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src/hotspot/share/runtime/synchronizer.cpp
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rev 59376 : 8153224.v2.10.patch merged with 8153224.v2.11.patch.
rev 59377 : CR1 changes from dcubed, dholmes, eosterlund and rehn.
rev 59378 : CR changes from dholmes, dcubed; fix is_being_async_deflated() race found by eosterlund; WB_ForceSafepoint() should request a special clean up with AsyncDeflateIdleMonitors; add a barrier in install_displaced_markword_in_object() to separate the header load from the preceding loads in is_being_async_deflated().
rev 59379 : eosterlund CR - Switch from three part async deflation protocol to a two part async deflation protocol where a negative contentions field is a linearization point.
@@ -35,15 +35,17 @@
#include "oops/markWord.hpp"
#include "oops/oop.inline.hpp"
#include "runtime/atomic.hpp"
#include "runtime/biasedLocking.hpp"
#include "runtime/handles.inline.hpp"
+#include "runtime/handshake.hpp"
#include "runtime/interfaceSupport.inline.hpp"
#include "runtime/mutexLocker.hpp"
#include "runtime/objectMonitor.hpp"
#include "runtime/objectMonitor.inline.hpp"
#include "runtime/osThread.hpp"
+#include "runtime/safepointMechanism.inline.hpp"
#include "runtime/safepointVerifiers.hpp"
#include "runtime/sharedRuntime.hpp"
#include "runtime/stubRoutines.hpp"
#include "runtime/synchronizer.hpp"
#include "runtime/thread.inline.hpp"
@@ -116,10 +118,13 @@
#define NINFLATIONLOCKS 256
static volatile intptr_t gInflationLocks[NINFLATIONLOCKS];
// global list of blocks of monitors
PaddedObjectMonitor* ObjectSynchronizer::g_block_list = NULL;
+bool volatile ObjectSynchronizer::_is_async_deflation_requested = false;
+bool volatile ObjectSynchronizer::_is_special_deflation_requested = false;
+jlong ObjectSynchronizer::_last_async_deflation_time_ns = 0;
struct ObjectMonitorListGlobals {
char _pad_prefix[OM_CACHE_LINE_SIZE];
// These are highly shared list related variables.
// To avoid false-sharing they need to be the sole occupants of a cache line.
@@ -132,18 +137,28 @@
// Global ObjectMonitor in-use list. When a JavaThread is exiting,
// ObjectMonitors on its per-thread in-use list are prepended here.
ObjectMonitor* _in_use_list;
DEFINE_PAD_MINUS_SIZE(2, OM_CACHE_LINE_SIZE, sizeof(ObjectMonitor*));
+ // Global ObjectMonitor wait list. Deflated ObjectMonitors wait on
+ // this list until after a handshake or a safepoint for platforms
+ // that don't support handshakes. After the handshake or safepoint,
+ // the deflated ObjectMonitors are prepended to free_list.
+ ObjectMonitor* _wait_list;
+ DEFINE_PAD_MINUS_SIZE(3, OM_CACHE_LINE_SIZE, sizeof(ObjectMonitor*));
+
int _free_count; // # on free_list
- DEFINE_PAD_MINUS_SIZE(3, OM_CACHE_LINE_SIZE, sizeof(int));
+ DEFINE_PAD_MINUS_SIZE(4, OM_CACHE_LINE_SIZE, sizeof(int));
int _in_use_count; // # on in_use_list
- DEFINE_PAD_MINUS_SIZE(4, OM_CACHE_LINE_SIZE, sizeof(int));
+ DEFINE_PAD_MINUS_SIZE(5, OM_CACHE_LINE_SIZE, sizeof(int));
int _population; // # Extant -- in circulation
- DEFINE_PAD_MINUS_SIZE(5, OM_CACHE_LINE_SIZE, sizeof(int));
+ DEFINE_PAD_MINUS_SIZE(6, OM_CACHE_LINE_SIZE, sizeof(int));
+
+ int _wait_count; // # on wait_list
+ DEFINE_PAD_MINUS_SIZE(7, OM_CACHE_LINE_SIZE, sizeof(int));
};
static ObjectMonitorListGlobals om_list_globals;
#define CHAINMARKER (cast_to_oop<intptr_t>(-1))
@@ -297,10 +312,19 @@
ObjectMonitor* tail, int count) {
prepend_list_to_common(list, tail, count, &om_list_globals._free_list,
&om_list_globals._free_count);
}
+// Prepend a list of ObjectMonitors to om_list_globals._wait_list.
+// 'tail' is the last ObjectMonitor in the list and there are 'count'
+// on the list. Also updates om_list_globals._wait_count.
+static void prepend_list_to_global_wait_list(ObjectMonitor* list,
+ ObjectMonitor* tail, int count) {
+ prepend_list_to_common(list, tail, count, &om_list_globals._wait_list,
+ &om_list_globals._wait_count);
+}
+
// Prepend a list of ObjectMonitors to om_list_globals._in_use_list.
// 'tail' is the last ObjectMonitor in the list and there are 'count'
// on the list. Also updates om_list_globals._in_use_list.
static void prepend_list_to_global_in_use_list(ObjectMonitor* list,
ObjectMonitor* tail, int count) {
@@ -314,11 +338,11 @@
int* count_p) {
while (true) {
om_lock(m); // Lock m so we can safely update its next field.
ObjectMonitor* cur = NULL;
// Lock the list head to guard against races with a list walker
- // thread:
+ // or async deflater thread (which only races in om_in_use_list):
if ((cur = get_list_head_locked(list_p)) != NULL) {
// List head is now locked so we can safely switch it.
m->set_next_om(cur); // m now points to cur (and unlocks m)
Atomic::store(list_p, m); // Switch list head to unlocked m.
om_unlock(cur);
@@ -352,11 +376,11 @@
// decrements the specified counter. Returns NULL if none are available.
static ObjectMonitor* take_from_start_of_common(ObjectMonitor** list_p,
int* count_p) {
ObjectMonitor* take = NULL;
// Lock the list head to guard against races with a list walker
- // thread:
+ // or async deflater thread (which only races in om_list_globals._free_list):
if ((take = get_list_head_locked(list_p)) == NULL) {
return NULL; // None are available.
}
ObjectMonitor* next = unmarked_next(take);
// Switch locked list head to next (which unlocks the list head, but
@@ -461,15 +485,25 @@
assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
assert(self->is_Java_thread(), "invariant");
assert(((JavaThread *) self)->thread_state() == _thread_in_Java, "invariant");
NoSafepointVerifier nsv;
if (obj == NULL) return false; // Need to throw NPE
+
const markWord mark = obj->mark();
if (mark.has_monitor()) {
ObjectMonitor* const m = mark.monitor();
+ if (AsyncDeflateIdleMonitors) {
+ // An async deflation can race us before we manage to make the
+ // ObjectMonitor busy by setting the owner below. If we detect
+ // that race we just bail out to the slow-path here.
+ if (m->object() == NULL) {
+ return false;
+ }
+ } else {
assert(m->object() == obj, "invariant");
+ }
Thread* const owner = (Thread *) m->_owner;
// Lock contention and Transactional Lock Elision (TLE) diagnostics
// and observability
// Case: light contention possibly amenable to TLE
@@ -545,11 +579,19 @@
// 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());
- inflate(THREAD, obj(), inflate_cause_monitor_enter)->enter(THREAD);
+ // 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(THREAD, obj(), inflate_cause_monitor_enter);
+ if (monitor->enter(THREAD)) {
+ return;
+ }
+ }
}
void ObjectSynchronizer::exit(oop object, BasicLock* lock, TRAPS) {
markWord mark = object->mark();
// We cannot check for Biased Locking if we are racing an inflation.
@@ -594,11 +636,14 @@
return;
}
}
// We have to take the slow-path of possible inflation and then exit.
- inflate(THREAD, object, inflate_cause_vm_internal)->exit(true, THREAD);
+ // The ObjectMonitor* can't be async deflated until ownership is
+ // dropped inside exit() and the ObjectMonitor* must be !is_busy().
+ ObjectMonitor* monitor = inflate(THREAD, object, inflate_cause_vm_internal);
+ monitor->exit(true, THREAD);
}
// -----------------------------------------------------------------------------
// Class Loader support to workaround deadlocks on the class loader lock objects
// Also used by GC
@@ -615,37 +660,55 @@
if (UseBiasedLocking) {
BiasedLocking::revoke(obj, THREAD);
assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
}
+ // The ObjectMonitor* can't be async deflated until ownership is
+ // dropped inside exit() and the ObjectMonitor* must be !is_busy().
ObjectMonitor* monitor = inflate(THREAD, obj(), inflate_cause_vm_internal);
-
- return monitor->complete_exit(THREAD);
+ intptr_t ret_code = monitor->complete_exit(THREAD);
+ return ret_code;
}
// NOTE: must use heavy weight monitor to handle complete_exit/reenter()
void ObjectSynchronizer::reenter(Handle obj, intx recursions, TRAPS) {
if (UseBiasedLocking) {
BiasedLocking::revoke(obj, THREAD);
assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
}
+ // An async deflation can race after the inflate() call and before
+ // reenter() -> enter() can make the ObjectMonitor busy. reenter() ->
+ // enter() returns false if we have lost the race to async deflation
+ // and we simply try again.
+ while (true) {
ObjectMonitor* monitor = inflate(THREAD, obj(), inflate_cause_vm_internal);
-
- monitor->reenter(recursions, THREAD);
+ if (monitor->reenter(recursions, THREAD)) {
+ return;
+ }
+ }
}
+
// -----------------------------------------------------------------------------
// JNI locks on java objects
// NOTE: must use heavy weight monitor to handle jni monitor enter
void ObjectSynchronizer::jni_enter(Handle obj, TRAPS) {
// the current locking is from JNI instead of Java code
if (UseBiasedLocking) {
BiasedLocking::revoke(obj, THREAD);
assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
}
THREAD->set_current_pending_monitor_is_from_java(false);
- inflate(THREAD, obj(), inflate_cause_jni_enter)->enter(THREAD);
+ // 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(THREAD, obj(), inflate_cause_jni_enter);
+ if (monitor->enter(THREAD)) {
+ break;
+ }
+ }
THREAD->set_current_pending_monitor_is_from_java(true);
}
// NOTE: must use heavy weight monitor to handle jni monitor exit
void ObjectSynchronizer::jni_exit(oop obj, Thread* THREAD) {
@@ -654,10 +717,12 @@
BiasedLocking::revoke(h_obj, THREAD);
obj = h_obj();
}
assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
+ // The ObjectMonitor* can't be async deflated until ownership is
+ // dropped inside exit() and the ObjectMonitor* must be !is_busy().
ObjectMonitor* monitor = inflate(THREAD, obj, inflate_cause_jni_exit);
// If this thread has locked the object, exit the monitor. We
// intentionally do not use CHECK here because we must exit the
// monitor even if an exception is pending.
if (monitor->check_owner(THREAD)) {
@@ -695,31 +760,39 @@
assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
}
if (millis < 0) {
THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
}
+ // The ObjectMonitor* can't be async deflated because the _waiters
+ // field is incremented before ownership is dropped and decremented
+ // after ownership is regained.
ObjectMonitor* monitor = inflate(THREAD, obj(), inflate_cause_wait);
DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), THREAD, millis);
monitor->wait(millis, true, THREAD);
// This dummy call is in place to get around dtrace bug 6254741. Once
// that's fixed we can uncomment the following line, remove the call
// and change this function back into a "void" func.
// DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD);
- return dtrace_waited_probe(monitor, obj, THREAD);
+ int ret_code = dtrace_waited_probe(monitor, obj, THREAD);
+ return ret_code;
}
void ObjectSynchronizer::wait_uninterruptibly(Handle obj, jlong millis, TRAPS) {
if (UseBiasedLocking) {
BiasedLocking::revoke(obj, THREAD);
assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
}
if (millis < 0) {
THROW_MSG(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
}
- inflate(THREAD, obj(), inflate_cause_wait)->wait(millis, false, THREAD);
+ // The ObjectMonitor* can't be async deflated because the _waiters
+ // field is incremented before ownership is dropped and decremented
+ // after ownership is regained.
+ ObjectMonitor* monitor = inflate(THREAD, obj(), inflate_cause_wait);
+ monitor->wait(millis, false, THREAD);
}
void ObjectSynchronizer::notify(Handle obj, TRAPS) {
if (UseBiasedLocking) {
BiasedLocking::revoke(obj, THREAD);
@@ -728,11 +801,14 @@
markWord mark = obj->mark();
if (mark.has_locker() && THREAD->is_lock_owned((address)mark.locker())) {
return;
}
- inflate(THREAD, obj(), inflate_cause_notify)->notify(THREAD);
+ // The ObjectMonitor* can't be async deflated until ownership is
+ // dropped by the calling thread.
+ ObjectMonitor* monitor = inflate(THREAD, obj(), inflate_cause_notify);
+ monitor->notify(THREAD);
}
// NOTE: see comment of notify()
void ObjectSynchronizer::notifyall(Handle obj, TRAPS) {
if (UseBiasedLocking) {
@@ -742,11 +818,14 @@
markWord mark = obj->mark();
if (mark.has_locker() && THREAD->is_lock_owned((address)mark.locker())) {
return;
}
- inflate(THREAD, obj(), inflate_cause_notify)->notifyAll(THREAD);
+ // The ObjectMonitor* can't be async deflated until ownership is
+ // dropped by the calling thread.
+ ObjectMonitor* monitor = inflate(THREAD, obj(), inflate_cause_notify);
+ monitor->notifyAll(THREAD);
}
// -----------------------------------------------------------------------------
// Hash Code handling
//
@@ -934,10 +1013,11 @@
assert(Universe::verify_in_progress() || DumpSharedSpaces ||
self->is_Java_thread() , "invariant");
assert(Universe::verify_in_progress() || DumpSharedSpaces ||
((JavaThread *)self)->thread_state() != _thread_blocked, "invariant");
+ while (true) {
ObjectMonitor* monitor = NULL;
markWord temp, test;
intptr_t hash;
markWord mark = read_stable_mark(obj);
@@ -963,11 +1043,30 @@
} else if (mark.has_monitor()) {
monitor = mark.monitor();
temp = monitor->header();
assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
hash = temp.hash();
- if (hash != 0) { // if it has a hash, just return it
+ if (hash != 0) {
+ // It has a hash.
+
+ // Separate load of dmw/header above from the loads in
+ // is_being_async_deflated().
+ if (support_IRIW_for_not_multiple_copy_atomic_cpu) {
+ // A non-multiple copy atomic (nMCA) machine needs a bigger
+ // hammer to separate the load above and the loads below.
+ OrderAccess::fence();
+ } else {
+ OrderAccess::loadload();
+ }
+ if (monitor->is_being_async_deflated()) {
+ // But we can't safely use the hash if we detect that async
+ // deflation has occurred. So we 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.
+ monitor->install_displaced_markword_in_object(obj);
+ continue;
+ }
return hash;
}
// Fall thru so we only have one place that installs the hash in
// the ObjectMonitor.
} else if (self->is_lock_owned((address)mark.locker())) {
@@ -988,10 +1087,13 @@
// during an inflate() call so any change to that stack memory
// may not propagate to other threads correctly.
}
// Inflate the monitor to set the hash.
+
+ // An async deflation can race after the inflate() call and before we
+ // can update the ObjectMonitor's header with the hash value below.
monitor = inflate(self, obj, inflate_cause_hash_code);
// Load ObjectMonitor's header/dmw field and see if it has a hash.
mark = monitor->header();
assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
hash = mark.hash();
@@ -1009,13 +1111,22 @@
// will need to be updated.
hash = test.hash();
assert(test.is_neutral(), "invariant: header=" INTPTR_FORMAT, test.value());
assert(hash != 0, "should only have lost the race to a thread that set a non-zero hash");
}
+ if (monitor->is_being_async_deflated()) {
+ // If we detect that async deflation has occurred, then we
+ // 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.
+ monitor->install_displaced_markword_in_object(obj);
+ continue;
+ }
}
// We finally get the hash.
return hash;
+ }
}
// Deprecated -- use FastHashCode() instead.
intptr_t ObjectSynchronizer::identity_hash_value_for(Handle obj) {
@@ -1039,10 +1150,12 @@
if (mark.has_locker()) {
return thread->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();
return monitor->is_entered(thread) != 0;
}
// Unlocked case, header in place
assert(mark.is_neutral(), "sanity check");
@@ -1080,13 +1193,16 @@
owner_self : owner_other;
}
// CASE: inflated. Mark (tagged pointer) points to an ObjectMonitor.
// The Object:ObjectMonitor relationship is stable as long as we're
- // not at a safepoint.
+ // not at a safepoint and AsyncDeflateIdleMonitors is false.
if (mark.has_monitor()) {
- void* owner = mark.monitor()->_owner;
+ // 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();
+ void* owner = monitor->owner();
if (owner == NULL) return owner_none;
return (owner == self ||
self->is_lock_owned((address)owner)) ? owner_self : owner_other;
}
@@ -1116,10 +1232,12 @@
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();
}
@@ -1142,13 +1260,19 @@
PaddedObjectMonitor* block = Atomic::load(&g_block_list);
while (block != NULL) {
assert(block->object() == CHAINMARKER, "must be a block header");
for (int i = _BLOCKSIZE - 1; i > 0; i--) {
ObjectMonitor* mid = (ObjectMonitor *)(block + i);
- oop object = (oop)mid->object();
- if (object != NULL) {
+ if (mid->object() != NULL) {
// Only process with closure if the object is set.
+
+ // monitors_iterate() is only called at a safepoint or when the
+ // target thread is suspended or when the target thread is
+ // operating on itself. The current closures in use today are
+ // only interested in an owned ObjectMonitor and ownership
+ // cannot be dropped under the calling contexts so the
+ // ObjectMonitor cannot be async deflated.
closure->do_monitor(mid);
}
}
// unmarked_next() is not needed with g_block_list (no locking
// used with block linkage _next_om fields).
@@ -1160,19 +1284,57 @@
int population = Atomic::load(&om_list_globals._population);
if (population == 0) {
return false;
}
if (MonitorUsedDeflationThreshold > 0) {
- int monitors_used = population - Atomic::load(&om_list_globals._free_count);
+ int monitors_used = population - Atomic::load(&om_list_globals._free_count) -
+ Atomic::load(&om_list_globals._wait_count);
int monitor_usage = (monitors_used * 100LL) / population;
return monitor_usage > MonitorUsedDeflationThreshold;
}
return false;
}
-bool ObjectSynchronizer::is_cleanup_needed() {
- return monitors_used_above_threshold();
+bool ObjectSynchronizer::is_async_deflation_needed() {
+ if (!AsyncDeflateIdleMonitors) {
+ return false;
+ }
+ if (is_async_deflation_requested()) {
+ // Async deflation request.
+ return true;
+ }
+ if (AsyncDeflationInterval > 0 &&
+ time_since_last_async_deflation_ms() > AsyncDeflationInterval &&
+ monitors_used_above_threshold()) {
+ // It's been longer than our specified deflate interval and there
+ // are too many monitors in use. We don't deflate more frequently
+ // than AsyncDeflationInterval (unless is_async_deflation_requested)
+ // in order to not swamp the ServiceThread.
+ _last_async_deflation_time_ns = os::javaTimeNanos();
+ return true;
+ }
+ return false;
+}
+
+bool ObjectSynchronizer::is_safepoint_deflation_needed() {
+ if (!AsyncDeflateIdleMonitors) {
+ if (monitors_used_above_threshold()) {
+ // Too many monitors in use.
+ return true;
+ }
+ return false;
+ }
+ if (is_special_deflation_requested()) {
+ // For AsyncDeflateIdleMonitors only do a safepoint deflation
+ // if there is a special deflation request.
+ return true;
+ }
+ return false;
+}
+
+jlong ObjectSynchronizer::time_since_last_async_deflation_ms() {
+ return (os::javaTimeNanos() - _last_async_deflation_time_ns) / (NANOUNITS / MILLIUNITS);
}
void ObjectSynchronizer::oops_do(OopClosure* f) {
// We only scan the global used list here (for moribund threads), and
// the thread-local monitors in Thread::oops_do().
@@ -1204,11 +1366,11 @@
// -----------------------------------------------------------------------------
// ObjectMonitor Lifecycle
// -----------------------
// Inflation unlinks monitors from om_list_globals._free_list or a per-thread
// free list and associates them with objects. Deflation -- which occurs at
-// STW-time -- disassociates idle monitors from objects.
+// STW-time or asynchronously -- disassociates idle monitors from objects.
// Such scavenged monitors are returned to the om_list_globals._free_list.
//
// ObjectMonitors reside in type-stable memory (TSM) and are immortal.
//
// Lifecycle:
@@ -1236,10 +1398,11 @@
// improve allocation latency, as well as reducing coherency traffic
// on the shared global list.
m = take_from_start_of_om_free_list(self);
if (m != NULL) {
guarantee(m->object() == NULL, "invariant");
+ m->set_allocation_state(ObjectMonitor::New);
prepend_to_om_in_use_list(self, m);
return m;
}
// 2: try to allocate from the global om_list_globals._free_list
@@ -1253,11 +1416,33 @@
ObjectMonitor* take = take_from_start_of_global_free_list();
if (take == NULL) {
break; // No more are available.
}
guarantee(take->object() == NULL, "invariant");
+ if (AsyncDeflateIdleMonitors) {
+ // We allowed 3 field values to linger during async deflation.
+ // Clear or restore them as appropriate.
+ take->set_header(markWord::zero());
+ // DEFLATER_MARKER is the only non-NULL value we should see here.
+ take->try_set_owner_from(DEFLATER_MARKER, NULL);
+ if (take->contentions() < 0) {
+ // Add back max_jint to restore the contentions field to its
+ // proper value.
+ take->add_to_contentions(max_jint);
+
+#ifdef ASSERT
+ jint l_contentions = take->contentions();
+#endif
+ assert(l_contentions >= 0, "must not be negative: l_contentions=%d, contentions=%d",
+ l_contentions, take->contentions());
+ }
+ }
take->Recycle();
+ // Since we're taking from the global free-list, take must be Free.
+ // om_release() also sets the allocation state to Free because it
+ // is called from other code paths.
+ assert(take->is_free(), "invariant");
om_release(self, take, false);
}
self->om_free_provision += 1 + (self->om_free_provision / 2);
if (self->om_free_provision > MAXPRIVATE) self->om_free_provision = MAXPRIVATE;
continue;
@@ -1287,10 +1472,11 @@
// linkage should be reconsidered. A better implementation would
// look like: class Block { Block * next; int N; ObjectMonitor Body [N] ; }
for (int i = 1; i < _BLOCKSIZE; i++) {
temp[i].set_next_om((ObjectMonitor*)&temp[i + 1]);
+ assert(temp[i].is_free(), "invariant");
}
// terminate the last monitor as the end of list
temp[_BLOCKSIZE - 1].set_next_om((ObjectMonitor*)NULL);
@@ -1312,12 +1498,12 @@
// a CAS attempt failed. This doesn't allow unbounded #s of monitors to
// accumulate on a thread's free list.
//
// Key constraint: all ObjectMonitors on a thread's free list and the global
// free list must have their object field set to null. This prevents the
-// scavenger -- deflate_monitor_list() -- from reclaiming them while we
-// are trying to release them.
+// scavenger -- deflate_monitor_list() or deflate_monitor_list_using_JT()
+// -- from reclaiming them while we are trying to release them.
void ObjectSynchronizer::om_release(Thread* self, ObjectMonitor* m,
bool from_per_thread_alloc) {
guarantee(m->header().value() == 0, "invariant");
guarantee(m->object() == NULL, "invariant");
@@ -1326,23 +1512,24 @@
if ((m->is_busy() | m->_recursions) != 0) {
stringStream ss;
fatal("freeing in-use monitor: %s, recursions=" INTX_FORMAT,
m->is_busy_to_string(&ss), m->_recursions);
}
+ m->set_allocation_state(ObjectMonitor::Free);
// _next_om is used for both per-thread in-use and free lists so
// we have to remove 'm' from the in-use list first (as needed).
if (from_per_thread_alloc) {
// Need to remove 'm' from om_in_use_list.
ObjectMonitor* mid = NULL;
ObjectMonitor* next = NULL;
- // This list walk can only race with another list walker since
- // deflation can only happen at a safepoint so we don't have to
- // worry about an ObjectMonitor being removed from this list
- // while we are walking it.
+ // This list walk can race with another list walker or with async
+ // deflation so we have to worry about an ObjectMonitor being
+ // removed from this list while we are walking it.
- // Lock the list head to avoid racing with another list walker.
+ // Lock the list head to avoid racing with another list walker
+ // or with async deflation.
if ((mid = get_list_head_locked(&self->om_in_use_list)) == NULL) {
fatal("thread=" INTPTR_FORMAT " in-use list must not be empty.", p2i(self));
}
next = unmarked_next(mid);
if (m == mid) {
@@ -1354,37 +1541,48 @@
} else if (m == next) {
// Second special case:
// 'm' matches next after the list head and we already have the list
// head locked so set mid to what we are extracting:
mid = next;
- // Lock mid to prevent races with a list walker:
+ // Lock mid to prevent races with a list walker or an async
+ // deflater thread that's ahead of us. The locked list head
+ // prevents races from behind us.
om_lock(mid);
// Update next to what follows mid (if anything):
next = unmarked_next(mid);
// Switch next after the list head to new next which unlocks the
// list head, but leaves the extracted mid locked:
self->om_in_use_list->set_next_om(next);
} else {
// We have to search the list to find 'm'.
- om_unlock(mid); // unlock the list head
guarantee(next != NULL, "thread=" INTPTR_FORMAT ": om_in_use_list=" INTPTR_FORMAT
" is too short.", p2i(self), p2i(self->om_in_use_list));
// Our starting anchor is next after the list head which is the
// last ObjectMonitor we checked:
ObjectMonitor* anchor = next;
+ // Lock anchor to prevent races with a list walker or an async
+ // deflater thread that's ahead of us. The locked list head
+ // prevents races from behind us.
+ om_lock(anchor);
+ om_unlock(mid); // Unlock the list head now that anchor is locked.
while ((mid = unmarked_next(anchor)) != NULL) {
if (m == mid) {
// We found 'm' on the per-thread in-use list so extract it.
- om_lock(anchor); // Lock the anchor so we can safely modify it.
// Update next to what follows mid (if anything):
next = unmarked_next(mid);
// Switch next after the anchor to new next which unlocks the
// anchor, but leaves the extracted mid locked:
anchor->set_next_om(next);
break;
} else {
- anchor = mid;
+ // Lock the next anchor to prevent races with a list walker
+ // or an async deflater thread that's ahead of us. The locked
+ // current anchor prevents races from behind us.
+ om_lock(mid);
+ // Unlock current anchor now that next anchor is locked:
+ om_unlock(anchor);
+ anchor = mid; // Advance to new anchor and try again.
}
}
}
if (mid == NULL) {
@@ -1401,10 +1599,11 @@
// the thread's free list:
om_unlock(mid);
}
prepend_to_om_free_list(self, m);
+ guarantee(m->is_free(), "invariant");
}
// Return ObjectMonitors on a moribund thread's free and in-use
// lists to the appropriate global lists. The ObjectMonitors on the
// per-thread in-use list may still be in use by other threads.
@@ -1415,20 +1614,28 @@
// a safepoint and interleave with deflate_idle_monitors(). In
// particular, this ensures that the thread's in-use monitors are
// scanned by a GC safepoint, either via Thread::oops_do() (before
// om_flush() is called) or via ObjectSynchronizer::oops_do() (after
// om_flush() is called).
+//
+// With AsyncDeflateIdleMonitors, deflate_global_idle_monitors_using_JT()
+// and deflate_per_thread_idle_monitors_using_JT() (in another thread) can
+// run at the same time as om_flush() so we have to follow a careful
+// protocol to prevent list corruption.
void ObjectSynchronizer::om_flush(Thread* self) {
// Process the per-thread in-use list first to be consistent.
int in_use_count = 0;
ObjectMonitor* in_use_list = NULL;
ObjectMonitor* in_use_tail = NULL;
NoSafepointVerifier nsv;
- // This function can race with a list walker thread so we lock the
- // list head to prevent confusion.
+ // This function can race with a list walker or with an async
+ // deflater thread so we lock the list head to prevent confusion.
+ // An async deflater thread checks to see if the target thread
+ // is exiting, but if it has made it past that check before we
+ // started exiting, then it is racing to get to the in-use list.
if ((in_use_list = get_list_head_locked(&self->om_in_use_list)) != NULL) {
// At this point, we have locked the in-use list head so a racing
// thread cannot come in after us. However, a racing thread could
// be ahead of us; we'll detect that and delay to let it finish.
//
@@ -1439,24 +1646,36 @@
//
// Account for the in-use list head before the loop since it is
// already locked (by this thread):
in_use_tail = in_use_list;
in_use_count++;
- for (ObjectMonitor* cur_om = unmarked_next(in_use_list); cur_om != NULL; cur_om = unmarked_next(cur_om)) {
+ for (ObjectMonitor* cur_om = unmarked_next(in_use_list); cur_om != NULL;) {
if (is_locked(cur_om)) {
- // cur_om is locked so there must be a racing walker thread ahead
- // of us so we'll give it a chance to finish.
+ // cur_om is locked so there must be a racing walker or async
+ // deflater thread ahead of us so we'll give it a chance to finish.
while (is_locked(cur_om)) {
os::naked_short_sleep(1);
}
+ // Refetch the possibly changed next field and try again.
+ cur_om = unmarked_next(in_use_tail);
+ continue;
+ }
+ if (cur_om->object() == NULL) {
+ // cur_om was deflated and the object ref was cleared while it
+ // was locked. We happened to see it just after it was unlocked
+ // (and added to the free list). Refetch the possibly changed
+ // next field and try again.
+ cur_om = unmarked_next(in_use_tail);
+ continue;
}
in_use_tail = cur_om;
in_use_count++;
+ cur_om = unmarked_next(cur_om);
}
guarantee(in_use_tail != NULL, "invariant");
int l_om_in_use_count = Atomic::load(&self->om_in_use_count);
- assert(l_om_in_use_count == in_use_count, "in-use counts don't match: "
+ ADIM_guarantee(l_om_in_use_count == in_use_count, "in-use counts don't match: "
"l_om_in_use_count=%d, in_use_count=%d", l_om_in_use_count, in_use_count);
Atomic::store(&self->om_in_use_count, 0);
// Clear the in-use list head (which also unlocks it):
Atomic::store(&self->om_in_use_list, (ObjectMonitor*)NULL);
om_unlock(in_use_list);
@@ -1495,11 +1714,11 @@
fatal("must be !is_busy: %s", s->is_busy_to_string(&ss));
}
}
guarantee(free_tail != NULL, "invariant");
int l_om_free_count = Atomic::load(&self->om_free_count);
- assert(l_om_free_count == free_count, "free counts don't match: "
+ ADIM_guarantee(l_om_free_count == free_count, "free counts don't match: "
"l_om_free_count=%d, free_count=%d", l_om_free_count, free_count);
Atomic::store(&self->om_free_count, 0);
Atomic::store(&self->om_free_list, (ObjectMonitor*)NULL);
om_unlock(free_list);
}
@@ -1541,19 +1760,21 @@
// Fast path code shared by multiple functions
void ObjectSynchronizer::inflate_helper(oop obj) {
markWord mark = obj->mark();
if (mark.has_monitor()) {
- assert(ObjectSynchronizer::verify_objmon_isinpool(mark.monitor()), "monitor is invalid");
- assert(mark.monitor()->header().is_neutral(), "monitor must record a good object header");
+ ObjectMonitor* monitor = mark.monitor();
+ assert(ObjectSynchronizer::verify_objmon_isinpool(monitor), "monitor=" INTPTR_FORMAT " is invalid", p2i(monitor));
+ markWord dmw = monitor->header();
+ assert(dmw.is_neutral(), "sanity check: header=" INTPTR_FORMAT, dmw.value());
return;
}
- inflate(Thread::current(), obj, inflate_cause_vm_internal);
+ (void)inflate(Thread::current(), obj, inflate_cause_vm_internal);
}
-ObjectMonitor* ObjectSynchronizer::inflate(Thread* self,
- oop object, const InflateCause cause) {
+ObjectMonitor* ObjectSynchronizer::inflate(Thread* self, oop object,
+ const InflateCause cause) {
// Inflate mutates the heap ...
// Relaxing assertion for bug 6320749.
assert(Universe::verify_in_progress() ||
!SafepointSynchronize::is_at_safepoint(), "invariant");
@@ -1573,11 +1794,11 @@
// CASE: inflated
if (mark.has_monitor()) {
ObjectMonitor* inf = mark.monitor();
markWord dmw = inf->header();
assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
- assert(inf->object() == object, "invariant");
+ assert(AsyncDeflateIdleMonitors || inf->object() == object, "invariant");
assert(ObjectSynchronizer::verify_objmon_isinpool(inf), "monitor is invalid");
return inf;
}
// CASE: inflation in progress - inflating over a stack-lock.
@@ -1621,10 +1842,11 @@
m->_Responsible = NULL;
m->_SpinDuration = ObjectMonitor::Knob_SpinLimit; // Consider: maintain by type/class
markWord cmp = object->cas_set_mark(markWord::INFLATING(), mark);
if (cmp != mark) {
+ // om_release() will reset the allocation state from New to Free.
om_release(self, m, true);
continue; // Interference -- just retry
}
// We've successfully installed INFLATING (0) into the mark-word.
@@ -1658,29 +1880,38 @@
// object is in the mark. Furthermore the owner can't complete
// an unlock on the object, either.
markWord dmw = mark.displaced_mark_helper();
// Catch if the object's header is not neutral (not locked and
// not marked is what we care about here).
- assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
+ ADIM_guarantee(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
// Setup monitor fields to proper values -- prepare the monitor
m->set_header(dmw);
// Optimization: if the mark.locker stack address is associated
// with this thread we could simply set m->_owner = self.
// Note that a thread can inflate an object
// that it has stack-locked -- as might happen in wait() -- directly
// with CAS. That is, we can avoid the xchg-NULL .... ST idiom.
+ if (AsyncDeflateIdleMonitors) {
+ m->set_owner_from(NULL, DEFLATER_MARKER, mark.locker());
+ } else {
m->set_owner_from(NULL, mark.locker());
+ }
m->set_object(object);
// TODO-FIXME: assert BasicLock->dhw != 0.
// Must preserve store ordering. The monitor state must
// be stable at the time of publishing the monitor address.
guarantee(object->mark() == markWord::INFLATING(), "invariant");
object->release_set_mark(markWord::encode(m));
+ // Once ObjectMonitor is configured and the object is associated
+ // with the ObjectMonitor, it is safe to allow async deflation:
+ assert(m->is_new(), "freshly allocated monitor must be new");
+ m->set_allocation_state(ObjectMonitor::Old);
+
// 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(self);
@@ -1703,31 +1934,41 @@
// to inflate and then CAS() again to try to swing _owner from NULL to self.
// An inflateTry() method that we could call from enter() would be useful.
// Catch if the object's header is not neutral (not locked and
// not marked is what we care about here).
- assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
+ ADIM_guarantee(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
ObjectMonitor* m = om_alloc(self);
// prepare m for installation - set monitor to initial state
m->Recycle();
m->set_header(mark);
+ if (AsyncDeflateIdleMonitors) {
+ // DEFLATER_MARKER is the only non-NULL value we should see here.
+ m->try_set_owner_from(DEFLATER_MARKER, NULL);
+ }
m->set_object(object);
m->_Responsible = NULL;
m->_SpinDuration = ObjectMonitor::Knob_SpinLimit; // consider: keep metastats by type/class
if (object->cas_set_mark(markWord::encode(m), mark) != mark) {
m->set_header(markWord::zero());
m->set_object(NULL);
m->Recycle();
+ // om_release() will reset the allocation state from New to Free.
om_release(self, m, true);
m = NULL;
continue;
// interference - the markword changed - just retry.
// The state-transitions are one-way, so there's no chance of
// live-lock -- "Inflated" is an absorbing state.
}
+ // Once the ObjectMonitor is configured and object is associated
+ // with the ObjectMonitor, it is safe to allow async deflation:
+ assert(m->is_new(), "freshly allocated monitor must be new");
+ m->set_allocation_state(ObjectMonitor::Old);
+
// 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(self);
@@ -1743,10 +1984,11 @@
}
// We maintain a list of in-use monitors for each thread.
//
+// For safepoint based deflation:
// deflate_thread_local_monitors() scans a single thread's in-use list, while
// deflate_idle_monitors() scans only a global list of in-use monitors which
// is populated only as a thread dies (see om_flush()).
//
// These operations are called at all safepoints, immediately after mutators
@@ -1761,10 +2003,44 @@
//
// Perversely, the heap size -- and thus the STW safepoint rate --
// typically drives the scavenge rate. Large heaps can mean infrequent GC,
// which in turn can mean large(r) numbers of ObjectMonitors in circulation.
// This is an unfortunate aspect of this design.
+//
+// For async deflation:
+// If a special deflation request is made, then the safepoint based
+// deflation mechanism is used. Otherwise, an async deflation request
+// is registered with the ServiceThread and it is notified.
+
+void ObjectSynchronizer::do_safepoint_work(DeflateMonitorCounters* counters) {
+ assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
+
+ // The per-thread in-use lists are handled in
+ // ParallelSPCleanupThreadClosure::do_thread().
+
+ if (!AsyncDeflateIdleMonitors || is_special_deflation_requested()) {
+ // Use the older mechanism for the global in-use list or if a
+ // special deflation has been requested before the safepoint.
+ ObjectSynchronizer::deflate_idle_monitors(counters);
+ return;
+ }
+
+ log_debug(monitorinflation)("requesting async deflation of idle monitors.");
+ // Request deflation of idle monitors by the ServiceThread:
+ set_is_async_deflation_requested(true);
+ MonitorLocker ml(Service_lock, Mutex::_no_safepoint_check_flag);
+ ml.notify_all();
+
+ if (log_is_enabled(Debug, monitorinflation)) {
+ // exit_globals()'s call to audit_and_print_stats() is done
+ // at the Info level and not at a safepoint.
+ // For safepoint based deflation, audit_and_print_stats() is called
+ // in ObjectSynchronizer::finish_deflate_idle_monitors() at the
+ // Debug level at a safepoint.
+ ObjectSynchronizer::audit_and_print_stats(false /* on_exit */);
+ }
+}
// Deflate a single monitor if not in-use
// Return true if deflated, false if in-use
bool ObjectSynchronizer::deflate_monitor(ObjectMonitor* mid, oop obj,
ObjectMonitor** free_head_p,
@@ -1796,14 +2072,20 @@
mark.value(), obj->klass()->external_name());
}
// Restore the header back to obj
obj->release_set_mark(dmw);
+ if (AsyncDeflateIdleMonitors) {
+ // clear() expects the owner field to be NULL.
+ // DEFLATER_MARKER is the only non-NULL value we should see here.
+ mid->try_set_owner_from(DEFLATER_MARKER, NULL);
+ }
mid->clear();
assert(mid->object() == NULL, "invariant: object=" INTPTR_FORMAT,
p2i(mid->object()));
+ assert(mid->is_free(), "invariant");
// Move the deflated ObjectMonitor to the working free list
// defined by free_head_p and free_tail_p.
if (*free_head_p == NULL) *free_head_p = mid;
if (*free_tail_p != NULL) {
@@ -1828,10 +2110,132 @@
deflated = true;
}
return deflated;
}
+// Deflate the specified ObjectMonitor if not in-use using a JavaThread.
+// Returns true if it was deflated and false otherwise.
+//
+// The async deflation protocol sets owner to DEFLATER_MARKER and
+// makes contentions negative as signals to contending threads that
+// an async deflation is in progress. There are a number of checks
+// as part of the protocol to make sure that the calling thread has
+// not lost the race to a contending thread.
+//
+// The ObjectMonitor has been successfully async deflated when:
+// (contentions < 0)
+// Contending threads that see that condition know to retry their operation.
+//
+bool ObjectSynchronizer::deflate_monitor_using_JT(ObjectMonitor* mid,
+ ObjectMonitor** free_head_p,
+ ObjectMonitor** free_tail_p) {
+ assert(AsyncDeflateIdleMonitors, "sanity check");
+ assert(Thread::current()->is_Java_thread(), "precondition");
+ // A newly allocated ObjectMonitor should not be seen here so we
+ // avoid an endless inflate/deflate cycle.
+ assert(mid->is_old(), "must be old: allocation_state=%d",
+ (int) mid->allocation_state());
+
+ if (mid->is_busy()) {
+ // Easy checks are first - the ObjectMonitor is busy so no deflation.
+ return false;
+ }
+
+ // Set a NULL owner to DEFLATER_MARKER to force any contending thread
+ // through the slow path. This is just the first part of the async
+ // deflation dance.
+ if (mid->try_set_owner_from(NULL, DEFLATER_MARKER) != NULL) {
+ // The owner field is no longer NULL so we lost the race since the
+ // ObjectMonitor is now busy.
+ return false;
+ }
+
+ if (mid->contentions() > 0 || mid->_waiters != 0) {
+ // Another thread has raced to enter the ObjectMonitor after
+ // mid->is_busy() above or has already entered and waited on
+ // it which makes it busy so no deflation. Restore owner to
+ // NULL if it is still DEFLATER_MARKER.
+ if (mid->try_set_owner_from(DEFLATER_MARKER, NULL) != DEFLATER_MARKER) {
+ // Deferred decrement for the JT EnterI() that cancelled the async deflation.
+ mid->add_to_contentions(-1);
+ }
+ return false;
+ }
+
+ // Make a zero contentions field negative to force any contending threads
+ // to retry. This is the second part of the async deflation dance.
+ if (Atomic::cmpxchg(&mid->_contentions, (jint)0, -max_jint) != 0) {
+ // Contentions was no longer 0 so we lost the race since the
+ // ObjectMonitor is now busy. Restore owner to NULL if it is
+ // still DEFLATER_MARKER:
+ if (mid->try_set_owner_from(DEFLATER_MARKER, NULL) != DEFLATER_MARKER) {
+ // Deferred decrement for the JT EnterI() that cancelled the async deflation.
+ mid->add_to_contentions(-1);
+ }
+ return false;
+ }
+
+ // Sanity checks for the races:
+ guarantee(mid->owner_is_DEFLATER_MARKER(), "must be deflater marker");
+ guarantee(mid->contentions() < 0, "must be negative: contentions=%d",
+ mid->contentions());
+ guarantee(mid->_waiters == 0, "must be 0: waiters=%d", mid->_waiters);
+ guarantee(mid->_cxq == NULL, "must be no contending threads: cxq="
+ INTPTR_FORMAT, p2i(mid->_cxq));
+ guarantee(mid->_EntryList == NULL,
+ "must be no entering threads: EntryList=" INTPTR_FORMAT,
+ p2i(mid->_EntryList));
+
+ const oop obj = (oop) mid->object();
+ if (log_is_enabled(Trace, monitorinflation)) {
+ ResourceMark rm;
+ log_trace(monitorinflation)("deflate_monitor_using_JT: "
+ "object=" INTPTR_FORMAT ", mark="
+ INTPTR_FORMAT ", type='%s'",
+ p2i(obj), obj->mark().value(),
+ obj->klass()->external_name());
+ }
+
+ // Install the old mark word if nobody else has already done it.
+ mid->install_displaced_markword_in_object(obj);
+ mid->clear_common();
+
+ assert(mid->object() == NULL, "must be NULL: object=" INTPTR_FORMAT,
+ p2i(mid->object()));
+ assert(mid->is_free(), "must be free: allocation_state=%d",
+ (int)mid->allocation_state());
+
+ // Move the deflated ObjectMonitor to the working free list
+ // defined by free_head_p and free_tail_p.
+ if (*free_head_p == NULL) {
+ // First one on the list.
+ *free_head_p = mid;
+ }
+ if (*free_tail_p != NULL) {
+ // We append to the list so the caller can use mid->_next_om
+ // to fix the linkages in its context.
+ ObjectMonitor* prevtail = *free_tail_p;
+ // prevtail should have been cleaned up by the caller:
+#ifdef ASSERT
+ ObjectMonitor* l_next_om = unmarked_next(prevtail);
+#endif
+ assert(l_next_om == NULL, "must be NULL: _next_om=" INTPTR_FORMAT, p2i(l_next_om));
+ om_lock(prevtail);
+ prevtail->set_next_om(mid); // prevtail now points to mid (and is unlocked)
+ }
+ *free_tail_p = mid;
+
+ // At this point, mid->_next_om still refers to its current
+ // value and another ObjectMonitor's _next_om field still
+ // refers to this ObjectMonitor. Those linkages have to be
+ // cleaned up by the caller who has the complete context.
+
+ // We leave owner == DEFLATER_MARKER and contentions < 0
+ // to force any racing threads to retry.
+ return true; // Success, ObjectMonitor has been deflated.
+}
+
// Walk a given monitor list, and deflate idle monitors.
// The given list could be a per-thread list or a global list.
//
// In the case of parallel processing of thread local monitor lists,
// work is done by Threads::parallel_threads_do() which ensures that
@@ -1878,20 +2282,170 @@
}
}
return deflated_count;
}
+// Walk a given ObjectMonitor list and deflate idle ObjectMonitors using
+// a JavaThread. Returns the number of deflated ObjectMonitors. The given
+// list could be a per-thread in-use list or the global in-use list.
+// If a safepoint has started, then we save state via saved_mid_in_use_p
+// and return to the caller to honor the safepoint.
+//
+int ObjectSynchronizer::deflate_monitor_list_using_JT(ObjectMonitor** list_p,
+ int* count_p,
+ ObjectMonitor** free_head_p,
+ ObjectMonitor** free_tail_p,
+ ObjectMonitor** saved_mid_in_use_p) {
+ assert(AsyncDeflateIdleMonitors, "sanity check");
+ JavaThread* self = JavaThread::current();
+
+ ObjectMonitor* cur_mid_in_use = NULL;
+ ObjectMonitor* mid = NULL;
+ ObjectMonitor* next = NULL;
+ ObjectMonitor* next_next = NULL;
+ int deflated_count = 0;
+ NoSafepointVerifier nsv;
+
+ // We use the more complicated lock-cur_mid_in_use-and-mid-as-we-go
+ // protocol because om_release() can do list deletions in parallel;
+ // this also prevents races with a list walker thread. We also
+ // lock-next-next-as-we-go to prevent an om_flush() that is behind
+ // this thread from passing us.
+ if (*saved_mid_in_use_p == NULL) {
+ // No saved state so start at the beginning.
+ // Lock the list head so we can possibly deflate it:
+ if ((mid = get_list_head_locked(list_p)) == NULL) {
+ return 0; // The list is empty so nothing to deflate.
+ }
+ next = unmarked_next(mid);
+ } else {
+ // We're restarting after a safepoint so restore the necessary state
+ // before we resume.
+ cur_mid_in_use = *saved_mid_in_use_p;
+ // Lock cur_mid_in_use so we can possibly update its
+ // next field to extract a deflated ObjectMonitor.
+ om_lock(cur_mid_in_use);
+ mid = unmarked_next(cur_mid_in_use);
+ if (mid == NULL) {
+ om_unlock(cur_mid_in_use);
+ *saved_mid_in_use_p = NULL;
+ return 0; // The remainder is empty so nothing more to deflate.
+ }
+ // Lock mid so we can possibly deflate it:
+ om_lock(mid);
+ next = unmarked_next(mid);
+ }
+
+ while (true) {
+ // The current mid is locked at this point. If we have a
+ // cur_mid_in_use, then it is also locked at this point.
+
+ if (next != NULL) {
+ // We lock next so that an om_flush() thread that is behind us
+ // cannot pass us when we unlock the current mid.
+ om_lock(next);
+ next_next = unmarked_next(next);
+ }
+
+ // Only try to deflate if there is an associated Java object and if
+ // mid is old (is not newly allocated and is not newly freed).
+ if (mid->object() != NULL && mid->is_old() &&
+ deflate_monitor_using_JT(mid, free_head_p, free_tail_p)) {
+ // Deflation succeeded and already updated free_head_p and
+ // free_tail_p as needed. Finish the move to the local free list
+ // by unlinking mid from the global or per-thread in-use list.
+ if (cur_mid_in_use == NULL) {
+ // mid is the list head and it is locked. Switch the list head
+ // to next which is also locked (if not NULL) and also leave
+ // mid locked:
+ Atomic::store(list_p, next);
+ } else {
+ ObjectMonitor* locked_next = mark_om_ptr(next);
+ // mid and cur_mid_in_use are locked. Switch cur_mid_in_use's
+ // next field to locked_next and also leave mid locked:
+ cur_mid_in_use->set_next_om(locked_next);
+ }
+ // At this point mid is disconnected from the in-use list so
+ // its lock longer has any effects on in-use list.
+ deflated_count++;
+ Atomic::dec(count_p);
+ // mid is current tail in the free_head_p list so NULL terminate it
+ // (which also unlocks it):
+ mid->set_next_om(NULL);
+
+ // All the list management is done so move on to the next one:
+ mid = next; // mid keeps non-NULL next's locked state
+ next = next_next;
+ } else {
+ // mid is considered in-use if it does not have an associated
+ // Java object or mid is not old or deflation did not succeed.
+ // A mid->is_new() node can be seen here when it is freshly
+ // returned by om_alloc() (and skips the deflation code path).
+ // A mid->is_old() node can be seen here when deflation failed.
+ // A mid->is_free() node can be seen here when a fresh node from
+ // om_alloc() is released by om_release() due to losing the race
+ // in inflate().
+
+ // All the list management is done so move on to the next one:
+ if (cur_mid_in_use != NULL) {
+ om_unlock(cur_mid_in_use);
+ }
+ // The next cur_mid_in_use keeps mid's lock state so
+ // that it is stable for a possible next field change. It
+ // cannot be modified by om_release() while it is locked.
+ cur_mid_in_use = mid;
+ mid = next; // mid keeps non-NULL next's locked state
+ next = next_next;
+
+ if (SafepointMechanism::should_block(self) &&
+ cur_mid_in_use != Atomic::load(list_p) && cur_mid_in_use->is_old()) {
+ // If a safepoint has started and cur_mid_in_use is not the list
+ // head and is old, then it is safe to use as saved state. Return
+ // to the caller before blocking.
+ *saved_mid_in_use_p = cur_mid_in_use;
+ om_unlock(cur_mid_in_use);
+ if (mid != NULL) {
+ om_unlock(mid);
+ }
+ return deflated_count;
+ }
+ }
+ if (mid == NULL) {
+ if (cur_mid_in_use != NULL) {
+ om_unlock(cur_mid_in_use);
+ }
+ break; // Reached end of the list so nothing more to deflate.
+ }
+
+ // The current mid's next field is locked at this point. If we have
+ // a cur_mid_in_use, then it is also locked at this point.
+ }
+ // We finished the list without a safepoint starting so there's
+ // no need to save state.
+ *saved_mid_in_use_p = NULL;
+ return deflated_count;
+}
+
void ObjectSynchronizer::prepare_deflate_idle_monitors(DeflateMonitorCounters* counters) {
counters->n_in_use = 0; // currently associated with objects
counters->n_in_circulation = 0; // extant
counters->n_scavenged = 0; // reclaimed (global and per-thread)
counters->per_thread_scavenged = 0; // per-thread scavenge total
counters->per_thread_times = 0.0; // per-thread scavenge times
}
void ObjectSynchronizer::deflate_idle_monitors(DeflateMonitorCounters* counters) {
assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
+
+ if (AsyncDeflateIdleMonitors) {
+ // Nothing to do when global idle ObjectMonitors are deflated using
+ // a JavaThread unless a special deflation has been requested.
+ if (!is_special_deflation_requested()) {
+ return;
+ }
+ }
+
bool deflated = false;
ObjectMonitor* free_head_p = NULL; // Local SLL of scavenged monitors
ObjectMonitor* free_tail_p = NULL;
elapsedTimer timer;
@@ -1940,39 +2494,257 @@
if (ls != NULL) {
ls->print_cr("deflating global idle monitors, %3.7f secs, %d monitors", timer.seconds(), deflated_count);
}
}
+class HandshakeForDeflation : public HandshakeClosure {
+ public:
+ HandshakeForDeflation() : HandshakeClosure("HandshakeForDeflation") {}
+
+ void do_thread(Thread* thread) {
+ log_trace(monitorinflation)("HandshakeForDeflation::do_thread: thread="
+ INTPTR_FORMAT, p2i(thread));
+ }
+};
+
+void ObjectSynchronizer::deflate_idle_monitors_using_JT() {
+ assert(AsyncDeflateIdleMonitors, "sanity check");
+
+ // Deflate any global idle monitors.
+ deflate_global_idle_monitors_using_JT();
+
+ int count = 0;
+ for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
+ if (Atomic::load(&jt->om_in_use_count) > 0 && !jt->is_exiting()) {
+ // This JavaThread is using ObjectMonitors so deflate any that
+ // are idle unless this JavaThread is exiting; do not race with
+ // ObjectSynchronizer::om_flush().
+ deflate_per_thread_idle_monitors_using_JT(jt);
+ count++;
+ }
+ }
+ if (count > 0) {
+ log_debug(monitorinflation)("did async deflation of idle monitors for %d thread(s).", count);
+ }
+
+ log_info(monitorinflation)("async global_population=%d, global_in_use_count=%d, "
+ "global_free_count=%d, global_wait_count=%d",
+ Atomic::load(&om_list_globals._population),
+ Atomic::load(&om_list_globals._in_use_count),
+ Atomic::load(&om_list_globals._free_count),
+ Atomic::load(&om_list_globals._wait_count));
+
+ // The ServiceThread's async deflation request has been processed.
+ set_is_async_deflation_requested(false);
+
+ if (Atomic::load(&om_list_globals._wait_count) > 0) {
+ // There are deflated ObjectMonitors waiting for a handshake
+ // (or a safepoint) for safety.
+
+ ObjectMonitor* list = Atomic::load(&om_list_globals._wait_list);
+ ADIM_guarantee(list != NULL, "om_list_globals._wait_list must not be NULL");
+ int count = Atomic::load(&om_list_globals._wait_count);
+ Atomic::store(&om_list_globals._wait_count, 0);
+ Atomic::store(&om_list_globals._wait_list, (ObjectMonitor*)NULL);
+
+ // Find the tail for prepend_list_to_common(). No need to mark
+ // ObjectMonitors for this list walk since only the deflater
+ // thread manages the wait list.
+ int l_count = 0;
+ ObjectMonitor* tail = NULL;
+ for (ObjectMonitor* n = list; n != NULL; n = unmarked_next(n)) {
+ tail = n;
+ l_count++;
+ }
+ ADIM_guarantee(count == l_count, "count=%d != l_count=%d", count, l_count);
+
+ // Will execute a safepoint if !ThreadLocalHandshakes:
+ HandshakeForDeflation hfd_hc;
+ Handshake::execute(&hfd_hc);
+
+ prepend_list_to_common(list, tail, count, &om_list_globals._free_list,
+ &om_list_globals._free_count);
+
+ log_info(monitorinflation)("moved %d idle monitors from global waiting list to global free list", count);
+ }
+}
+
+// Deflate global idle ObjectMonitors using a JavaThread.
+//
+void ObjectSynchronizer::deflate_global_idle_monitors_using_JT() {
+ assert(AsyncDeflateIdleMonitors, "sanity check");
+ assert(Thread::current()->is_Java_thread(), "precondition");
+ JavaThread* self = JavaThread::current();
+
+ deflate_common_idle_monitors_using_JT(true /* is_global */, self);
+}
+
+// Deflate the specified JavaThread's idle ObjectMonitors using a JavaThread.
+//
+void ObjectSynchronizer::deflate_per_thread_idle_monitors_using_JT(JavaThread* target) {
+ assert(AsyncDeflateIdleMonitors, "sanity check");
+ assert(Thread::current()->is_Java_thread(), "precondition");
+
+ deflate_common_idle_monitors_using_JT(false /* !is_global */, target);
+}
+
+// Deflate global or per-thread idle ObjectMonitors using a JavaThread.
+//
+void ObjectSynchronizer::deflate_common_idle_monitors_using_JT(bool is_global, JavaThread* target) {
+ JavaThread* self = JavaThread::current();
+
+ int deflated_count = 0;
+ ObjectMonitor* free_head_p = NULL; // Local SLL of scavenged ObjectMonitors
+ ObjectMonitor* free_tail_p = NULL;
+ ObjectMonitor* saved_mid_in_use_p = NULL;
+ elapsedTimer timer;
+
+ if (log_is_enabled(Info, monitorinflation)) {
+ timer.start();
+ }
+
+ if (is_global) {
+ OM_PERFDATA_OP(MonExtant, set_value(Atomic::load(&om_list_globals._in_use_count)));
+ } else {
+ OM_PERFDATA_OP(MonExtant, inc(Atomic::load(&target->om_in_use_count)));
+ }
+
+ do {
+ if (saved_mid_in_use_p != NULL) {
+ // We looped around because deflate_monitor_list_using_JT()
+ // detected a pending safepoint. Honoring the safepoint is good,
+ // but as long as is_special_deflation_requested() is supported,
+ // we can't safely restart using saved_mid_in_use_p. That saved
+ // ObjectMonitor could have been deflated by safepoint based
+ // deflation and would no longer be on the in-use list where we
+ // originally found it.
+ saved_mid_in_use_p = NULL;
+ }
+ int local_deflated_count;
+ if (is_global) {
+ local_deflated_count =
+ deflate_monitor_list_using_JT(&om_list_globals._in_use_list,
+ &om_list_globals._in_use_count,
+ &free_head_p, &free_tail_p,
+ &saved_mid_in_use_p);
+ } else {
+ local_deflated_count =
+ deflate_monitor_list_using_JT(&target->om_in_use_list,
+ &target->om_in_use_count, &free_head_p,
+ &free_tail_p, &saved_mid_in_use_p);
+ }
+ deflated_count += local_deflated_count;
+
+ if (free_head_p != NULL) {
+ // Move the deflated ObjectMonitors to the global free list.
+ guarantee(free_tail_p != NULL && local_deflated_count > 0, "free_tail_p=" INTPTR_FORMAT ", local_deflated_count=%d", p2i(free_tail_p), local_deflated_count);
+ // Note: The target thread can be doing an om_alloc() that
+ // is trying to prepend an ObjectMonitor on its in-use list
+ // at the same time that we have deflated the current in-use
+ // list head and put it on the local free list. prepend_to_common()
+ // will detect the race and retry which avoids list corruption,
+ // but the next field in free_tail_p can flicker to marked
+ // and then unmarked while prepend_to_common() is sorting it
+ // all out.
+#ifdef ASSERT
+ ObjectMonitor* l_next_om = unmarked_next(free_tail_p);
+#endif
+ assert(l_next_om == NULL, "must be NULL: _next_om=" INTPTR_FORMAT, p2i(l_next_om));
+
+ prepend_list_to_global_wait_list(free_head_p, free_tail_p, local_deflated_count);
+
+ OM_PERFDATA_OP(Deflations, inc(local_deflated_count));
+ }
+
+ if (saved_mid_in_use_p != NULL) {
+ // deflate_monitor_list_using_JT() detected a safepoint starting.
+ timer.stop();
+ {
+ if (is_global) {
+ log_debug(monitorinflation)("pausing deflation of global idle monitors for a safepoint.");
+ } else {
+ log_debug(monitorinflation)("jt=" INTPTR_FORMAT ": pausing deflation of per-thread idle monitors for a safepoint.", p2i(target));
+ }
+ assert(SafepointMechanism::should_block(self), "sanity check");
+ ThreadBlockInVM blocker(self);
+ }
+ // Prepare for another loop after the safepoint.
+ free_head_p = NULL;
+ free_tail_p = NULL;
+ if (log_is_enabled(Info, monitorinflation)) {
+ timer.start();
+ }
+ }
+ } while (saved_mid_in_use_p != NULL);
+ timer.stop();
+
+ LogStreamHandle(Debug, monitorinflation) lsh_debug;
+ LogStreamHandle(Info, monitorinflation) lsh_info;
+ LogStream* ls = NULL;
+ if (log_is_enabled(Debug, monitorinflation)) {
+ ls = &lsh_debug;
+ } else if (deflated_count != 0 && log_is_enabled(Info, monitorinflation)) {
+ ls = &lsh_info;
+ }
+ if (ls != NULL) {
+ if (is_global) {
+ ls->print_cr("async-deflating global idle monitors, %3.7f secs, %d monitors", timer.seconds(), deflated_count);
+ } else {
+ ls->print_cr("jt=" INTPTR_FORMAT ": async-deflating per-thread idle monitors, %3.7f secs, %d monitors", p2i(target), timer.seconds(), deflated_count);
+ }
+ }
+}
+
void ObjectSynchronizer::finish_deflate_idle_monitors(DeflateMonitorCounters* counters) {
// Report the cumulative time for deflating each thread's idle
// monitors. Note: if the work is split among more than one
// worker thread, then the reported time will likely be more
// than a beginning to end measurement of the phase.
log_info(safepoint, cleanup)("deflating per-thread idle monitors, %3.7f secs, monitors=%d", counters->per_thread_times, counters->per_thread_scavenged);
+ bool needs_special_deflation = is_special_deflation_requested();
+ if (AsyncDeflateIdleMonitors && !needs_special_deflation) {
+ // Nothing to do when idle ObjectMonitors are deflated using
+ // a JavaThread unless a special deflation has been requested.
+ return;
+ }
+
if (log_is_enabled(Debug, monitorinflation)) {
// exit_globals()'s call to audit_and_print_stats() is done
// at the Info level and not at a safepoint.
+ // For async deflation, audit_and_print_stats() is called in
+ // ObjectSynchronizer::do_safepoint_work() at the Debug level
+ // at a safepoint.
ObjectSynchronizer::audit_and_print_stats(false /* on_exit */);
} else if (log_is_enabled(Info, monitorinflation)) {
log_info(monitorinflation)("global_population=%d, global_in_use_count=%d, "
- "global_free_count=%d",
+ "global_free_count=%d, global_wait_count=%d",
Atomic::load(&om_list_globals._population),
Atomic::load(&om_list_globals._in_use_count),
- Atomic::load(&om_list_globals._free_count));
+ Atomic::load(&om_list_globals._free_count),
+ Atomic::load(&om_list_globals._wait_count));
}
OM_PERFDATA_OP(Deflations, inc(counters->n_scavenged));
OM_PERFDATA_OP(MonExtant, set_value(counters->n_in_circulation));
GVars.stw_random = os::random();
GVars.stw_cycle++;
+
+ if (needs_special_deflation) {
+ set_is_special_deflation_requested(false); // special deflation is done
+ }
}
void ObjectSynchronizer::deflate_thread_local_monitors(Thread* thread, DeflateMonitorCounters* counters) {
assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
+ if (AsyncDeflateIdleMonitors && !is_special_deflation_requested()) {
+ // Nothing to do if a special deflation has NOT been requested.
+ return;
+ }
+
ObjectMonitor* free_head_p = NULL; // Local SLL of scavenged monitors
ObjectMonitor* free_tail_p = NULL;
elapsedTimer timer;
if (log_is_enabled(Info, safepoint, cleanup) ||
@@ -2142,10 +2914,13 @@
chk_global_in_use_list_and_count(ls, &error_cnt);
// Check om_list_globals._free_list and om_list_globals._free_count:
chk_global_free_list_and_count(ls, &error_cnt);
+ // Check om_list_globals._wait_list and om_list_globals._wait_count:
+ chk_global_wait_list_and_count(ls, &error_cnt);
+
ls->print_cr("Checking per-thread lists:");
for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
// Check om_in_use_list and om_in_use_count:
chk_per_thread_in_use_list_and_count(jt, ls, &error_cnt);
@@ -2192,17 +2967,18 @@
if (jt != NULL) {
out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
": free per-thread monitor must have NULL _header "
"field: _header=" INTPTR_FORMAT, p2i(jt), p2i(n),
n->header().value());
- } else {
+ *error_cnt_p = *error_cnt_p + 1;
+ } else if (!AsyncDeflateIdleMonitors) {
out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": free global monitor "
"must have NULL _header field: _header=" INTPTR_FORMAT,
p2i(n), n->header().value());
- }
*error_cnt_p = *error_cnt_p + 1;
}
+ }
if (n->object() != NULL) {
if (jt != NULL) {
out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
": free per-thread monitor must have NULL _object "
"field: _object=" INTPTR_FORMAT, p2i(jt), p2i(n),
@@ -2264,10 +3040,40 @@
out->print_cr("WARNING: global_free_count=%d is not equal to "
"chk_om_free_count=%d", l_free_count, chk_om_free_count);
}
}
+// Check the global wait list and count; log the results of the checks.
+void ObjectSynchronizer::chk_global_wait_list_and_count(outputStream * out,
+ int *error_cnt_p) {
+ int chk_om_wait_count = 0;
+ ObjectMonitor* cur = NULL;
+ if ((cur = get_list_head_locked(&om_list_globals._wait_list)) != NULL) {
+ // Marked the global wait list head so process the list.
+ while (true) {
+ // Rules for om_list_globals._wait_list are the same as for
+ // om_list_globals._free_list:
+ chk_free_entry(NULL /* jt */, cur, out, error_cnt_p);
+ chk_om_wait_count++;
+
+ cur = lock_next_for_traversal(cur);
+ if (cur == NULL) {
+ break;
+ }
+ }
+ }
+ if (Atomic::load(&om_list_globals._wait_count) == chk_om_wait_count) {
+ out->print_cr("global_wait_count=%d equals chk_om_wait_count=%d",
+ Atomic::load(&om_list_globals._wait_count), chk_om_wait_count);
+ } else {
+ out->print_cr("ERROR: global_wait_count=%d is not equal to "
+ "chk_om_wait_count=%d",
+ Atomic::load(&om_list_globals._wait_count), chk_om_wait_count);
+ *error_cnt_p = *error_cnt_p + 1;
+ }
+}
+
// Check the global in-use list and count; log the results of the checks.
void ObjectSynchronizer::chk_global_in_use_list_and_count(outputStream * out,
int *error_cnt_p) {
int chk_om_in_use_count = 0;
ObjectMonitor* cur = NULL;
@@ -2487,18 +3293,20 @@
// Log counts for the global and per-thread monitor lists and return
// the population count.
int ObjectSynchronizer::log_monitor_list_counts(outputStream * out) {
int pop_count = 0;
- out->print_cr("%18s %10s %10s %10s",
- "Global Lists:", "InUse", "Free", "Total");
- out->print_cr("================== ========== ========== ==========");
+ out->print_cr("%18s %10s %10s %10s %10s",
+ "Global Lists:", "InUse", "Free", "Wait", "Total");
+ out->print_cr("================== ========== ========== ========== ==========");
int l_in_use_count = Atomic::load(&om_list_globals._in_use_count);
int l_free_count = Atomic::load(&om_list_globals._free_count);
- out->print_cr("%18s %10d %10d %10d", "", l_in_use_count,
- l_free_count, Atomic::load(&om_list_globals._population));
- pop_count += l_in_use_count + l_free_count;
+ int l_wait_count = Atomic::load(&om_list_globals._wait_count);
+ out->print_cr("%18s %10d %10d %10d %10d", "", l_in_use_count,
+ l_free_count, l_wait_count,
+ Atomic::load(&om_list_globals._population));
+ pop_count += l_in_use_count + l_free_count + l_wait_count;
out->print_cr("%18s %10s %10s %10s",
"Per-Thread Lists:", "InUse", "Free", "Provision");
out->print_cr("================== ========== ========== ==========");
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