1 /*
2 * Copyright (c) 2003, 2018, 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/placeholders.hpp"
32 #include "classfile/protectionDomainCache.hpp"
33 #include "classfile/stringTable.hpp"
34 #include "logging/log.hpp"
35 #include "memory/allocation.inline.hpp"
36 #include "memory/metaspaceShared.hpp"
37 #include "memory/resourceArea.hpp"
38 #include "oops/oop.inline.hpp"
39 #include "oops/weakHandle.inline.hpp"
40 #include "runtime/safepoint.hpp"
41 #include "utilities/dtrace.hpp"
42 #include "utilities/hashtable.hpp"
43 #include "utilities/hashtable.inline.hpp"
44 #include "utilities/numberSeq.hpp"
45
46
47 // This hashtable is implemented as an open hash table with a fixed number of buckets.
48
new_entry_free_list()49 template <MEMFLAGS F> BasicHashtableEntry<F>* BasicHashtable<F>::new_entry_free_list() {
50 BasicHashtableEntry<F>* entry = NULL;
51 if (_free_list != NULL) {
52 entry = _free_list;
53 _free_list = _free_list->next();
54 }
55 return entry;
56 }
57
58 // HashtableEntrys are allocated in blocks to reduce the space overhead.
new_entry(unsigned int hashValue)59 template <MEMFLAGS F> BasicHashtableEntry<F>* BasicHashtable<F>::new_entry(unsigned int hashValue) {
60 BasicHashtableEntry<F>* entry = new_entry_free_list();
61
62 if (entry == NULL) {
63 if (_first_free_entry + _entry_size >= _end_block) {
64 int block_size = MIN2(512, MAX2((int)_table_size / 2, (int)_number_of_entries));
65 int len = _entry_size * block_size;
66 len = 1 << log2_int(len); // round down to power of 2
67 assert(len >= _entry_size, "");
68 _first_free_entry = NEW_C_HEAP_ARRAY2(char, len, F, CURRENT_PC);
69 _end_block = _first_free_entry + len;
70 }
71 entry = (BasicHashtableEntry<F>*)_first_free_entry;
72 _first_free_entry += _entry_size;
73 }
74
75 assert(_entry_size % HeapWordSize == 0, "");
76 entry->set_hash(hashValue);
77 return entry;
78 }
79
80
new_entry(unsigned int hashValue,T obj)81 template <class T, MEMFLAGS F> HashtableEntry<T, F>* Hashtable<T, F>::new_entry(unsigned int hashValue, T obj) {
82 HashtableEntry<T, F>* entry;
83
84 entry = (HashtableEntry<T, F>*)BasicHashtable<F>::new_entry(hashValue);
85 entry->set_literal(obj);
86 return entry;
87 }
88
89 // Version of hashtable entry allocation that allocates in the C heap directly.
90 // The allocator in blocks is preferable but doesn't have free semantics.
allocate_new_entry(unsigned int hashValue,T obj)91 template <class T, MEMFLAGS F> HashtableEntry<T, F>* Hashtable<T, F>::allocate_new_entry(unsigned int hashValue, T obj) {
92 HashtableEntry<T, F>* entry = (HashtableEntry<T, F>*) NEW_C_HEAP_ARRAY(char, this->entry_size(), F);
93
94 entry->set_hash(hashValue);
95 entry->set_literal(obj);
96 entry->set_next(NULL);
97 return entry;
98 }
99
100 // Check to see if the hashtable is unbalanced. The caller set a flag to
101 // rehash at the next safepoint. If this bucket is 60 times greater than the
102 // expected average bucket length, it's an unbalanced hashtable.
103 // This is somewhat an arbitrary heuristic but if one bucket gets to
104 // rehash_count which is currently 100, there's probably something wrong.
105
check_rehash_table(int count)106 template <class T, MEMFLAGS F> bool RehashableHashtable<T, F>::check_rehash_table(int count) {
107 assert(this->table_size() != 0, "underflow");
108 if (count > (((double)this->number_of_entries()/(double)this->table_size())*rehash_multiple)) {
109 // Set a flag for the next safepoint, which should be at some guaranteed
110 // safepoint interval.
111 return true;
112 }
113 return false;
114 }
115
116 // Create a new table and using alternate hash code, populate the new table
117 // with the existing elements. This can be used to change the hash code
118 // and could in the future change the size of the table.
119
move_to(RehashableHashtable<T,F> * new_table)120 template <class T, MEMFLAGS F> void RehashableHashtable<T, F>::move_to(RehashableHashtable<T, F>* new_table) {
121
122 // Initialize the global seed for hashing.
123 _seed = AltHashing::compute_seed();
124 assert(seed() != 0, "shouldn't be zero");
125
126 int saved_entry_count = this->number_of_entries();
127
128 // Iterate through the table and create a new entry for the new table
129 for (int i = 0; i < new_table->table_size(); ++i) {
130 for (HashtableEntry<T, F>* p = this->bucket(i); p != NULL; ) {
131 HashtableEntry<T, F>* next = p->next();
132 T string = p->literal();
133 // Use alternate hashing algorithm on the symbol in the first table
134 unsigned int hashValue = string->new_hash(seed());
135 // Get a new index relative to the new table (can also change size)
136 int index = new_table->hash_to_index(hashValue);
137 p->set_hash(hashValue);
138 // Keep the shared bit in the Hashtable entry to indicate that this entry
139 // can't be deleted. The shared bit is the LSB in the _next field so
140 // walking the hashtable past these entries requires
141 // BasicHashtableEntry::make_ptr() call.
142 bool keep_shared = p->is_shared();
143 this->unlink_entry(p);
144 new_table->add_entry(index, p);
145 if (keep_shared) {
146 p->set_shared();
147 }
148 p = next;
149 }
150 }
151 // give the new table the free list as well
152 new_table->copy_freelist(this);
153
154 // Destroy memory used by the buckets in the hashtable. The memory
155 // for the elements has been used in a new table and is not
156 // destroyed. The memory reuse will benefit resizing the SystemDictionary
157 // to avoid a memory allocation spike at safepoint.
158 BasicHashtable<F>::free_buckets();
159 }
160
free_buckets()161 template <MEMFLAGS F> void BasicHashtable<F>::free_buckets() {
162 if (NULL != _buckets) {
163 // Don't delete the buckets in the shared space. They aren't
164 // allocated by os::malloc
165 if (!MetaspaceShared::is_in_shared_metaspace(_buckets)) {
166 FREE_C_HEAP_ARRAY(HashtableBucket, _buckets);
167 }
168 _buckets = NULL;
169 }
170 }
171
free_entry(BasicHashtableEntry<F> * entry)172 template <MEMFLAGS F> void BasicHashtable<F>::BucketUnlinkContext::free_entry(BasicHashtableEntry<F>* entry) {
173 entry->set_next(_removed_head);
174 _removed_head = entry;
175 if (_removed_tail == NULL) {
176 _removed_tail = entry;
177 }
178 _num_removed++;
179 }
180
bulk_free_entries(BucketUnlinkContext * context)181 template <MEMFLAGS F> void BasicHashtable<F>::bulk_free_entries(BucketUnlinkContext* context) {
182 if (context->_num_removed == 0) {
183 assert(context->_removed_head == NULL && context->_removed_tail == NULL,
184 "Zero entries in the unlink context, but elements linked from " PTR_FORMAT " to " PTR_FORMAT,
185 p2i(context->_removed_head), p2i(context->_removed_tail));
186 return;
187 }
188
189 // MT-safe add of the list of BasicHashTableEntrys from the context to the free list.
190 BasicHashtableEntry<F>* current = _free_list;
191 while (true) {
192 context->_removed_tail->set_next(current);
193 BasicHashtableEntry<F>* old = Atomic::cmpxchg(context->_removed_head, &_free_list, current);
194 if (old == current) {
195 break;
196 }
197 current = old;
198 }
199 Atomic::add(-context->_num_removed, &_number_of_entries);
200 }
201 // Copy the table to the shared space.
count_bytes_for_table()202 template <MEMFLAGS F> size_t BasicHashtable<F>::count_bytes_for_table() {
203 size_t bytes = 0;
204 bytes += sizeof(intptr_t); // len
205
206 for (int i = 0; i < _table_size; ++i) {
207 for (BasicHashtableEntry<F>** p = _buckets[i].entry_addr();
208 *p != NULL;
209 p = (*p)->next_addr()) {
210 bytes += entry_size();
211 }
212 }
213
214 return bytes;
215 }
216
217 // Dump the hash table entries (into CDS archive)
copy_table(char * top,char * end)218 template <MEMFLAGS F> void BasicHashtable<F>::copy_table(char* top, char* end) {
219 assert(is_aligned(top, sizeof(intptr_t)), "bad alignment");
220 intptr_t *plen = (intptr_t*)(top);
221 top += sizeof(*plen);
222
223 int i;
224 for (i = 0; i < _table_size; ++i) {
225 for (BasicHashtableEntry<F>** p = _buckets[i].entry_addr();
226 *p != NULL;
227 p = (*p)->next_addr()) {
228 *p = (BasicHashtableEntry<F>*)memcpy(top, (void*)*p, entry_size());
229 top += entry_size();
230 }
231 }
232 *plen = (char*)(top) - (char*)plen - sizeof(*plen);
233 assert(top == end, "count_bytes_for_table is wrong");
234 // Set the shared bit.
235
236 for (i = 0; i < _table_size; ++i) {
237 for (BasicHashtableEntry<F>* p = bucket(i); p != NULL; p = p->next()) {
238 p->set_shared();
239 }
240 }
241 }
242
243 // For oops and Strings the size of the literal is interesting. For other types, nobody cares.
literal_size(ConstantPool *)244 static int literal_size(ConstantPool*) { return 0; }
literal_size(Klass *)245 static int literal_size(Klass*) { return 0; }
literal_size(nmethod *)246 static int literal_size(nmethod*) { return 0; }
247
literal_size(Symbol * symbol)248 static int literal_size(Symbol *symbol) {
249 return symbol->size() * HeapWordSize;
250 }
251
literal_size(oop obj)252 static int literal_size(oop obj) {
253 // NOTE: this would over-count if (pre-JDK8) java_lang_Class::has_offset_field() is true,
254 // and the String.value array is shared by several Strings. However, starting from JDK8,
255 // the String.value array is not shared anymore.
256 if (obj == NULL) {
257 return 0;
258 } else if (obj->klass() == SystemDictionary::String_klass()) {
259 return (obj->size() + java_lang_String::value(obj)->size()) * HeapWordSize;
260 } else {
261 return obj->size();
262 }
263 }
264
literal_size(ClassLoaderWeakHandle v)265 static int literal_size(ClassLoaderWeakHandle v) {
266 return literal_size(v.peek());
267 }
268
resize(int new_size)269 template <MEMFLAGS F> bool BasicHashtable<F>::resize(int new_size) {
270 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
271
272 // Allocate new buckets
273 HashtableBucket<F>* buckets_new = NEW_C_HEAP_ARRAY2_RETURN_NULL(HashtableBucket<F>, new_size, F, CURRENT_PC);
274 if (buckets_new == NULL) {
275 return false;
276 }
277
278 // Clear the new buckets
279 for (int i = 0; i < new_size; i++) {
280 buckets_new[i].clear();
281 }
282
283 int table_size_old = _table_size;
284 // hash_to_index() uses _table_size, so switch the sizes now
285 _table_size = new_size;
286
287 // Move entries from the old table to a new table
288 for (int index_old = 0; index_old < table_size_old; index_old++) {
289 for (BasicHashtableEntry<F>* p = _buckets[index_old].get_entry(); p != NULL; ) {
290 BasicHashtableEntry<F>* next = p->next();
291 bool keep_shared = p->is_shared();
292 int index_new = hash_to_index(p->hash());
293
294 p->set_next(buckets_new[index_new].get_entry());
295 buckets_new[index_new].set_entry(p);
296
297 if (keep_shared) {
298 p->set_shared();
299 }
300 p = next;
301 }
302 }
303
304 // The old backets now can be released
305 BasicHashtable<F>::free_buckets();
306
307 // Switch to the new storage
308 _buckets = buckets_new;
309
310 return true;
311 }
312
313 // Dump footprint and bucket length statistics
314 //
315 // Note: if you create a new subclass of Hashtable<MyNewType, F>, you will need to
316 // add a new function static int literal_size(MyNewType lit)
317 // because I can't get template <class T> int literal_size(T) to pick the specializations for Symbol and oop.
318 //
319 // The StringTable and SymbolTable dumping print how much footprint is used by the String and Symbol
320 // literals.
321
print_table_statistics(outputStream * st,const char * table_name,T (* literal_load_barrier)(HashtableEntry<T,F> *))322 template <class T, MEMFLAGS F> void Hashtable<T, F>::print_table_statistics(outputStream* st,
323 const char *table_name,
324 T (*literal_load_barrier)(HashtableEntry<T, F>*)) {
325 NumberSeq summary;
326 int literal_bytes = 0;
327 for (int i = 0; i < this->table_size(); ++i) {
328 int count = 0;
329 for (HashtableEntry<T, F>* e = this->bucket(i);
330 e != NULL; e = e->next()) {
331 count++;
332 T l = (literal_load_barrier != NULL) ? literal_load_barrier(e) : e->literal();
333 literal_bytes += literal_size(l);
334 }
335 summary.add((double)count);
336 }
337 double num_buckets = summary.num();
338 double num_entries = summary.sum();
339
340 int bucket_bytes = (int)num_buckets * sizeof(HashtableBucket<F>);
341 int entry_bytes = (int)num_entries * sizeof(HashtableEntry<T, F>);
342 int total_bytes = literal_bytes + bucket_bytes + entry_bytes;
343
344 int bucket_size = (num_buckets <= 0) ? 0 : (bucket_bytes / num_buckets);
345 int entry_size = (num_entries <= 0) ? 0 : (entry_bytes / num_entries);
346
347 st->print_cr("%s statistics:", table_name);
348 st->print_cr("Number of buckets : %9d = %9d bytes, each %d", (int)num_buckets, bucket_bytes, bucket_size);
349 st->print_cr("Number of entries : %9d = %9d bytes, each %d", (int)num_entries, entry_bytes, entry_size);
350 if (literal_bytes != 0) {
351 double literal_avg = (num_entries <= 0) ? 0 : (literal_bytes / num_entries);
352 st->print_cr("Number of literals : %9d = %9d bytes, avg %7.3f", (int)num_entries, literal_bytes, literal_avg);
353 }
354 st->print_cr("Total footprint : %9s = %9d bytes", "", total_bytes);
355 st->print_cr("Average bucket size : %9.3f", summary.avg());
356 st->print_cr("Variance of bucket size : %9.3f", summary.variance());
357 st->print_cr("Std. dev. of bucket size: %9.3f", summary.sd());
358 st->print_cr("Maximum bucket size : %9d", (int)summary.maximum());
359 }
360
361
362 // Dump the hash table buckets.
363
count_bytes_for_buckets()364 template <MEMFLAGS F> size_t BasicHashtable<F>::count_bytes_for_buckets() {
365 size_t bytes = 0;
366 bytes += sizeof(intptr_t); // len
367 bytes += sizeof(intptr_t); // _number_of_entries
368 bytes += _table_size * sizeof(HashtableBucket<F>); // the buckets
369
370 return bytes;
371 }
372
373 // Dump the buckets (into CDS archive)
copy_buckets(char * top,char * end)374 template <MEMFLAGS F> void BasicHashtable<F>::copy_buckets(char* top, char* end) {
375 assert(is_aligned(top, sizeof(intptr_t)), "bad alignment");
376 intptr_t len = _table_size * sizeof(HashtableBucket<F>);
377 *(intptr_t*)(top) = len;
378 top += sizeof(intptr_t);
379
380 *(intptr_t*)(top) = _number_of_entries;
381 top += sizeof(intptr_t);
382
383 _buckets = (HashtableBucket<F>*)memcpy(top, (void*)_buckets, len);
384 top += len;
385
386 assert(top == end, "count_bytes_for_buckets is wrong");
387 }
388
389 #ifndef PRODUCT
print_literal(T l)390 template <class T> void print_literal(T l) {
391 l->print();
392 }
393
print_literal(ClassLoaderWeakHandle l)394 static void print_literal(ClassLoaderWeakHandle l) {
395 l.print();
396 }
397
print()398 template <class T, MEMFLAGS F> void Hashtable<T, F>::print() {
399 ResourceMark rm;
400
401 for (int i = 0; i < BasicHashtable<F>::table_size(); i++) {
402 HashtableEntry<T, F>* entry = bucket(i);
403 while(entry != NULL) {
404 tty->print("%d : ", i);
405 print_literal(entry->literal());
406 tty->cr();
407 entry = entry->next();
408 }
409 }
410 }
411
412 template <MEMFLAGS F>
verify_table(const char * table_name)413 template <class T> void BasicHashtable<F>::verify_table(const char* table_name) {
414 int element_count = 0;
415 int max_bucket_count = 0;
416 int max_bucket_number = 0;
417 for (int index = 0; index < table_size(); index++) {
418 int bucket_count = 0;
419 for (T* probe = (T*)bucket(index); probe != NULL; probe = probe->next()) {
420 probe->verify();
421 bucket_count++;
422 }
423 element_count += bucket_count;
424 if (bucket_count > max_bucket_count) {
425 max_bucket_count = bucket_count;
426 max_bucket_number = index;
427 }
428 }
429 guarantee(number_of_entries() == element_count,
430 "Verify of %s failed", table_name);
431
432 // Log some statistics about the hashtable
433 log_info(hashtables)("%s max bucket size %d bucket %d element count %d table size %d", table_name,
434 max_bucket_count, max_bucket_number, _number_of_entries, _table_size);
435 if (_number_of_entries > 0 && log_is_enabled(Debug, hashtables)) {
436 for (int index = 0; index < table_size(); index++) {
437 int bucket_count = 0;
438 for (T* probe = (T*)bucket(index); probe != NULL; probe = probe->next()) {
439 log_debug(hashtables)("bucket %d hash " INTPTR_FORMAT, index, (intptr_t)probe->hash());
440 bucket_count++;
441 }
442 if (bucket_count > 0) {
443 log_debug(hashtables)("bucket %d count %d", index, bucket_count);
444 }
445 }
446 }
447 }
448 #endif // PRODUCT
449
450 // Explicitly instantiate these types
451 template class Hashtable<nmethod*, mtGC>;
452 template class HashtableEntry<nmethod*, mtGC>;
453 template class BasicHashtable<mtGC>;
454 template class Hashtable<ConstantPool*, mtClass>;
455 template class RehashableHashtable<Symbol*, mtSymbol>;
456 template class RehashableHashtable<oop, mtSymbol>;
457 template class Hashtable<Symbol*, mtSymbol>;
458 template class Hashtable<Klass*, mtClass>;
459 template class Hashtable<InstanceKlass*, mtClass>;
460 template class Hashtable<ClassLoaderWeakHandle, mtClass>;
461 template class Hashtable<Symbol*, mtModule>;
462 template class Hashtable<oop, mtSymbol>;
463 template class Hashtable<ClassLoaderWeakHandle, mtSymbol>;
464 template class Hashtable<Symbol*, mtClass>;
465 template class HashtableEntry<Symbol*, mtSymbol>;
466 template class HashtableEntry<Symbol*, mtClass>;
467 template class HashtableEntry<oop, mtSymbol>;
468 template class HashtableEntry<ClassLoaderWeakHandle, mtSymbol>;
469 template class HashtableBucket<mtClass>;
470 template class BasicHashtableEntry<mtSymbol>;
471 template class BasicHashtableEntry<mtCode>;
472 template class BasicHashtable<mtClass>;
473 template class BasicHashtable<mtClassShared>;
474 template class BasicHashtable<mtSymbol>;
475 template class BasicHashtable<mtCode>;
476 template class BasicHashtable<mtInternal>;
477 template class BasicHashtable<mtModule>;
478 template class BasicHashtable<mtCompiler>;
479
480 template void BasicHashtable<mtClass>::verify_table<DictionaryEntry>(char const*);
481 template void BasicHashtable<mtModule>::verify_table<ModuleEntry>(char const*);
482 template void BasicHashtable<mtModule>::verify_table<PackageEntry>(char const*);
483 template void BasicHashtable<mtClass>::verify_table<ProtectionDomainCacheEntry>(char const*);
484 template void BasicHashtable<mtClass>::verify_table<PlaceholderEntry>(char const*);
485