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* version 2 for more details (a copy is included in the LICENSE file that
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* 2 along with this work; if not, write to the Free Software Foundation,
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#ifndef SHARE_VM_RUNTIME_OBJECTMONITOR_HPP
#define SHARE_VM_RUNTIME_OBJECTMONITOR_HPP
#include "memory/padded.hpp"
#include "runtime/os.hpp"
#include "runtime/park.hpp"
#include "runtime/perfData.hpp"
// ObjectWaiter serves as a "proxy" or surrogate thread.
// TODO-FIXME: Eliminate ObjectWaiter and use the thread-specific
// ParkEvent instead. Beware, however, that the JVMTI code
// knows about ObjectWaiters, so we'll have to reconcile that code.
// See next_waiter(), first_waiter(), etc.
class ObjectWaiter : public StackObj {
public:
enum TStates { TS_UNDEF, TS_READY, TS_RUN, TS_WAIT, TS_ENTER, TS_CXQ };
enum Sorted { PREPEND, APPEND, SORTED };
ObjectWaiter * volatile _next;
ObjectWaiter * volatile _prev;
Thread* _thread;
jlong _notifier_tid;
ParkEvent * _event;
volatile int _notified;
volatile TStates TState;
Sorted _Sorted; // List placement disposition
bool _active; // Contention monitoring is enabled
public:
ObjectWaiter(Thread* thread);
void wait_reenter_begin(ObjectMonitor *mon);
void wait_reenter_end(ObjectMonitor *mon);
};
// forward declaration to avoid include tracing.hpp
class EventJavaMonitorWait;
// The ObjectMonitor class implements the heavyweight version of a
// JavaMonitor. The lightweight BasicLock/stack lock version has been
// inflated into an ObjectMonitor. This inflation is typically due to
// contention or use of Object.wait().
//
// WARNING: This is a very sensitive and fragile class. DO NOT make any
// changes unless you are fully aware of the underlying semantics.
//
// Class JvmtiRawMonitor currently inherits from ObjectMonitor so
// changes in this class must be careful to not break JvmtiRawMonitor.
// These two subsystems should be separated.
//
// ObjectMonitor Layout Overview/Highlights/Restrictions:
//
// - The _header field must be at offset 0 because the displaced header
// from markOop is stored there. We do not want markOop.hpp to include
// ObjectMonitor.hpp to avoid exposing ObjectMonitor everywhere. This
// means that ObjectMonitor cannot inherit from any other class nor can
// it use any virtual member functions. This restriction is critical to
// the proper functioning of the VM.
// - The _header and _owner fields should be separated by enough space
// to avoid false sharing due to parallel access by different threads.
// This is an advisory recommendation.
// - The general layout of the fields in ObjectMonitor is:
// _header
// <lightly_used_fields>
// <optional padding>
// _owner
// <remaining_fields>
// - The VM assumes write ordering and machine word alignment with
// respect to the _owner field and the <remaining_fields> that can
// be read in parallel by other threads.
// - Generally fields that are accessed closely together in time should
// be placed proximally in space to promote data cache locality. That
// is, temporal locality should condition spatial locality.
// - We have to balance avoiding false sharing with excessive invalidation
// from coherence traffic. As such, we try to cluster fields that tend
// to be _written_ at approximately the same time onto the same data
// cache line.
// - We also have to balance the natural tension between minimizing
// single threaded capacity misses with excessive multi-threaded
// coherency misses. There is no single optimal layout for both
// single-threaded and multi-threaded environments.
//
// - See ObjectMonitor::sanity_checks() for how critical restrictions are
// enforced and advisory recommendations are reported.
// - Adjacent ObjectMonitors should be separated by enough space to avoid
// false sharing. This is handled by the ObjectMonitor allocation code
// in synchronizer.cpp. Also see ObjectSynchronizer::sanity_checks().
//
// Futures notes:
// - Separating _owner from the <remaining_fields> by enough space to
// avoid false sharing might be profitable. Given
// http://blogs.oracle.com/dave/entry/cas_and_cache_trivia_invalidate
// we know that the CAS in monitorenter will invalidate the line
// underlying _owner. We want to avoid an L1 data cache miss on that
// same line for monitorexit. Putting these <remaining_fields>:
// _recursions, _EntryList, _cxq, and _succ, all of which may be
// fetched in the inflated unlock path, on a different cache line
// would make them immune to CAS-based invalidation from the _owner
// field.
//
// - The _recursions field should be of type int, or int32_t but not
// intptr_t. There's no reason to use a 64-bit type for this field
// in a 64-bit JVM.
class ObjectMonitor {
public:
enum {
OM_OK, // no error
OM_SYSTEM_ERROR, // operating system error
OM_ILLEGAL_MONITOR_STATE, // IllegalMonitorStateException
OM_INTERRUPTED, // Thread.interrupt()
OM_TIMED_OUT // Object.wait() timed out
};
private:
friend class ObjectSynchronizer;
friend class ObjectWaiter;
friend class VMStructs;
volatile markOop _header; // displaced object header word - mark
void* volatile _object; // backward object pointer - strong root
public:
ObjectMonitor * FreeNext; // Free list linkage
private:
DEFINE_PAD_MINUS_SIZE(0, DEFAULT_CACHE_LINE_SIZE,
sizeof(volatile markOop) + sizeof(void * volatile) +
sizeof(ObjectMonitor *));
protected: // protected for JvmtiRawMonitor
void * volatile _owner; // pointer to owning thread OR BasicLock
volatile jlong _previous_owner_tid; // thread id of the previous owner of the monitor
volatile intptr_t _recursions; // recursion count, 0 for first entry
ObjectWaiter * volatile _EntryList; // Threads blocked on entry or reentry.
// The list is actually composed of WaitNodes,
// acting as proxies for Threads.
private:
ObjectWaiter * volatile _cxq; // LL of recently-arrived threads blocked on entry.
Thread * volatile _succ; // Heir presumptive thread - used for futile wakeup throttling
Thread * volatile _Responsible;
volatile int _Spinner; // for exit->spinner handoff optimization
volatile int _SpinDuration;
volatile jint _count; // reference count to prevent reclamation/deflation
// at stop-the-world time. See deflate_idle_monitors().
// _count is approximately |_WaitSet| + |_EntryList|
protected:
ObjectWaiter * volatile _WaitSet; // LL of threads wait()ing on the monitor
volatile jint _waiters; // number of waiting threads
private:
volatile int _WaitSetLock; // protects Wait Queue - simple spinlock
public:
static void Initialize();
// Only perform a PerfData operation if the PerfData object has been
// allocated and if the PerfDataManager has not freed the PerfData
// objects which can happen at normal VM shutdown.
//
#define OM_PERFDATA_OP(f, op_str) \
do { \
if (ObjectMonitor::_sync_ ## f != NULL && \
PerfDataManager::has_PerfData()) { \
ObjectMonitor::_sync_ ## f->op_str; \
} \
} while (0)
static PerfCounter * _sync_ContendedLockAttempts;
static PerfCounter * _sync_FutileWakeups;
static PerfCounter * _sync_Parks;
static PerfCounter * _sync_EmptyNotifications;
static PerfCounter * _sync_Notifications;
static PerfCounter * _sync_SlowEnter;
static PerfCounter * _sync_SlowExit;
static PerfCounter * _sync_SlowNotify;
static PerfCounter * _sync_SlowNotifyAll;
static PerfCounter * _sync_FailedSpins;
static PerfCounter * _sync_SuccessfulSpins;
static PerfCounter * _sync_PrivateA;
static PerfCounter * _sync_PrivateB;
static PerfCounter * _sync_MonInCirculation;
static PerfCounter * _sync_MonScavenged;
static PerfCounter * _sync_Inflations;
static PerfCounter * _sync_Deflations;
static PerfLongVariable * _sync_MonExtant;
static int Knob_ExitRelease;
static int Knob_Verbose;
static int Knob_VerifyInUse;
static int Knob_VerifyMatch;
static int Knob_SpinLimit;
void* operator new (size_t size) throw() {
return AllocateHeap(size, mtInternal);
}
void* operator new[] (size_t size) throw() {
return operator new (size);
}
void operator delete(void* p) {
FreeHeap(p);
}
void operator delete[] (void *p) {
operator delete(p);
}
// TODO-FIXME: the "offset" routines should return a type of off_t instead of int ...
// ByteSize would also be an appropriate type.
static int header_offset_in_bytes() { return offset_of(ObjectMonitor, _header); }
static int object_offset_in_bytes() { return offset_of(ObjectMonitor, _object); }
static int owner_offset_in_bytes() { return offset_of(ObjectMonitor, _owner); }
static int count_offset_in_bytes() { return offset_of(ObjectMonitor, _count); }
static int recursions_offset_in_bytes() { return offset_of(ObjectMonitor, _recursions); }
static int cxq_offset_in_bytes() { return offset_of(ObjectMonitor, _cxq); }
static int succ_offset_in_bytes() { return offset_of(ObjectMonitor, _succ); }
static int EntryList_offset_in_bytes() { return offset_of(ObjectMonitor, _EntryList); }
// ObjectMonitor references can be ORed with markOopDesc::monitor_value
// as part of the ObjectMonitor tagging mechanism. When we combine an
// ObjectMonitor reference with an offset, we need to remove the tag
// value in order to generate the proper address.
//
// We can either adjust the ObjectMonitor reference and then add the
// offset or we can adjust the offset that is added to the ObjectMonitor
// reference. The latter avoids an AGI (Address Generation Interlock)
// stall so the helper macro adjusts the offset value that is returned
// to the ObjectMonitor reference manipulation code:
//
#define OM_OFFSET_NO_MONITOR_VALUE_TAG(f) \
((ObjectMonitor::f ## _offset_in_bytes()) - markOopDesc::monitor_value)
markOop header() const;
void set_header(markOop hdr);
intptr_t is_busy() const {
// TODO-FIXME: merge _count and _waiters.
// TODO-FIXME: assert _owner == null implies _recursions = 0
// TODO-FIXME: assert _WaitSet != null implies _count > 0
return _count|_waiters|intptr_t(_owner)|intptr_t(_cxq)|intptr_t(_EntryList);
}
intptr_t is_entered(Thread* current) const;
void* owner() const;
void set_owner(void* owner);
jint waiters() const;
jint count() const;
void set_count(jint count);
jint contentions() const;
intptr_t recursions() const { return _recursions; }
// JVM/TI GetObjectMonitorUsage() needs this:
ObjectWaiter* first_waiter() { return _WaitSet; }
ObjectWaiter* next_waiter(ObjectWaiter* o) { return o->_next; }
Thread* thread_of_waiter(ObjectWaiter* o) { return o->_thread; }
protected:
// We don't typically expect or want the ctors or dtors to run.
// normal ObjectMonitors are type-stable and immortal.
ObjectMonitor() { ::memset((void *)this, 0, sizeof(*this)); }
~ObjectMonitor() {
// TODO: Add asserts ...
// _cxq == 0 _succ == NULL _owner == NULL _waiters == 0
// _count == 0 _EntryList == NULL etc
}
private:
void Recycle() {
// TODO: add stronger asserts ...
// _cxq == 0 _succ == NULL _owner == NULL _waiters == 0
// _count == 0 EntryList == NULL
// _recursions == 0 _WaitSet == NULL
assert(((is_busy()|_recursions) == 0), "freeing inuse monitor");
_succ = NULL;
_EntryList = NULL;
_cxq = NULL;
_WaitSet = NULL;
_recursions = 0;
}
public:
void* object() const;
void* object_addr();
void set_object(void* obj);
bool check(TRAPS); // true if the thread owns the monitor.
void check_slow(TRAPS);
void clear();
static void sanity_checks(); // public for -XX:+ExecuteInternalVMTests
// in PRODUCT for -XX:SyncKnobs=Verbose=1
#ifndef PRODUCT
void verify();
void print();
#endif
void enter(TRAPS);
void exit(bool not_suspended, TRAPS);
void wait(jlong millis, bool interruptable, TRAPS);
void notify(TRAPS);
void notifyAll(TRAPS);
// Use the following at your own risk
intptr_t complete_exit(TRAPS);
void reenter(intptr_t recursions, TRAPS);
private:
void AddWaiter(ObjectWaiter * waiter);
static void DeferredInitialize();
void INotify(Thread * Self);
ObjectWaiter * DequeueWaiter();
void DequeueSpecificWaiter(ObjectWaiter * waiter);
void EnterI(TRAPS);
void ReenterI(Thread * Self, ObjectWaiter * SelfNode);
void UnlinkAfterAcquire(Thread * Self, ObjectWaiter * SelfNode);
int TryLock(Thread * Self);
int NotRunnable(Thread * Self, Thread * Owner);
int TrySpin(Thread * Self);
void ExitEpilog(Thread * Self, ObjectWaiter * Wakee);
bool ExitSuspendEquivalent(JavaThread * Self);
void post_monitor_wait_event(EventJavaMonitorWait * event,
jlong notifier_tid,
jlong timeout,
bool timedout);
};
#undef TEVENT
#define TEVENT(nom) { if (SyncVerbose) FEVENT(nom); }
#define FEVENT(nom) \
{ \
static volatile int ctr = 0; \
int v = ++ctr; \
if ((v & (v - 1)) == 0) { \
tty->print_cr("INFO: " #nom " : %d", v); \
tty->flush(); \
} \
}
#undef TEVENT
#define TEVENT(nom) {;}
#endif // SHARE_VM_RUNTIME_OBJECTMONITOR_HPP