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#include "cppstdlib/type_traits.hpp"
#include "metaprogramming/primitiveConversions.hpp"
#include "oops/compressedKlass.hpp"
#include "oops/oopsHierarchy.hpp"
#include "runtime/globals.hpp"
+ #include "utilities/powerOfTwo.hpp"
// The markWord describes the header of an object.
//
// Bit-format of an object header (most significant first, big endian layout below):
//
// 32 bits:
// --------
- // hash:25 ------------>| age:4 self-fwd:1 lock:2 (normal object)
+ // hash:25 age:4 self-fwd:1 lock:2
//
- // 64 bits:
- // --------
- // unused:22 hash:31 -->| unused_gap:4 age:4 self-fwd:1 lock:2 (normal object)
+ // 64 bits (without compact headers):
+ // ----------------------------------
+ // unused:22 hash:31 valhalla:4 age:4 self-fwd:1 lock:2
//
// 64 bits (with compact headers):
// -------------------------------
- // klass:22 hash:31 -->| unused_gap:4 age:4 self-fwd:1 lock:2 (normal object)
- //
- // - hash contains the identity hash value: largest value is
- // 31 bits, see os::random(). Also, 64-bit vm's require
- // a hash value no bigger than 32 bits because they will not
- // properly generate a mask larger than that: see library_call.cpp
+ // klass:22 hash:31 valhalla:4 age:4 self-fwd:1 lock:2
//
- // - the two lock bits are used to describe three states: locked/unlocked and monitor.
+ // - lock bits are used to describe lock states: locked/unlocked/monitor-locked
+ // and to indicate that an object has been GC marked / forwarded.
//
// [header | 00] locked locked regular object header (fast-locking in use)
// [header | 01] unlocked regular object header
- // [ptr | 10] monitor inflated lock (header is swapped out, UseObjectMonitorTable == false)
// [header | 10] monitor inflated lock (UseObjectMonitorTable == true)
- // [ptr | 11] marked used to mark an object
+ // [ptr | 10] monitor inflated lock (UseObjectMonitorTable == false, header is swapped out)
+ // [ptr | 11] marked used to mark an object (header is swapped out)
+ //
+ // - self-fwd - used by some GCs to indicate in-place forwarding.
+ //
+ // Note the position of 'self-fwd' is not by accident. When forwarding an
+ // object to a new heap position, HeapWord alignment guarantees the lower
+ // bits, including 'self-fwd' are 0. "is_self_forwarded()" will be correctly
+ // set to false. Otherwise encode_pointer_as_mark() may have 'self-fwd' set.
+ //
+ // - age - used by some GCs to track the age of objects.
+ //
+ // - valhalla - only supported on 64-bit VMs
+ //
+ // * inline types: A value class instance
+ // * flat arrays: An array with flattened value class elements
+ // * null-free arrays: An array instance without null elements
+ // * valhalla reserved: Reserved for future use
+ //
+ // Inline types cannot be locked and do not have an identity hash.
+ //
+ // - hash - contains the identity hash value: largest value is 31 bits, see
+ // os::random(). Also, 64-bit VMs require a hash value no bigger than 32
+ // bits because they will not properly generate a mask larger than that:
+ // see library_call.cpp
+ //
+ // - klass - klass identifier used when UseCompactObjectHeaders == true
- class BasicLock;
class ObjectMonitor;
- class JavaThread;
class outputStream;
class markWord {
private:
uintptr_t _value;
}
// Conversion
uintptr_t value() const { return _value; }
- // Constants
- static const int age_bits = 4;
+ // Constants, in least significant bit order
+
+ // Number of bits
static const int lock_bits = 2;
static const int self_fwd_bits = 1;
- static const int max_hash_bits = BitsPerWord - age_bits - lock_bits - self_fwd_bits;
+ static const int age_bits = 4;
+ static const int inline_type_bits = LP64_ONLY(1) NOT_LP64(0);
+ static const int null_free_array_bits = LP64_ONLY(1) NOT_LP64(0);
+ static const int flat_array_bits = LP64_ONLY(1) NOT_LP64(0);
+ static const int valhalla_reserved_bits = LP64_ONLY(1) NOT_LP64(0);
+ static const int max_hash_bits = BitsPerWord - age_bits - lock_bits - inline_type_bits - valhalla_reserved_bits - flat_array_bits - null_free_array_bits - self_fwd_bits;
static const int hash_bits = max_hash_bits > 31 ? 31 : max_hash_bits;
- static const int unused_gap_bits = LP64_ONLY(4) NOT_LP64(0); // Reserved for Valhalla.
+ // Shifts
static const int lock_shift = 0;
static const int self_fwd_shift = lock_shift + lock_bits;
static const int age_shift = self_fwd_shift + self_fwd_bits;
- static const int hash_shift = age_shift + age_bits + unused_gap_bits;
+ static const int inline_type_shift = age_shift + age_bits;
+ static const int null_free_array_shift = inline_type_shift + inline_type_bits;
+ static const int flat_array_shift = null_free_array_shift + null_free_array_bits;
+ static const int valhalla_reserved_shift = flat_array_shift + flat_array_bits;
+ static const int hash_shift = valhalla_reserved_shift + valhalla_reserved_bits;
+
+ // Masks (in-place)
+ static const uintptr_t lock_mask_in_place = right_n_bits(lock_bits) << lock_shift;
+ static const uintptr_t self_fwd_bit_in_place = right_n_bits(self_fwd_bits) << self_fwd_shift;
+ static const uintptr_t age_mask_in_place = right_n_bits(age_bits) << age_shift;
+ static const uintptr_t inline_type_bit_in_place = right_n_bits(inline_type_bits) << inline_type_shift;
+ static const uintptr_t null_free_array_bit_in_place = right_n_bits(null_free_array_bits) << null_free_array_shift;
+ static const uintptr_t flat_array_bit_in_place = right_n_bits(flat_array_bits) << flat_array_shift;
+ static const uintptr_t valhalla_reserved_bit_in_place = right_n_bits(valhalla_reserved_bits) << valhalla_reserved_shift;
+ static const uintptr_t hash_mask_in_place = right_n_bits(hash_bits) << hash_shift;
+
+ // Verify that _bit_in_place refers to constants with only one bit.
+ static_assert(is_power_of_2(self_fwd_bit_in_place));
+ #ifdef _LP64
+ static_assert(is_power_of_2(inline_type_bit_in_place));
+ static_assert(is_power_of_2(null_free_array_bit_in_place));
+ static_assert(is_power_of_2(flat_array_bit_in_place));
+ static_assert(is_power_of_2(valhalla_reserved_bit_in_place));
+ #endif
- static const uintptr_t lock_mask = right_n_bits(lock_bits);
- static const uintptr_t lock_mask_in_place = lock_mask << lock_shift;
- static const uintptr_t self_fwd_mask = right_n_bits(self_fwd_bits);
- static const uintptr_t self_fwd_mask_in_place = self_fwd_mask << self_fwd_shift;
- static const uintptr_t age_mask = right_n_bits(age_bits);
- static const uintptr_t age_mask_in_place = age_mask << age_shift;
- static const uintptr_t hash_mask = right_n_bits(hash_bits);
- static const uintptr_t hash_mask_in_place = hash_mask << hash_shift;
+ // Masks (unshifted)
+ static const uintptr_t lock_mask = lock_mask_in_place >> lock_shift;
+ static const uintptr_t age_mask = age_mask_in_place >> age_shift;
+ static const uintptr_t hash_mask = hash_mask_in_place >> hash_shift;
#ifdef _LP64
// Used only with compact headers:
// We store the (narrow) Klass* in the bits 43 to 64.
- // These are for bit-precise extraction of the narrow Klass* from the 64-bit Markword
+ // These are for bit-precise extraction of the narrow Klass* from the 64-bit markWord
static constexpr int klass_offset_in_bytes = 4;
static constexpr int klass_shift = hash_shift + hash_bits;
static constexpr int klass_shift_at_offset = klass_shift - klass_offset_in_bytes * BitsPerByte;
static constexpr int klass_bits = 22;
static constexpr uintptr_t klass_mask = right_n_bits(klass_bits);
static constexpr uintptr_t klass_mask_in_place = klass_mask << klass_shift;
#endif
-
static const uintptr_t locked_value = 0;
static const uintptr_t unlocked_value = 1;
static const uintptr_t monitor_value = 2;
static const uintptr_t marked_value = 3;
+ static const uintptr_t inline_type_pattern = inline_type_bit_in_place | unlocked_value;
+ static const uintptr_t inline_type_pattern_mask = inline_type_bit_in_place | lock_mask_in_place;
+
static const uintptr_t no_hash = 0 ; // no hash value assigned
static const uintptr_t no_hash_in_place = (uintptr_t)no_hash << hash_shift;
static const uintptr_t no_lock_in_place = unlocked_value;
static const uint max_age = age_mask;
// Creates a markWord with all bits set to zero.
static markWord zero() { return markWord(uintptr_t(0)); }
+ bool is_inline_type() const {
+ #ifdef _LP64 // 64 bit encodings only
+ return (mask_bits(value(), inline_type_pattern_mask) == inline_type_pattern);
+ #else
+ return false;
+ #endif
+ }
+
// lock accessors (note that these assume lock_shift == 0)
bool is_locked() const {
return (mask_bits(value(), lock_mask_in_place) != unlocked_value);
}
bool is_unlocked() const {
return (mask_bits(value(), lock_mask_in_place) == unlocked_value);
}
bool is_marked() const {
return (mask_bits(value(), lock_mask_in_place) == marked_value);
}
- bool is_forwarded() const {
- // Returns true for normal forwarded (0b011) and self-forwarded (0b1xx).
- return mask_bits(value(), lock_mask_in_place | self_fwd_mask_in_place) >= static_cast<intptr_t>(marked_value);
- }
+
bool is_neutral() const { // Not locked, or marked - a "clean" neutral state
+ LP64_ONLY(assert(!is_unlocked() || mask_bits(value(), inline_type_bit_in_place) == 0,
+ "Inline types should not be used for locking. _value: " PTR_FORMAT, _value));
return (mask_bits(value(), lock_mask_in_place) == unlocked_value);
}
+ bool is_forwarded() const {
+ // Returns true for normal forwarded (0b011) and self-forwarded (0b1xx).
+ return mask_bits(value(), lock_mask_in_place | self_fwd_bit_in_place) >= static_cast<intptr_t>(marked_value);
+ }
+
// Should this header be preserved during GC?
bool must_be_preserved() const {
- return (!is_unlocked() || !has_no_hash());
+ // The reserved bits are only guaranteed to be unset if the mark word is "unlocked"
+ LP64_ONLY(assert(!is_unlocked() || mask_bits(value(), valhalla_reserved_bit_in_place) == 0,
+ "Reserved bits should not be used. _value: " PTR_FORMAT, _value));
+ return !is_unlocked() || !has_no_hash();
}
// WARNING: The following routines are used EXCLUSIVELY by
// synchronization functions. They are not really gc safe.
// They must get updated if markWord layout get changed.
assert(!UseObjectMonitorTable, "Locking with OM table does not use markWord for monitors");
uintptr_t tmp = (uintptr_t) monitor;
return markWord(tmp | monitor_value);
}
- bool has_displaced_mark_helper() const {
+ bool has_monitor_pointer() const {
intptr_t lockbits = value() & lock_mask_in_place;
return !UseObjectMonitorTable && lockbits == monitor_value;
}
+
+ bool has_displaced_mark_helper() const {
+ return has_monitor_pointer();
+ }
markWord displaced_mark_helper() const;
void set_displaced_mark_helper(markWord m) const;
// used to encode pointers during GC
markWord clear_lock_bits() const { return markWord(value() & ~lock_mask_in_place); }
bool has_no_hash() const {
return hash() == no_hash;
}
+ bool is_flat_array() const {
+ assert(!has_monitor_pointer(), "Bits are not valid if replaced by a monitor pointer: " PTR_FORMAT, value());
+ assert(!is_marked(), "Bits might not be valid if marked by the GC: " PTR_FORMAT, value());
+ #ifdef _LP64 // 64 bit encodings only
+ return (mask_bits(value(), flat_array_bit_in_place) != 0);
+ #else
+ return false;
+ #endif
+ }
+
+ bool is_null_free_array() const {
+ assert(!has_monitor_pointer(), "Bits are not valid if replaced by a monitor pointer: " PTR_FORMAT, value());
+ assert(!is_marked(), "Bits might not be valid if marked by the GC: " PTR_FORMAT, value());
+ #ifdef _LP64 // 64 bit encodings only
+ return (mask_bits(value(), null_free_array_bit_in_place) != 0);
+ #else
+ return false;
+ #endif
+ }
+
markWord copy_set_hash(intptr_t hash) const {
uintptr_t tmp = value() & (~hash_mask_in_place);
tmp |= ((hash & hash_mask) << hash_shift);
return markWord(tmp);
}
inline Klass* klass_or_null() const;
inline Klass* klass_without_asserts() const;
inline narrowKlass narrow_klass() const;
inline markWord set_narrow_klass(narrowKlass narrow_klass) const;
- // Prototype mark for initialization
+ // Prototype marks for initialization
+
static markWord prototype() {
- return markWord( no_hash_in_place | no_lock_in_place );
+ return markWord(unlocked_value);
+ }
+
+ static markWord inline_type_prototype() {
+ NOT_LP64(assert(false, "Should not be called in 32 bit mode"));
+ return markWord(unlocked_value | inline_type_bit_in_place);
+ }
+
+ static markWord flat_array_prototype(bool null_free) {
+ NOT_LP64(assert(false, "Should not be called in 32 bit mode"));
+ if (null_free) {
+ return markWord(unlocked_value | flat_array_bit_in_place | null_free_array_bit_in_place);
+ } else {
+ return markWord(unlocked_value | flat_array_bit_in_place);
+ }
+ }
+
+ static markWord null_free_array_prototype() {
+ NOT_LP64(assert(false, "Should not be called in 32 bit mode"));
+ return markWord(unlocked_value | null_free_array_bit_in_place);
}
// Debugging
void print_on(outputStream* st, bool print_monitor_info = true) const;
// Recover address of oop from encoded form used in mark
inline void* decode_pointer() const { return (void*)clear_lock_bits().value(); }
inline bool is_self_forwarded() const {
- return mask_bits(value(), self_fwd_mask_in_place) != 0;
+ return mask_bits(value(), self_fwd_bit_in_place) != 0;
}
inline markWord set_self_forwarded() const {
- return markWord(value() | self_fwd_mask_in_place);
+ return markWord(value() | self_fwd_bit_in_place);
}
inline markWord unset_self_forwarded() const {
- return markWord(value() & ~self_fwd_mask_in_place);
+ return markWord(value() & ~self_fwd_bit_in_place);
}
inline oop forwardee() const {
return cast_to_oop(decode_pointer());
}
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