1 /*
2 * Copyright (c) 2003, 2014, 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 #include "precompiled.hpp"
26 #include "classfile/altHashing.hpp"
27 #include "classfile/javaClasses.hpp"
28 #include "memory/allocation.inline.hpp"
29 #include "memory/filemap.hpp"
30 #include "memory/resourceArea.hpp"
31 #include "oops/oop.inline.hpp"
32 #include "runtime/safepoint.hpp"
33 #include "utilities/dtrace.hpp"
34 #include "utilities/hashtable.hpp"
35 #include "utilities/hashtable.inline.hpp"
36 #include "utilities/numberSeq.hpp"
37
38
39 // This is a generic hashtable, designed to be used for the symbol
40 // and string tables.
41 //
42 // It is implemented as an open hash table with a fixed number of buckets.
43 //
44 // %note:
45 // - HashtableEntrys are allocated in blocks to reduce the space overhead.
46
47 template <MEMFLAGS F> BasicHashtableEntry<F>* BasicHashtable<F>::new_entry(unsigned int hashValue) {
48 BasicHashtableEntry<F>* entry;
49
50 if (_free_list) {
51 entry = _free_list;
52 _free_list = _free_list->next();
53 } else {
54 if (_first_free_entry + _entry_size >= _end_block) {
55 int block_size = MIN2(512, MAX2((int)_table_size / 2, (int)_number_of_entries));
56 int len = _entry_size * block_size;
57 len = 1 << log2_intptr(len); // round down to power of 2
58 assert(len >= _entry_size, "");
59 _first_free_entry = NEW_C_HEAP_ARRAY2(char, len, F, CURRENT_PC);
60 _end_block = _first_free_entry + len;
61 }
62 entry = (BasicHashtableEntry<F>*)_first_free_entry;
63 _first_free_entry += _entry_size;
64 }
65
66 assert(_entry_size % HeapWordSize == 0, "");
67 entry->set_hash(hashValue);
68 return entry;
69 }
70
71
72 template <class T, MEMFLAGS F> HashtableEntry<T, F>* Hashtable<T, F>::new_entry(unsigned int hashValue, T obj) {
73 HashtableEntry<T, F>* entry;
74
75 entry = (HashtableEntry<T, F>*)BasicHashtable<F>::new_entry(hashValue);
76 entry->set_literal(obj);
77 return entry;
78 }
79
80 // Check to see if the hashtable is unbalanced. The caller set a flag to
81 // rehash at the next safepoint. If this bucket is 60 times greater than the
82 // expected average bucket length, it's an unbalanced hashtable.
83 // This is somewhat an arbitrary heuristic but if one bucket gets to
84 // rehash_count which is currently 100, there's probably something wrong.
85
86 template <MEMFLAGS F> bool BasicHashtable<F>::check_rehash_table(int count) {
87 assert(table_size() != 0, "underflow");
88 if (count > (((double)number_of_entries()/(double)table_size())*rehash_multiple)) {
89 // Set a flag for the next safepoint, which should be at some guaranteed
90 // safepoint interval.
91 return true;
92 }
93 return false;
94 }
95
96 template <class T, MEMFLAGS F> juint Hashtable<T, F>::_seed = 0;
97
98 // Create a new table and using alternate hash code, populate the new table
99 // with the existing elements. This can be used to change the hash code
100 // and could in the future change the size of the table.
101
102 template <class T, MEMFLAGS F> void Hashtable<T, F>::move_to(Hashtable<T, F>* new_table) {
103
104 // Initialize the global seed for hashing.
105 _seed = AltHashing::compute_seed();
106 assert(seed() != 0, "shouldn't be zero");
107
108 int saved_entry_count = this->number_of_entries();
109
110 // Iterate through the table and create a new entry for the new table
111 for (int i = 0; i < new_table->table_size(); ++i) {
112 for (HashtableEntry<T, F>* p = bucket(i); p != NULL; ) {
113 HashtableEntry<T, F>* next = p->next();
114 T string = p->literal();
115 // Use alternate hashing algorithm on the symbol in the first table
116 unsigned int hashValue = string->new_hash(seed());
117 // Get a new index relative to the new table (can also change size)
118 int index = new_table->hash_to_index(hashValue);
119 p->set_hash(hashValue);
120 // Keep the shared bit in the Hashtable entry to indicate that this entry
121 // can't be deleted. The shared bit is the LSB in the _next field so
122 // walking the hashtable past these entries requires
123 // BasicHashtableEntry::make_ptr() call.
124 bool keep_shared = p->is_shared();
125 this->unlink_entry(p);
126 new_table->add_entry(index, p);
127 if (keep_shared) {
128 p->set_shared();
129 }
130 p = next;
131 }
132 }
133 // give the new table the free list as well
134 new_table->copy_freelist(this);
135 assert(new_table->number_of_entries() == saved_entry_count, "lost entry on dictionary copy?");
136
137 // Destroy memory used by the buckets in the hashtable. The memory
138 // for the elements has been used in a new table and is not
139 // destroyed. The memory reuse will benefit resizing the SystemDictionary
140 // to avoid a memory allocation spike at safepoint.
141 BasicHashtable<F>::free_buckets();
142 }
143
144 template <MEMFLAGS F> void BasicHashtable<F>::free_buckets() {
145 if (NULL != _buckets) {
146 // Don't delete the buckets in the shared space. They aren't
147 // allocated by os::malloc
148 if (!UseSharedSpaces ||
149 !FileMapInfo::current_info()->is_in_shared_space(_buckets)) {
150 FREE_C_HEAP_ARRAY(HashtableBucket, _buckets, F);
151 }
152 _buckets = NULL;
153 }
154 }
155
156
157 // Reverse the order of elements in the hash buckets.
158
159 template <MEMFLAGS F> void BasicHashtable<F>::reverse() {
160
161 for (int i = 0; i < _table_size; ++i) {
162 BasicHashtableEntry<F>* new_list = NULL;
163 BasicHashtableEntry<F>* p = bucket(i);
164 while (p != NULL) {
165 BasicHashtableEntry<F>* next = p->next();
166 p->set_next(new_list);
167 new_list = p;
168 p = next;
169 }
170 *bucket_addr(i) = new_list;
171 }
172 }
173
174
175 // Copy the table to the shared space.
176
177 template <MEMFLAGS F> void BasicHashtable<F>::copy_table(char** top, char* end) {
178
179 // Dump the hash table entries.
180
181 intptr_t *plen = (intptr_t*)(*top);
182 *top += sizeof(*plen);
183
184 int i;
185 for (i = 0; i < _table_size; ++i) {
186 for (BasicHashtableEntry<F>** p = _buckets[i].entry_addr();
187 *p != NULL;
188 p = (*p)->next_addr()) {
189 if (*top + entry_size() > end) {
190 report_out_of_shared_space(SharedMiscData);
191 }
192 *p = (BasicHashtableEntry<F>*)memcpy(*top, *p, entry_size());
193 *top += entry_size();
194 }
195 }
196 *plen = (char*)(*top) - (char*)plen - sizeof(*plen);
197
198 // Set the shared bit.
199
200 for (i = 0; i < _table_size; ++i) {
201 for (BasicHashtableEntry<F>* p = bucket(i); p != NULL; p = p->next()) {
202 p->set_shared();
203 }
204 }
205 }
206
207
208
209 // Reverse the order of elements in the hash buckets.
210
211 template <class T, MEMFLAGS F> void Hashtable<T, F>::reverse(void* boundary) {
212
213 for (int i = 0; i < this->table_size(); ++i) {
214 HashtableEntry<T, F>* high_list = NULL;
215 HashtableEntry<T, F>* low_list = NULL;
216 HashtableEntry<T, F>* last_low_entry = NULL;
217 HashtableEntry<T, F>* p = bucket(i);
218 while (p != NULL) {
219 HashtableEntry<T, F>* next = p->next();
220 if ((void*)p->literal() >= boundary) {
221 p->set_next(high_list);
222 high_list = p;
223 } else {
224 p->set_next(low_list);
225 low_list = p;
226 if (last_low_entry == NULL) {
227 last_low_entry = p;
228 }
229 }
230 p = next;
231 }
232 if (low_list != NULL) {
233 *bucket_addr(i) = low_list;
234 last_low_entry->set_next(high_list);
235 } else {
236 *bucket_addr(i) = high_list;
237 }
238 }
239 }
240
241 template <class T, MEMFLAGS F> int Hashtable<T, F>::literal_size(Symbol *symbol) {
242 return symbol->size() * HeapWordSize;
243 }
244
245 template <class T, MEMFLAGS F> int Hashtable<T, F>::literal_size(oop oop) {
246 // NOTE: this would over-count if (pre-JDK8) java_lang_Class::has_offset_field() is true,
247 // and the String.value array is shared by several Strings. However, starting from JDK8,
248 // the String.value array is not shared anymore.
249 assert(oop != NULL && oop->klass() == SystemDictionary::String_klass(), "only strings are supported");
250 return (oop->size() + java_lang_String::value(oop)->size()) * HeapWordSize;
251 }
252
253 // Dump footprint and bucket length statistics
254 //
255 // Note: if you create a new subclass of Hashtable<MyNewType, F>, you will need to
256 // add a new function Hashtable<T, F>::literal_size(MyNewType lit)
257
258 template <class T, MEMFLAGS F> void Hashtable<T, F>::dump_table(outputStream* st, const char *table_name) {
259 NumberSeq summary;
260 int literal_bytes = 0;
261 for (int i = 0; i < this->table_size(); ++i) {
262 int count = 0;
263 for (HashtableEntry<T, F>* e = bucket(i);
264 e != NULL; e = e->next()) {
265 count++;
266 literal_bytes += literal_size(e->literal());
267 }
268 summary.add((double)count);
269 }
270 double num_buckets = summary.num();
271 double num_entries = summary.sum();
272
273 int bucket_bytes = (int)num_buckets * sizeof(bucket(0));
274 int entry_bytes = (int)num_entries * sizeof(HashtableEntry<T, F>);
275 int total_bytes = literal_bytes + bucket_bytes + entry_bytes;
276
277 double bucket_avg = (num_buckets <= 0) ? 0 : (bucket_bytes / num_buckets);
278 double entry_avg = (num_entries <= 0) ? 0 : (entry_bytes / num_entries);
279 double literal_avg = (num_entries <= 0) ? 0 : (literal_bytes / num_entries);
280
281 st->print_cr("%s statistics:", table_name);
282 st->print_cr("Number of buckets : %9d = %9d bytes, avg %7.3f", (int)num_buckets, bucket_bytes, bucket_avg);
283 st->print_cr("Number of entries : %9d = %9d bytes, avg %7.3f", (int)num_entries, entry_bytes, entry_avg);
284 st->print_cr("Number of literals : %9d = %9d bytes, avg %7.3f", (int)num_entries, literal_bytes, literal_avg);
285 st->print_cr("Total footprint : %9s = %9d bytes", "", total_bytes);
286 st->print_cr("Average bucket size : %9.3f", summary.avg());
287 st->print_cr("Variance of bucket size : %9.3f", summary.variance());
288 st->print_cr("Std. dev. of bucket size: %9.3f", summary.sd());
289 st->print_cr("Maximum bucket size : %9d", (int)summary.maximum());
290 }
291
292
293 // Dump the hash table buckets.
294
295 template <MEMFLAGS F> void BasicHashtable<F>::copy_buckets(char** top, char* end) {
296 intptr_t len = _table_size * sizeof(HashtableBucket<F>);
297 *(intptr_t*)(*top) = len;
298 *top += sizeof(intptr_t);
299
300 *(intptr_t*)(*top) = _number_of_entries;
301 *top += sizeof(intptr_t);
302
303 if (*top + len > end) {
304 report_out_of_shared_space(SharedMiscData);
305 }
306 _buckets = (HashtableBucket<F>*)memcpy(*top, _buckets, len);
307 *top += len;
308 }
309
310
311 #ifndef PRODUCT
312
313 template <class T, MEMFLAGS F> void Hashtable<T, F>::print() {
314 ResourceMark rm;
315
316 for (int i = 0; i < BasicHashtable<F>::table_size(); i++) {
317 HashtableEntry<T, F>* entry = bucket(i);
318 while(entry != NULL) {
319 tty->print("%d : ", i);
320 entry->literal()->print();
321 tty->cr();
322 entry = entry->next();
323 }
324 }
325 }
326
327
328 template <MEMFLAGS F> void BasicHashtable<F>::verify() {
329 int count = 0;
330 for (int i = 0; i < table_size(); i++) {
331 for (BasicHashtableEntry<F>* p = bucket(i); p != NULL; p = p->next()) {
332 ++count;
333 }
334 }
335 assert(count == number_of_entries(), "number of hashtable entries incorrect");
336 }
337
338
339 #endif // PRODUCT
340
341 #ifdef ASSERT
342
343 template <MEMFLAGS F> void BasicHashtable<F>::verify_lookup_length(double load) {
344 if ((double)_lookup_length / (double)_lookup_count > load * 2.0) {
345 warning("Performance bug: SystemDictionary lookup_count=%d "
346 "lookup_length=%d average=%lf load=%f",
347 _lookup_count, _lookup_length,
348 (double) _lookup_length / _lookup_count, load);
349 }
350 }
351
352 #endif
353
354
355 // Explicitly instantiate these types
356 template class Hashtable<ConstantPool*, mtClass>;
357 template class Hashtable<Symbol*, mtSymbol>;
358 template class Hashtable<Klass*, mtClass>;
359 template class Hashtable<oop, mtClass>;
360 #if defined(SOLARIS) || defined(CHECK_UNHANDLED_OOPS)
361 template class Hashtable<oop, mtSymbol>;
362 #endif // SOLARIS || CHECK_UNHANDLED_OOPS
363 template class Hashtable<oopDesc*, mtSymbol>;
364 template class Hashtable<Symbol*, mtClass>;
365 template class HashtableEntry<Symbol*, mtSymbol>;
366 template class HashtableEntry<Symbol*, mtClass>;
367 template class HashtableEntry<oop, mtSymbol>;
368 template class BasicHashtableEntry<mtSymbol>;
369 template class BasicHashtableEntry<mtCode>;
370 template class BasicHashtable<mtClass>;
371 template class BasicHashtable<mtSymbol>;
372 template class BasicHashtable<mtCode>;
373 template class BasicHashtable<mtInternal>;