1 /*
2 * Copyright (c) 1997, 2023, 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.
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23 */
24
25 #ifndef SHARE_CLASSFILE_COMPACTHASHTABLE_HPP
26 #define SHARE_CLASSFILE_COMPACTHASHTABLE_HPP
27
28 #include "cds/cds_globals.hpp"
29 #include "oops/array.hpp"
30 #include "oops/symbol.hpp"
31 #include "runtime/globals.hpp"
32 #include "utilities/growableArray.hpp"
33
34
35 template <
36 typename K,
37 typename V,
38 V (*DECODE)(address base_address, u4 offset),
39 bool (*EQUALS)(V value, K key, int len)
40 >
41 class CompactHashtable;
42 class NumberSeq;
43 class SimpleCompactHashtable;
44 class SerializeClosure;
45
46 // Stats for symbol tables in the CDS archive
47 class CompactHashtableStats {
48 public:
49 int hashentry_count;
50 int hashentry_bytes;
51 int bucket_count;
52 int bucket_bytes;
53
54 CompactHashtableStats() :
55 hashentry_count(0), hashentry_bytes(0),
56 bucket_count(0), bucket_bytes(0) {}
57 };
58
59 #if INCLUDE_CDS
60 /////////////////////////////////////////////////////////////////////////
61 //
62 // The compact hash table writer. Used at dump time for writing out
63 // the compact table to the shared archive.
64 //
65 // At dump time, the CompactHashtableWriter obtains all entries from the
66 // symbol/string table and adds them to a new temporary hash table. The hash
67 // table size (number of buckets) is calculated using
68 // '(num_entries + bucket_size - 1) / bucket_size'. The default bucket
69 // size is 4 and can be changed by -XX:SharedSymbolTableBucketSize option.
70 // 4 is chosen because it produces smaller sized bucket on average for
71 // faster lookup. It also has relatively small number of empty buckets and
72 // good distribution of the entries.
73 //
74 // We use a simple hash function (hash % num_bucket) for the table.
75 // The new table is compacted when written out. Please see comments
76 // above the CompactHashtable class for the table layout detail. The bucket
77 // offsets are written to the archive as part of the compact table. The
78 // bucket offset is encoded in the low 30-bit (0-29) and the bucket type
79 // (regular or compact) are encoded in bit[31, 30]. For buckets with more
80 // than one entry, both hash and entry offset are written to the
81 // table. For buckets with only one entry, only the entry offset is written
82 // to the table and the buckets are tagged as compact in their type bits.
83 // Buckets without entry are skipped from the table. Their offsets are
84 // still written out for faster lookup.
85 //
86 class CompactHashtableWriter: public StackObj {
87 public:
88 class Entry {
89 unsigned int _hash;
90 u4 _value;
91
92 public:
93 Entry() {}
94 Entry(unsigned int hash, u4 val) : _hash(hash), _value(val) {}
95
96 u4 value() {
97 return _value;
98 }
99 unsigned int hash() {
100 return _hash;
101 }
102
103 bool operator==(const CompactHashtableWriter::Entry& other) {
104 return (_value == other._value && _hash == other._hash);
105 }
106 }; // class CompactHashtableWriter::Entry
107
108 private:
109 int _num_entries_written;
110 int _num_buckets;
111 int _num_empty_buckets;
112 int _num_value_only_buckets;
113 int _num_other_buckets;
114 GrowableArray<Entry>** _buckets;
115 CompactHashtableStats* _stats;
116 Array<u4>* _compact_buckets;
117 Array<u4>* _compact_entries;
118
119 public:
120 // This is called at dump-time only
121 CompactHashtableWriter(int num_entries, CompactHashtableStats* stats);
122 ~CompactHashtableWriter();
123
124 void add(unsigned int hash, u4 value);
125
126 private:
127 void allocate_table();
128 void dump_table(NumberSeq* summary);
129 static int calculate_num_buckets(int num_entries) {
130 int num_buckets = num_entries / SharedSymbolTableBucketSize;
131 // calculation of num_buckets can result in zero buckets, we need at least one
132 return (num_buckets < 1) ? 1 : num_buckets;
133 }
134
135 public:
136 void dump(SimpleCompactHashtable *cht, const char* table_name);
137
138 static size_t estimate_size(int num_entries);
139 };
140 #endif // INCLUDE_CDS
141
142 #define REGULAR_BUCKET_TYPE 0
143 #define VALUE_ONLY_BUCKET_TYPE 1
144 #define TABLEEND_BUCKET_TYPE 3
145 #define BUCKET_OFFSET_MASK 0x3FFFFFFF
146 #define BUCKET_OFFSET(info) ((info) & BUCKET_OFFSET_MASK)
147 #define BUCKET_TYPE_SHIFT 30
148 #define BUCKET_TYPE(info) (((info) & ~BUCKET_OFFSET_MASK) >> BUCKET_TYPE_SHIFT)
149 #define BUCKET_INFO(offset, type) (((type) << BUCKET_TYPE_SHIFT) | ((offset) & BUCKET_OFFSET_MASK))
150
151 /////////////////////////////////////////////////////////////////////////////
152 //
153 // CompactHashtable is used to store the CDS archive's symbol/string tables.
154 //
155 // Because these tables are read-only (no entries can be added/deleted) at run-time
156 // and tend to have large number of entries, we try to minimize the footprint
157 // cost per entry.
158 //
159 // The CompactHashtable is split into two arrays
160 //
161 // u4 buckets[num_buckets+1]; // bit[31,30]: type; bit[29-0]: offset
162 // u4 entries[<variable size>]
163 //
164 // The size of buckets[] is 'num_buckets + 1'. Each entry of
165 // buckets[] is a 32-bit encoding of the bucket type and bucket offset,
166 // with the type in the left-most 2-bit and offset in the remaining 30-bit.
167 // The last entry is a special type. It contains the end of the last
168 // bucket.
169 //
170 // There are two types of buckets, regular buckets and value_only buckets. The
171 // value_only buckets have '01' in their highest 2-bit, and regular buckets have
172 // '00' in their highest 2-bit.
173 //
174 // For normal buckets, each entry is 8 bytes in the entries[]:
175 // u4 hash; /* symbol/string hash */
176 // union {
177 // u4 offset; /* Symbol* sym = (Symbol*)(base_address + offset) */
178 // narrowOop str; /* String narrowOop encoding */
179 // }
180 //
181 //
182 // For value_only buckets, each entry has only the 4-byte 'offset' in the entries[].
183 //
184 // Example -- note that the second bucket is a VALUE_ONLY_BUCKET_TYPE so the hash code
185 // is skipped.
186 // buckets[0, 4, 5, ....]
187 // | | |
188 // | | +---+
189 // | | |
190 // | +----+ |
191 // v v v
192 // entries[H,O,H,O,O,H,O,H,O.....]
193 //
194 // See CompactHashtable::lookup() for how the table is searched at runtime.
195 // See CompactHashtableWriter::dump() for how the table is written at CDS
196 // dump time.
197 //
198 class SimpleCompactHashtable {
199 protected:
200 address _base_address;
201 u4 _bucket_count;
202 u4 _entry_count;
203 u4* _buckets;
204 u4* _entries;
205
206 public:
207 SimpleCompactHashtable() {
208 _entry_count = 0;
209 _bucket_count = 0;
210 _buckets = 0;
211 _entries = 0;
212 }
213
214 void reset() {
215 _bucket_count = 0;
216 _entry_count = 0;
217 _buckets = 0;
218 _entries = 0;
219 }
220
221 void init(address base_address, u4 entry_count, u4 bucket_count, u4* buckets, u4* entries);
222
223 // Read/Write the table's header from/to the CDS archive
224 void serialize_header(SerializeClosure* soc) NOT_CDS_RETURN;
225
226 inline bool empty() const {
227 return (_entry_count == 0);
228 }
229
230 inline size_t entry_count() const {
231 return _entry_count;
232 }
233
234 static size_t calculate_header_size();
235 };
236
237 template <
238 typename K,
239 typename V,
240 V (*DECODE)(address base_address, u4 offset),
241 bool (*EQUALS)(V value, K key, int len)
242 >
243 class CompactHashtable : public SimpleCompactHashtable {
244 friend class VMStructs;
245
246 V decode(u4 offset) const {
247 return DECODE(_base_address, offset);
248 }
249
250 public:
251 // Lookup a value V from the compact table using key K
252 inline V lookup(K key, unsigned int hash, int len) const {
253 if (_entry_count > 0) {
254 int index = hash % _bucket_count;
255 u4 bucket_info = _buckets[index];
256 u4 bucket_offset = BUCKET_OFFSET(bucket_info);
257 int bucket_type = BUCKET_TYPE(bucket_info);
258 u4* entry = _entries + bucket_offset;
259
260 if (bucket_type == VALUE_ONLY_BUCKET_TYPE) {
261 V value = decode(entry[0]);
262 if (EQUALS(value, key, len)) {
263 return value;
264 }
265 } else {
266 // This is a regular bucket, which has more than one
267 // entries. Each entry is a pair of entry (hash, offset).
268 // Seek until the end of the bucket.
269 u4* entry_max = _entries + BUCKET_OFFSET(_buckets[index + 1]);
270 while (entry < entry_max) {
271 unsigned int h = (unsigned int)(entry[0]);
272 if (h == hash) {
273 V value = decode(entry[1]);
274 if (EQUALS(value, key, len)) {
275 return value;
276 }
277 }
278 entry += 2;
279 }
280 }
281 }
282 return nullptr;
283 }
284
285 template <class ITER>
286 inline void iterate(ITER* iter) const {
287 for (u4 i = 0; i < _bucket_count; i++) {
288 u4 bucket_info = _buckets[i];
289 u4 bucket_offset = BUCKET_OFFSET(bucket_info);
290 int bucket_type = BUCKET_TYPE(bucket_info);
291 u4* entry = _entries + bucket_offset;
292
293 if (bucket_type == VALUE_ONLY_BUCKET_TYPE) {
294 iter->do_value(decode(entry[0]));
295 } else {
296 u4*entry_max = _entries + BUCKET_OFFSET(_buckets[i + 1]);
297 while (entry < entry_max) {
298 iter->do_value(decode(entry[1]));
299 entry += 2;
300 }
301 }
302 }
303 }
304
305 void print_table_statistics(outputStream* st, const char* name) {
306 st->print_cr("%s statistics:", name);
307 int total_entries = 0;
308 int max_bucket = 0;
309 for (u4 i = 0; i < _bucket_count; i++) {
310 u4 bucket_info = _buckets[i];
311 int bucket_type = BUCKET_TYPE(bucket_info);
312 int bucket_size;
313
314 if (bucket_type == VALUE_ONLY_BUCKET_TYPE) {
315 bucket_size = 1;
316 } else {
317 bucket_size = (BUCKET_OFFSET(_buckets[i + 1]) - BUCKET_OFFSET(bucket_info)) / 2;
318 }
319 total_entries += bucket_size;
320 if (max_bucket < bucket_size) {
321 max_bucket = bucket_size;
322 }
323 }
324 st->print_cr("Number of buckets : %9d", _bucket_count);
325 st->print_cr("Number of entries : %9d", total_entries);
326 st->print_cr("Maximum bucket size : %9d", max_bucket);
327 }
328 };
329
330 ////////////////////////////////////////////////////////////////////////
331 //
332 // OffsetCompactHashtable -- This is used to store many types of objects
333 // in the CDS archive. On 64-bit platforms, we save space by using a 32-bit
334 // offset from the CDS base address.
335
336 template <typename V>
337 inline V read_value_from_compact_hashtable(address base_address, u4 offset) {
338 return (V)(base_address + offset);
339 }
340
341 template <
342 typename K,
343 typename V,
344 bool (*EQUALS)(V value, K key, int len)
345 >
346 class OffsetCompactHashtable : public CompactHashtable<
347 K, V, read_value_from_compact_hashtable<V>, EQUALS> {
348 };
349
350
351 ////////////////////////////////////////////////////////////////////////
352 //
353 // Read/Write the contents of a hashtable textual dump (created by
354 // SymbolTable::dump and StringTable::dump).
355 // Because the dump file may be big (hundred of MB in extreme cases),
356 // we use mmap for fast access when reading it.
357 //
358 class HashtableTextDump {
359 int _fd;
360 const char* _base;
361 const char* _p;
362 const char* _end;
363 const char* _filename;
364 size_t _size;
365 int _prefix_type;
366 int _line_no;
367 public:
368 HashtableTextDump(const char* filename);
369 ~HashtableTextDump();
370
371 enum {
372 SymbolPrefix = 1 << 0,
373 StringPrefix = 1 << 1,
374 Unknown = 1 << 2
375 };
376
377 void quit(const char* err, const char* msg);
378
379 inline int remain() {
380 return (int)(_end - _p);
381 }
382 int last_line_no() {
383 return _line_no - 1;
384 }
385
386 void corrupted(const char *p, const char *msg);
387
388 inline void corrupted_if(bool cond, const char *msg) {
389 if (cond) {
390 corrupted(_p, msg);
391 }
392 }
393
394 bool skip_newline();
395 int skip(char must_be_char);
396 void skip_past(char c);
397 void check_version(const char* ver);
398
399 inline void get_num(char delim, int *num) {
400 const char* p = _p;
401 const char* end = _end;
402 u8 n = 0;
403
404 while (p < end) {
405 char c = *p++;
406 if ('0' <= c && c <= '9') {
407 n = n * 10 + (c - '0');
408 if (n > (u8)INT_MAX) {
409 corrupted(_p, "Num overflow");
410 }
411 } else if (c == delim) {
412 _p = p;
413 *num = (int)n;
414 return;
415 } else {
416 // Not [0-9], not 'delim'
417 corrupted(_p, "Unrecognized format");;
418 }
419 }
420
421 corrupted(_end, "Incorrect format");
422 ShouldNotReachHere();
423 }
424
425 void scan_prefix_type();
426 int scan_prefix(int* utf8_length);
427 int scan_string_prefix();
428 int scan_symbol_prefix();
429
430 int unescape(const char* from, const char* end, int count);
431 void get_utf8(char* utf8_buffer, int utf8_length);
432 static void put_utf8(outputStream* st, const char* utf8_string, int utf8_length);
433 };
434
435 #endif // SHARE_CLASSFILE_COMPACTHASHTABLE_HPP