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#ifndef SHARE_RUNTIME_OBJECTMONITOR_HPP
#define SHARE_RUNTIME_OBJECTMONITOR_HPP
#include "memory/allocation.hpp"
#include "memory/padded.hpp"
#include "oops/markWord.hpp"
#include "runtime/os.hpp"
#include "runtime/park.hpp"
#include "runtime/perfData.hpp"
class ObjectMonitor;
// 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 };
ObjectWaiter* volatile _next;
ObjectWaiter* volatile _prev;
Thread* _thread;
jlong _notifier_tid;
ParkEvent * _event;
volatile int _notified;
volatile TStates TState;
bool _active; // Contention monitoring is enabled
public:
ObjectWaiter(Thread* thread);
void wait_reenter_begin(ObjectMonitor *mon);
void wait_reenter_end(ObjectMonitor *mon);
};
// 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.
//
// ObjectMonitor Layout Overview/Highlights/Restrictions:
//
// - The _header field must be at offset 0 because the displaced header
// from markWord is stored there. We do not want markWord.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 TEST_VM(ObjectMonitor, sanity) gtest for how critical restrictions are
// enforced.
// - 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 TEST_VM(SynchronizerTest, sanity) gtest.
//
// 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.
#ifndef OM_CACHE_LINE_SIZE
// Use DEFAULT_CACHE_LINE_SIZE if not already specified for
// the current build platform.
#define OM_CACHE_LINE_SIZE DEFAULT_CACHE_LINE_SIZE
#endif
class ObjectMonitor {
friend class ObjectSynchronizer;
friend class ObjectWaiter;
friend class VMStructs;
JVMCI_ONLY(friend class JVMCIVMStructs;)
// The sync code expects the header field to be at offset zero (0).
// Enforced by the assert() in header_addr().
volatile markWord _header; // displaced object header word - mark
void* volatile _object; // backward object pointer - strong root
typedef enum {
Free = 0, // Free must be 0 for monitor to be free after memset(..,0,..).
New,
Old
} AllocationState;
AllocationState _allocation_state;
// Separate _header and _owner on different cache lines since both can
// have busy multi-threaded access. _header, _object and _allocation_state
// are set at initial inflation. _object and _allocation_state don't
// change until deflation so _object and _allocation_state are good
// choices to share the cache line with _header.
DEFINE_PAD_MINUS_SIZE(0, OM_CACHE_LINE_SIZE, sizeof(volatile markWord) +
sizeof(void* volatile) + sizeof(AllocationState));
// Used by async deflation as a marker in the _owner field:
#define DEFLATER_MARKER reinterpret_cast<void*>(-1)
void* volatile _owner; // pointer to owning thread OR BasicLock
volatile jlong _previous_owner_tid; // thread id of the previous owner of the monitor
// Separate _owner and _next_om on different cache lines since
// both can have busy multi-threaded access. _previous_owner_tid is only
// changed by ObjectMonitor::exit() so it is a good choice to share the
// cache line with _owner.
DEFINE_PAD_MINUS_SIZE(1, OM_CACHE_LINE_SIZE, sizeof(void* volatile) +
sizeof(volatile jlong));
ObjectMonitor* _next_om; // Next ObjectMonitor* linkage
volatile intx _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.
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;
jint _contentions; // Number of active contentions in enter(). It is used by is_busy()
// along with other fields to determine if an ObjectMonitor can be
// deflated. It is also used by the async deflation protocol. See
// ObjectSynchronizer::deflate_monitor() and deflate_monitor_using_JT().
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_Notifications;
static PerfCounter * _sync_Inflations;
static PerfCounter * _sync_Deflations;
static PerfLongVariable * _sync_MonExtant;
static int Knob_SpinLimit;
void* operator new (size_t size) throw();
void* operator new[] (size_t size) throw();
void operator delete(void* p);
void operator delete[] (void* 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 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 markWord::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()) - markWord::monitor_value)
markWord header() const;
volatile markWord* header_addr();
void set_header(markWord hdr);
intptr_t is_busy() const {
// TODO-FIXME: assert _owner == null implies _recursions = 0
intptr_t ret_code = _waiters | intptr_t(_cxq) | intptr_t(_EntryList);
if (!AsyncDeflateIdleMonitors) {
ret_code |= contentions() | intptr_t(_owner);
} else {
if (contentions() > 0) {
ret_code |= contentions();
}
if (_owner != DEFLATER_MARKER) {
ret_code |= intptr_t(_owner);
}
}
return ret_code;
}
const char* is_busy_to_string(stringStream* ss);
intptr_t is_entered(Thread* current) const;
void* owner() const; // Returns NULL if DEFLATER_MARKER is observed.
// Returns true if owner field == DEFLATER_MARKER and false otherwise.
bool owner_is_DEFLATER_MARKER();
// Returns true if 'this' is being async deflated and false otherwise.
bool is_being_async_deflated();
// Clear _owner field; current value must match old_value.
void release_clear_owner(void* old_value);
// Simply set _owner field to new_value; current value must match old_value.
void set_owner_from(void* old_value, void* new_value);
// Simply set _owner field to new_value; current value must match old_value1 or old_value2.
void set_owner_from(void* old_value1, void* old_value2, void* new_value);
// Simply set _owner field to self; current value must match basic_lock_p.
void set_owner_from_BasicLock(void* basic_lock_p, Thread* self);
// Try to set _owner field to new_value if the current value matches
// old_value, using Atomic::cmpxchg(). Otherwise, does not change the
// _owner field. Returns the prior value of the _owner field.
void* try_set_owner_from(void* old_value, void* new_value);
ObjectMonitor* next_om() const;
// Simply set _next_om field to new_value.
void set_next_om(ObjectMonitor* new_value);
// Try to set _next_om field to new_value if the current value matches
// old_value, using Atomic::cmpxchg(). Otherwise, does not change the
// _next_om field. Returns the prior value of the _next_om field.
ObjectMonitor* try_set_next_om(ObjectMonitor* old_value, ObjectMonitor* new_value);
jint waiters() const;
jint contentions() const;
void add_to_contentions(jint value);
intx 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
// _contentions == 0 _EntryList == NULL etc
}
private:
void Recycle() {
// TODO: add stronger asserts ...
// _cxq == 0 _succ == NULL _owner == NULL _waiters == 0
// _contentions == 0 EntryList == NULL
// _recursions == 0 _WaitSet == NULL
#ifdef ASSERT
stringStream ss;
#endif
assert((is_busy() | _recursions) == 0, "freeing in-use monitor: %s, "
"recursions=" INTX_FORMAT, is_busy_to_string(&ss), _recursions);
_succ = NULL;
_EntryList = NULL;
_cxq = NULL;
_WaitSet = NULL;
_recursions = 0;
}
public:
void* object() const;
void* object_addr();
void set_object(void* obj);
void release_set_allocation_state(AllocationState s);
void set_allocation_state(AllocationState s);
AllocationState allocation_state() const;
AllocationState allocation_state_acquire() const;
bool is_free() const;
bool is_old() const;
bool is_new() const;
// Returns true if the specified thread owns the ObjectMonitor. Otherwise
// returns false and throws IllegalMonitorStateException (IMSE).
bool check_owner(Thread* THREAD);
void clear();
void clear_common();
bool enter(TRAPS);
void exit(bool not_suspended, TRAPS);
void wait(jlong millis, bool interruptable, TRAPS);
void notify(TRAPS);
void notifyAll(TRAPS);
void print() const;
#ifdef ASSERT
void print_debug_style_on(outputStream* st) const;
#endif
void print_on(outputStream* st) const;
// Use the following at your own risk
intx complete_exit(TRAPS);
bool reenter(intx recursions, TRAPS);
private:
void AddWaiter(ObjectWaiter* waiter);
void INotify(Thread* self);
ObjectWaiter* DequeueWaiter();
void DequeueSpecificWaiter(ObjectWaiter* waiter);
void EnterI(TRAPS);
void ReenterI(Thread* self, ObjectWaiter* self_node);
void UnlinkAfterAcquire(Thread* self, ObjectWaiter* self_node);
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 install_displaced_markword_in_object(const oop obj);
};
// Macro to use guarantee() for more strict AsyncDeflateIdleMonitors
// checks and assert() otherwise.
#define ADIM_guarantee(p, ...) \
do { \
if (AsyncDeflateIdleMonitors) { \
guarantee(p, __VA_ARGS__); \
} else { \
assert(p, __VA_ARGS__); \
} \
} while (0)
#endif // SHARE_RUNTIME_OBJECTMONITOR_HPP