1 /*
2 * Copyright (c) 2003, 2005, 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
25 // This is a generic hashtable, designed to be used for the symbol
26 // and string tables.
27 //
28 // It is implemented as an open hash table with a fixed number of buckets.
29 //
30 // %note:
31 // - TableEntrys are allocated in blocks to reduce the space overhead.
32
33
34
35 class BasicHashtableEntry : public CHeapObj {
36 friend class VMStructs;
37 private:
38 unsigned int _hash; // 32-bit hash for item
39
40 // Link to next element in the linked list for this bucket. EXCEPT
41 // bit 0 set indicates that this entry is shared and must not be
42 // unlinked from the table. Bit 0 is set during the dumping of the
43 // archive. Since shared entries are immutable, _next fields in the
44 // shared entries will not change. New entries will always be
261
262 TwoOopHashtable(int table_size, int entry_size, HashtableBucket* t,
263 int number_of_entries)
264 : Hashtable(table_size, entry_size, t, number_of_entries) {}
265
266 public:
267 unsigned int compute_hash(symbolHandle name, Handle loader) {
268 // Be careful with identity_hash(), it can safepoint and if this
269 // were one expression, the compiler could choose to unhandle each
270 // oop before calling identity_hash() for either of them. If the first
271 // causes a GC, the next would fail.
272 unsigned int name_hash = name->identity_hash();
273 unsigned int loader_hash = loader.is_null() ? 0 : loader->identity_hash();
274 return name_hash ^ loader_hash;
275 }
276
277 int index_for(symbolHandle name, Handle loader) {
278 return hash_to_index(compute_hash(name, loader));
279 }
280 };
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1 /*
2 * Copyright (c) 2003, 2010, 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
25 #ifndef SHARE_VM_UTILITIES_HASHTABLE_HPP
26 #define SHARE_VM_UTILITIES_HASHTABLE_HPP
27
28 #include "memory/allocation.hpp"
29 #include "oops/oop.hpp"
30 #include "oops/symbolOop.hpp"
31 #include "runtime/handles.hpp"
32
33 // This is a generic hashtable, designed to be used for the symbol
34 // and string tables.
35 //
36 // It is implemented as an open hash table with a fixed number of buckets.
37 //
38 // %note:
39 // - TableEntrys are allocated in blocks to reduce the space overhead.
40
41
42
43 class BasicHashtableEntry : public CHeapObj {
44 friend class VMStructs;
45 private:
46 unsigned int _hash; // 32-bit hash for item
47
48 // Link to next element in the linked list for this bucket. EXCEPT
49 // bit 0 set indicates that this entry is shared and must not be
50 // unlinked from the table. Bit 0 is set during the dumping of the
51 // archive. Since shared entries are immutable, _next fields in the
52 // shared entries will not change. New entries will always be
269
270 TwoOopHashtable(int table_size, int entry_size, HashtableBucket* t,
271 int number_of_entries)
272 : Hashtable(table_size, entry_size, t, number_of_entries) {}
273
274 public:
275 unsigned int compute_hash(symbolHandle name, Handle loader) {
276 // Be careful with identity_hash(), it can safepoint and if this
277 // were one expression, the compiler could choose to unhandle each
278 // oop before calling identity_hash() for either of them. If the first
279 // causes a GC, the next would fail.
280 unsigned int name_hash = name->identity_hash();
281 unsigned int loader_hash = loader.is_null() ? 0 : loader->identity_hash();
282 return name_hash ^ loader_hash;
283 }
284
285 int index_for(symbolHandle name, Handle loader) {
286 return hash_to_index(compute_hash(name, loader));
287 }
288 };
289
290 #endif // SHARE_VM_UTILITIES_HASHTABLE_HPP
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