of calls to BiasedLocking::enabled() before // BiasedLocking::init(). return _biased_locking_enabled || BiasedLockingStartupDelay == 0; } // 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). void BiasedLocking::single_revoke_at_safepoint(oop obj, bool is_bulk, JavaThread* requesting_thread, JavaThread** biased_locker) { assert(SafepointSynchronize::is_at_safepoint(), "must be done at safepoint"); assert(Thread::current()->is_VM_thread(), "must be VMThread"); markWord 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), mark.value(), obj->klass()->external_name(), (intptr_t) requesting_thread); } return; } uint age = mark.age(); markWord unbiased_prototype = markWord::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 ", requesting thread " INTPTR_FORMAT, p2i((void *)obj), mark.value(), obj->klass()->external_name(), obj->klass()->prototype_header().value(), (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 " , requesting thread " INTPTR_FORMAT, p2i((void *)obj), mark.value(), obj->klass()->external_name(), obj->klass()->prototype_header().value(), (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. 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; } // 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 { ThreadsListHandle tlh; thread_is_alive = tlh.includes(biased_thread); } if (!thread_is_alive) { 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; } // 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 below markWord mark = markWord::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 store the lock address for platforms without TSO // ordering (e.g. ppc). obj->release_set_mark(markWord::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"); } // 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; } } enum HeuristicsResult { HR_NOT_BIASED = 1, HR_SINGLE_REVOKE = 2, HR_BULK_REBIAS = 3, HR_BULK_REVOKE = 4 }; static HeuristicsResult update_heuristics(oop o) { markWord 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 = nanos_to_millis(os::javaTimeNanos()); 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; } void BiasedLocking::bulk_revoke_at_safepoint(oop o, bool bulk_rebias, JavaThread* requesting_thread) { assert(SafepointSynchronize::is_at_safepoint(), "must be done at safepoint"); assert(Thread::current()->is_VM_thread(), "must be VMThread"); 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), o->mark().value(), o->klass()->external_name()); jlong cur_time = nanos_to_millis(os::javaTimeNanos()); 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(); markWord 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. single_revoke_at_safepoint(o, 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(markWord::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(); markWord mark = owner->mark(); if ((owner->klass() == k_o) && mark.has_bias_pattern()) { single_revoke_at_safepoint(owner, true, requesting_thread, NULL); } } } // Must force the bias of the passed object to be forcibly revoked // as well to ensure guarantees to callers single_revoke_at_safepoint(o, true, requesting_thread, NULL); } } // ThreadsListHandle is destroyed here. log_info(biasedlocking)("* Ending bulk revocation"); assert(!o->mark().has_bias_pattern(), "bug in bulk bias revocation"); } static void clean_up_cached_monitor_info(JavaThread* thread = NULL) { if (thread != NULL) { thread->set_cached_monitor_info(NULL); } else { // Walk the thread list clearing out the cached monitors for (JavaThreadIteratorWithHandle jtiwh; JavaThread *thr = jtiwh.next(); ) { thr->set_cached_monitor_info(NULL); } } } class VM_BulkRevokeBias : public VM_Operation { private: Handle* _obj; JavaThread* _requesting_thread; bool _bulk_rebias; uint64_t _safepoint_id; public: VM_BulkRevokeBias(Handle* obj, JavaThread* requesting_thread, bool bulk_rebias) : _obj(obj) , _requesting_thread(requesting_thread) , _bulk_rebias(bulk_rebias) , _safepoint_id(0) {} virtual VMOp_Type type() const { return VMOp_BulkRevokeBias; } virtual void doit() { BiasedLocking::bulk_revoke_at_safepoint((*_obj)(), _bulk_rebias, _requesting_thread); _safepoint_id = SafepointSynchronize::safepoint_id(); clean_up_cached_monitor_info(); } bool is_bulk_rebias() const { return _bulk_rebias; } uint64_t safepoint_id() const { return _safepoint_id; } }; class RevokeOneBias : public HandshakeClosure { protected: Handle _obj; JavaThread* _requesting_thread; JavaThread* _biased_locker; BiasedLocking::Condition _status_code; traceid _biased_locker_id; public: RevokeOneBias(Handle obj, JavaThread* requesting_thread, JavaThread* biased_locker) : HandshakeClosure("RevokeOneBias") , _obj(obj) , _requesting_thread(requesting_thread) , _biased_locker(biased_locker) , _status_code(BiasedLocking::NOT_BIASED) , _biased_locker_id(0) {} void do_thread(Thread* target) { assert(target == _biased_locker, "Wrong thread"); oop o = _obj(); markWord mark = o->mark(); if (!mark.has_bias_pattern()) { return; } markWord prototype = o->klass()->prototype_header(); if (!prototype.has_bias_pattern()) { // This object has a stale bias from before the handshake // was requested. If we fail this race, the object's bias // has been revoked by another thread so we simply return. markWord biased_value = mark; mark = o->cas_set_mark(markWord::prototype().set_age(mark.age()), mark); assert(!o->mark().has_bias_pattern(), "even if we raced, should still be revoked"); if (biased_value == mark) { _status_code = BiasedLocking::BIAS_REVOKED; } return; } if (_biased_locker == mark.biased_locker()) { if (mark.bias_epoch() == prototype.bias_epoch()) { // Epoch is still valid. This means biaser could be currently // synchronized on this object. We must walk its stack looking // for monitor records associated with this object and change // them to be stack locks if any are found. ResourceMark rm; BiasedLocking::walk_stack_and_revoke(o, _biased_locker); _biased_locker->set_cached_monitor_info(NULL); assert(!o->mark().has_bias_pattern(), "invariant"); _biased_locker_id = JFR_THREAD_ID(_biased_locker); _status_code = BiasedLocking::BIAS_REVOKED; return; } else { markWord biased_value = mark; mark = o->cas_set_mark(markWord::prototype().set_age(mark.age()), mark); if (mark == biased_value || !mark.has_bias_pattern()) { assert(!o->mark().has_bias_pattern(), "should be revoked"); _status_code = (biased_value == mark) ? BiasedLocking::BIAS_REVOKED : BiasedLocking::NOT_BIASED; return; } } } _status_code = BiasedLocking::NOT_REVOKED; } BiasedLocking::Condition status_code() const { return _status_code; } traceid biased_locker() const { return _biased_locker_id; } }; static void post_self_revocation_event(EventBiasedLockSelfRevocation* event, Klass* k) { assert(event != NULL, "invariant"); assert(k != NULL, "invariant"); assert(event->should_commit(), "invariant"); event->set_lockClass(k); event->commit(); } static void post_revocation_event(EventBiasedLockRevocation* event, Klass* k, RevokeOneBias* op) { assert(event != NULL, "invariant"); assert(k != NULL, "invariant"); assert(op != NULL, "invariant"); assert(event->should_commit(), "invariant"); event->set_lockClass(k); event->set_safepointId(0); event->set_previousOwner(op->biased_locker()); event->commit(); } static void post_class_revocation_event(EventBiasedLockClassRevocation* event, Klass* k, VM_BulkRevokeBias* op) { assert(event != NULL, "invariant"); assert(k != NULL, "invariant"); assert(op != NULL, "invariant"); assert(event->should_commit(), "invariant"); event->set_revokedClass(k); event->set_disableBiasing(!op->is_bulk_rebias()); event->set_safepointId(op->safepoint_id()); event->commit(); } BiasedLocking::Condition BiasedLocking::single_revoke_with_handshake(Handle obj, JavaThread *requester, JavaThread *biaser) { EventBiasedLockRevocation event; if (PrintBiasedLockingStatistics) { Atomic::inc(handshakes_count_addr()); } log_info(biasedlocking, handshake)("JavaThread " INTPTR_FORMAT " handshaking JavaThread " INTPTR_FORMAT " to revoke object " INTPTR_FORMAT, p2i(requester), p2i(biaser), p2i(obj())); RevokeOneBias revoke(obj, requester, biaser); bool executed = Handshake::execute_direct(&revoke, biaser); if (revoke.status_code() == NOT_REVOKED) { return NOT_REVOKED; } if (executed) { log_info(biasedlocking, handshake)("Handshake revocation for object " INTPTR_FORMAT " succeeded. Bias was %srevoked", p2i(obj()), (revoke.status_code() == BIAS_REVOKED ? "" : "already ")); if (event.should_commit() && revoke.status_code() == BIAS_REVOKED) { post_revocation_event(&event, obj->klass(), &revoke); } assert(!obj->mark().has_bias_pattern(), "invariant"); return revoke.status_code(); } else { // Thread was not alive. // Grab Threads_lock before manually trying to revoke bias. This avoids race with a newly // created JavaThread (that happens to get the same memory address as biaser) synchronizing // on this object. { MutexLocker ml(Threads_lock); markWord mark = obj->mark(); // Check if somebody else was able to revoke it before biased thread exited. if (!mark.has_bias_pattern()) { return NOT_BIASED; } ThreadsListHandle tlh; markWord prototype = obj->klass()->prototype_header(); if (!prototype.has_bias_pattern() || (!tlh.includes(biaser) && biaser == mark.biased_locker() && prototype.bias_epoch() == mark.bias_epoch())) { obj->cas_set_mark(markWord::prototype().set_age(mark.age()), mark); if (event.should_commit()) { post_revocation_event(&event, obj->klass(), &revoke); } assert(!obj->mark().has_bias_pattern(), "bias should be revoked by now"); return BIAS_REVOKED; } } } return NOT_REVOKED; } // Caller should have instantiated a ResourceMark object before calling this method void BiasedLocking::walk_stack_and_revoke(oop obj, JavaThread* biased_locker) { Thread* cur = Thread::current(); assert(!SafepointSynchronize::is_at_safepoint(), "this should always be executed outside safepoints"); assert(cur == biased_locker || cur == biased_locker->get_active_handshaker(), "wrong thread"); markWord mark = obj->mark(); assert(mark.biased_locker() == biased_locker && obj->klass()->prototype_header().bias_epoch() == mark.bias_epoch(), "invariant"); log_trace(biasedlocking)("JavaThread(" INTPTR_FORMAT ") revoking object " INTPTR_FORMAT ", mark " INTPTR_FORMAT ", type %s, prototype header " INTPTR_FORMAT ", biaser " INTPTR_FORMAT " %s", p2i(cur), p2i(obj), mark.value(), obj->klass()->external_name(), obj->klass()->prototype_header().value(), p2i(biased_locker), cur != biased_locker ? "" : "(walking own stack)"); markWord unbiased_prototype = markWord::prototype().set_age(obj->mark().age()); GrowableArray* cached_monitor_info = get_or_compute_monitor_info(biased_locker); 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(mon_info->owner()), p2i(obj)); // Assume recursive case and fix up highest lock below markWord mark = markWord::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(mon_info->owner()), p2i(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 store the lock address for platforms without TSO // ordering (e.g. ppc). obj->release_set_mark(markWord::encode(highest_lock)); assert(!obj->mark().has_bias_pattern(), "illegal mark state: stack lock used bias bit"); log_info(biasedlocking)(" Revoked bias of currently-locked object"); } else { log_info(biasedlocking)(" Revoked bias of currently-unlocked object"); // Store the unlocked value into the object's header. obj->set_mark(unbiased_prototype); } assert(!obj->mark().has_bias_pattern(), "must not be biased"); } void BiasedLocking::revoke_own_lock(Handle obj, TRAPS) { assert(THREAD->is_Java_thread(), "must be called by a JavaThread"); JavaThread* thread = (JavaThread*)THREAD; markWord mark = obj->mark(); if (!mark.has_bias_pattern()) { return; } Klass *k = obj->klass(); assert(mark.biased_locker() == thread && k->prototype_header().bias_epoch() == mark.bias_epoch(), "Revoke failed, unhandled biased lock state"); ResourceMark rm; log_info(biasedlocking)("Revoking bias by walking my own stack:"); EventBiasedLockSelfRevocation event; BiasedLocking::walk_stack_and_revoke(obj(), (JavaThread*) thread); thread->set_cached_monitor_info(NULL); assert(!obj->mark().has_bias_pattern(), "invariant"); if (event.should_commit()) { post_self_revocation_event(&event, k); } } void BiasedLocking::revoke(Handle obj, TRAPS) { assert(!SafepointSynchronize::is_at_safepoint(), "must not be called while at safepoint"); while (true) { // 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. markWord mark = obj->mark(); if (!mark.has_bias_pattern()) { return; } if (mark.is_biased_anonymously()) { // 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. markWord biased_value = mark; markWord unbiased_prototype = markWord::prototype().set_age(mark.age()); markWord res_mark = obj->cas_set_mark(unbiased_prototype, mark); if (res_mark == biased_value) { return; } mark = res_mark; // Refresh mark with the latest value. } else { Klass* k = obj->klass(); markWord 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. obj->cas_set_mark(prototype_header.set_age(mark.age()), mark); assert(!obj->mark().has_bias_pattern(), "even if we raced, should still be revoked"); return; } else if (prototype_header.bias_epoch() != mark.bias_epoch()) { // The epoch of this biasing has expired indicating that the // object is effectively unbiased. We can revoke the bias of this // object 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. markWord res_mark; markWord biased_value = mark; markWord unbiased_prototype = markWord::prototype().set_age(mark.age()); res_mark = obj->cas_set_mark(unbiased_prototype, mark); if (res_mark == biased_value) { return; } mark = res_mark; // Refresh mark with the latest value. } } HeuristicsResult heuristics = update_heuristics(obj()); if (heuristics == HR_NOT_BIASED) { return; } else if (heuristics == HR_SINGLE_REVOKE) { JavaThread *blt = mark.biased_locker(); assert(blt != NULL, "invariant"); if (blt == THREAD) { // 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/handshake 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. EventBiasedLockSelfRevocation event; ResourceMark rm; walk_stack_and_revoke(obj(), blt); blt->set_cached_monitor_info(NULL); assert(!obj->mark().has_bias_pattern(), "invariant"); if (event.should_commit()) { post_self_revocation_event(&event, obj->klass()); } return; } else { BiasedLocking::Condition cond = single_revoke_with_handshake(obj, (JavaThread*)THREAD, blt); if (cond != NOT_REVOKED) { return; } } } else { assert((heuristics == HR_BULK_REVOKE) || (heuristics == HR_BULK_REBIAS), "?"); EventBiasedLockClassRevocation event; VM_BulkRevokeBias bulk_revoke(&obj, (JavaThread*)THREAD, (heuristics == HR_BULK_REBIAS)); VMThread::execute(&bulk_revoke); if (event.should_commit()) { post_class_revocation_event(&event, obj->klass(), &bulk_revoke); } return; } } } // All objects in objs should be locked by biaser void BiasedLocking::revoke(GrowableArray* objs, JavaThread *biaser) { bool clean_my_cache = false; for (int i = 0; i < objs->length(); i++) { oop obj = (objs->at(i))(); markWord mark = obj->mark(); if (mark.has_bias_pattern()) { walk_stack_and_revoke(obj, biaser); clean_my_cache = true; } } if (clean_my_cache) { clean_up_cached_monitor_info(biaser); } } 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); if (heuristics == HR_SINGLE_REVOKE) { JavaThread* biased_locker = NULL; single_revoke_at_safepoint(obj, false, NULL, &biased_locker); if (biased_locker) { clean_up_cached_monitor_info(biased_locker); } } else if ((heuristics == HR_BULK_REBIAS) || (heuristics == HR_BULK_REVOKE)) { bulk_revoke_at_safepoint(obj, (heuristics == HR_BULK_REBIAS), 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) { markWord 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); markWord 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::handshakes_count_addr() { return _counters.handshakes_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() const { 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) const { 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("# handshakes entries: %d", _handshakes_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()); } void BiasedLockingCounters::print() const { print_on(tty); }