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/dictionary.hpp"
28 #include "classfile/javaClasses.inline.hpp"
29 #include "classfile/moduleEntry.hpp"
30 #include "classfile/packageEntry.hpp"
31 #include "classfile/protectionDomainCache.hpp"
32 #include "classfile/stringTable.hpp"
33 #include "memory/allocation.inline.hpp"
34 #include "memory/filemap.hpp"
35 #include "memory/resourceArea.hpp"
36 #include "oops/oop.inline.hpp"
37 #include "runtime/safepoint.hpp"
38 #include "utilities/dtrace.hpp"
39 #include "utilities/hashtable.hpp"
40 #include "utilities/hashtable.inline.hpp"
41 #include "utilities/numberSeq.hpp"
42
43
44 // This hashtable is implemented as an open hash table with a fixed number of buckets.
45
46 template <MEMFLAGS F> BasicHashtableEntry<F>* BasicHashtable<F>::new_entry_free_list() {
47 BasicHashtableEntry<F>* entry = NULL;
48 if (_free_list != NULL) {
49 entry = _free_list;
50 _free_list = _free_list->next();
51 }
52 return entry;
53 }
54
55 // HashtableEntrys are allocated in blocks to reduce the space overhead.
56 template <MEMFLAGS F> BasicHashtableEntry<F>* BasicHashtable<F>::new_entry(unsigned int hashValue) {
57 BasicHashtableEntry<F>* entry = new_entry_free_list();
58
59 if (entry == NULL) {
60 if (_first_free_entry + _entry_size >= _end_block) {
61 int block_size = MIN2(512, MAX2((int)_table_size / 2, (int)_number_of_entries));
62 int len = _entry_size * block_size;
63 len = 1 << log2_intptr(len); // round down to power of 2
64 assert(len >= _entry_size, "");
65 _first_free_entry = NEW_C_HEAP_ARRAY2(char, len, F, CURRENT_PC);
66 _end_block = _first_free_entry + len;
67 }
68 entry = (BasicHashtableEntry<F>*)_first_free_entry;
69 _first_free_entry += _entry_size;
70 }
71
72 assert(_entry_size % HeapWordSize == 0, "");
73 entry->set_hash(hashValue);
74 return entry;
75 }
76
77
78 template <class T, MEMFLAGS F> HashtableEntry<T, F>* Hashtable<T, F>::new_entry(unsigned int hashValue, T obj) {
79 HashtableEntry<T, F>* entry;
80
81 entry = (HashtableEntry<T, F>*)BasicHashtable<F>::new_entry(hashValue);
82 entry->set_literal(obj);
83 return entry;
84 }
85
86 // Check to see if the hashtable is unbalanced. The caller set a flag to
87 // rehash at the next safepoint. If this bucket is 60 times greater than the
88 // expected average bucket length, it's an unbalanced hashtable.
89 // This is somewhat an arbitrary heuristic but if one bucket gets to
90 // rehash_count which is currently 100, there's probably something wrong.
91
92 template <class T, MEMFLAGS F> bool RehashableHashtable<T, F>::check_rehash_table(int count) {
93 assert(this->table_size() != 0, "underflow");
94 if (count > (((double)this->number_of_entries()/(double)this->table_size())*rehash_multiple)) {
95 // Set a flag for the next safepoint, which should be at some guaranteed
96 // safepoint interval.
97 return true;
98 }
99 return false;
100 }
101
102 template <class T, MEMFLAGS F> juint RehashableHashtable<T, F>::_seed = 0;
103
104 // Create a new table and using alternate hash code, populate the new table
105 // with the existing elements. This can be used to change the hash code
106 // and could in the future change the size of the table.
107
108 template <class T, MEMFLAGS F> void RehashableHashtable<T, F>::move_to(RehashableHashtable<T, F>* new_table) {
109
110 // Initialize the global seed for hashing.
111 _seed = AltHashing::compute_seed();
112 assert(seed() != 0, "shouldn't be zero");
113
114 int saved_entry_count = this->number_of_entries();
115
116 // Iterate through the table and create a new entry for the new table
117 for (int i = 0; i < new_table->table_size(); ++i) {
118 for (HashtableEntry<T, F>* p = this->bucket(i); p != NULL; ) {
119 HashtableEntry<T, F>* next = p->next();
120 T string = p->literal();
121 // Use alternate hashing algorithm on the symbol in the first table
122 unsigned int hashValue = string->new_hash(seed());
123 // Get a new index relative to the new table (can also change size)
124 int index = new_table->hash_to_index(hashValue);
125 p->set_hash(hashValue);
126 // Keep the shared bit in the Hashtable entry to indicate that this entry
127 // can't be deleted. The shared bit is the LSB in the _next field so
128 // walking the hashtable past these entries requires
129 // BasicHashtableEntry::make_ptr() call.
130 bool keep_shared = p->is_shared();
131 this->unlink_entry(p);
132 new_table->add_entry(index, p);
133 if (keep_shared) {
134 p->set_shared();
135 }
136 p = next;
137 }
138 }
139 // give the new table the free list as well
140 new_table->copy_freelist(this);
141 assert(new_table->number_of_entries() == saved_entry_count, "lost entry on dictionary copy?");
142
143 // Destroy memory used by the buckets in the hashtable. The memory
144 // for the elements has been used in a new table and is not
145 // destroyed. The memory reuse will benefit resizing the SystemDictionary
146 // to avoid a memory allocation spike at safepoint.
147 BasicHashtable<F>::free_buckets();
148 }
149
150 template <MEMFLAGS F> void BasicHashtable<F>::free_buckets() {
151 if (NULL != _buckets) {
152 // Don't delete the buckets in the shared space. They aren't
153 // allocated by os::malloc
154 if (!UseSharedSpaces ||
155 !FileMapInfo::current_info()->is_in_shared_space(_buckets)) {
156 FREE_C_HEAP_ARRAY(HashtableBucket, _buckets);
157 }
158 _buckets = NULL;
159 }
160 }
161
162 template <MEMFLAGS F> void BasicHashtable<F>::BucketUnlinkContext::free_entry(BasicHashtableEntry<F>* entry) {
163 entry->set_next(_removed_head);
164 _removed_head = entry;
165 if (_removed_tail == NULL) {
166 _removed_tail = entry;
167 }
168 _num_removed++;
169 }
170
171 template <MEMFLAGS F> void BasicHashtable<F>::bulk_free_entries(BucketUnlinkContext* context) {
172 if (context->_num_removed == 0) {
173 assert(context->_removed_head == NULL && context->_removed_tail == NULL,
174 "Zero entries in the unlink context, but elements linked from " PTR_FORMAT " to " PTR_FORMAT,
175 p2i(context->_removed_head), p2i(context->_removed_tail));
176 return;
177 }
178
179 // MT-safe add of the list of BasicHashTableEntrys from the context to the free list.
180 BasicHashtableEntry<F>* current = _free_list;
181 while (true) {
182 context->_removed_tail->set_next(current);
183 BasicHashtableEntry<F>* old = (BasicHashtableEntry<F>*)Atomic::cmpxchg_ptr(context->_removed_head, &_free_list, current);
184 if (old == current) {
185 break;
186 }
187 current = old;
188 }
189 Atomic::add(-context->_num_removed, &_number_of_entries);
190 }
191
192 // Copy the table to the shared space.
193
194 template <MEMFLAGS F> void BasicHashtable<F>::copy_table(char** top, char* end) {
195
196 // Dump the hash table entries.
197
198 intptr_t *plen = (intptr_t*)(*top);
199 *top += sizeof(*plen);
200
201 int i;
202 for (i = 0; i < _table_size; ++i) {
203 for (BasicHashtableEntry<F>** p = _buckets[i].entry_addr();
204 *p != NULL;
205 p = (*p)->next_addr()) {
206 if (*top + entry_size() > end) {
207 report_out_of_shared_space(SharedMiscData);
208 }
209 *p = (BasicHashtableEntry<F>*)memcpy(*top, *p, entry_size());
210 *top += entry_size();
211 }
212 }
213 *plen = (char*)(*top) - (char*)plen - sizeof(*plen);
214
215 // Set the shared bit.
216
217 for (i = 0; i < _table_size; ++i) {
218 for (BasicHashtableEntry<F>* p = bucket(i); p != NULL; p = p->next()) {
219 p->set_shared();
220 }
221 }
222 }
223
224 template <class T, MEMFLAGS F> int RehashableHashtable<T, F>::literal_size(Symbol *symbol) {
225 return symbol->size() * HeapWordSize;
226 }
227
228 template <class T, MEMFLAGS F> int RehashableHashtable<T, F>::literal_size(oop oop) {
229 // NOTE: this would over-count if (pre-JDK8) java_lang_Class::has_offset_field() is true,
230 // and the String.value array is shared by several Strings. However, starting from JDK8,
231 // the String.value array is not shared anymore.
232 assert(oop != NULL && oop->klass() == SystemDictionary::String_klass(), "only strings are supported");
233 return (oop->size() + java_lang_String::value(oop)->size()) * HeapWordSize;
234 }
235
236 // Dump footprint and bucket length statistics
237 //
238 // Note: if you create a new subclass of Hashtable<MyNewType, F>, you will need to
239 // add a new function Hashtable<T, F>::literal_size(MyNewType lit)
240
241 template <class T, MEMFLAGS F> void RehashableHashtable<T, F>::dump_table(outputStream* st, const char *table_name) {
242 NumberSeq summary;
243 int literal_bytes = 0;
244 for (int i = 0; i < this->table_size(); ++i) {
245 int count = 0;
246 for (HashtableEntry<T, F>* e = this->bucket(i);
247 e != NULL; e = e->next()) {
248 count++;
249 literal_bytes += literal_size(e->literal());
250 }
251 summary.add((double)count);
252 }
253 double num_buckets = summary.num();
254 double num_entries = summary.sum();
255
256 int bucket_bytes = (int)num_buckets * sizeof(HashtableBucket<F>);
257 int entry_bytes = (int)num_entries * sizeof(HashtableEntry<T, F>);
258 int total_bytes = literal_bytes + bucket_bytes + entry_bytes;
259
260 double bucket_avg = (num_buckets <= 0) ? 0 : (bucket_bytes / num_buckets);
261 double entry_avg = (num_entries <= 0) ? 0 : (entry_bytes / num_entries);
262 double literal_avg = (num_entries <= 0) ? 0 : (literal_bytes / num_entries);
263
264 st->print_cr("%s statistics:", table_name);
265 st->print_cr("Number of buckets : %9d = %9d bytes, avg %7.3f", (int)num_buckets, bucket_bytes, bucket_avg);
266 st->print_cr("Number of entries : %9d = %9d bytes, avg %7.3f", (int)num_entries, entry_bytes, entry_avg);
267 st->print_cr("Number of literals : %9d = %9d bytes, avg %7.3f", (int)num_entries, literal_bytes, literal_avg);
268 st->print_cr("Total footprint : %9s = %9d bytes", "", total_bytes);
269 st->print_cr("Average bucket size : %9.3f", summary.avg());
270 st->print_cr("Variance of bucket size : %9.3f", summary.variance());
271 st->print_cr("Std. dev. of bucket size: %9.3f", summary.sd());
272 st->print_cr("Maximum bucket size : %9d", (int)summary.maximum());
273 }
274
275
276 // Dump the hash table buckets.
277
278 template <MEMFLAGS F> void BasicHashtable<F>::copy_buckets(char** top, char* end) {
279 intptr_t len = _table_size * sizeof(HashtableBucket<F>);
280 *(intptr_t*)(*top) = len;
281 *top += sizeof(intptr_t);
282
283 *(intptr_t*)(*top) = _number_of_entries;
284 *top += sizeof(intptr_t);
285
286 if (*top + len > end) {
287 report_out_of_shared_space(SharedMiscData);
288 }
289 _buckets = (HashtableBucket<F>*)memcpy(*top, _buckets, len);
290 *top += len;
291 }
292
293
294 #ifndef PRODUCT
295
296 template <class T, MEMFLAGS F> void Hashtable<T, F>::print() {
297 ResourceMark rm;
298
299 for (int i = 0; i < BasicHashtable<F>::table_size(); i++) {
300 HashtableEntry<T, F>* entry = bucket(i);
301 while(entry != NULL) {
302 tty->print("%d : ", i);
303 entry->literal()->print();
304 tty->cr();
305 entry = entry->next();
306 }
307 }
308 }
309
310
311 template <MEMFLAGS F>
312 template <class T> void BasicHashtable<F>::verify_table(const char* table_name) {
313 int element_count = 0;
314 int max_bucket_count = 0;
315 for (int index = 0; index < table_size(); index++) {
316 int bucket_count = 0;
317 for (T* probe = (T*)bucket(index); probe != NULL; probe = probe->next()) {
318 probe->verify();
319 bucket_count++;
320 }
321 element_count += bucket_count;
322 max_bucket_count = MAX2(max_bucket_count, bucket_count);
323 }
324 guarantee(number_of_entries() == element_count,
325 "Verify of %s failed", table_name);
326 DEBUG_ONLY(verify_lookup_length(max_bucket_count, table_name));
327 }
328
329
330 #endif // PRODUCT
331
332 #ifdef ASSERT
333
334 // Assert if the longest bucket is 10x longer than the average bucket size.
335 // Could change back to a warning, but warnings are not noticed.
336 template <MEMFLAGS F> void BasicHashtable<F>::verify_lookup_length(int max_bucket_count, const char *table_name) {
337 log_info(hashtables)("%s max bucket size %d element count %d table size %d", table_name,
338 max_bucket_count, _number_of_entries, _table_size);
339 assert (max_bucket_count < ((1 + number_of_entries()/table_size())*10), "Table is unbalanced");
340 }
341
342 #endif
343
344
345 // Explicitly instantiate these types
346 #if INCLUDE_ALL_GCS
347 template class Hashtable<nmethod*, mtGC>;
348 template class HashtableEntry<nmethod*, mtGC>;
349 template class BasicHashtable<mtGC>;
350 #endif
351 template class Hashtable<ConstantPool*, mtClass>;
352 template class RehashableHashtable<Symbol*, mtSymbol>;
353 template class RehashableHashtable<oopDesc*, mtSymbol>;
354 template class Hashtable<Symbol*, mtSymbol>;
355 template class Hashtable<Klass*, mtClass>;
356 template class Hashtable<InstanceKlass*, mtClass>;
357 template class Hashtable<oop, mtClass>;
358 #if defined(SOLARIS) || defined(CHECK_UNHANDLED_OOPS)
359 template class Hashtable<oop, mtSymbol>;
360 template class RehashableHashtable<oop, mtSymbol>;
361 #endif // SOLARIS || CHECK_UNHANDLED_OOPS
362 template class Hashtable<oopDesc*, mtSymbol>;
363 template class Hashtable<Symbol*, mtClass>;
364 template class HashtableEntry<Symbol*, mtSymbol>;
365 template class HashtableEntry<Symbol*, mtClass>;
366 template class HashtableEntry<oop, mtSymbol>;
367 template class BasicHashtableEntry<mtSymbol>;
368 template class BasicHashtableEntry<mtCode>;
369 template class BasicHashtable<mtClass>;
370 template class BasicHashtable<mtClassShared>;
371 template class BasicHashtable<mtSymbol>;
372 template class BasicHashtable<mtCode>;
373 template class BasicHashtable<mtInternal>;
374 template class BasicHashtable<mtModule>;
375 #if INCLUDE_TRACE
376 template class Hashtable<Symbol*, mtTracing>;
377 template class HashtableEntry<Symbol*, mtTracing>;
378 template class BasicHashtable<mtTracing>;
379 #endif
380 template class BasicHashtable<mtCompiler>;
381
382 template void BasicHashtable<mtClass>::verify_table<DictionaryEntry>(char const*);
383 template void BasicHashtable<mtModule>::verify_table<ModuleEntry>(char const*);
384 template void BasicHashtable<mtModule>::verify_table<PackageEntry>(char const*);
385 template void BasicHashtable<mtClass>::verify_table<ProtectionDomainCacheEntry>(char const*);