33 ObjArrayAllocator(klass, word_size, length, do_zero, thread) {}
34
35 void XObjArrayAllocator::yield_for_safepoint() const {
36 ThreadBlockInVM tbivm(JavaThread::cast(_thread));
37 }
38
39 oop XObjArrayAllocator::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 = XUtils::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 arrayOopDesc::set_mark(mem, markWord::prototype());
67 arrayOopDesc::release_set_klass(mem, _klass);
68 assert(_length >= 0, "length should be non-negative");
69 arrayOopDesc::set_length(mem, _length);
70
71 // Keep the array alive across safepoints through an invisible
72 // root. Invisible roots are not visited by the heap itarator
73 // and the marking logic will not attempt to follow its elements.
74 // Relocation knows how to dodge iterating over such objects.
75 XThreadLocalData::set_invisible_root(_thread, (oop*)&mem);
76
77 for (size_t processed = 0; processed < payload_size; processed += segment_max) {
78 // Calculate segment
79 HeapWord* const start = (HeapWord*)(mem + header + processed);
80 const size_t remaining = payload_size - processed;
81 const size_t segment_size = MIN2(remaining, segment_max);
82
83 // Clear segment
84 Copy::zero_to_words(start, segment_size);
85
86 // Safepoint
87 yield_for_safepoint();
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33 ObjArrayAllocator(klass, word_size, length, do_zero, thread) {}
34
35 void XObjArrayAllocator::yield_for_safepoint() const {
36 ThreadBlockInVM tbivm(JavaThread::cast(_thread));
37 }
38
39 oop XObjArrayAllocator::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 = XUtils::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 if (UseCompactObjectHeaders) {
77 arrayOopDesc::release_set_mark(mem, _klass->prototype_header());
78 } else {
79 arrayOopDesc::set_mark(mem, markWord::prototype());
80 arrayOopDesc::release_set_klass(mem, _klass);
81 }
82 assert(_length >= 0, "length should be non-negative");
83 arrayOopDesc::set_length(mem, _length);
84
85 // Keep the array alive across safepoints through an invisible
86 // root. Invisible roots are not visited by the heap itarator
87 // and the marking logic will not attempt to follow its elements.
88 // Relocation knows how to dodge iterating over such objects.
89 XThreadLocalData::set_invisible_root(_thread, (oop*)&mem);
90
91 for (size_t processed = 0; processed < payload_size; processed += segment_max) {
92 // Calculate segment
93 HeapWord* const start = (HeapWord*)(mem + header + processed);
94 const size_t remaining = payload_size - processed;
95 const size_t segment_size = MIN2(remaining, segment_max);
96
97 // Clear segment
98 Copy::zero_to_words(start, segment_size);
99
100 // Safepoint
101 yield_for_safepoint();
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