33 : ObjArrayAllocator(klass, word_size, length, do_zero, thread) {}
34
35 void ZObjArrayAllocator::yield_for_safepoint() const {
36 ThreadBlockInVM tbivm(JavaThread::cast(_thread));
37 }
38
39 oop ZObjArrayAllocator::initialize(HeapWord* mem) const {
40 // ZGC specializes the initialization by performing segmented clearing
41 // to allow shorter time-to-safepoints.
42
43 if (!_do_zero) {
44 // No need for ZGC specialization
45 return ObjArrayAllocator::initialize(mem);
46 }
47
48 // A max segment size of 64K was chosen because microbenchmarking
49 // suggested that it offered a good trade-off between allocation
50 // time and time-to-safepoint
51 const size_t segment_max = ZUtils::bytes_to_words(64 * K);
52 const BasicType element_type = ArrayKlass::cast(_klass)->element_type();
53 const size_t header = arrayOopDesc::header_size(element_type);
54 const size_t payload_size = _word_size - header;
55
56 if (payload_size <= segment_max) {
57 // To small to use segmented clearing
58 return ObjArrayAllocator::initialize(mem);
59 }
60
61 // Segmented clearing
62
63 // The array is going to be exposed before it has been completely
64 // cleared, therefore we can't expose the header at the end of this
65 // function. Instead explicitly initialize it according to our needs.
66
67 // Signal to the ZIterator that this is an invisible root, by setting
68 // the mark word to "marked". Reset to prototype() after the clearing.
69 arrayOopDesc::set_mark(mem, markWord::prototype().set_marked());
70 arrayOopDesc::release_set_klass(mem, _klass);
71 assert(_length >= 0, "length should be non-negative");
72 arrayOopDesc::set_length(mem, _length);
73
74 // Keep the array alive across safepoints through an invisible
75 // root. Invisible roots are not visited by the heap iterator
76 // and the marking logic will not attempt to follow its elements.
77 // Relocation and remembered set code know how to dodge iterating
78 // over such objects.
79 ZThreadLocalData::set_invisible_root(_thread, (zaddress_unsafe*)&mem);
80
81 uint32_t old_seqnum_before = ZGeneration::old()->seqnum();
82 uint32_t young_seqnum_before = ZGeneration::young()->seqnum();
83 uintptr_t color_before = ZPointerStoreGoodMask;
84 auto gc_safepoint_happened = [&]() {
85 return old_seqnum_before != ZGeneration::old()->seqnum() ||
86 young_seqnum_before != ZGeneration::young()->seqnum() ||
87 color_before != ZPointerStoreGoodMask;
88 };
89
90 bool seen_gc_safepoint = false;
118 // Deal with safepoints
119 if (!seen_gc_safepoint && gc_safepoint_happened()) {
120 // The first time we observe a GC safepoint in the yield point,
121 // we have to restart processing with 11 remembered bits.
122 seen_gc_safepoint = true;
123 return false;
124 }
125 }
126 return true;
127 };
128
129 if (!initialize_memory()) {
130 // Re-color with 11 remset bits if we got intercepted by a GC safepoint
131 const bool result = initialize_memory();
132 assert(result, "Array initialization should always succeed the second time");
133 }
134
135 ZThreadLocalData::clear_invisible_root(_thread);
136
137 // Signal to the ZIterator that this is no longer an invisible root
138 oopDesc::release_set_mark(mem, markWord::prototype());
139
140 return cast_to_oop(mem);
141 }
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33 : ObjArrayAllocator(klass, word_size, length, do_zero, thread) {}
34
35 void ZObjArrayAllocator::yield_for_safepoint() const {
36 ThreadBlockInVM tbivm(JavaThread::cast(_thread));
37 }
38
39 oop ZObjArrayAllocator::initialize(HeapWord* mem) const {
40 // ZGC specializes the initialization by performing segmented clearing
41 // to allow shorter time-to-safepoints.
42
43 if (!_do_zero) {
44 // No need for ZGC specialization
45 return ObjArrayAllocator::initialize(mem);
46 }
47
48 // A max segment size of 64K was chosen because microbenchmarking
49 // suggested that it offered a good trade-off between allocation
50 // time and time-to-safepoint
51 const size_t segment_max = ZUtils::bytes_to_words(64 * K);
52 const BasicType element_type = ArrayKlass::cast(_klass)->element_type();
53
54 // Clear leading 32 bits, if necessary.
55 int base_offset = arrayOopDesc::base_offset_in_bytes(element_type);
56 if (!is_aligned(base_offset, HeapWordSize)) {
57 assert(is_aligned(base_offset, BytesPerInt), "array base must be 32 bit aligned");
58 *reinterpret_cast<jint*>(reinterpret_cast<char*>(mem) + base_offset) = 0;
59 base_offset += BytesPerInt;
60 }
61 assert(is_aligned(base_offset, HeapWordSize), "remaining array base must be 64 bit aligned");
62
63 const size_t header = heap_word_size(base_offset);
64 const size_t payload_size = _word_size - header;
65
66 if (payload_size <= segment_max) {
67 // To small to use segmented clearing
68 return ObjArrayAllocator::initialize(mem);
69 }
70
71 // Segmented clearing
72
73 // The array is going to be exposed before it has been completely
74 // cleared, therefore we can't expose the header at the end of this
75 // function. Instead explicitly initialize it according to our needs.
76
77 // Signal to the ZIterator that this is an invisible root, by setting
78 // the mark word to "marked". Reset to prototype() after the clearing.
79 if (UseCompactObjectHeaders) {
80 arrayOopDesc::release_set_mark(mem, _klass->prototype_header().set_marked());
81 } else {
82 arrayOopDesc::set_mark(mem, markWord::prototype().set_marked());
83 arrayOopDesc::release_set_klass(mem, _klass);
84 }
85 assert(_length >= 0, "length should be non-negative");
86 arrayOopDesc::set_length(mem, _length);
87
88 // Keep the array alive across safepoints through an invisible
89 // root. Invisible roots are not visited by the heap iterator
90 // and the marking logic will not attempt to follow its elements.
91 // Relocation and remembered set code know how to dodge iterating
92 // over such objects.
93 ZThreadLocalData::set_invisible_root(_thread, (zaddress_unsafe*)&mem);
94
95 uint32_t old_seqnum_before = ZGeneration::old()->seqnum();
96 uint32_t young_seqnum_before = ZGeneration::young()->seqnum();
97 uintptr_t color_before = ZPointerStoreGoodMask;
98 auto gc_safepoint_happened = [&]() {
99 return old_seqnum_before != ZGeneration::old()->seqnum() ||
100 young_seqnum_before != ZGeneration::young()->seqnum() ||
101 color_before != ZPointerStoreGoodMask;
102 };
103
104 bool seen_gc_safepoint = false;
132 // Deal with safepoints
133 if (!seen_gc_safepoint && gc_safepoint_happened()) {
134 // The first time we observe a GC safepoint in the yield point,
135 // we have to restart processing with 11 remembered bits.
136 seen_gc_safepoint = true;
137 return false;
138 }
139 }
140 return true;
141 };
142
143 if (!initialize_memory()) {
144 // Re-color with 11 remset bits if we got intercepted by a GC safepoint
145 const bool result = initialize_memory();
146 assert(result, "Array initialization should always succeed the second time");
147 }
148
149 ZThreadLocalData::clear_invisible_root(_thread);
150
151 // Signal to the ZIterator that this is no longer an invisible root
152 if (UseCompactObjectHeaders) {
153 oopDesc::release_set_mark(mem, _klass->prototype_header());
154 } else {
155 oopDesc::release_set_mark(mem, markWord::prototype());
156 }
157
158 return cast_to_oop(mem);
159 }
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