symbolTable.hpp

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/* Copyright 1994, 1995 LongView Technologies L.L.C. $Revision: 1.8 $ */
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// The symbol table (Memory->symbol_table) holds all canonical symbols. 
// It is implemented as an open hash table with a fixed number of buckets.
// A bucket (symbolTableEntry) is a union containing either:
//   NULL             => bucket is empty.
//   symbolOop        => bucket has one element.
//   symbolTableLink* => bucket has more than one element.

// SPACE HACK:
//  - symbolTableLinks are allocated in blocks to reduce the malloc overhead.

const int symbol_table_size = 20011;

int hash(char* name, int len);

struct symbolTableLink {
  // instance variable
  symbolOop symbol;
  symbolTableLink* next;
  
  // memory operations
  bool verify(int i);
};

struct symbolTableEntry {
  void* symbol_or_link;
  bool is_empty()  { return symbol_or_link == NULL; }
  bool is_symbol() { return oop(symbol_or_link)->is_mem(); }
  void clear()     { symbol_or_link = NULL; }

  symbolOop get_symbol() {
    return symbolOop(symbol_or_link); }
  void set_symbol(symbolOop s) {
    symbol_or_link = (void*) s; }

  symbolTableLink* get_link() {
    return (symbolTableLink*) symbol_or_link; }
  void set_link(symbolTableLink* l) {
    symbol_or_link = (void*) l; }

  // memory operations
  bool verify(int i);
  void deallocate();
  
  int length();
};

class symbolTable: public CHeapObj {
 private:
  // instance variables
  symbolTableEntry buckets[symbol_table_size];
  symbolTableLink* free_list;
  symbolTableLink* first_free_link;
  symbolTableLink* end_block;
 public:
  // constructor
  symbolTable();

  // operations
  symbolOop lookup(char* name, int len);

  // Used in bootstrap for checking
  bool is_present(symbolOop sym);
 protected:
  void add_symbol(symbolOop s); // Only used by bootstrap

  symbolOop basic_add(char *name, int len, int hashValue);
  symbolOop basic_add(symbolOop s, int hashValue);
  symbolTableEntry* bucketFor(int hashValue) {
    assert(hashValue % symbol_table_size >= 0, "must be positive");
    return &buckets[hashValue % symbol_table_size]; }
  symbolTableEntry* firstBucket() { return &buckets[0]; }
  symbolTableEntry* lastBucket()  { return &buckets[symbol_table_size-1]; }
 public:
  void add(symbolOop s);
  
  // memory operations
  void follow_used_symbols(); // Used during phase1 of garbage collection

  void switch_pointers(oop from, oop to);
  void relocate();
  void verify();

  // memory management for symbolTableLinks
  symbolTableLink* new_link(symbolOop s, symbolTableLink* n = NULL);
  void             delete_link(symbolTableLink* l);

  // histogram
  void print_histogram();

  friend bootstrap;
};

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