1 /*
   2  * Copyright (c) 1997, 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 #ifndef SHARE_VM_CLASSFILE_STRINGTABLE_HPP
  26 #define SHARE_VM_CLASSFILE_STRINGTABLE_HPP
  27 
  28 #include "memory/allocation.inline.hpp"
  29 #include "utilities/hashtable.hpp"
  30 
  31 template <class T, class N> class CompactHashtable;
  32 class CompactStringTableWriter;
  33 class FileMapInfo;
  34 class SerializeClosure;
  35 
  36 class StringTable : public RehashableHashtable<oop, mtSymbol> {
  37   friend class VMStructs;
  38   friend class Symbol;
  39 
  40 private:
  41   // The string table
  42   static StringTable* _the_table;
  43 
  44   // Shared string table
  45   static CompactHashtable<oop, char> _shared_table;
  46   static bool _shared_string_mapped;
  47 
  48   // Set if one bucket is out of balance due to hash algorithm deficiency
  49   static bool _needs_rehashing;
  50 
  51   // Claimed high water mark for parallel chunked scanning
  52   static volatile int _parallel_claimed_idx;
  53 
  54   static oop intern(Handle string_or_null, jchar* chars, int length, TRAPS);
  55   oop basic_add(int index, Handle string_or_null, jchar* name, int len,
  56                 unsigned int hashValue, TRAPS);
  57 
  58   oop lookup_in_main_table(int index, jchar* chars, int length, unsigned int hashValue);
  59   static oop lookup_shared(jchar* name, int len, unsigned int hash);
  60 
  61   // Apply the give oop closure to the entries to the buckets
  62   // in the range [start_idx, end_idx).
  63   static void buckets_oops_do(OopClosure* f, int start_idx, int end_idx);
  64 
  65   typedef StringTable::BucketUnlinkContext BucketUnlinkContext;
  66   // Unlink or apply the give oop closure to the entries to the buckets
  67   // in the range [start_idx, end_idx). Unlinked bucket entries are collected in the given
  68   // context to be freed later.
  69   // This allows multiple threads to work on the table at once.
  70   static void buckets_unlink_or_oops_do(BoolObjectClosure* is_alive, OopClosure* f, int start_idx, int end_idx, BucketUnlinkContext* context);
  71 
  72   // Hashing algorithm, used as the hash value used by the
  73   //     StringTable for bucket selection and comparison (stored in the
  74   //     HashtableEntry structures).  This is used in the String.intern() method.
  75   static unsigned int hash_string(const jchar* s, int len);
  76   static unsigned int hash_string(oop string);
  77   static unsigned int alt_hash_string(const jchar* s, int len);
  78 
  79   // Accessors for the string roots in the hashtable entries.
  80   // Use string_object_no_keepalive() only when the value is not returned
  81   // outside of a scope where a thread transition is possible.
  82   static oop string_object(HashtableEntry<oop, mtSymbol>* entry);
  83   static oop string_object_no_keepalive(HashtableEntry<oop, mtSymbol>* entry);
  84   static void set_string_object(HashtableEntry<oop, mtSymbol>* entry, oop string);
  85 
  86   StringTable() : RehashableHashtable<oop, mtSymbol>((int)StringTableSize,
  87                               sizeof (HashtableEntry<oop, mtSymbol>)) {}
  88 
  89   StringTable(HashtableBucket<mtSymbol>* t, int number_of_entries)
  90     : RehashableHashtable<oop, mtSymbol>((int)StringTableSize, sizeof (HashtableEntry<oop, mtSymbol>), t,
  91                      number_of_entries) {}
  92 public:
  93   // The string table
  94   static StringTable* the_table() { return _the_table; }
  95 
  96   // Size of one bucket in the string table.  Used when checking for rollover.
  97   static uint bucket_size() { return sizeof(HashtableBucket<mtSymbol>); }
  98 
  99   static void create_table() {
 100     assert(_the_table == NULL, "One string table allowed.");
 101     _the_table = new StringTable();
 102   }
 103 
 104   // GC support
 105   //   Delete pointers to otherwise-unreachable objects.
 106   static void unlink_or_oops_do(BoolObjectClosure* cl, OopClosure* f) {
 107     int processed = 0;
 108     int removed = 0;
 109     unlink_or_oops_do(cl, f, &processed, &removed);
 110   }
 111   static void unlink(BoolObjectClosure* cl) {
 112     int processed = 0;
 113     int removed = 0;
 114     unlink_or_oops_do(cl, NULL, &processed, &removed);
 115   }
 116   static void unlink_or_oops_do(BoolObjectClosure* cl, OopClosure* f, int* processed, int* removed);
 117   static void unlink(BoolObjectClosure* cl, int* processed, int* removed) {
 118     unlink_or_oops_do(cl, NULL, processed, removed);
 119   }
 120   // Serially invoke "f->do_oop" on the locations of all oops in the table.
 121   static void oops_do(OopClosure* f);
 122 
 123   // Possibly parallel versions of the above
 124   static void possibly_parallel_unlink_or_oops_do(BoolObjectClosure* cl, OopClosure* f, int* processed, int* removed);
 125   static void possibly_parallel_unlink(BoolObjectClosure* cl, int* processed, int* removed) {
 126     possibly_parallel_unlink_or_oops_do(cl, NULL, processed, removed);
 127   }
 128   static void possibly_parallel_oops_do(OopClosure* f);
 129 
 130   // Internal test.
 131   static void test_alt_hash() PRODUCT_RETURN;
 132 
 133   // Probing
 134   static oop lookup(Symbol* symbol);
 135   static oop lookup(jchar* chars, int length);
 136 
 137   // Interning
 138   static oop intern(Symbol* symbol, TRAPS);
 139   static oop intern(oop string, TRAPS);
 140   static oop intern(const char *utf8_string, TRAPS);
 141 
 142   // Debugging
 143   static void verify();
 144   static void dump(outputStream* st, bool verbose=false);
 145 
 146   enum VerifyMesgModes {
 147     _verify_quietly    = 0,
 148     _verify_with_mesgs = 1
 149   };
 150 
 151   enum VerifyRetTypes {
 152     _verify_pass          = 0,
 153     _verify_fail_continue = 1,
 154     _verify_fail_done     = 2
 155   };
 156 
 157   static VerifyRetTypes compare_entries(int bkt1, int e_cnt1,
 158                                         HashtableEntry<oop, mtSymbol>* e_ptr1,
 159                                         int bkt2, int e_cnt2,
 160                                         HashtableEntry<oop, mtSymbol>* e_ptr2);
 161   static VerifyRetTypes verify_entry(int bkt, int e_cnt,
 162                                      HashtableEntry<oop, mtSymbol>* e_ptr,
 163                                      VerifyMesgModes mesg_mode);
 164   static int verify_and_compare_entries();
 165 
 166   // Sharing
 167   static void set_shared_string_mapped() { _shared_string_mapped = true; }
 168   static bool shared_string_mapped()       { return _shared_string_mapped; }
 169   static void shared_oops_do(OopClosure* f) NOT_CDS_JAVA_HEAP_RETURN;
 170   static bool copy_shared_string(GrowableArray<MemRegion> *string_space,
 171                                  CompactStringTableWriter* ch_table) NOT_CDS_JAVA_HEAP_RETURN_(false);
 172   static oop  create_archived_string(oop s, Thread* THREAD) NOT_CDS_JAVA_HEAP_RETURN_(NULL);
 173   static void write_to_archive(GrowableArray<MemRegion> *string_space) NOT_CDS_JAVA_HEAP_RETURN;
 174   static void serialize(SerializeClosure* soc) NOT_CDS_JAVA_HEAP_RETURN;
 175 
 176   // Rehash the symbol table if it gets out of balance
 177   static void rehash_table();
 178   static bool needs_rehashing() { return _needs_rehashing; }
 179 
 180   // Parallel chunked scanning
 181   static void clear_parallel_claimed_index() { _parallel_claimed_idx = 0; }
 182   static int parallel_claimed_index() { return _parallel_claimed_idx; }
 183 };
 184 #endif // SHARE_VM_CLASSFILE_STRINGTABLE_HPP