duke@435: 
duke@435: /*
duke@435:  * Copyright 2005-2007 Sun Microsystems, Inc.  All Rights Reserved.
duke@435:  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
duke@435:  *
duke@435:  * This code is free software; you can redistribute it and/or modify it
duke@435:  * under the terms of the GNU General Public License version 2 only, as
duke@435:  * published by the Free Software Foundation.
duke@435:  *
duke@435:  * This code is distributed in the hope that it will be useful, but WITHOUT
duke@435:  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
duke@435:  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
duke@435:  * version 2 for more details (a copy is included in the LICENSE file that
duke@435:  * accompanied this code).
duke@435:  *
duke@435:  * You should have received a copy of the GNU General Public License version
duke@435:  * 2 along with this work; if not, write to the Free Software Foundation,
duke@435:  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
duke@435:  *
duke@435:  * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
duke@435:  * CA 95054 USA or visit www.sun.com if you need additional information or
duke@435:  * have any questions.
duke@435:  *
duke@435:  */
duke@435: 
duke@435: # include "incls/_precompiled.incl"
duke@435: # include "incls/_biasedLocking.cpp.incl"
duke@435: 
duke@435: static bool _biased_locking_enabled = false;
duke@435: BiasedLockingCounters BiasedLocking::_counters;
duke@435: 
duke@435: static GrowableArray<Handle>*  _preserved_oop_stack  = NULL;
duke@435: static GrowableArray<markOop>* _preserved_mark_stack = NULL;
duke@435: 
duke@435: static void enable_biased_locking(klassOop k) {
duke@435:   Klass::cast(k)->set_prototype_header(markOopDesc::biased_locking_prototype());
duke@435: }
duke@435: 
duke@435: class VM_EnableBiasedLocking: public VM_Operation {
duke@435:  public:
duke@435:   VM_EnableBiasedLocking() {}
duke@435:   VMOp_Type type() const   { return VMOp_EnableBiasedLocking; }
duke@435:   void doit() {
duke@435:     // Iterate the system dictionary enabling biased locking for all
duke@435:     // currently loaded classes
duke@435:     SystemDictionary::classes_do(enable_biased_locking);
duke@435:     // Indicate that future instances should enable it as well
duke@435:     _biased_locking_enabled = true;
duke@435: 
duke@435:     if (TraceBiasedLocking) {
duke@435:       tty->print_cr("Biased locking enabled");
duke@435:     }
duke@435:   }
duke@435: 
duke@435:   bool allow_nested_vm_operations() const        { return false; }
duke@435: };
duke@435: 
duke@435: 
duke@435: // One-shot PeriodicTask subclass for enabling biased locking
duke@435: class EnableBiasedLockingTask : public PeriodicTask {
duke@435:  public:
duke@435:   EnableBiasedLockingTask(size_t interval_time) : PeriodicTask(interval_time) {}
duke@435: 
duke@435:   virtual void task() {
duke@435:     VM_EnableBiasedLocking op;
duke@435:     VMThread::execute(&op);
duke@435: 
duke@435:     // Reclaim our storage and disenroll ourself
duke@435:     delete this;
duke@435:   }
duke@435: };
duke@435: 
duke@435: 
duke@435: void BiasedLocking::init() {
duke@435:   // If biased locking is enabled, schedule a task to fire a few
duke@435:   // seconds into the run which turns on biased locking for all
duke@435:   // currently loaded classes as well as future ones. This is a
duke@435:   // workaround for startup time regressions due to a large number of
duke@435:   // safepoints being taken during VM startup for bias revocation.
duke@435:   // Ideally we would have a lower cost for individual bias revocation
duke@435:   // and not need a mechanism like this.
duke@435:   if (UseBiasedLocking) {
duke@435:     if (BiasedLockingStartupDelay > 0) {
duke@435:       EnableBiasedLockingTask* task = new EnableBiasedLockingTask(BiasedLockingStartupDelay);
duke@435:       task->enroll();
duke@435:     } else {
duke@435:       VM_EnableBiasedLocking op;
duke@435:       VMThread::execute(&op);
duke@435:     }
duke@435:   }
duke@435: }
duke@435: 
duke@435: 
duke@435: bool BiasedLocking::enabled() {
duke@435:   return _biased_locking_enabled;
duke@435: }
duke@435: 
duke@435: // Returns MonitorInfos for all objects locked on this thread in youngest to oldest order
duke@435: static GrowableArray<MonitorInfo*>* get_or_compute_monitor_info(JavaThread* thread) {
duke@435:   GrowableArray<MonitorInfo*>* info = thread->cached_monitor_info();
duke@435:   if (info != NULL) {
duke@435:     return info;
duke@435:   }
duke@435: 
duke@435:   info = new GrowableArray<MonitorInfo*>();
duke@435: 
duke@435:   // It's possible for the thread to not have any Java frames on it,
duke@435:   // i.e., if it's the main thread and it's already returned from main()
duke@435:   if (thread->has_last_Java_frame()) {
duke@435:     RegisterMap rm(thread);
duke@435:     for (javaVFrame* vf = thread->last_java_vframe(&rm); vf != NULL; vf = vf->java_sender()) {
duke@435:       GrowableArray<MonitorInfo*> *monitors = vf->monitors();
duke@435:       if (monitors != NULL) {
duke@435:         int len = monitors->length();
duke@435:         // Walk monitors youngest to oldest
duke@435:         for (int i = len - 1; i >= 0; i--) {
duke@435:           MonitorInfo* mon_info = monitors->at(i);
duke@435:           oop owner = mon_info->owner();
duke@435:           if (owner != NULL) {
duke@435:             info->append(mon_info);
duke@435:           }
duke@435:         }
duke@435:       }
duke@435:     }
duke@435:   }
duke@435: 
duke@435:   thread->set_cached_monitor_info(info);
duke@435:   return info;
duke@435: }
duke@435: 
duke@435: 
duke@435: static BiasedLocking::Condition revoke_bias(oop obj, bool allow_rebias, bool is_bulk, JavaThread* requesting_thread) {
duke@435:   markOop mark = obj->mark();
duke@435:   if (!mark->has_bias_pattern()) {
duke@435:     if (TraceBiasedLocking) {
duke@435:       ResourceMark rm;
duke@435:       tty->print_cr("  (Skipping revocation of object of type %s because it's no longer biased)",
duke@435:                     Klass::cast(obj->klass())->external_name());
duke@435:     }
duke@435:     return BiasedLocking::NOT_BIASED;
duke@435:   }
duke@435: 
duke@435:   int age = mark->age();
duke@435:   markOop   biased_prototype = markOopDesc::biased_locking_prototype()->set_age(age);
duke@435:   markOop unbiased_prototype = markOopDesc::prototype()->set_age(age);
duke@435: 
duke@435:   if (TraceBiasedLocking && (Verbose || !is_bulk)) {
duke@435:     ResourceMark rm;
duke@435:     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,
duke@435:                   (intptr_t) obj, (intptr_t) mark, Klass::cast(obj->klass())->external_name(), (intptr_t) Klass::cast(obj->klass())->prototype_header(), (allow_rebias ? 1 : 0), (intptr_t) requesting_thread);
duke@435:   }
duke@435: 
duke@435:   JavaThread* biased_thread = mark->biased_locker();
duke@435:   if (biased_thread == NULL) {
duke@435:     // Object is anonymously biased. We can get here if, for
duke@435:     // example, we revoke the bias due to an identity hash code
duke@435:     // being computed for an object.
duke@435:     if (!allow_rebias) {
duke@435:       obj->set_mark(unbiased_prototype);
duke@435:     }
duke@435:     if (TraceBiasedLocking && (Verbose || !is_bulk)) {
duke@435:       tty->print_cr("  Revoked bias of anonymously-biased object");
duke@435:     }
duke@435:     return BiasedLocking::BIAS_REVOKED;
duke@435:   }
duke@435: 
duke@435:   // Handle case where the thread toward which the object was biased has exited
duke@435:   bool thread_is_alive = false;
duke@435:   if (requesting_thread == biased_thread) {
duke@435:     thread_is_alive = true;
duke@435:   } else {
duke@435:     for (JavaThread* cur_thread = Threads::first(); cur_thread != NULL; cur_thread = cur_thread->next()) {
duke@435:       if (cur_thread == biased_thread) {
duke@435:         thread_is_alive = true;
duke@435:         break;
duke@435:       }
duke@435:     }
duke@435:   }
duke@435:   if (!thread_is_alive) {
duke@435:     if (allow_rebias) {
duke@435:       obj->set_mark(biased_prototype);
duke@435:     } else {
duke@435:       obj->set_mark(unbiased_prototype);
duke@435:     }
duke@435:     if (TraceBiasedLocking && (Verbose || !is_bulk)) {
duke@435:       tty->print_cr("  Revoked bias of object biased toward dead thread");
duke@435:     }
duke@435:     return BiasedLocking::BIAS_REVOKED;
duke@435:   }
duke@435: 
duke@435:   // Thread owning bias is alive.
duke@435:   // Check to see whether it currently owns the lock and, if so,
duke@435:   // write down the needed displaced headers to the thread's stack.
duke@435:   // Otherwise, restore the object's header either to the unlocked
duke@435:   // or unbiased state.
duke@435:   GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(biased_thread);
duke@435:   BasicLock* highest_lock = NULL;
duke@435:   for (int i = 0; i < cached_monitor_info->length(); i++) {
duke@435:     MonitorInfo* mon_info = cached_monitor_info->at(i);
duke@435:     if (mon_info->owner() == obj) {
duke@435:       if (TraceBiasedLocking && Verbose) {
duke@435:         tty->print_cr("   mon_info->owner (" PTR_FORMAT ") == obj (" PTR_FORMAT ")",
duke@435:                       (intptr_t) mon_info->owner(),
duke@435:                       (intptr_t) obj);
duke@435:       }
duke@435:       // Assume recursive case and fix up highest lock later
duke@435:       markOop mark = markOopDesc::encode((BasicLock*) NULL);
duke@435:       highest_lock = mon_info->lock();
duke@435:       highest_lock->set_displaced_header(mark);
duke@435:     } else {
duke@435:       if (TraceBiasedLocking && Verbose) {
duke@435:         tty->print_cr("   mon_info->owner (" PTR_FORMAT ") != obj (" PTR_FORMAT ")",
duke@435:                       (intptr_t) mon_info->owner(),
duke@435:                       (intptr_t) obj);
duke@435:       }
duke@435:     }
duke@435:   }
duke@435:   if (highest_lock != NULL) {
duke@435:     // Fix up highest lock to contain displaced header and point
duke@435:     // object at it
duke@435:     highest_lock->set_displaced_header(unbiased_prototype);
duke@435:     // Reset object header to point to displaced mark
duke@435:     obj->set_mark(markOopDesc::encode(highest_lock));
duke@435:     assert(!obj->mark()->has_bias_pattern(), "illegal mark state: stack lock used bias bit");
duke@435:     if (TraceBiasedLocking && (Verbose || !is_bulk)) {
duke@435:       tty->print_cr("  Revoked bias of currently-locked object");
duke@435:     }
duke@435:   } else {
duke@435:     if (TraceBiasedLocking && (Verbose || !is_bulk)) {
duke@435:       tty->print_cr("  Revoked bias of currently-unlocked object");
duke@435:     }
duke@435:     if (allow_rebias) {
duke@435:       obj->set_mark(biased_prototype);
duke@435:     } else {
duke@435:       // Store the unlocked value into the object's header.
duke@435:       obj->set_mark(unbiased_prototype);
duke@435:     }
duke@435:   }
duke@435: 
duke@435:   return BiasedLocking::BIAS_REVOKED;
duke@435: }
duke@435: 
duke@435: 
duke@435: enum HeuristicsResult {
duke@435:   HR_NOT_BIASED    = 1,
duke@435:   HR_SINGLE_REVOKE = 2,
duke@435:   HR_BULK_REBIAS   = 3,
duke@435:   HR_BULK_REVOKE   = 4
duke@435: };
duke@435: 
duke@435: 
duke@435: static HeuristicsResult update_heuristics(oop o, bool allow_rebias) {
duke@435:   markOop mark = o->mark();
duke@435:   if (!mark->has_bias_pattern()) {
duke@435:     return HR_NOT_BIASED;
duke@435:   }
duke@435: 
duke@435:   // Heuristics to attempt to throttle the number of revocations.
duke@435:   // Stages:
duke@435:   // 1. Revoke the biases of all objects in the heap of this type,
duke@435:   //    but allow rebiasing of those objects if unlocked.
duke@435:   // 2. Revoke the biases of all objects in the heap of this type
duke@435:   //    and don't allow rebiasing of these objects. Disable
duke@435:   //    allocation of objects of that type with the bias bit set.
duke@435:   Klass* k = o->blueprint();
duke@435:   jlong cur_time = os::javaTimeMillis();
duke@435:   jlong last_bulk_revocation_time = k->last_biased_lock_bulk_revocation_time();
duke@435:   int revocation_count = k->biased_lock_revocation_count();
duke@435:   if ((revocation_count >= BiasedLockingBulkRebiasThreshold) &&
duke@435:       (revocation_count <  BiasedLockingBulkRevokeThreshold) &&
duke@435:       (last_bulk_revocation_time != 0) &&
duke@435:       (cur_time - last_bulk_revocation_time >= BiasedLockingDecayTime)) {
duke@435:     // This is the first revocation we've seen in a while of an
duke@435:     // object of this type since the last time we performed a bulk
duke@435:     // rebiasing operation. The application is allocating objects in
duke@435:     // bulk which are biased toward a thread and then handing them
duke@435:     // off to another thread. We can cope with this allocation
duke@435:     // pattern via the bulk rebiasing mechanism so we reset the
duke@435:     // klass's revocation count rather than allow it to increase
duke@435:     // monotonically. If we see the need to perform another bulk
duke@435:     // rebias operation later, we will, and if subsequently we see
duke@435:     // many more revocation operations in a short period of time we
duke@435:     // will completely disable biasing for this type.
duke@435:     k->set_biased_lock_revocation_count(0);
duke@435:     revocation_count = 0;
duke@435:   }
duke@435: 
duke@435:   // Make revocation count saturate just beyond BiasedLockingBulkRevokeThreshold
duke@435:   if (revocation_count <= BiasedLockingBulkRevokeThreshold) {
duke@435:     revocation_count = k->atomic_incr_biased_lock_revocation_count();
duke@435:   }
duke@435: 
duke@435:   if (revocation_count == BiasedLockingBulkRevokeThreshold) {
duke@435:     return HR_BULK_REVOKE;
duke@435:   }
duke@435: 
duke@435:   if (revocation_count == BiasedLockingBulkRebiasThreshold) {
duke@435:     return HR_BULK_REBIAS;
duke@435:   }
duke@435: 
duke@435:   return HR_SINGLE_REVOKE;
duke@435: }
duke@435: 
duke@435: 
duke@435: static BiasedLocking::Condition bulk_revoke_or_rebias_at_safepoint(oop o,
duke@435:                                                                    bool bulk_rebias,
duke@435:                                                                    bool attempt_rebias_of_object,
duke@435:                                                                    JavaThread* requesting_thread) {
duke@435:   assert(SafepointSynchronize::is_at_safepoint(), "must be done at safepoint");
duke@435: 
duke@435:   if (TraceBiasedLocking) {
duke@435:     tty->print_cr("* Beginning bulk revocation (kind == %s) because of object "
duke@435:                   INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s",
duke@435:                   (bulk_rebias ? "rebias" : "revoke"),
duke@435:                   (intptr_t) o, (intptr_t) o->mark(), Klass::cast(o->klass())->external_name());
duke@435:   }
duke@435: 
duke@435:   jlong cur_time = os::javaTimeMillis();
duke@435:   o->blueprint()->set_last_biased_lock_bulk_revocation_time(cur_time);
duke@435: 
duke@435: 
duke@435:   klassOop k_o = o->klass();
duke@435:   Klass* klass = Klass::cast(k_o);
duke@435: 
duke@435:   if (bulk_rebias) {
duke@435:     // Use the epoch in the klass of the object to implicitly revoke
duke@435:     // all biases of objects of this data type and force them to be
duke@435:     // reacquired. However, we also need to walk the stacks of all
duke@435:     // threads and update the headers of lightweight locked objects
duke@435:     // with biases to have the current epoch.
duke@435: 
duke@435:     // If the prototype header doesn't have the bias pattern, don't
duke@435:     // try to update the epoch -- assume another VM operation came in
duke@435:     // and reset the header to the unbiased state, which will
duke@435:     // implicitly cause all existing biases to be revoked
duke@435:     if (klass->prototype_header()->has_bias_pattern()) {
duke@435:       int prev_epoch = klass->prototype_header()->bias_epoch();
duke@435:       klass->set_prototype_header(klass->prototype_header()->incr_bias_epoch());
duke@435:       int cur_epoch = klass->prototype_header()->bias_epoch();
duke@435: 
duke@435:       // Now walk all threads' stacks and adjust epochs of any biased
duke@435:       // and locked objects of this data type we encounter
duke@435:       for (JavaThread* thr = Threads::first(); thr != NULL; thr = thr->next()) {
duke@435:         GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr);
duke@435:         for (int i = 0; i < cached_monitor_info->length(); i++) {
duke@435:           MonitorInfo* mon_info = cached_monitor_info->at(i);
duke@435:           oop owner = mon_info->owner();
duke@435:           markOop mark = owner->mark();
duke@435:           if ((owner->klass() == k_o) && mark->has_bias_pattern()) {
duke@435:             // We might have encountered this object already in the case of recursive locking
duke@435:             assert(mark->bias_epoch() == prev_epoch || mark->bias_epoch() == cur_epoch, "error in bias epoch adjustment");
duke@435:             owner->set_mark(mark->set_bias_epoch(cur_epoch));
duke@435:           }
duke@435:         }
duke@435:       }
duke@435:     }
duke@435: 
duke@435:     // At this point we're done. All we have to do is potentially
duke@435:     // adjust the header of the given object to revoke its bias.
duke@435:     revoke_bias(o, attempt_rebias_of_object && klass->prototype_header()->has_bias_pattern(), true, requesting_thread);
duke@435:   } else {
duke@435:     if (TraceBiasedLocking) {
duke@435:       ResourceMark rm;
duke@435:       tty->print_cr("* Disabling biased locking for type %s", klass->external_name());
duke@435:     }
duke@435: 
duke@435:     // Disable biased locking for this data type. Not only will this
duke@435:     // cause future instances to not be biased, but existing biased
duke@435:     // instances will notice that this implicitly caused their biases
duke@435:     // to be revoked.
duke@435:     klass->set_prototype_header(markOopDesc::prototype());
duke@435: 
duke@435:     // Now walk all threads' stacks and forcibly revoke the biases of
duke@435:     // any locked and biased objects of this data type we encounter.
duke@435:     for (JavaThread* thr = Threads::first(); thr != NULL; thr = thr->next()) {
duke@435:       GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr);
duke@435:       for (int i = 0; i < cached_monitor_info->length(); i++) {
duke@435:         MonitorInfo* mon_info = cached_monitor_info->at(i);
duke@435:         oop owner = mon_info->owner();
duke@435:         markOop mark = owner->mark();
duke@435:         if ((owner->klass() == k_o) && mark->has_bias_pattern()) {
duke@435:           revoke_bias(owner, false, true, requesting_thread);
duke@435:         }
duke@435:       }
duke@435:     }
duke@435: 
duke@435:     // Must force the bias of the passed object to be forcibly revoked
duke@435:     // as well to ensure guarantees to callers
duke@435:     revoke_bias(o, false, true, requesting_thread);
duke@435:   }
duke@435: 
duke@435:   if (TraceBiasedLocking) {
duke@435:     tty->print_cr("* Ending bulk revocation");
duke@435:   }
duke@435: 
duke@435:   BiasedLocking::Condition status_code = BiasedLocking::BIAS_REVOKED;
duke@435: 
duke@435:   if (attempt_rebias_of_object &&
duke@435:       o->mark()->has_bias_pattern() &&
duke@435:       klass->prototype_header()->has_bias_pattern()) {
duke@435:     markOop new_mark = markOopDesc::encode(requesting_thread, o->mark()->age(),
duke@435:                                            klass->prototype_header()->bias_epoch());
duke@435:     o->set_mark(new_mark);
duke@435:     status_code = BiasedLocking::BIAS_REVOKED_AND_REBIASED;
duke@435:     if (TraceBiasedLocking) {
duke@435:       tty->print_cr("  Rebiased object toward thread " INTPTR_FORMAT, (intptr_t) requesting_thread);
duke@435:     }
duke@435:   }
duke@435: 
duke@435:   assert(!o->mark()->has_bias_pattern() ||
duke@435:          (attempt_rebias_of_object && (o->mark()->biased_locker() == requesting_thread)),
duke@435:          "bug in bulk bias revocation");
duke@435: 
duke@435:   return status_code;
duke@435: }
duke@435: 
duke@435: 
duke@435: static void clean_up_cached_monitor_info() {
duke@435:   // Walk the thread list clearing out the cached monitors
duke@435:   for (JavaThread* thr = Threads::first(); thr != NULL; thr = thr->next()) {
duke@435:     thr->set_cached_monitor_info(NULL);
duke@435:   }
duke@435: }
duke@435: 
duke@435: 
duke@435: class VM_RevokeBias : public VM_Operation {
duke@435: protected:
duke@435:   Handle* _obj;
duke@435:   GrowableArray<Handle>* _objs;
duke@435:   JavaThread* _requesting_thread;
duke@435:   BiasedLocking::Condition _status_code;
duke@435: 
duke@435: public:
duke@435:   VM_RevokeBias(Handle* obj, JavaThread* requesting_thread)
duke@435:     : _obj(obj)
duke@435:     , _objs(NULL)
duke@435:     , _requesting_thread(requesting_thread)
duke@435:     , _status_code(BiasedLocking::NOT_BIASED) {}
duke@435: 
duke@435:   VM_RevokeBias(GrowableArray<Handle>* objs, JavaThread* requesting_thread)
duke@435:     : _obj(NULL)
duke@435:     , _objs(objs)
duke@435:     , _requesting_thread(requesting_thread)
duke@435:     , _status_code(BiasedLocking::NOT_BIASED) {}
duke@435: 
duke@435:   virtual VMOp_Type type() const { return VMOp_RevokeBias; }
duke@435: 
duke@435:   virtual bool doit_prologue() {
duke@435:     // Verify that there is actual work to do since the callers just
duke@435:     // give us locked object(s). If we don't find any biased objects
duke@435:     // there is nothing to do and we avoid a safepoint.
duke@435:     if (_obj != NULL) {
duke@435:       markOop mark = (*_obj)()->mark();
duke@435:       if (mark->has_bias_pattern()) {
duke@435:         return true;
duke@435:       }
duke@435:     } else {
duke@435:       for ( int i = 0 ; i < _objs->length(); i++ ) {
duke@435:         markOop mark = (_objs->at(i))()->mark();
duke@435:         if (mark->has_bias_pattern()) {
duke@435:           return true;
duke@435:         }
duke@435:       }
duke@435:     }
duke@435:     return false;
duke@435:   }
duke@435: 
duke@435:   virtual void doit() {
duke@435:     if (_obj != NULL) {
duke@435:       if (TraceBiasedLocking) {
duke@435:         tty->print_cr("Revoking bias with potentially per-thread safepoint:");
duke@435:       }
duke@435:       _status_code = revoke_bias((*_obj)(), false, false, _requesting_thread);
duke@435:       clean_up_cached_monitor_info();
duke@435:       return;
duke@435:     } else {
duke@435:       if (TraceBiasedLocking) {
duke@435:         tty->print_cr("Revoking bias with global safepoint:");
duke@435:       }
duke@435:       BiasedLocking::revoke_at_safepoint(_objs);
duke@435:     }
duke@435:   }
duke@435: 
duke@435:   BiasedLocking::Condition status_code() const {
duke@435:     return _status_code;
duke@435:   }
duke@435: };
duke@435: 
duke@435: 
duke@435: class VM_BulkRevokeBias : public VM_RevokeBias {
duke@435: private:
duke@435:   bool _bulk_rebias;
duke@435:   bool _attempt_rebias_of_object;
duke@435: 
duke@435: public:
duke@435:   VM_BulkRevokeBias(Handle* obj, JavaThread* requesting_thread,
duke@435:                     bool bulk_rebias,
duke@435:                     bool attempt_rebias_of_object)
duke@435:     : VM_RevokeBias(obj, requesting_thread)
duke@435:     , _bulk_rebias(bulk_rebias)
duke@435:     , _attempt_rebias_of_object(attempt_rebias_of_object) {}
duke@435: 
duke@435:   virtual VMOp_Type type() const { return VMOp_BulkRevokeBias; }
duke@435:   virtual bool doit_prologue()   { return true; }
duke@435: 
duke@435:   virtual void doit() {
duke@435:     _status_code = bulk_revoke_or_rebias_at_safepoint((*_obj)(), _bulk_rebias, _attempt_rebias_of_object, _requesting_thread);
duke@435:     clean_up_cached_monitor_info();
duke@435:   }
duke@435: };
duke@435: 
duke@435: 
duke@435: BiasedLocking::Condition BiasedLocking::revoke_and_rebias(Handle obj, bool attempt_rebias, TRAPS) {
duke@435:   assert(!SafepointSynchronize::is_at_safepoint(), "must not be called while at safepoint");
duke@435: 
duke@435:   // We can revoke the biases of anonymously-biased objects
duke@435:   // efficiently enough that we should not cause these revocations to
duke@435:   // update the heuristics because doing so may cause unwanted bulk
duke@435:   // revocations (which are expensive) to occur.
duke@435:   markOop mark = obj->mark();
duke@435:   if (mark->is_biased_anonymously() && !attempt_rebias) {
duke@435:     // We are probably trying to revoke the bias of this object due to
duke@435:     // an identity hash code computation. Try to revoke the bias
duke@435:     // without a safepoint. This is possible if we can successfully
duke@435:     // compare-and-exchange an unbiased header into the mark word of
duke@435:     // the object, meaning that no other thread has raced to acquire
duke@435:     // the bias of the object.
duke@435:     markOop biased_value       = mark;
duke@435:     markOop unbiased_prototype = markOopDesc::prototype()->set_age(mark->age());
duke@435:     markOop res_mark = (markOop) Atomic::cmpxchg_ptr(unbiased_prototype, obj->mark_addr(), mark);
duke@435:     if (res_mark == biased_value) {
duke@435:       return BIAS_REVOKED;
duke@435:     }
duke@435:   } else if (mark->has_bias_pattern()) {
duke@435:     Klass* k = Klass::cast(obj->klass());
duke@435:     markOop prototype_header = k->prototype_header();
duke@435:     if (!prototype_header->has_bias_pattern()) {
duke@435:       // This object has a stale bias from before the bulk revocation
duke@435:       // for this data type occurred. It's pointless to update the
duke@435:       // heuristics at this point so simply update the header with a
duke@435:       // CAS. If we fail this race, the object's bias has been revoked
duke@435:       // by another thread so we simply return and let the caller deal
duke@435:       // with it.
duke@435:       markOop biased_value       = mark;
duke@435:       markOop res_mark = (markOop) Atomic::cmpxchg_ptr(prototype_header, obj->mark_addr(), mark);
duke@435:       assert(!(*(obj->mark_addr()))->has_bias_pattern(), "even if we raced, should still be revoked");
duke@435:       return BIAS_REVOKED;
duke@435:     } else if (prototype_header->bias_epoch() != mark->bias_epoch()) {
duke@435:       // The epoch of this biasing has expired indicating that the
duke@435:       // object is effectively unbiased. Depending on whether we need
duke@435:       // to rebias or revoke the bias of this object we can do it
duke@435:       // efficiently enough with a CAS that we shouldn't update the
duke@435:       // heuristics. This is normally done in the assembly code but we
duke@435:       // can reach this point due to various points in the runtime
duke@435:       // needing to revoke biases.
duke@435:       if (attempt_rebias) {
duke@435:         assert(THREAD->is_Java_thread(), "");
duke@435:         markOop biased_value       = mark;
duke@435:         markOop rebiased_prototype = markOopDesc::encode((JavaThread*) THREAD, mark->age(), prototype_header->bias_epoch());
duke@435:         markOop res_mark = (markOop) Atomic::cmpxchg_ptr(rebiased_prototype, obj->mark_addr(), mark);
duke@435:         if (res_mark == biased_value) {
duke@435:           return BIAS_REVOKED_AND_REBIASED;
duke@435:         }
duke@435:       } else {
duke@435:         markOop biased_value       = mark;
duke@435:         markOop unbiased_prototype = markOopDesc::prototype()->set_age(mark->age());
duke@435:         markOop res_mark = (markOop) Atomic::cmpxchg_ptr(unbiased_prototype, obj->mark_addr(), mark);
duke@435:         if (res_mark == biased_value) {
duke@435:           return BIAS_REVOKED;
duke@435:         }
duke@435:       }
duke@435:     }
duke@435:   }
duke@435: 
duke@435:   HeuristicsResult heuristics = update_heuristics(obj(), attempt_rebias);
duke@435:   if (heuristics == HR_NOT_BIASED) {
duke@435:     return NOT_BIASED;
duke@435:   } else if (heuristics == HR_SINGLE_REVOKE) {
duke@435:     if (mark->biased_locker() == THREAD) {
duke@435:       // A thread is trying to revoke the bias of an object biased
duke@435:       // toward it, again likely due to an identity hash code
duke@435:       // computation. We can again avoid a safepoint in this case
duke@435:       // since we are only going to walk our own stack. There are no
duke@435:       // races with revocations occurring in other threads because we
duke@435:       // reach no safepoints in the revocation path.
duke@435:       ResourceMark rm;
duke@435:       if (TraceBiasedLocking) {
duke@435:         tty->print_cr("Revoking bias by walking my own stack:");
duke@435:       }
duke@435:       BiasedLocking::Condition cond = revoke_bias(obj(), false, false, (JavaThread*) THREAD);
duke@435:       ((JavaThread*) THREAD)->set_cached_monitor_info(NULL);
duke@435:       assert(cond == BIAS_REVOKED, "why not?");
duke@435:       return cond;
duke@435:     } else {
duke@435:       VM_RevokeBias revoke(&obj, (JavaThread*) THREAD);
duke@435:       VMThread::execute(&revoke);
duke@435:       return revoke.status_code();
duke@435:     }
duke@435:   }
duke@435: 
duke@435:   assert((heuristics == HR_BULK_REVOKE) ||
duke@435:          (heuristics == HR_BULK_REBIAS), "?");
duke@435:   VM_BulkRevokeBias bulk_revoke(&obj, (JavaThread*) THREAD,
duke@435:                                 (heuristics == HR_BULK_REBIAS),
duke@435:                                 attempt_rebias);
duke@435:   VMThread::execute(&bulk_revoke);
duke@435:   return bulk_revoke.status_code();
duke@435: }
duke@435: 
duke@435: 
duke@435: void BiasedLocking::revoke(GrowableArray<Handle>* objs) {
duke@435:   assert(!SafepointSynchronize::is_at_safepoint(), "must not be called while at safepoint");
duke@435:   if (objs->length() == 0) {
duke@435:     return;
duke@435:   }
duke@435:   VM_RevokeBias revoke(objs, JavaThread::current());
duke@435:   VMThread::execute(&revoke);
duke@435: }
duke@435: 
duke@435: 
duke@435: void BiasedLocking::revoke_at_safepoint(Handle h_obj) {
duke@435:   assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint");
duke@435:   oop obj = h_obj();
duke@435:   HeuristicsResult heuristics = update_heuristics(obj, false);
duke@435:   if (heuristics == HR_SINGLE_REVOKE) {
duke@435:     revoke_bias(obj, false, false, NULL);
duke@435:   } else if ((heuristics == HR_BULK_REBIAS) ||
duke@435:              (heuristics == HR_BULK_REVOKE)) {
duke@435:     bulk_revoke_or_rebias_at_safepoint(obj, (heuristics == HR_BULK_REBIAS), false, NULL);
duke@435:   }
duke@435:   clean_up_cached_monitor_info();
duke@435: }
duke@435: 
duke@435: 
duke@435: void BiasedLocking::revoke_at_safepoint(GrowableArray<Handle>* objs) {
duke@435:   assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint");
duke@435:   int len = objs->length();
duke@435:   for (int i = 0; i < len; i++) {
duke@435:     oop obj = (objs->at(i))();
duke@435:     HeuristicsResult heuristics = update_heuristics(obj, false);
duke@435:     if (heuristics == HR_SINGLE_REVOKE) {
duke@435:       revoke_bias(obj, false, false, NULL);
duke@435:     } else if ((heuristics == HR_BULK_REBIAS) ||
duke@435:                (heuristics == HR_BULK_REVOKE)) {
duke@435:       bulk_revoke_or_rebias_at_safepoint(obj, (heuristics == HR_BULK_REBIAS), false, NULL);
duke@435:     }
duke@435:   }
duke@435:   clean_up_cached_monitor_info();
duke@435: }
duke@435: 
duke@435: 
duke@435: void BiasedLocking::preserve_marks() {
duke@435:   if (!UseBiasedLocking)
duke@435:     return;
duke@435: 
duke@435:   assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint");
duke@435: 
duke@435:   assert(_preserved_oop_stack  == NULL, "double initialization");
duke@435:   assert(_preserved_mark_stack == NULL, "double initialization");
duke@435: 
duke@435:   // In order to reduce the number of mark words preserved during GC
duke@435:   // due to the presence of biased locking, we reinitialize most mark
duke@435:   // words to the class's prototype during GC -- even those which have
duke@435:   // a currently valid bias owner. One important situation where we
duke@435:   // must not clobber a bias is when a biased object is currently
duke@435:   // locked. To handle this case we iterate over the currently-locked
duke@435:   // monitors in a prepass and, if they are biased, preserve their
duke@435:   // mark words here. This should be a relatively small set of objects
duke@435:   // especially compared to the number of objects in the heap.
duke@435:   _preserved_mark_stack = new (ResourceObj::C_HEAP) GrowableArray<markOop>(10, true);
duke@435:   _preserved_oop_stack = new (ResourceObj::C_HEAP) GrowableArray<Handle>(10, true);
duke@435: 
duke@435:   ResourceMark rm;
duke@435:   Thread* cur = Thread::current();
duke@435:   for (JavaThread* thread = Threads::first(); thread != NULL; thread = thread->next()) {
duke@435:     if (thread->has_last_Java_frame()) {
duke@435:       RegisterMap rm(thread);
duke@435:       for (javaVFrame* vf = thread->last_java_vframe(&rm); vf != NULL; vf = vf->java_sender()) {
duke@435:         GrowableArray<MonitorInfo*> *monitors = vf->monitors();
duke@435:         if (monitors != NULL) {
duke@435:           int len = monitors->length();
duke@435:           // Walk monitors youngest to oldest
duke@435:           for (int i = len - 1; i >= 0; i--) {
duke@435:             MonitorInfo* mon_info = monitors->at(i);
duke@435:             oop owner = mon_info->owner();
duke@435:             if (owner != NULL) {
duke@435:               markOop mark = owner->mark();
duke@435:               if (mark->has_bias_pattern()) {
duke@435:                 _preserved_oop_stack->push(Handle(cur, owner));
duke@435:                 _preserved_mark_stack->push(mark);
duke@435:               }
duke@435:             }
duke@435:           }
duke@435:         }
duke@435:       }
duke@435:     }
duke@435:   }
duke@435: }
duke@435: 
duke@435: 
duke@435: void BiasedLocking::restore_marks() {
duke@435:   if (!UseBiasedLocking)
duke@435:     return;
duke@435: 
duke@435:   assert(_preserved_oop_stack  != NULL, "double free");
duke@435:   assert(_preserved_mark_stack != NULL, "double free");
duke@435: 
duke@435:   int len = _preserved_oop_stack->length();
duke@435:   for (int i = 0; i < len; i++) {
duke@435:     Handle owner = _preserved_oop_stack->at(i);
duke@435:     markOop mark = _preserved_mark_stack->at(i);
duke@435:     owner->set_mark(mark);
duke@435:   }
duke@435: 
duke@435:   delete _preserved_oop_stack;
duke@435:   _preserved_oop_stack = NULL;
duke@435:   delete _preserved_mark_stack;
duke@435:   _preserved_mark_stack = NULL;
duke@435: }
duke@435: 
duke@435: 
duke@435: int* BiasedLocking::total_entry_count_addr()                   { return _counters.total_entry_count_addr(); }
duke@435: int* BiasedLocking::biased_lock_entry_count_addr()             { return _counters.biased_lock_entry_count_addr(); }
duke@435: int* BiasedLocking::anonymously_biased_lock_entry_count_addr() { return _counters.anonymously_biased_lock_entry_count_addr(); }
duke@435: int* BiasedLocking::rebiased_lock_entry_count_addr()           { return _counters.rebiased_lock_entry_count_addr(); }
duke@435: int* BiasedLocking::revoked_lock_entry_count_addr()            { return _counters.revoked_lock_entry_count_addr(); }
duke@435: int* BiasedLocking::fast_path_entry_count_addr()               { return _counters.fast_path_entry_count_addr(); }
duke@435: int* BiasedLocking::slow_path_entry_count_addr()               { return _counters.slow_path_entry_count_addr(); }
duke@435: 
duke@435: 
duke@435: // BiasedLockingCounters
duke@435: 
duke@435: int BiasedLockingCounters::slow_path_entry_count() {
duke@435:   if (_slow_path_entry_count != 0) {
duke@435:     return _slow_path_entry_count;
duke@435:   }
duke@435:   int sum = _biased_lock_entry_count   + _anonymously_biased_lock_entry_count +
duke@435:             _rebiased_lock_entry_count + _revoked_lock_entry_count +
duke@435:             _fast_path_entry_count;
duke@435: 
duke@435:   return _total_entry_count - sum;
duke@435: }
duke@435: 
duke@435: void BiasedLockingCounters::print_on(outputStream* st) {
duke@435:   tty->print_cr("# total entries: %d", _total_entry_count);
duke@435:   tty->print_cr("# biased lock entries: %d", _biased_lock_entry_count);
duke@435:   tty->print_cr("# anonymously biased lock entries: %d", _anonymously_biased_lock_entry_count);
duke@435:   tty->print_cr("# rebiased lock entries: %d", _rebiased_lock_entry_count);
duke@435:   tty->print_cr("# revoked lock entries: %d", _revoked_lock_entry_count);
duke@435:   tty->print_cr("# fast path lock entries: %d", _fast_path_entry_count);
duke@435:   tty->print_cr("# slow path lock entries: %d", slow_path_entry_count());
duke@435: }