1 /*
 2  * Copyright (c) 2019, 2021, Oracle and/or its affiliates. All rights reserved.
 3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 4  *
 5  * This code is free software; you can redistribute it and/or modify it
 6  * under the terms of the GNU General Public License version 2 only, as
 7  * published by the Free Software Foundation.
 8  *
 9  * This code is distributed in the hope that it will be useful, but WITHOUT
10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
12  * version 2 for more details (a copy is included in the LICENSE file that
13  * accompanied this code).
14  *
15  * You should have received a copy of the GNU General Public License version
16  * 2 along with this work; if not, write to the Free Software Foundation,
17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18  *
19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20  * or visit www.oracle.com if you need additional information or have any
21  * questions.
22  */
23 
24 #include "precompiled.hpp"
25 #include "gc/z/zThreadLocalData.hpp"
26 #include "gc/z/zObjArrayAllocator.hpp"
27 #include "gc/z/zUtils.inline.hpp"
28 #include "oops/arrayKlass.hpp"
29 #include "runtime/interfaceSupport.inline.hpp"
30 #include "utilities/debug.hpp"
31 
32 ZObjArrayAllocator::ZObjArrayAllocator(Klass* klass, size_t word_size, int length, bool do_zero, Thread* thread) :
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   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   ZThreadLocalData::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();
88   }
89 
90   ZThreadLocalData::clear_invisible_root(_thread);
91 
92   return cast_to_oop(mem);
93 }
--- EOF ---