1 /*
   2  * Copyright (c) 1997, 2009, 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 // A symbolOop is a canonicalized string.
  26 // All symbolOops reside in global symbolTable.
  27 // See oopFactory::new_symbol for how to allocate a symbolOop
  28 
  29 class symbolOopDesc : public oopDesc {
  30   friend class VMStructs;
  31  private:
  32   unsigned short _length; // number of UTF8 characters in the symbol
  33   jbyte _body[1];
  34 
  35   enum {
  36     // max_symbol_length is constrained by type of _length
  37     max_symbol_length = (1 << 16) -1
  38   };
  39  public:
  40 
  41   // Low-level access (used with care, since not GC-safe)
  42   jbyte* base() { return &_body[0]; }
  43 
  44 
  45   // Returns the largest size symbol we can safely hold.
  46   static int max_length() {
  47     return max_symbol_length;
  48   }
  49 
  50   static int object_size(int length) {
  51     int size = header_size() + (sizeof(unsigned short) + length + HeapWordSize - 1) / HeapWordSize;
  52     return align_object_size(size);
  53   }
  54 
  55   int object_size() { return object_size(utf8_length()); }
  56 
  57   int byte_at(int index) const {
  58     assert(index >=0 && index < _length, "symbol index overflow");
  59     return ((symbolOopDesc*)this)->base()[index];
  60   }
  61 
  62   void byte_at_put(int index, int value) {
  63     assert(index >=0 && index < _length, "symbol index overflow");
  64     ((symbolOopDesc*)this)->base()[index] = value;
  65   }
  66 
  67   jbyte* bytes() { return base(); }
  68 
  69   int utf8_length() const { return _length; }
  70 
  71   void set_utf8_length(int len) { _length = len; }
  72 
  73   // Compares the symbol with a string.
  74   bool equals(const char* str, int len) const;
  75   bool equals(const char* str) const { return equals(str, (int) strlen(str)); }
  76 
  77   // Tests if the symbol starts with the given prefix.
  78   bool starts_with(const char* prefix, int len) const;
  79   bool starts_with(const char* prefix) const {
  80     return starts_with(prefix, (int) strlen(prefix));
  81   }
  82 
  83   // Tests if the symbol starts with the given prefix.
  84   int index_of_at(int i, const char* str, int len) const;
  85   int index_of_at(int i, const char* str) const {
  86     return index_of_at(i, str, (int) strlen(str));
  87   }
  88 
  89   // Three-way compare for sorting; returns -1/0/1 if receiver is </==/> than arg
  90   // note that the ordering is not alfabetical
  91   inline int fast_compare(symbolOop other) const;
  92 
  93   // Returns receiver converted to null-terminated UTF-8 string; string is
  94   // allocated in resource area, or in the char buffer provided by caller.
  95   char* as_C_string() const;
  96   char* as_C_string(char* buf, int size) const;
  97   // Use buf if needed buffer length is <= size.
  98   char* as_C_string_flexible_buffer(Thread* t, char* buf, int size) const;
  99 
 100 
 101   // Returns a null terminated utf8 string in a resource array
 102   char* as_utf8() const { return as_C_string(); }
 103   char* as_utf8_flexible_buffer(Thread* t, char* buf, int size) const {
 104     return as_C_string_flexible_buffer(t, buf, size);
 105   }
 106 
 107   jchar* as_unicode(int& length) const;
 108 
 109   // Treating this symbol as a class name, returns the Java name for the class.
 110   // String is allocated in resource area if buffer is not provided.
 111   // See Klass::external_name()
 112   const char* as_klass_external_name() const;
 113   const char* as_klass_external_name(char* buf, int size) const;
 114 
 115   bool object_is_parsable() const {
 116     return (utf8_length() > 0 || (oop)this == Universe::emptySymbol());
 117   }
 118 
 119   // Printing
 120   void print_symbol_on(outputStream* st = NULL);
 121 };
 122 
 123 
 124 // Note: this comparison is used for vtable sorting only; it doesn't matter
 125 // what order it defines, as long as it is a total, time-invariant order
 126 // Since symbolOops are in permSpace, their relative order in memory never changes,
 127 // so use address comparison for speed
 128 int symbolOopDesc::fast_compare(symbolOop other) const {
 129  return (((uintptr_t)this < (uintptr_t)other) ? -1
 130    : ((uintptr_t)this == (uintptr_t) other) ? 0 : 1);
 131 }