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src/hotspot/share/runtime/objectMonitor.cpp
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rev 58110 : v2.09a with 8235795, 8235931 and 8236035 extracted; rebased to jdk-14+28; merge with 8236035.patch.cr1; merge with 8235795.patch.cr1; merge with 8236035.patch.cr2; merge with 8235795.patch.cr2; merge with 8235795.patch.cr3.
rev 58111 : See CR9-to-CR10-changes; merge with jdk-15+11.
@@ -239,10 +239,13 @@
// -----------------------------------------------------------------------------
// Enter support
void ObjectMonitor::enter(TRAPS) {
+ jint l_ref_count = ref_count();
+ ADIM_guarantee(l_ref_count > 0, "must be positive: l_ref_count=%d, ref_count=%d", l_ref_count, ref_count());
+
// The following code is ordered to check the most common cases first
// and to reduce RTS->RTO cache line upgrades on SPARC and IA32 processors.
Thread * const Self = THREAD;
void* cur = try_set_owner_from(NULL, Self);
@@ -262,10 +265,19 @@
_recursions = 1;
set_owner_from_BasicLock(cur, Self); // Convert from BasicLock* to Thread*.
return;
}
+ if (AsyncDeflateIdleMonitors &&
+ try_set_owner_from(DEFLATER_MARKER, Self) == DEFLATER_MARKER) {
+ // The deflation protocol finished the first part (setting owner),
+ // but it failed the second part (making ref_count negative) and
+ // bailed. Acquired the monitor.
+ assert(_recursions == 0, "invariant");
+ return;
+ }
+
// We've encountered genuine contention.
assert(Self->_Stalled == 0, "invariant");
Self->_Stalled = intptr_t(this);
// Try one round of spinning *before* enqueueing Self
@@ -289,14 +301,13 @@
assert(Self->is_Java_thread(), "invariant");
JavaThread * jt = (JavaThread *) Self;
assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
assert(jt->thread_state() != _thread_blocked, "invariant");
assert(this->object() != NULL, "invariant");
- assert(_contentions >= 0, "invariant");
+ assert(_contentions >= 0, "must not be negative: contentions=%d", _contentions);
- // Prevent deflation at STW-time. See deflate_idle_monitors() and is_busy().
- // Ensure the object-monitor relationship remains stable while there's contention.
+ // Keep track of contention for JVM/TI and M&M queries.
Atomic::inc(&_contentions);
JFR_ONLY(JfrConditionalFlushWithStacktrace<EventJavaMonitorEnter> flush(jt);)
EventJavaMonitorEnter event;
if (event.should_commit()) {
@@ -355,11 +366,11 @@
// states will still report that the thread is blocked trying to
// acquire it.
}
Atomic::dec(&_contentions);
- assert(_contentions >= 0, "invariant");
+ assert(_contentions >= 0, "must not be negative: contentions=%d", _contentions);
Self->_Stalled = 0;
// Must either set _recursions = 0 or ASSERT _recursions == 0.
assert(_recursions == 0, "invariant");
assert(_owner == Self, "invariant");
@@ -410,22 +421,83 @@
// We can either return -1 or retry.
// Retry doesn't make as much sense because the lock was just acquired.
return -1;
}
+// Install the displaced mark word (dmw) of a deflating ObjectMonitor
+// into the header of the object associated with the monitor. This
+// idempotent method is called by a thread that is deflating a
+// monitor and by other threads that have detected a race with the
+// deflation process.
+void ObjectMonitor::install_displaced_markword_in_object(const oop obj) {
+ // This function must only be called when (owner == DEFLATER_MARKER
+ // && ref_count <= 0), but we can't guarantee that here because
+ // those values could change when the ObjectMonitor gets moved from
+ // the global free list to a per-thread free list.
+
+ guarantee(obj != NULL, "must be non-NULL");
+ if (object() != obj) {
+ // ObjectMonitor's object ref no longer refers to the target object
+ // so the object's header has already been restored.
+ return;
+ }
+
+ markWord dmw = header();
+ if (dmw.value() == 0) {
+ // ObjectMonitor's header/dmw has been cleared so the ObjectMonitor
+ // has been deflated and taken off the global free list.
+ return;
+ }
+
+ // A non-NULL dmw has to be neutral (not locked and not marked).
+ ADIM_guarantee(dmw.is_neutral(), "must be neutral: dmw=" INTPTR_FORMAT, dmw.value());
+
+ // Install displaced mark word if the object's header still points
+ // to this ObjectMonitor. All racing callers to this function will
+ // reach this point, but only one can win.
+ markWord res = obj->cas_set_mark(dmw, markWord::encode(this));
+ if (res != markWord::encode(this)) {
+ // This should be rare so log at the Info level when it happens.
+ log_info(monitorinflation)("install_displaced_markword_in_object: "
+ "failed cas_set_mark: new_mark=" INTPTR_FORMAT
+ ", old_mark=" INTPTR_FORMAT ", res=" INTPTR_FORMAT,
+ dmw.value(), markWord::encode(this).value(),
+ res.value());
+ }
+
+ // Note: It does not matter which thread restored the header/dmw
+ // into the object's header. The thread deflating the monitor just
+ // wanted the object's header restored and it is. The threads that
+ // detected a race with the deflation process also wanted the
+ // object's header restored before they retry their operation and
+ // because it is restored they will only retry once.
+}
+
// Convert the fields used by is_busy() to a string that can be
// used for diagnostic output.
const char* ObjectMonitor::is_busy_to_string(stringStream* ss) {
- ss->print("is_busy: contentions=%d, waiters=%d, owner=" INTPTR_FORMAT
- ", cxq=" INTPTR_FORMAT ", EntryList=" INTPTR_FORMAT, _contentions,
- _waiters, p2i(_owner), p2i(_cxq), p2i(_EntryList));
+ ss->print("is_busy: contentions=%d, waiters=%d, ", _contentions, _waiters);
+ if (!AsyncDeflateIdleMonitors) {
+ ss->print("owner=" INTPTR_FORMAT, p2i(_owner));
+ } else if (_owner != DEFLATER_MARKER) {
+ ss->print("owner=" INTPTR_FORMAT, p2i(_owner));
+ } else {
+ // We report NULL instead of DEFLATER_MARKER here because is_busy()
+ // ignores DEFLATER_MARKER values.
+ ss->print("owner=" INTPTR_FORMAT, NULL);
+ }
+ ss->print(", cxq=" INTPTR_FORMAT ", EntryList=" INTPTR_FORMAT, p2i(_cxq),
+ p2i(_EntryList));
return ss->base();
}
#define MAX_RECHECK_INTERVAL 1000
void ObjectMonitor::EnterI(TRAPS) {
+ jint l_ref_count = ref_count();
+ ADIM_guarantee(l_ref_count > 0, "must be positive: l_ref_count=%d, ref_count=%d", l_ref_count, ref_count());
+
Thread * const Self = THREAD;
assert(Self->is_Java_thread(), "invariant");
assert(((JavaThread *) Self)->thread_state() == _thread_blocked, "invariant");
// Try the lock - TATAS
@@ -434,10 +506,20 @@
assert(_owner == Self, "invariant");
assert(_Responsible != Self, "invariant");
return;
}
+ if (AsyncDeflateIdleMonitors &&
+ try_set_owner_from(DEFLATER_MARKER, Self) == DEFLATER_MARKER) {
+ // The deflation protocol finished the first part (setting owner),
+ // but it failed the second part (making ref_count negative) and
+ // bailed. Acquired the monitor.
+ assert(_succ != Self, "invariant");
+ assert(_Responsible != Self, "invariant");
+ return;
+ }
+
assert(InitDone, "Unexpectedly not initialized");
// We try one round of spinning *before* enqueueing Self.
//
// If the _owner is ready but OFFPROC we could use a YieldTo()
@@ -550,10 +632,18 @@
Self->_ParkEvent->park();
}
if (TryLock(Self) > 0) break;
+ if (AsyncDeflateIdleMonitors &&
+ try_set_owner_from(DEFLATER_MARKER, Self) == DEFLATER_MARKER) {
+ // The deflation protocol finished the first part (setting owner),
+ // but it failed the second part (making ref_count negative) and
+ // bailed. Acquired the monitor.
+ break;
+ }
+
// The lock is still contested.
// Keep a tally of the # of futile wakeups.
// Note that the counter is not protected by a lock or updated by atomics.
// That is by design - we trade "lossy" counters which are exposed to
// races during updates for a lower probe effect.
@@ -654,10 +744,13 @@
// monitor reentry in wait().
//
// In the future we should reconcile EnterI() and ReenterI().
void ObjectMonitor::ReenterI(Thread * Self, ObjectWaiter * SelfNode) {
+ jint l_ref_count = ref_count();
+ ADIM_guarantee(l_ref_count > 0, "must be positive: l_ref_count=%d, ref_count=%d", l_ref_count, ref_count());
+
assert(Self != NULL, "invariant");
assert(SelfNode != NULL, "invariant");
assert(SelfNode->_thread == Self, "invariant");
assert(_waiters > 0, "invariant");
assert(((oop)(object()))->mark() == markWord::encode(this), "invariant");
@@ -671,10 +764,18 @@
assert(_owner != Self, "invariant");
if (TryLock(Self) > 0) break;
if (TrySpin(Self) > 0) break;
+ if (AsyncDeflateIdleMonitors &&
+ try_set_owner_from(DEFLATER_MARKER, Self) == DEFLATER_MARKER) {
+ // The deflation protocol finished the first part (setting owner),
+ // but it failed the second part (making ref_count negative) and
+ // bailed. Acquired the monitor.
+ break;
+ }
+
// State transition wrappers around park() ...
// ReenterI() wisely defers state transitions until
// it's clear we must park the thread.
{
OSThreadContendState osts(Self->osthread());
@@ -814,12 +915,12 @@
// inopportune) reclamation of "this".
//
// We'd like to assert that: (THREAD->thread_state() != _thread_blocked) ;
// There's one exception to the claim above, however. EnterI() can call
// exit() to drop a lock if the acquirer has been externally suspended.
-// In that case exit() is called with _thread_state as _thread_blocked,
-// but the monitor's _contentions field is > 0, which inhibits reclamation.
+// In that case exit() is called with _thread_state == _thread_blocked,
+// but the monitor's ref_count is > 0, which inhibits reclamation.
//
// 1-0 exit
// ~~~~~~~~
// ::exit() uses a canonical 1-1 idiom with a MEMBAR although some of
// the fast-path operators have been optimized so the common ::exit()
@@ -1089,11 +1190,11 @@
// Hygiene -- once we've set _owner = NULL we can't safely dereference Wakee again.
// The thread associated with Wakee may have grabbed the lock and "Wakee" may be
// out-of-scope (non-extant).
Wakee = NULL;
- // Drop the lock
+ // Drop the lock.
// Uses a fence to separate release_store(owner) from the LD in unpark().
release_clear_owner(Self);
OrderAccess::fence();
DTRACE_MONITOR_PROBE(contended__exit, this, object(), Self);
@@ -1143,14 +1244,14 @@
Thread * const Self = THREAD;
assert(Self->is_Java_thread(), "Must be Java thread!");
JavaThread *jt = (JavaThread *)THREAD;
guarantee(_owner != Self, "reenter already owner");
- enter(THREAD); // enter the monitor
+ enter(THREAD);
+ // Entered the monitor.
guarantee(_recursions == 0, "reenter recursion");
_recursions = recursions;
- return;
}
// Checks that the current THREAD owns this monitor and causes an
// immediate return if it doesn't. We don't use the CHECK macro
// because we want the IMSE to be the only exception that is thrown
@@ -1945,10 +2046,137 @@
}
DEBUG_ONLY(InitDone = true;)
}
+ObjectMonitorHandle::~ObjectMonitorHandle() {
+ if (_om_ptr != NULL) {
+ _om_ptr->dec_ref_count();
+ _om_ptr = NULL;
+ }
+}
+
+// Save the ObjectMonitor* associated with the specified markWord and
+// increment the ref_count. This function should only be called if
+// the caller has verified mark.has_monitor() == true. The object
+// parameter is needed to verify that ObjectMonitor* has not been
+// deflated and reused for another object.
+//
+// This function returns true if the ObjectMonitor* has been safely
+// saved. This function returns false if we have lost a race with
+// async deflation; the caller should retry as appropriate.
+//
+bool ObjectMonitorHandle::save_om_ptr(oop object, markWord mark) {
+ // is_marked() is a superset of has_monitor() so make sure we
+ // are called with the proper markWord value.
+ guarantee(mark.has_monitor() && !mark.is_marked(), "sanity check: mark="
+ INTPTR_FORMAT, mark.value());
+
+ ObjectMonitor* om_ptr = mark.monitor();
+ om_ptr->inc_ref_count();
+
+ if (AsyncDeflateIdleMonitors) {
+ // Race here if monitor is not owned! The above ref_count bump
+ // will cause subsequent async deflation to skip it. However,
+ // previous or concurrent async deflation is a race.
+ if (om_ptr->owner_is_DEFLATER_MARKER() && om_ptr->ref_count() <= 0) {
+ // Async deflation is in progress and our ref_count increment
+ // above lost the race to async deflation. Attempt to restore
+ // the header/dmw to the object's header so that we only retry
+ // once if the deflater thread happens to be slow.
+ om_ptr->install_displaced_markword_in_object(object);
+ om_ptr->dec_ref_count();
+ return false;
+ }
+ if (om_ptr->ref_count() <= 0) {
+ // Async deflation is in the process of bailing out, but has not
+ // yet restored the ref_count field so we return false to force
+ // a retry. We want a positive ref_count value for a true return.
+ om_ptr->dec_ref_count();
+ return false;
+ }
+ // The ObjectMonitor could have been deflated and reused for
+ // another object before we bumped the ref_count so make sure
+ // our object still refers to this ObjectMonitor.
+ // Note: With handshakes after deflation is this race even
+ // possible anymore?
+ const markWord tmp = object->mark();
+ if (!tmp.has_monitor() || tmp.monitor() != om_ptr) {
+ // Async deflation and reuse won the race so we have to retry.
+ // Skip object header restoration since that's already done.
+ om_ptr->dec_ref_count();
+ return false;
+ }
+ }
+
+ ADIM_guarantee(_om_ptr == NULL, "sanity check: _om_ptr=" INTPTR_FORMAT,
+ p2i(_om_ptr));
+ _om_ptr = om_ptr;
+ return true;
+}
+
+// For internal use by ObjectSynchronizer::inflate().
+// This function is only used when we don't have to worry about async
+// deflation of the specified ObjectMonitor*.
+void ObjectMonitorHandle::set_om_ptr(ObjectMonitor* om_ptr) {
+ if (_om_ptr == NULL) {
+ ADIM_guarantee(om_ptr != NULL, "cannot clear an unset om_ptr");
+ om_ptr->inc_ref_count();
+ _om_ptr = om_ptr;
+ } else {
+ ADIM_guarantee(om_ptr == NULL, "can only clear a set om_ptr");
+ _om_ptr->dec_ref_count();
+ _om_ptr = NULL;
+ }
+}
+
+// Save the specified ObjectMonitor* if it is safe, i.e., not being
+// async deflated.
+//
+// This function returns true if the ObjectMonitor* has been safely
+// saved. This function returns false if the specified ObjectMonitor*
+// is NULL or if we have lost a race with async deflation; the caller
+// can retry as appropriate.
+bool ObjectMonitorHandle::save_om_ptr_if_safe(ObjectMonitor* om_ptr) {
+ if (om_ptr == NULL) {
+ return false; // Nothing to save if input is NULL
+ }
+
+ om_ptr->inc_ref_count();
+
+ if (AsyncDeflateIdleMonitors) {
+ if (om_ptr->owner_is_DEFLATER_MARKER() && om_ptr->ref_count() <= 0) {
+ // Async deflation is in progress and our ref_count increment
+ // above lost the race to async deflation.
+ om_ptr->dec_ref_count();
+ return false;
+ }
+ if (om_ptr->ref_count() <= 0) {
+ // Async deflation is in the process of bailing out, but has not
+ // yet restored the ref_count field so we return false to force
+ // a retry. We want a positive ref_count value for a true return.
+ om_ptr->dec_ref_count();
+ return false;
+ }
+ // Unlike save_om_ptr(), we don't have context to determine if
+ // the ObjectMonitor has been deflated and reused for another
+ // object.
+ }
+
+ ADIM_guarantee(_om_ptr == NULL, "sanity check: _om_ptr=" INTPTR_FORMAT,
+ p2i(_om_ptr));
+ _om_ptr = om_ptr;
+ return true;
+}
+
+// Unset the _om_ptr field and decrement the ref_count field.
+void ObjectMonitorHandle::unset_om_ptr() {
+ ADIM_guarantee(_om_ptr != NULL, "_om_ptr must not be NULL");
+ _om_ptr->dec_ref_count();
+ _om_ptr = NULL;
+}
+
void ObjectMonitor::print_on(outputStream* st) const {
// The minimal things to print for markWord printing, more can be added for debugging and logging.
st->print("{contentions=0x%08x,waiters=0x%08x"
",recursions=" INTX_FORMAT ",owner=" INTPTR_FORMAT "}",
contentions(), waiters(), recursions(),
@@ -1960,18 +2188,30 @@
// Print the ObjectMonitor like a debugger would:
//
// (ObjectMonitor) 0x00007fdfb6012e40 = {
// _header = 0x0000000000000001
// _object = 0x000000070ff45fd0
-// _next_om = 0x0000000000000000
+// _allocation_state = Old
// _pad_buf0 = {
// [0] = '\0'
// ...
-// [103] = '\0'
+// [43] = '\0'
// }
// _owner = 0x0000000000000000
// _previous_owner_tid = 0
+// _pad_buf1 = {
+// [0] = '\0'
+// ...
+// [47] = '\0'
+// }
+// _ref_count = 1
+// _pad_buf2 = {
+// [0] = '\0'
+// ...
+// [47] = '\0'
+// }
+// _next_om = 0x0000000000000000
// _recursions = 0
// _EntryList = 0x0000000000000000
// _cxq = 0x0000000000000000
// _succ = 0x0000000000000000
// _Responsible = 0x0000000000000000
@@ -1985,18 +2225,40 @@
//
void ObjectMonitor::print_debug_style_on(outputStream* st) const {
st->print_cr("(ObjectMonitor*) " INTPTR_FORMAT " = {", p2i(this));
st->print_cr(" _header = " INTPTR_FORMAT, header().value());
st->print_cr(" _object = " INTPTR_FORMAT, p2i(_object));
- st->print_cr(" _next_om = " INTPTR_FORMAT, p2i(next_om()));
+ st->print(" _allocation_state = ");
+ if (is_free()) {
+ st->print("Free");
+ } else if (is_old()) {
+ st->print("Old");
+ } else if (is_new()) {
+ st->print("New");
+ } else {
+ st->print("unknown=%d", _allocation_state);
+ }
+ st->cr();
st->print_cr(" _pad_buf0 = {");
st->print_cr(" [0] = '\\0'");
st->print_cr(" ...");
st->print_cr(" [%d] = '\\0'", (int)sizeof(_pad_buf0) - 1);
st->print_cr(" }");
st->print_cr(" _owner = " INTPTR_FORMAT, p2i(_owner));
st->print_cr(" _previous_owner_tid = " JLONG_FORMAT, _previous_owner_tid);
+ st->print_cr(" _pad_buf1 = {");
+ st->print_cr(" [0] = '\\0'");
+ st->print_cr(" ...");
+ st->print_cr(" [%d] = '\\0'", (int)sizeof(_pad_buf1) - 1);
+ st->print_cr(" }");
+ st->print_cr(" _ref_count = %d", ref_count());
+ st->print_cr(" _pad_buf2 = {");
+ st->print_cr(" [0] = '\\0'");
+ st->print_cr(" ...");
+ st->print_cr(" [%d] = '\\0'", (int)sizeof(_pad_buf2) - 1);
+ st->print_cr(" }");
+ st->print_cr(" _next_om = " INTPTR_FORMAT, p2i(next_om()));
st->print_cr(" _recursions = " INTX_FORMAT, _recursions);
st->print_cr(" _EntryList = " INTPTR_FORMAT, p2i(_EntryList));
st->print_cr(" _cxq = " INTPTR_FORMAT, p2i(_cxq));
st->print_cr(" _succ = " INTPTR_FORMAT, p2i(_succ));
st->print_cr(" _Responsible = " INTPTR_FORMAT, p2i(_Responsible));
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