1 /*
   2  * Copyright (c) 1997, 2019, 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 
  26 #include "precompiled.hpp"
  27 #include "classfile/altHashing.hpp"
  28 #include "classfile/classLoaderData.hpp"
  29 #include "gc/shared/collectedHeap.hpp"
  30 #include "logging/log.hpp"
  31 #include "logging/logStream.hpp"
  32 #include "memory/allocation.inline.hpp"
  33 #include "memory/resourceArea.hpp"
  34 #include "memory/universe.hpp"
  35 #include "oops/symbol.hpp"
  36 #include "runtime/atomic.hpp"
  37 #include "runtime/os.hpp"
  38 #include "utilities/utf8.hpp"
  39 
  40 uint32_t Symbol::pack_length_and_refcount(int length, int refcount) {
  41   STATIC_ASSERT(max_symbol_length == ((1 << 16) - 1));
  42   STATIC_ASSERT(PERM_REFCOUNT == ((1 << 16) - 1));
  43   assert(length >= 0, "negative length");
  44   assert(length <= max_symbol_length, "too long symbol");
  45   assert(refcount >= 0, "negative refcount");
  46   assert(refcount <= PERM_REFCOUNT, "invalid refcount");
  47   uint32_t hi = length;
  48   uint32_t lo = refcount;
  49   return (hi << 16) | lo;
  50 }
  51 
  52 Symbol::Symbol(const u1* name, int length, int refcount) {
  53   _length_and_refcount =  pack_length_and_refcount(length, refcount);
  54   _identity_hash = (short)os::random();
  55   for (int i = 0; i < length; i++) {
  56     byte_at_put(i, name[i]);
  57   }
  58 }
  59 
  60 void* Symbol::operator new(size_t sz, int len) throw() {
  61   int alloc_size = size(len)*wordSize;
  62   address res = (address) AllocateHeap(alloc_size, mtSymbol);
  63   return res;
  64 }
  65 
  66 void* Symbol::operator new(size_t sz, int len, Arena* arena) throw() {
  67   int alloc_size = size(len)*wordSize;
  68   address res = (address)arena->Amalloc_4(alloc_size);
  69   return res;
  70 }
  71 
  72 void Symbol::operator delete(void *p) {
  73   assert(((Symbol*)p)->refcount() == 0, "should not call this");
  74   FreeHeap(p);
  75 }
  76 
  77 void Symbol::set_permanent() {
  78   // This is called at a safepoint during dumping of a dynamic CDS archive.
  79   assert(SafepointSynchronize::is_at_safepoint(), "must be at a safepoint");
  80   _length_and_refcount =  pack_length_and_refcount(length(), PERM_REFCOUNT);
  81 }
  82 
  83 
  84 // ------------------------------------------------------------------
  85 // Symbol::starts_with
  86 //
  87 // Tests if the symbol starts with the specified prefix of the given
  88 // length.
  89 bool Symbol::starts_with(const char* prefix, int len) const {
  90   if (len > utf8_length()) return false;
  91   while (len-- > 0) {
  92     if (prefix[len] != char_at(len))
  93       return false;
  94   }
  95   assert(len == -1, "we should be at the beginning");
  96   return true;
  97 }
  98 
  99 
 100 // ------------------------------------------------------------------
 101 // Symbol::index_of
 102 //
 103 // Finds if the given string is a substring of this symbol's utf8 bytes.
 104 // Return -1 on failure.  Otherwise return the first index where str occurs.
 105 int Symbol::index_of_at(int i, const char* str, int len) const {
 106   assert(i >= 0 && i <= utf8_length(), "oob");
 107   if (len <= 0)  return 0;
 108   char first_char = str[0];
 109   address bytes = (address) ((Symbol*)this)->base();
 110   address limit = bytes + utf8_length() - len;  // inclusive limit
 111   address scan = bytes + i;
 112   if (scan > limit)
 113     return -1;
 114   for (; scan <= limit; scan++) {
 115     scan = (address) memchr(scan, first_char, (limit + 1 - scan));
 116     if (scan == NULL)
 117       return -1;  // not found
 118     assert(scan >= bytes+i && scan <= limit, "scan oob");
 119     if (memcmp(scan, str, len) == 0)
 120       return (int)(scan - bytes);
 121   }
 122   return -1;
 123 }
 124 
 125 
 126 char* Symbol::as_C_string(char* buf, int size) const {
 127   if (size > 0) {
 128     int len = MIN2(size - 1, utf8_length());
 129     for (int i = 0; i < len; i++) {
 130       buf[i] = char_at(i);
 131     }
 132     buf[len] = '\0';
 133   }
 134   return buf;
 135 }
 136 
 137 char* Symbol::as_C_string() const {
 138   int len = utf8_length();
 139   char* str = NEW_RESOURCE_ARRAY(char, len + 1);
 140   return as_C_string(str, len + 1);
 141 }
 142 
 143 void Symbol::print_utf8_on(outputStream* st) const {
 144   st->print("%s", as_C_string());
 145 }
 146 
 147 void Symbol::print_symbol_on(outputStream* st) const {
 148   char *s;
 149   st = st ? st : tty;
 150   {
 151     // ResourceMark may not affect st->print(). If st is a string
 152     // stream it could resize, using the same resource arena.
 153     ResourceMark rm;
 154     s = as_quoted_ascii();
 155     s = os::strdup(s);
 156   }
 157   if (s == NULL) {
 158     st->print("(null)");
 159   } else {
 160     st->print("%s", s);
 161     os::free(s);
 162   }
 163 }
 164 
 165 char* Symbol::as_quoted_ascii() const {
 166   const char *ptr = (const char *)&_body[0];
 167   int quoted_length = UTF8::quoted_ascii_length(ptr, utf8_length());
 168   char* result = NEW_RESOURCE_ARRAY(char, quoted_length + 1);
 169   UTF8::as_quoted_ascii(ptr, utf8_length(), result, quoted_length + 1);
 170   return result;
 171 }
 172 
 173 jchar* Symbol::as_unicode(int& length) const {
 174   Symbol* this_ptr = (Symbol*)this;
 175   length = UTF8::unicode_length((char*)this_ptr->bytes(), utf8_length());
 176   jchar* result = NEW_RESOURCE_ARRAY(jchar, length);
 177   if (length > 0) {
 178     UTF8::convert_to_unicode((char*)this_ptr->bytes(), result, length);
 179   }
 180   return result;
 181 }
 182 
 183 const char* Symbol::as_klass_external_name(char* buf, int size) const {
 184   if (size > 0) {
 185     char* str    = as_C_string(buf, size);
 186     int   length = (int)strlen(str);
 187     // Turn all '/'s into '.'s (also for array klasses)
 188     for (int index = 0; index < length; index++) {
 189       if (str[index] == '/') {
 190         str[index] = '.';
 191       }
 192     }
 193     return str;
 194   } else {
 195     return buf;
 196   }
 197 }
 198 
 199 const char* Symbol::as_klass_external_name() const {
 200   char* str    = as_C_string();
 201   int   length = (int)strlen(str);
 202   // Turn all '/'s into '.'s (also for array klasses)
 203   for (int index = 0; index < length; index++) {
 204     if (str[index] == '/') {
 205       str[index] = '.';
 206     }
 207   }
 208   return str;
 209 }
 210 
 211 static void print_class(outputStream *os, char *class_str, int len) {
 212   for (int i = 0; i < len; ++i) {
 213     if (class_str[i] == '/') {
 214       os->put('.');
 215     } else {
 216       os->put(class_str[i]);
 217     }
 218   }
 219 }
 220 
 221 static void print_array(outputStream *os, char *array_str, int len) {
 222   int dimensions = 0;
 223   for (int i = 0; i < len; ++i) {
 224     if (array_str[i] == '[') {
 225       dimensions++;
 226     } else if (array_str[i] == 'L') {
 227       // Expected format: L<type name>;. Skip 'L' and ';' delimiting the type name.
 228       print_class(os, array_str+i+1, len-i-2);
 229       break;
 230     } else {
 231       os->print("%s", type2name(char2type(array_str[i])));
 232     }
 233   }
 234   for (int i = 0; i < dimensions; ++i) {
 235     os->print("[]");
 236   }
 237 }
 238 
 239 void Symbol::print_as_signature_external_return_type(outputStream *os) {
 240   for (SignatureStream ss(this); !ss.is_done(); ss.next()) {
 241     if (ss.at_return_type()) {
 242       if (ss.is_array()) {
 243         print_array(os, (char*)ss.raw_bytes(), (int)ss.raw_length());
 244       } else if (ss.is_object()) {
 245         // Expected format: L<type name>;. Skip 'L' and ';' delimiting the class name.
 246         print_class(os, (char*)ss.raw_bytes()+1, (int)ss.raw_length()-2);
 247       } else {
 248         os->print("%s", type2name(ss.type()));
 249       }
 250     }
 251   }
 252 }
 253 
 254 void Symbol::print_as_signature_external_parameters(outputStream *os) {
 255   bool first = true;
 256   for (SignatureStream ss(this); !ss.is_done(); ss.next()) {
 257     if (ss.at_return_type()) break;
 258     if (!first) { os->print(", "); }
 259     if (ss.is_array()) {
 260       print_array(os, (char*)ss.raw_bytes(), (int)ss.raw_length());
 261     } else if (ss.is_object()) {
 262       // Skip 'L' and ';'.
 263       print_class(os, (char*)ss.raw_bytes()+1, (int)ss.raw_length()-2);
 264     } else {
 265       os->print("%s", type2name(ss.type()));
 266     }
 267     first = false;
 268   }
 269 }
 270 
 271 // Increment refcount while checking for zero.  If the Symbol's refcount becomes zero
 272 // a thread could be concurrently removing the Symbol.  This is used during SymbolTable
 273 // lookup to avoid reviving a dead Symbol.
 274 bool Symbol::try_increment_refcount() {
 275   uint32_t found = _length_and_refcount;
 276   while (true) {
 277     uint32_t old_value = found;
 278     int refc = extract_refcount(old_value);
 279     if (refc == PERM_REFCOUNT) {
 280       return true;  // sticky max or created permanent
 281     } else if (refc == 0) {
 282       return false; // dead, can't revive.
 283     } else {
 284       found = Atomic::cmpxchg(old_value + 1, &_length_and_refcount, old_value);
 285       if (found == old_value) {
 286         return true; // successfully updated.
 287       }
 288       // refcount changed, try again.
 289     }
 290   }
 291 }
 292 
 293 // The increment_refcount() is called when not doing lookup. It is assumed that you
 294 // have a symbol with a non-zero refcount and it can't become zero while referenced by
 295 // this caller.
 296 void Symbol::increment_refcount() {
 297   if (!try_increment_refcount()) {
 298 #ifdef ASSERT
 299     print();
 300     fatal("refcount has gone to zero");
 301 #endif
 302   }
 303 #ifndef PRODUCT
 304   if (refcount() != PERM_REFCOUNT) { // not a permanent symbol
 305     NOT_PRODUCT(Atomic::inc(&_total_count);)
 306   }
 307 #endif
 308 }
 309 
 310 // Decrement refcount potentially while racing increment, so we need
 311 // to check the value after attempting to decrement so that if another
 312 // thread increments to PERM_REFCOUNT the value is not decremented.
 313 void Symbol::decrement_refcount() {
 314   uint32_t found = _length_and_refcount;
 315   while (true) {
 316     uint32_t old_value = found;
 317     int refc = extract_refcount(old_value);
 318     if (refc == PERM_REFCOUNT) {
 319       return;  // refcount is permanent, permanent is sticky
 320     } else if (refc == 0) {
 321 #ifdef ASSERT
 322       print();
 323       fatal("refcount underflow");
 324 #endif
 325       return;
 326     } else {
 327       found = Atomic::cmpxchg(old_value - 1, &_length_and_refcount, old_value);
 328       if (found == old_value) {
 329         return;  // successfully updated.
 330       }
 331       // refcount changed, try again.
 332     }
 333   }
 334 }
 335 
 336 void Symbol::make_permanent() {
 337   uint32_t found = _length_and_refcount;
 338   while (true) {
 339     uint32_t old_value = found;
 340     int refc = extract_refcount(old_value);
 341     if (refc == PERM_REFCOUNT) {
 342       return;  // refcount is permanent, permanent is sticky
 343     } else if (refc == 0) {
 344 #ifdef ASSERT
 345       print();
 346       fatal("refcount underflow");
 347 #endif
 348       return;
 349     } else {
 350       int len = extract_length(old_value);
 351       found = Atomic::cmpxchg(pack_length_and_refcount(len, PERM_REFCOUNT), &_length_and_refcount, old_value);
 352       if (found == old_value) {
 353         return;  // successfully updated.
 354       }
 355       // refcount changed, try again.
 356     }
 357   }
 358 }
 359 
 360 void Symbol::metaspace_pointers_do(MetaspaceClosure* it) {
 361   if (log_is_enabled(Trace, cds)) {
 362     LogStream trace_stream(Log(cds)::trace());
 363     trace_stream.print("Iter(Symbol): %p ", this);
 364     print_value_on(&trace_stream);
 365     trace_stream.cr();
 366   }
 367 }
 368 
 369 void Symbol::print_on(outputStream* st) const {
 370   st->print("Symbol: '");
 371   print_symbol_on(st);
 372   st->print("'");
 373   st->print(" count %d", refcount());
 374 }
 375 
 376 void Symbol::print() const { print_on(tty); }
 377 
 378 // The print_value functions are present in all builds, to support the
 379 // disassembler and error reporting.
 380 void Symbol::print_value_on(outputStream* st) const {
 381   st->print("'");
 382   for (int i = 0; i < utf8_length(); i++) {
 383     st->print("%c", char_at(i));
 384   }
 385   st->print("'");
 386 }
 387 
 388 void Symbol::print_value() const { print_value_on(tty); }
 389 
 390 bool Symbol::is_valid(Symbol* s) {
 391   if (!is_aligned(s, sizeof(MetaWord))) return false;
 392   if ((size_t)s < os::min_page_size()) return false;
 393 
 394   if (!os::is_readable_range(s, s + 1)) return false;
 395 
 396   // Symbols are not allocated in Java heap.
 397   if (Universe::heap()->is_in_reserved(s)) return false;
 398 
 399   int len = s->utf8_length();
 400   if (len < 0) return false;
 401 
 402   jbyte* bytes = (jbyte*) s->bytes();
 403   return os::is_readable_range(bytes, bytes + len);
 404 }
 405 
 406 // SymbolTable prints this in its statistics
 407 NOT_PRODUCT(size_t Symbol::_total_count = 0;)