1 /*
2 * Copyright (c) 2003, 2017, 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 hashtable is implemented as an open hash table with a fixed number of buckets.
40
41 template <MEMFLAGS F> BasicHashtableEntry<F>* BasicHashtable<F>::new_entry_free_list() {
42 BasicHashtableEntry<F>* entry = NULL;
43 if (_free_list != NULL) {
44 entry = _free_list;
45 _free_list = _free_list->next();
46 }
47 return entry;
48 }
49
50 // HashtableEntrys are allocated in blocks to reduce the space overhead.
51 template <MEMFLAGS F> BasicHashtableEntry<F>* BasicHashtable<F>::new_entry(unsigned int hashValue) {
52 BasicHashtableEntry<F>* entry = new_entry_free_list();
53
54 if (entry == NULL) {
55 if (_first_free_entry + _entry_size >= _end_block) {
56 int block_size = MIN2(512, MAX2((int)_table_size / 2, (int)_number_of_entries));
57 int len = _entry_size * block_size;
58 len = 1 << log2_int(len); // round down to power of 2
59 assert(len >= _entry_size, "");
60 _first_free_entry = NEW_C_HEAP_ARRAY2(char, len, F, CURRENT_PC);
61 _end_block = _first_free_entry + len;
62 }
63 entry = (BasicHashtableEntry<F>*)_first_free_entry;
64 _first_free_entry += _entry_size;
65 }
66
67 assert(_entry_size % HeapWordSize == 0, "");
68 entry->set_hash(hashValue);
69 return entry;
70 }
71
72
73 template <class T, MEMFLAGS F> HashtableEntry<T, F>* Hashtable<T, F>::new_entry(unsigned int hashValue, T obj) {
74 HashtableEntry<T, F>* entry;
75
76 entry = (HashtableEntry<T, F>*)BasicHashtable<F>::new_entry(hashValue);
77 entry->set_literal(obj);
78 return entry;
79 }
80
81 // Check to see if the hashtable is unbalanced. The caller set a flag to
82 // rehash at the next safepoint. If this bucket is 60 times greater than the
83 // expected average bucket length, it's an unbalanced hashtable.
84 // This is somewhat an arbitrary heuristic but if one bucket gets to
85 // rehash_count which is currently 100, there's probably something wrong.
86
87 template <class T, MEMFLAGS F> bool RehashableHashtable<T, F>::check_rehash_table(int count) {
88 assert(this->table_size() != 0, "underflow");
89 if (count > (((double)this->number_of_entries()/(double)this->table_size())*rehash_multiple)) {
90 // Set a flag for the next safepoint, which should be at some guaranteed
91 // safepoint interval.
92 return true;
93 }
94 return false;
95 }
96
97 template <class T, MEMFLAGS F> juint RehashableHashtable<T, F>::_seed = 0;
98
99 // Create a new table and using alternate hash code, populate the new table
100 // with the existing elements. This can be used to change the hash code
101 // and could in the future change the size of the table.
102
103 template <class T, MEMFLAGS F> void RehashableHashtable<T, F>::move_to(RehashableHashtable<T, F>* new_table) {
104
105 // Initialize the global seed for hashing.
106 _seed = AltHashing::compute_seed();
107 assert(seed() != 0, "shouldn't be zero");
108
109 int saved_entry_count = this->number_of_entries();
110
111 // Iterate through the table and create a new entry for the new table
112 for (int i = 0; i < new_table->table_size(); ++i) {
113 for (HashtableEntry<T, F>* p = this->bucket(i); p != NULL; ) {
114 HashtableEntry<T, F>* next = p->next();
115 T string = p->literal();
116 // Use alternate hashing algorithm on the symbol in the first table
117 unsigned int hashValue = string->new_hash(seed());
118 // Get a new index relative to the new table (can also change size)
119 int index = new_table->hash_to_index(hashValue);
120 p->set_hash(hashValue);
121 // Keep the shared bit in the Hashtable entry to indicate that this entry
122 // can't be deleted. The shared bit is the LSB in the _next field so
123 // walking the hashtable past these entries requires
124 // BasicHashtableEntry::make_ptr() call.
125 bool keep_shared = p->is_shared();
126 this->unlink_entry(p);
127 new_table->add_entry(index, p);
128 if (keep_shared) {
129 p->set_shared();
130 }
131 p = next;
132 }
133 }
134 // give the new table the free list as well
135 new_table->copy_freelist(this);
136 assert(new_table->number_of_entries() == saved_entry_count, "lost entry on dictionary copy?");
137
138 // Destroy memory used by the buckets in the hashtable. The memory
139 // for the elements has been used in a new table and is not
140 // destroyed. The memory reuse will benefit resizing the SystemDictionary
141 // to avoid a memory allocation spike at safepoint.
142 BasicHashtable<F>::free_buckets();
143 }
144
145 template <MEMFLAGS F> void BasicHashtable<F>::free_buckets() {
146 if (NULL != _buckets) {
147 // Don't delete the buckets in the shared space. They aren't
148 // allocated by os::malloc
149 if (!UseSharedSpaces ||
150 !FileMapInfo::current_info()->is_in_shared_space(_buckets)) {
151 FREE_C_HEAP_ARRAY(HashtableBucket, _buckets, F);
152 }
153 _buckets = NULL;
154 }
155 }
156
157
158 // Reverse the order of elements in the hash buckets.
159
160 template <MEMFLAGS F> void BasicHashtable<F>::reverse() {
161
162 for (int i = 0; i < _table_size; ++i) {
163 BasicHashtableEntry<F>* new_list = NULL;
164 BasicHashtableEntry<F>* p = bucket(i);
165 while (p != NULL) {
166 BasicHashtableEntry<F>* next = p->next();
167 p->set_next(new_list);
168 new_list = p;
169 p = next;
170 }
171 *bucket_addr(i) = new_list;
172 }
173 }
174
175 template <MEMFLAGS F> void BasicHashtable<F>::BucketUnlinkContext::free_entry(BasicHashtableEntry<F>* entry) {
176 entry->set_next(_removed_head);
177 _removed_head = entry;
178 if (_removed_tail == NULL) {
179 _removed_tail = entry;
180 }
181 _num_removed++;
182 }
183
184 template <MEMFLAGS F> void BasicHashtable<F>::bulk_free_entries(BucketUnlinkContext* context) {
185 if (context->_num_removed == 0) {
186 assert(context->_removed_head == NULL && context->_removed_tail == NULL,
187 err_msg("Zero entries in the unlink context, but elements linked from " PTR_FORMAT " to " PTR_FORMAT,
188 p2i(context->_removed_head), p2i(context->_removed_tail)));
189 return;
190 }
191
192 // MT-safe add of the list of BasicHashTableEntrys from the context to the free list.
193 BasicHashtableEntry<F>* current = _free_list;
194 while (true) {
195 context->_removed_tail->set_next(current);
196 BasicHashtableEntry<F>* old = (BasicHashtableEntry<F>*)Atomic::cmpxchg_ptr(context->_removed_head, &_free_list, current);
197 if (old == current) {
198 break;
199 }
200 current = old;
201 }
202 Atomic::add(-context->_num_removed, &_number_of_entries);
203 }
204
205 // Copy the table to the shared space.
206
207 template <MEMFLAGS F> void BasicHashtable<F>::copy_table(char** top, char* end) {
208
209 // Dump the hash table entries.
210
211 intptr_t *plen = (intptr_t*)(*top);
212 *top += sizeof(*plen);
213
214 int i;
215 for (i = 0; i < _table_size; ++i) {
216 for (BasicHashtableEntry<F>** p = _buckets[i].entry_addr();
217 *p != NULL;
218 p = (*p)->next_addr()) {
219 if (*top + entry_size() > end) {
220 report_out_of_shared_space(SharedMiscData);
221 }
222 *p = (BasicHashtableEntry<F>*)memcpy(*top, *p, entry_size());
223 *top += entry_size();
224 }
225 }
226 *plen = (char*)(*top) - (char*)plen - sizeof(*plen);
227
228 // Set the shared bit.
229
230 for (i = 0; i < _table_size; ++i) {
231 for (BasicHashtableEntry<F>* p = bucket(i); p != NULL; p = p->next()) {
232 p->set_shared();
233 }
234 }
235 }
236
237
238
239 // Reverse the order of elements in the hash buckets.
240
241 template <class T, MEMFLAGS F> void Hashtable<T, F>::reverse(void* boundary) {
242
243 for (int i = 0; i < this->table_size(); ++i) {
244 HashtableEntry<T, F>* high_list = NULL;
245 HashtableEntry<T, F>* low_list = NULL;
246 HashtableEntry<T, F>* last_low_entry = NULL;
247 HashtableEntry<T, F>* p = bucket(i);
248 while (p != NULL) {
249 HashtableEntry<T, F>* next = p->next();
250 if ((void*)p->literal() >= boundary) {
251 p->set_next(high_list);
252 high_list = p;
253 } else {
254 p->set_next(low_list);
255 low_list = p;
256 if (last_low_entry == NULL) {
257 last_low_entry = p;
258 }
259 }
260 p = next;
261 }
262 if (low_list != NULL) {
263 *bucket_addr(i) = low_list;
264 last_low_entry->set_next(high_list);
265 } else {
266 *bucket_addr(i) = high_list;
267 }
268 }
269 }
270
271 template <class T, MEMFLAGS F> int RehashableHashtable<T, F>::literal_size(Symbol *symbol) {
272 return symbol->size() * HeapWordSize;
273 }
274
275 template <class T, MEMFLAGS F> int RehashableHashtable<T, F>::literal_size(oop oop) {
276 // NOTE: this would over-count if (pre-JDK8) java_lang_Class::has_offset_field() is true,
277 // and the String.value array is shared by several Strings. However, starting from JDK8,
278 // the String.value array is not shared anymore.
279 assert(oop != NULL && oop->klass() == SystemDictionary::String_klass(), "only strings are supported");
280 return (oop->size() + java_lang_String::value(oop)->size()) * HeapWordSize;
281 }
282
283 // Dump footprint and bucket length statistics
284 //
285 // Note: if you create a new subclass of Hashtable<MyNewType, F>, you will need to
286 // add a new function Hashtable<T, F>::literal_size(MyNewType lit)
287
288 template <class T, MEMFLAGS F> void RehashableHashtable<T, F>::dump_table(outputStream* st, const char *table_name) {
289 NumberSeq summary;
290 int literal_bytes = 0;
291 for (int i = 0; i < this->table_size(); ++i) {
292 int count = 0;
293 for (HashtableEntry<T, F>* e = this->bucket(i);
294 e != NULL; e = e->next()) {
295 count++;
296 literal_bytes += literal_size(e->literal());
297 }
298 summary.add((double)count);
299 }
300 double num_buckets = summary.num();
301 double num_entries = summary.sum();
302
303 int bucket_bytes = (int)num_buckets * sizeof(HashtableBucket<F>);
304 int entry_bytes = (int)num_entries * sizeof(HashtableEntry<T, F>);
305 int total_bytes = literal_bytes + bucket_bytes + entry_bytes;
306
307 double bucket_avg = (num_buckets <= 0) ? 0 : (bucket_bytes / num_buckets);
308 double entry_avg = (num_entries <= 0) ? 0 : (entry_bytes / num_entries);
309 double literal_avg = (num_entries <= 0) ? 0 : (literal_bytes / num_entries);
310
311 st->print_cr("%s statistics:", table_name);
312 st->print_cr("Number of buckets : %9d = %9d bytes, avg %7.3f", (int)num_buckets, bucket_bytes, bucket_avg);
313 st->print_cr("Number of entries : %9d = %9d bytes, avg %7.3f", (int)num_entries, entry_bytes, entry_avg);
314 st->print_cr("Number of literals : %9d = %9d bytes, avg %7.3f", (int)num_entries, literal_bytes, literal_avg);
315 st->print_cr("Total footprint : %9s = %9d bytes", "", total_bytes);
316 st->print_cr("Average bucket size : %9.3f", summary.avg());
317 st->print_cr("Variance of bucket size : %9.3f", summary.variance());
318 st->print_cr("Std. dev. of bucket size: %9.3f", summary.sd());
319 st->print_cr("Maximum bucket size : %9d", (int)summary.maximum());
320 }
321
322
323 // Dump the hash table buckets.
324
325 template <MEMFLAGS F> void BasicHashtable<F>::copy_buckets(char** top, char* end) {
326 intptr_t len = _table_size * sizeof(HashtableBucket<F>);
327 *(intptr_t*)(*top) = len;
328 *top += sizeof(intptr_t);
329
330 *(intptr_t*)(*top) = _number_of_entries;
331 *top += sizeof(intptr_t);
332
333 if (*top + len > end) {
334 report_out_of_shared_space(SharedMiscData);
335 }
336 _buckets = (HashtableBucket<F>*)memcpy(*top, _buckets, len);
337 *top += len;
338 }
339
340
341 #ifndef PRODUCT
342
343 template <class T, MEMFLAGS F> void Hashtable<T, F>::print() {
344 ResourceMark rm;
345
346 for (int i = 0; i < BasicHashtable<F>::table_size(); i++) {
347 HashtableEntry<T, F>* entry = bucket(i);
348 while(entry != NULL) {
349 tty->print("%d : ", i);
350 entry->literal()->print();
351 tty->cr();
352 entry = entry->next();
353 }
354 }
355 }
356
357
358 template <MEMFLAGS F> void BasicHashtable<F>::verify() {
359 int count = 0;
360 for (int i = 0; i < table_size(); i++) {
361 for (BasicHashtableEntry<F>* p = bucket(i); p != NULL; p = p->next()) {
362 ++count;
363 }
364 }
365 assert(count == number_of_entries(), "number of hashtable entries incorrect");
366 }
367
368
369 #endif // PRODUCT
370
371
372 #ifdef ASSERT
373
374 template <MEMFLAGS F> void BasicHashtable<F>::verify_lookup_length(double load) {
375 if ((double)_lookup_length / (double)_lookup_count > load * 2.0) {
376 warning("Performance bug: SystemDictionary lookup_count=%d "
377 "lookup_length=%d average=%lf load=%f",
378 _lookup_count, _lookup_length,
379 (double) _lookup_length / _lookup_count, load);
380 }
381 }
382
383 #endif
384 // Explicitly instantiate these types
385 #if INCLUDE_ALL_GCS
386 template class Hashtable<nmethod*, mtGC>;
387 template class HashtableEntry<nmethod*, mtGC>;
388 template class BasicHashtable<mtGC>;
389 #endif
390 template class Hashtable<ConstantPool*, mtClass>;
391 template class RehashableHashtable<Symbol*, mtSymbol>;
392 template class RehashableHashtable<oopDesc*, mtSymbol>;
393 template class Hashtable<Symbol*, mtSymbol>;
394 template class Hashtable<Klass*, mtClass>;
395 template class Hashtable<oop, mtClass>;
396 #if defined(SOLARIS) || defined(CHECK_UNHANDLED_OOPS)
397 template class Hashtable<oop, mtSymbol>;
398 template class RehashableHashtable<oop, mtSymbol>;
399 #endif // SOLARIS || CHECK_UNHANDLED_OOPS
400 template class Hashtable<oopDesc*, mtSymbol>;
401 template class Hashtable<Symbol*, mtClass>;
402 template class HashtableEntry<Symbol*, mtSymbol>;
403 template class HashtableEntry<Symbol*, mtClass>;
404 template class HashtableEntry<oop, mtSymbol>;
405 template class BasicHashtableEntry<mtSymbol>;
406 template class BasicHashtableEntry<mtCode>;
407 template class BasicHashtable<mtClass>;
408 template class BasicHashtable<mtSymbol>;
409 template class BasicHashtable<mtCode>;
410 template class BasicHashtable<mtInternal>;