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/*
! * Copyright (c) 1998, 2021, 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.
/*
! * Copyright (c) 1998, 2024, 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.
*/
#include "precompiled.hpp"
#include "classfile/vmSymbols.hpp"
#include "jfr/jfrEvents.hpp"
+ #include "gc/shared/suspendibleThreadSet.hpp"
#include "logging/log.hpp"
#include "logging/logStream.hpp"
#include "memory/allocation.inline.hpp"
#include "memory/padded.hpp"
#include "memory/resourceArea.hpp"
#include "memory/universe.hpp"
#include "oops/markWord.hpp"
#include "oops/oop.inline.hpp"
#include "runtime/atomic.hpp"
#include "runtime/biasedLocking.hpp"
+ #include "runtime/globals.hpp"
#include "runtime/handles.inline.hpp"
#include "runtime/handshake.hpp"
#include "runtime/interfaceSupport.inline.hpp"
+ #include "runtime/lockStack.inline.hpp"
#include "runtime/mutexLocker.hpp"
#include "runtime/objectMonitor.hpp"
#include "runtime/objectMonitor.inline.hpp"
#include "runtime/os.inline.hpp"
#include "runtime/osThread.hpp"
#include "runtime/vframe.hpp"
#include "runtime/vmThread.hpp"
#include "utilities/align.hpp"
#include "utilities/dtrace.hpp"
#include "utilities/events.hpp"
+ #include "utilities/globalDefinitions.hpp"
#include "utilities/preserveException.hpp"
void MonitorList::add(ObjectMonitor* m) {
ObjectMonitor* head;
do {
assert(current->thread_state() == _thread_in_Java, "invariant");
NoSafepointVerifier nsv;
if (obj == NULL) return false; // slow-path for invalid obj
const markWord mark = obj->mark();
! if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
! // Degenerate notify
! // stack-locked by caller so by definition the implied waitset is empty.
! return true;
}
if (mark.has_monitor()) {
ObjectMonitor* const mon = mark.monitor();
assert(mon->object() == oop(obj), "invariant");
assert(current->thread_state() == _thread_in_Java, "invariant");
NoSafepointVerifier nsv;
if (obj == NULL) return false; // slow-path for invalid obj
const markWord mark = obj->mark();
! if (LockingMode == LM_LIGHTWEIGHT) {
! if (mark.is_fast_locked() && current->lock_stack().contains(cast_to_oop(obj))) {
! // Degenerate notify
! // fast-locked by caller so by definition the implied waitset is empty.
+ return true;
+ }
+ } else if (LockingMode == LM_LEGACY) {
+ if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
+ // Degenerate notify
+ // stack-locked by caller so by definition the implied waitset is empty.
+ return true;
+ }
}
if (mark.has_monitor()) {
ObjectMonitor* const mon = mark.monitor();
assert(mon->object() == oop(obj), "invariant");
if (obj->klass()->is_value_based()) {
return false;
}
+ if (LockingMode == LM_LIGHTWEIGHT) {
+ LockStack& lock_stack = current->lock_stack();
+ if (lock_stack.is_full()) {
+ // Always go into runtime if the lock stack is full.
+ return false;
+ }
+ if (lock_stack.try_recursive_enter(obj)) {
+ // Recursive lock successful.
+ return true;
+ }
+ }
+
const markWord mark = obj->mark();
if (mark.has_monitor()) {
ObjectMonitor* const m = mark.monitor();
// An async deflation or GC can race us before we manage to make
if (owner == current) {
m->_recursions++;
return true;
}
! // This Java Monitor is inflated so obj's header will never be
! // displaced to this thread's BasicLock. Make the displaced header
! // non-NULL so this BasicLock is not seen as recursive nor as
! // being locked. We do this unconditionally so that this thread's
! // BasicLock cannot be mis-interpreted by any stack walkers. For
! // performance reasons, stack walkers generally first check for
! // Biased Locking in the object's header, the second check is for
! // stack-locking in the object's header, the third check is for
! // recursive stack-locking in the displaced header in the BasicLock,
! // and last are the inflated Java Monitor (ObjectMonitor) checks.
! lock->set_displaced_header(markWord::unused_mark());
if (owner == NULL && m->try_set_owner_from(NULL, current) == NULL) {
assert(m->_recursions == 0, "invariant");
return true;
}
if (owner == current) {
m->_recursions++;
return true;
}
! if (LockingMode != LM_LIGHTWEIGHT) {
! // This Java Monitor is inflated so obj's header will never be
! // displaced to this thread's BasicLock. Make the displaced header
! // non-NULL so this BasicLock is not seen as recursive nor as
! // being locked. We do this unconditionally so that this thread's
! // BasicLock cannot be mis-interpreted by any stack walkers. For
! // performance reasons, stack walkers generally first check for
! // Biased Locking in the object's header, the second check is for
! // stack-locking in the object's header, the third check is for
! // recursive stack-locking in the displaced header in the BasicLock,
! // and last are the inflated Java Monitor (ObjectMonitor) checks.
+ lock->set_displaced_header(markWord::unused_mark());
+ }
if (owner == NULL && m->try_set_owner_from(NULL, current) == NULL) {
assert(m->_recursions == 0, "invariant");
return true;
}
return false; // revert to slow-path
}
// Handle notifications when synchronizing on value based classes
! void ObjectSynchronizer::handle_sync_on_value_based_class(Handle obj, JavaThread* current) {
! frame last_frame = current->last_frame();
bool bcp_was_adjusted = false;
// Don't decrement bcp if it points to the frame's first instruction. This happens when
// handle_sync_on_value_based_class() is called because of a synchronized method. There
// is no actual monitorenter instruction in the byte code in this case.
if (last_frame.is_interpreted_frame() &&
return false; // revert to slow-path
}
// Handle notifications when synchronizing on value based classes
! void ObjectSynchronizer::handle_sync_on_value_based_class(Handle obj, JavaThread* locking_thread) {
! assert(locking_thread == Thread::current() || locking_thread->is_obj_deopt_suspend(), "must be");
+ frame last_frame = locking_thread->last_frame();
bool bcp_was_adjusted = false;
// Don't decrement bcp if it points to the frame's first instruction. This happens when
// handle_sync_on_value_based_class() is called because of a synchronized method. There
// is no actual monitorenter instruction in the byte code in this case.
if (last_frame.is_interpreted_frame() &&
last_frame.interpreter_frame_set_bcp(last_frame.interpreter_frame_bcp() - 1);
bcp_was_adjusted = true;
}
if (DiagnoseSyncOnValueBasedClasses == FATAL_EXIT) {
! ResourceMark rm(current);
stringStream ss;
! current->print_stack_on(&ss);
char* base = (char*)strstr(ss.base(), "at");
char* newline = (char*)strchr(ss.base(), '\n');
if (newline != NULL) {
*newline = '\0';
}
fatal("Synchronizing on object " INTPTR_FORMAT " of klass %s %s", p2i(obj()), obj->klass()->external_name(), base);
} else {
assert(DiagnoseSyncOnValueBasedClasses == LOG_WARNING, "invalid value for DiagnoseSyncOnValueBasedClasses");
! ResourceMark rm(current);
Log(valuebasedclasses) vblog;
vblog.info("Synchronizing on object " INTPTR_FORMAT " of klass %s", p2i(obj()), obj->klass()->external_name());
! if (current->has_last_Java_frame()) {
LogStream info_stream(vblog.info());
! current->print_stack_on(&info_stream);
} else {
vblog.info("Cannot find the last Java frame");
}
EventSyncOnValueBasedClass event;
last_frame.interpreter_frame_set_bcp(last_frame.interpreter_frame_bcp() - 1);
bcp_was_adjusted = true;
}
if (DiagnoseSyncOnValueBasedClasses == FATAL_EXIT) {
! ResourceMark rm;
stringStream ss;
! locking_thread->print_stack_on(&ss);
char* base = (char*)strstr(ss.base(), "at");
char* newline = (char*)strchr(ss.base(), '\n');
if (newline != NULL) {
*newline = '\0';
}
fatal("Synchronizing on object " INTPTR_FORMAT " of klass %s %s", p2i(obj()), obj->klass()->external_name(), base);
} else {
assert(DiagnoseSyncOnValueBasedClasses == LOG_WARNING, "invalid value for DiagnoseSyncOnValueBasedClasses");
! ResourceMark rm;
Log(valuebasedclasses) vblog;
vblog.info("Synchronizing on object " INTPTR_FORMAT " of klass %s", p2i(obj()), obj->klass()->external_name());
! if (locking_thread->has_last_Java_frame()) {
LogStream info_stream(vblog.info());
! locking_thread->print_stack_on(&info_stream);
} else {
vblog.info("Cannot find the last Java frame");
}
EventSyncOnValueBasedClass event;
if (bcp_was_adjusted) {
last_frame.interpreter_frame_set_bcp(last_frame.interpreter_frame_bcp() + 1);
}
}
// -----------------------------------------------------------------------------
// Monitor Enter/Exit
// The interpreter and compiler assembly code tries to lock using the fast path
// of this algorithm. Make sure to update that code if the following function is
// changed. The implementation is extremely sensitive to race condition. Be careful.
- void ObjectSynchronizer::enter(Handle obj, BasicLock* lock, JavaThread* current) {
if (obj->klass()->is_value_based()) {
! handle_sync_on_value_based_class(obj, current);
! }
! if (UseBiasedLocking) {
! BiasedLocking::revoke(current, obj);
! }
! markWord mark = obj->mark();
! assert(!mark.has_bias_pattern(), "should not see bias pattern here");
! if (mark.is_neutral()) {
! // Anticipate successful CAS -- the ST of the displaced mark must
! // be visible <= the ST performed by the CAS.
! lock->set_displaced_header(mark);
! if (mark == obj()->cas_set_mark(markWord::from_pointer(lock), mark)) {
! return;
- }
- // Fall through to inflate() ...
- } else if (mark.has_locker() &&
- current->is_lock_owned((address)mark.locker())) {
- assert(lock != mark.locker(), "must not re-lock the same lock");
- assert(lock != (BasicLock*)obj->mark().value(), "don't relock with same BasicLock");
- lock->set_displaced_header(markWord::from_pointer(NULL));
- return;
- }
! // The object header will never be displaced to this lock,
! // so it does not matter what the value is, except that it
! // must be non-zero to avoid looking like a re-entrant lock,
! // and must not look locked either.
! lock->set_displaced_header(markWord::unused_mark());
! // An async deflation can race after the inflate() call and before
! // enter() can make the ObjectMonitor busy. enter() returns false if
! // we have lost the race to async deflation and we simply try again.
! while (true) {
! ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_monitor_enter);
! if (monitor->enter(current)) {
! return;
}
}
}
void ObjectSynchronizer::exit(oop object, BasicLock* lock, JavaThread* current) {
! markWord mark = object->mark();
! // We cannot check for Biased Locking if we are racing an inflation.
! assert(mark == markWord::INFLATING() ||
! !mark.has_bias_pattern(), "should not see bias pattern here");
!
! markWord dhw = lock->displaced_header();
! if (dhw.value() == 0) {
! // If the displaced header is NULL, then this exit matches up with
- // a recursive enter. No real work to do here except for diagnostics.
- #ifndef PRODUCT
- if (mark != markWord::INFLATING()) {
- // Only do diagnostics if we are not racing an inflation. Simply
- // exiting a recursive enter of a Java Monitor that is being
- // inflated is safe; see the has_monitor() comment below.
- assert(!mark.is_neutral(), "invariant");
- assert(!mark.has_locker() ||
- current->is_lock_owned((address)mark.locker()), "invariant");
- if (mark.has_monitor()) {
- // The BasicLock's displaced_header is marked as a recursive
- // enter and we have an inflated Java Monitor (ObjectMonitor).
- // This is a special case where the Java Monitor was inflated
- // after this thread entered the stack-lock recursively. When a
- // Java Monitor is inflated, we cannot safely walk the Java
- // Monitor owner's stack and update the BasicLocks because a
- // Java Monitor can be asynchronously inflated by a thread that
- // does not own the Java Monitor.
- ObjectMonitor* m = mark.monitor();
- assert(m->object()->mark() == mark, "invariant");
- assert(m->is_entered(current), "invariant");
}
! }
#endif
! return;
! }
! if (mark == markWord::from_pointer(lock)) {
! // If the object is stack-locked by the current thread, try to
! // swing the displaced header from the BasicLock back to the mark.
! assert(dhw.is_neutral(), "invariant");
! if (object->cas_set_mark(dhw, mark) == mark) {
! return;
}
}
// We have to take the slow-path of possible inflation and then exit.
// The ObjectMonitor* can't be async deflated until ownership is
// dropped inside exit() and the ObjectMonitor* must be !is_busy().
ObjectMonitor* monitor = inflate(current, object, inflate_cause_vm_internal);
monitor->exit(current);
}
// -----------------------------------------------------------------------------
// Class Loader support to workaround deadlocks on the class loader lock objects
if (bcp_was_adjusted) {
last_frame.interpreter_frame_set_bcp(last_frame.interpreter_frame_bcp() + 1);
}
}
+ static bool useHeavyMonitors() {
+ #if defined(X86) || defined(AARCH64) || defined(PPC64) || defined(RISCV64)
+ return LockingMode == LM_MONITOR;
+ #else
+ return false;
+ #endif
+ }
+
// -----------------------------------------------------------------------------
// Monitor Enter/Exit
+
+ void ObjectSynchronizer::enter_for(Handle obj, BasicLock* lock, JavaThread* locking_thread) {
+ // When called with locking_thread != Thread::current() some mechanism must synchronize
+ // the locking_thread with respect to the current thread. Currently only used when
+ // deoptimizing and re-locking locks. See Deoptimization::relock_objects
+ assert(locking_thread == Thread::current() || locking_thread->is_obj_deopt_suspend(), "must be");
+ if (!enter_fast_impl(obj, lock, locking_thread)) {
+ // Inflated ObjectMonitor::enter_for is required
+
+ // An async deflation can race after the inflate_for() call and before
+ // enter_for() can make the ObjectMonitor busy. enter_for() returns false
+ // if we have lost the race to async deflation and we simply try again.
+ while (true) {
+ ObjectMonitor* monitor = inflate_for(locking_thread, obj(), inflate_cause_monitor_enter);
+ if (monitor->enter_for(locking_thread)) {
+ return;
+ }
+ assert(monitor->is_being_async_deflated(), "must be");
+ }
+ }
+ }
+
+ void ObjectSynchronizer::enter(Handle obj, BasicLock* lock, JavaThread* current) {
+ assert(current == Thread::current(), "must be");
+ if (!enter_fast_impl(obj, lock, current)) {
+ // Inflated ObjectMonitor::enter is required
+
+ // An async deflation can race after the inflate() call and before
+ // enter() can make the ObjectMonitor busy. enter() returns false if
+ // we have lost the race to async deflation and we simply try again.
+ while (true) {
+ ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_monitor_enter);
+ if (monitor->enter(current)) {
+ return;
+ }
+ }
+ }
+ }
+
// The interpreter and compiler assembly code tries to lock using the fast path
// of this algorithm. Make sure to update that code if the following function is
// changed. The implementation is extremely sensitive to race condition. Be careful.
+ bool ObjectSynchronizer::enter_fast_impl(Handle obj, BasicLock* lock, JavaThread* locking_thread) {
if (obj->klass()->is_value_based()) {
! handle_sync_on_value_based_class(obj, locking_thread);
! }
+
+ if (!useHeavyMonitors()) {
+ if (LockingMode == LM_LIGHTWEIGHT) {
+ // Fast-locking does not use the 'lock' argument.
+ LockStack& lock_stack = locking_thread->lock_stack();
+ if (lock_stack.is_full()) {
+ // We unconditionally make room on the lock stack by inflating
+ // the least recently locked object on the lock stack.
+
+ // About the choice to inflate least recently locked object.
+ // First we must chose to inflate a lock, either some lock on
+ // the lock-stack or the lock that is currently being entered
+ // (which may or may not be on the lock-stack).
+ // Second the best lock to inflate is a lock which is entered
+ // in a control flow where there are only a very few locks being
+ // used, as the costly part of inflated locking is inflation,
+ // not locking. But this property is entirely program dependent.
+ // Third inflating the lock currently being entered on when it
+ // is not present on the lock-stack will result in a still full
+ // lock-stack. This creates a scenario where every deeper nested
+ // monitorenter must call into the runtime.
+ // The rational here is as follows:
+ // Because we cannot (currently) figure out the second, and want
+ // to avoid the third, we inflate a lock on the lock-stack.
+ // The least recently locked lock is chosen as it is the lock
+ // with the longest critical section.
+
+ log_info(monitorinflation)("LockStack capacity exceeded, inflating.");
+ ObjectMonitor* monitor = inflate_for(locking_thread, lock_stack.bottom(), inflate_cause_vm_internal);
+ assert(monitor->owner() == Thread::current(), "must be owner=" PTR_FORMAT " current=" PTR_FORMAT " mark=" PTR_FORMAT,
+ p2i(monitor->owner()), p2i(Thread::current()), monitor->object()->mark_acquire().value());
+ assert(!lock_stack.is_full(), "must have made room here");
+ }
! markWord mark = obj()->mark_acquire();
! while (mark.is_neutral()) {
! // Retry until a lock state change has been observed. cas_set_mark() may collide with non lock bits modifications.
+ // Try to swing into 'fast-locked' state.
+ assert(!lock_stack.contains(obj()), "thread must not already hold the lock");
+ const markWord locked_mark = mark.set_fast_locked();
+ const markWord old_mark = obj()->cas_set_mark(locked_mark, mark);
+ if (old_mark == mark) {
+ // Successfully fast-locked, push object to lock-stack and return.
+ lock_stack.push(obj());
+ return true;
+ }
+ mark = old_mark;
+ }
! if (mark.is_fast_locked() && lock_stack.try_recursive_enter(obj())) {
! // Recursive lock successful.
+ return true;
+ }
! // Failed to fast lock.
! return false;
! } else if (LockingMode == LM_LEGACY) {
! if (UseBiasedLocking) {
! BiasedLocking::revoke(locking_thread, obj);
! }
! markWord mark = obj->mark();
! if (mark.is_neutral()) {
! // Anticipate successful CAS -- the ST of the displaced mark must
! // be visible <= the ST performed by the CAS.
! lock->set_displaced_header(mark);
! if (mark == obj()->cas_set_mark(markWord::from_pointer(lock), mark)) {
! return true;
! }
! } else if (mark.has_locker() &&
! locking_thread->is_lock_owned((address) mark.locker())) {
! assert(lock != mark.locker(), "must not re-lock the same lock");
! assert(lock != (BasicLock*) obj->mark().value(), "don't relock with same BasicLock");
+ lock->set_displaced_header(markWord::from_pointer(NULL));
+ return true;
+ }
+
+ // The object header will never be displaced to this lock,
+ // so it does not matter what the value is, except that it
+ // must be non-zero to avoid looking like a re-entrant lock,
+ // and must not look locked either.
+ lock->set_displaced_header(markWord::unused_mark());
+
+ // Failed to fast lock.
+ return false;
}
}
+
+ return false;
}
void ObjectSynchronizer::exit(oop object, BasicLock* lock, JavaThread* current) {
! if (!useHeavyMonitors()) {
! markWord mark = object->mark();
! if (LockingMode == LM_LIGHTWEIGHT) {
! // Fast-locking does not use the 'lock' argument.
! LockStack& lock_stack = current->lock_stack();
! if (mark.is_fast_locked() && lock_stack.try_recursive_exit(object)) {
! // Recursively unlocked.
! return;
}
!
+ if (mark.is_fast_locked() && lock_stack.is_recursive(object)) {
+ // This lock is recursive but is not at the top of the lock stack so we're
+ // doing an unbalanced exit. We have to fall thru to inflation below and
+ // let ObjectMonitor::exit() do the unlock.
+ } else {
+ while (mark.is_fast_locked()) {
+ // Retry until a lock state change has been observed. cas_set_mark() may collide with non lock bits modifications.
+ const markWord unlocked_mark = mark.set_unlocked();
+ const markWord old_mark = object->cas_set_mark(unlocked_mark, mark);
+ if (old_mark == mark) {
+ size_t recursions = lock_stack.remove(object) - 1;
+ assert(recursions == 0, "must not be recursive here");
+ return;
+ }
+ mark = old_mark;
+ }
+ }
+ } else if (LockingMode == LM_LEGACY) {
+ markWord dhw = lock->displaced_header();
+ if (dhw.value() == 0) {
+ // If the displaced header is NULL, then this exit matches up with
+ // a recursive enter. No real work to do here except for diagnostics.
+ #ifndef PRODUCT
+ if (mark != markWord::INFLATING()) {
+ // Only do diagnostics if we are not racing an inflation. Simply
+ // exiting a recursive enter of a Java Monitor that is being
+ // inflated is safe; see the has_monitor() comment below.
+ assert(!mark.is_neutral(), "invariant");
+ assert(!mark.has_locker() ||
+ current->is_lock_owned((address)mark.locker()), "invariant");
+ if (mark.has_monitor()) {
+ // The BasicLock's displaced_header is marked as a recursive
+ // enter and we have an inflated Java Monitor (ObjectMonitor).
+ // This is a special case where the Java Monitor was inflated
+ // after this thread entered the stack-lock recursively. When a
+ // Java Monitor is inflated, we cannot safely walk the Java
+ // Monitor owner's stack and update the BasicLocks because a
+ // Java Monitor can be asynchronously inflated by a thread that
+ // does not own the Java Monitor.
+ ObjectMonitor* m = mark.monitor();
+ assert(m->object()->mark() == mark, "invariant");
+ assert(m->is_entered(current), "invariant");
+ }
+ }
#endif
! return;
! }
! if (mark == markWord::from_pointer(lock)) {
! // If the object is stack-locked by the current thread, try to
! // swing the displaced header from the BasicLock back to the mark.
! assert(dhw.is_neutral(), "invariant");
! if (object->cas_set_mark(dhw, mark) == mark) {
! return;
+ }
+ }
}
}
// We have to take the slow-path of possible inflation and then exit.
// The ObjectMonitor* can't be async deflated until ownership is
// dropped inside exit() and the ObjectMonitor* must be !is_busy().
ObjectMonitor* monitor = inflate(current, object, inflate_cause_vm_internal);
+ assert(!monitor->is_owner_anonymous(), "must not be");
monitor->exit(current);
}
// -----------------------------------------------------------------------------
// Class Loader support to workaround deadlocks on the class loader lock objects
BiasedLocking::revoke(current, obj);
assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
}
markWord mark = obj->mark();
! if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
! // Not inflated so there can't be any waiters to notify.
! return;
}
// The ObjectMonitor* can't be async deflated until ownership is
// dropped by the calling thread.
ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_notify);
monitor->notify(CHECK);
BiasedLocking::revoke(current, obj);
assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
}
markWord mark = obj->mark();
! if (LockingMode == LM_LIGHTWEIGHT) {
! if ((mark.is_fast_locked() && current->lock_stack().contains(obj()))) {
! // Not inflated so there can't be any waiters to notify.
+ return;
+ }
+ } else if (LockingMode == LM_LEGACY) {
+ if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
+ // Not inflated so there can't be any waiters to notify.
+ return;
+ }
}
// The ObjectMonitor* can't be async deflated until ownership is
// dropped by the calling thread.
ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_notify);
monitor->notify(CHECK);
BiasedLocking::revoke(current, obj);
assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
}
markWord mark = obj->mark();
! if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
! // Not inflated so there can't be any waiters to notify.
! return;
}
// The ObjectMonitor* can't be async deflated until ownership is
// dropped by the calling thread.
ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_notify);
monitor->notifyAll(CHECK);
BiasedLocking::revoke(current, obj);
assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
}
markWord mark = obj->mark();
! if (LockingMode == LM_LIGHTWEIGHT) {
! if ((mark.is_fast_locked() && current->lock_stack().contains(obj()))) {
! // Not inflated so there can't be any waiters to notify.
+ return;
+ }
+ } else if (LockingMode == LM_LEGACY) {
+ if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
+ // Not inflated so there can't be any waiters to notify.
+ return;
+ }
}
// The ObjectMonitor* can't be async deflated until ownership is
// dropped by the calling thread.
ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_notify);
monitor->notifyAll(CHECK);
static SharedGlobals GVars;
static markWord read_stable_mark(oop obj) {
markWord mark = obj->mark_acquire();
! if (!mark.is_being_inflated()) {
return mark; // normal fast-path return
}
int its = 0;
for (;;) {
static SharedGlobals GVars;
static markWord read_stable_mark(oop obj) {
markWord mark = obj->mark_acquire();
! if (!mark.is_being_inflated() || LockingMode == LM_LIGHTWEIGHT) {
+ // New lightweight locking does not use the markWord::INFLATING() protocol.
return mark; // normal fast-path return
}
int its = 0;
for (;;) {
v = (v ^ (v >> 19)) ^ (t ^ (t >> 8));
current->_hashStateW = v;
value = v;
}
! value &= markWord::hash_mask;
if (value == 0) value = 0xBAD;
assert(value != markWord::no_hash, "invariant");
return value;
}
v = (v ^ (v >> 19)) ^ (t ^ (t >> 8));
current->_hashStateW = v;
value = v;
}
! value &= UseCompactObjectHeaders ? markWord::hash_mask_compact : markWord::hash_mask;
if (value == 0) value = 0xBAD;
assert(value != markWord::no_hash, "invariant");
return value;
}
markWord mark = read_stable_mark(obj);
// object should remain ineligible for biased locking
assert(!mark.has_bias_pattern(), "invariant");
! if (mark.is_neutral()) { // if this is a normal header
hash = mark.hash();
if (hash != 0) { // if it has a hash, just return it
return hash;
}
hash = get_next_hash(current, obj); // get a new hash
markWord mark = read_stable_mark(obj);
// object should remain ineligible for biased locking
assert(!mark.has_bias_pattern(), "invariant");
! if (mark.is_neutral() || (LockingMode == LM_LIGHTWEIGHT && mark.is_fast_locked())) {
hash = mark.hash();
if (hash != 0) { // if it has a hash, just return it
return hash;
}
hash = get_next_hash(current, obj); // get a new hash
// try to install the hash
test = obj->cas_set_mark(temp, mark);
if (test == mark) { // if the hash was installed, return it
return hash;
}
+ if (LockingMode == LM_LIGHTWEIGHT) {
+ // CAS failed, retry
+ continue;
+ }
// Failed to install the hash. It could be that another thread
// installed the hash just before our attempt or inflation has
// occurred or... so we fall thru to inflate the monitor for
// stability and then install the hash.
} else if (mark.has_monitor()) {
}
return hash;
}
// Fall thru so we only have one place that installs the hash in
// the ObjectMonitor.
! } else if (current->is_lock_owned((address)mark.locker())) {
// This is a stack lock owned by the calling thread so fetch the
// displaced markWord from the BasicLock on the stack.
temp = mark.displaced_mark_helper();
assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
hash = temp.hash();
}
return hash;
}
// Fall thru so we only have one place that installs the hash in
// the ObjectMonitor.
! } else if (LockingMode == LM_LEGACY && mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
// This is a stack lock owned by the calling thread so fetch the
// displaced markWord from the BasicLock on the stack.
temp = mark.displaced_mark_helper();
assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
hash = temp.hash();
assert(current == JavaThread::current(), "Can only be called on current thread");
oop obj = h_obj();
markWord mark = read_stable_mark(obj);
! // Uncontended case, header points to stack
! if (mark.has_locker()) {
return current->is_lock_owned((address)mark.locker());
}
// Contended case, header points to ObjectMonitor (tagged pointer)
if (mark.has_monitor()) {
// The first stage of async deflation does not affect any field
// used by this comparison so the ObjectMonitor* is usable here.
ObjectMonitor* monitor = mark.monitor();
assert(current == JavaThread::current(), "Can only be called on current thread");
oop obj = h_obj();
markWord mark = read_stable_mark(obj);
! if (LockingMode == LM_LEGACY && mark.has_locker()) {
! // stack-locked case, header points into owner's stack
return current->is_lock_owned((address)mark.locker());
}
+
+ if (LockingMode == LM_LIGHTWEIGHT && mark.is_fast_locked()) {
+ // fast-locking case, see if lock is in current's lock stack
+ return current->lock_stack().contains(h_obj());
+ }
+
// Contended case, header points to ObjectMonitor (tagged pointer)
if (mark.has_monitor()) {
// The first stage of async deflation does not affect any field
// used by this comparison so the ObjectMonitor* is usable here.
ObjectMonitor* monitor = mark.monitor();
}
assert(!h_obj->mark().has_bias_pattern(), "biases should be revoked by now");
}
oop obj = h_obj();
- address owner = NULL;
-
markWord mark = read_stable_mark(obj);
! // Uncontended case, header points to stack
! if (mark.has_locker()) {
! owner = (address) mark.locker();
}
// Contended case, header points to ObjectMonitor (tagged pointer)
! else if (mark.has_monitor()) {
// The first stage of async deflation does not affect any field
// used by this comparison so the ObjectMonitor* is usable here.
ObjectMonitor* monitor = mark.monitor();
assert(monitor != NULL, "monitor should be non-null");
! owner = (address) monitor->owner();
! }
-
- if (owner != NULL) {
- // owning_thread_from_monitor_owner() may also return NULL here
- return Threads::owning_thread_from_monitor_owner(t_list, owner);
}
// Unlocked case, header in place
// Cannot have assertion since this object may have been
// locked by another thread when reaching here.
}
assert(!h_obj->mark().has_bias_pattern(), "biases should be revoked by now");
}
oop obj = h_obj();
markWord mark = read_stable_mark(obj);
! if (LockingMode == LM_LEGACY && mark.has_locker()) {
! // stack-locked so header points into owner's stack.
! // owning_thread_from_monitor_owner() may also return null here:
+ return Threads::owning_thread_from_monitor_owner(t_list, (address) mark.locker());
+ }
+
+ if (LockingMode == LM_LIGHTWEIGHT && mark.is_fast_locked()) {
+ // fast-locked so get owner from the object.
+ // owning_thread_from_object() may also return null here:
+ return Threads::owning_thread_from_object(t_list, h_obj());
}
// Contended case, header points to ObjectMonitor (tagged pointer)
! if (mark.has_monitor()) {
// The first stage of async deflation does not affect any field
// used by this comparison so the ObjectMonitor* is usable here.
ObjectMonitor* monitor = mark.monitor();
assert(monitor != NULL, "monitor should be non-null");
! // owning_thread_from_monitor() may also return null here:
! return Threads::owning_thread_from_monitor(t_list, monitor);
}
// Unlocked case, header in place
// Cannot have assertion since this object may have been
// locked by another thread when reaching here.
return;
}
(void)inflate(Thread::current(), obj, inflate_cause_vm_internal);
}
! ObjectMonitor* ObjectSynchronizer::inflate(Thread* current, oop object,
! const InflateCause cause) {
EventJavaMonitorInflate event;
for (;;) {
const markWord mark = object->mark_acquire();
assert(!mark.has_bias_pattern(), "invariant");
// The mark can be in one of the following states:
! // * Inflated - just return
! // * Stack-locked - coerce it to inflated
// * INFLATING - busy wait for conversion to complete
// * Neutral - aggressively inflate the object.
// * BIASED - Illegal. We should never see this
// CASE: inflated
if (mark.has_monitor()) {
ObjectMonitor* inf = mark.monitor();
markWord dmw = inf->header();
assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
return inf;
}
// CASE: inflation in progress - inflating over a stack-lock.
// Some other thread is converting from stack-locked to inflated.
// Only that thread can complete inflation -- other threads must wait.
// The INFLATING value is transient.
// Currently, we spin/yield/park and poll the markword, waiting for inflation to finish.
// We could always eliminate polling by parking the thread on some auxiliary list.
! if (mark == markWord::INFLATING()) {
! read_stable_mark(object);
! continue;
}
// CASE: stack-locked
// Could be stack-locked either by this thread or by some other thread.
//
return;
}
(void)inflate(Thread::current(), obj, inflate_cause_vm_internal);
}
! ObjectMonitor* ObjectSynchronizer::inflate(Thread* current, oop obj, const InflateCause cause) {
! assert(current == Thread::current(), "must be");
+ if (LockingMode == LM_LIGHTWEIGHT && current->is_Java_thread()) {
+ return inflate_impl(current->as_Java_thread(), obj, cause);
+ }
+ return inflate_impl(nullptr, obj, cause);
+ }
+
+ ObjectMonitor* ObjectSynchronizer::inflate_for(JavaThread* thread, oop obj, const InflateCause cause) {
+ assert(thread == Thread::current() || thread->is_obj_deopt_suspend(), "must be");
+ return inflate_impl(thread, obj, cause);
+ }
+
+ ObjectMonitor* ObjectSynchronizer::inflate_impl(JavaThread* inflating_thread, oop object, const InflateCause cause) {
+ // The JavaThread* inflating_thread parameter is only used by LM_LIGHTWEIGHT and requires
+ // that the inflating_thread == Thread::current() or is suspended throughout the call by
+ // some other mechanism.
+ // Even with LM_LIGHTWEIGHT the thread might be nullptr when called from a non
+ // JavaThread. (As may still be the case from FastHashCode). However it is only
+ // important for the correctness of the LM_LIGHTWEIGHT algorithm that the thread
+ // is set when called from ObjectSynchronizer::enter from the owning thread,
+ // ObjectSynchronizer::enter_for from any thread, or ObjectSynchronizer::exit.
EventJavaMonitorInflate event;
for (;;) {
const markWord mark = object->mark_acquire();
assert(!mark.has_bias_pattern(), "invariant");
// The mark can be in one of the following states:
! // * inflated - Just return if using stack-locking.
! // If using fast-locking and the ObjectMonitor owner
+ // is anonymous and the inflating_thread owns the
+ // object lock, then we make the inflating_thread
+ // the ObjectMonitor owner and remove the lock from
+ // the inflating_thread's lock stack.
+ // * fast-locked - Coerce it to inflated from fast-locked.
+ // * stack-locked - Coerce it to inflated from stack-locked.
// * INFLATING - busy wait for conversion to complete
// * Neutral - aggressively inflate the object.
// * BIASED - Illegal. We should never see this
// CASE: inflated
if (mark.has_monitor()) {
ObjectMonitor* inf = mark.monitor();
markWord dmw = inf->header();
assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
+ if (LockingMode == LM_LIGHTWEIGHT && inf->is_owner_anonymous() &&
+ inflating_thread != nullptr && inflating_thread->lock_stack().contains(object)) {
+ inf->set_owner_from_anonymous(inflating_thread);
+ size_t removed = inflating_thread->lock_stack().remove(object);
+ inf->set_recursions(removed - 1);
+ }
return inf;
}
// CASE: inflation in progress - inflating over a stack-lock.
// Some other thread is converting from stack-locked to inflated.
// Only that thread can complete inflation -- other threads must wait.
// The INFLATING value is transient.
// Currently, we spin/yield/park and poll the markword, waiting for inflation to finish.
// We could always eliminate polling by parking the thread on some auxiliary list.
! if (LockingMode != LM_LIGHTWEIGHT) {
! // New lightweight locking does not use INFLATING.
! // CASE: inflation in progress - inflating over a stack-lock.
+ // Some other thread is converting from stack-locked to inflated.
+ // Only that thread can complete inflation -- other threads must wait.
+ // The INFLATING value is transient.
+ // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish.
+ // We could always eliminate polling by parking the thread on some auxiliary list.
+ if (mark == markWord::INFLATING()) {
+ read_stable_mark(object);
+ continue;
+ }
+ }
+
+ // CASE: fast-locked
+ // Could be fast-locked either by the inflating_thread or by some other thread.
+ //
+ // Note that we allocate the ObjectMonitor speculatively, _before_
+ // attempting to set the object's mark to the new ObjectMonitor. If
+ // the inflating_thread owns the monitor, then we set the ObjectMonitor's
+ // owner to the inflating_thread. Otherwise, we set the ObjectMonitor's owner
+ // to anonymous. If we lose the race to set the object's mark to the
+ // new ObjectMonitor, then we just delete it and loop around again.
+ //
+ LogStreamHandle(Trace, monitorinflation) lsh;
+ if (LockingMode == LM_LIGHTWEIGHT && mark.is_fast_locked()) {
+ ObjectMonitor* monitor = new ObjectMonitor(object);
+ monitor->set_header(mark.set_unlocked());
+ bool own = inflating_thread != nullptr && inflating_thread->lock_stack().contains(object);
+ if (own) {
+ // Owned by us.
+ monitor->set_owner_from(NULL, inflating_thread);
+ } else {
+ // Owned by somebody else.
+ monitor->set_owner_anonymous();
+ }
+ markWord monitor_mark = markWord::encode(monitor);
+ markWord old_mark = object->cas_set_mark(monitor_mark, mark);
+ if (old_mark == mark) {
+ // Success! Return inflated monitor.
+ if (own) {
+ size_t removed = inflating_thread->lock_stack().remove(object);
+ monitor->set_recursions(removed - 1);
+ }
+ // Once the ObjectMonitor is configured and object is associated
+ // with the ObjectMonitor, it is safe to allow async deflation:
+ _in_use_list.add(monitor);
+
+ // Hopefully the performance counters are allocated on distinct
+ // cache lines to avoid false sharing on MP systems ...
+ OM_PERFDATA_OP(Inflations, inc());
+ if (log_is_enabled(Trace, monitorinflation)) {
+ ResourceMark rm;
+ lsh.print_cr("inflate(has_locker): object=" INTPTR_FORMAT ", mark="
+ INTPTR_FORMAT ", type='%s'", p2i(object),
+ object->mark().value(), object->klass()->external_name());
+ }
+ if (event.should_commit()) {
+ post_monitor_inflate_event(&event, object, cause);
+ }
+ return monitor;
+ } else {
+ delete monitor;
+ continue; // Interference -- just retry
+ }
}
// CASE: stack-locked
// Could be stack-locked either by this thread or by some other thread.
//
// allocated the ObjectMonitor, and then finally STed the address of the
// ObjectMonitor into the mark. This was correct, but artificially lengthened
// the interval in which INFLATING appeared in the mark, thus increasing
// the odds of inflation contention.
! LogStreamHandle(Trace, monitorinflation) lsh;
!
- if (mark.has_locker()) {
ObjectMonitor* m = new ObjectMonitor(object);
// Optimistically prepare the ObjectMonitor - anticipate successful CAS
// We do this before the CAS in order to minimize the length of time
// in which INFLATING appears in the mark.
// allocated the ObjectMonitor, and then finally STed the address of the
// ObjectMonitor into the mark. This was correct, but artificially lengthened
// the interval in which INFLATING appeared in the mark, thus increasing
// the odds of inflation contention.
! if (LockingMode == LM_LEGACY && mark.has_locker()) {
! assert(LockingMode != LM_LIGHTWEIGHT, "cannot happen with new lightweight locking");
ObjectMonitor* m = new ObjectMonitor(object);
// Optimistically prepare the ObjectMonitor - anticipate successful CAS
// We do this before the CAS in order to minimize the length of time
// in which INFLATING appears in the mark.
// Hopefully the performance counters are allocated on distinct cache lines
// to avoid false sharing on MP systems ...
OM_PERFDATA_OP(Inflations, inc());
if (log_is_enabled(Trace, monitorinflation)) {
! ResourceMark rm(current);
lsh.print_cr("inflate(has_locker): object=" INTPTR_FORMAT ", mark="
INTPTR_FORMAT ", type='%s'", p2i(object),
object->mark().value(), object->klass()->external_name());
}
if (event.should_commit()) {
// Hopefully the performance counters are allocated on distinct cache lines
// to avoid false sharing on MP systems ...
OM_PERFDATA_OP(Inflations, inc());
if (log_is_enabled(Trace, monitorinflation)) {
! ResourceMark rm;
lsh.print_cr("inflate(has_locker): object=" INTPTR_FORMAT ", mark="
INTPTR_FORMAT ", type='%s'", p2i(object),
object->mark().value(), object->klass()->external_name());
}
if (event.should_commit()) {
// Hopefully the performance counters are allocated on distinct
// cache lines to avoid false sharing on MP systems ...
OM_PERFDATA_OP(Inflations, inc());
if (log_is_enabled(Trace, monitorinflation)) {
! ResourceMark rm(current);
lsh.print_cr("inflate(neutral): object=" INTPTR_FORMAT ", mark="
INTPTR_FORMAT ", type='%s'", p2i(object),
object->mark().value(), object->klass()->external_name());
}
if (event.should_commit()) {
// Hopefully the performance counters are allocated on distinct
// cache lines to avoid false sharing on MP systems ...
OM_PERFDATA_OP(Inflations, inc());
if (log_is_enabled(Trace, monitorinflation)) {
! ResourceMark rm;
lsh.print_cr("inflate(neutral): object=" INTPTR_FORMAT ", mark="
INTPTR_FORMAT ", type='%s'", p2i(object),
object->mark().value(), object->klass()->external_name());
}
if (event.should_commit()) {
log_trace(monitorinflation)("HandshakeForDeflation::do_thread: thread="
INTPTR_FORMAT, p2i(thread));
}
};
+ class VM_RendezvousGCThreads : public VM_Operation {
+ public:
+ bool evaluate_at_safepoint() const override { return false; }
+ VMOp_Type type() const override { return VMOp_RendezvousGCThreads; }
+ void doit() override {
+ SuspendibleThreadSet::synchronize();
+ SuspendibleThreadSet::desynchronize();
+ };
+ };
+
// This function is called by the MonitorDeflationThread to deflate
// ObjectMonitors. It is also called via do_final_audit_and_print_stats()
// by the VMThread.
size_t ObjectSynchronizer::deflate_idle_monitors() {
Thread* current = Thread::current();
_in_use_list.count(), _in_use_list.max());
}
// A JavaThread needs to handshake in order to safely free the
// ObjectMonitors that were deflated in this cycle.
+ // Also, we sync and desync GC threads around the handshake, so that they can
+ // safely read the mark-word and look-through to the object-monitor, without
+ // being afraid that the object-monitor is going away.
HandshakeForDeflation hfd_hc;
Handshake::execute(&hfd_hc);
+ VM_RendezvousGCThreads sync_gc;
+ VMThread::execute(&sync_gc);
if (ls != NULL) {
ls->print_cr("after handshaking: in_use_list stats: ceiling="
SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max());
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