jdk8-mips64-public/hotspot: src/share/vm/oops/symbol.hpp@fc9d8850ab8b (annotated)

src/share/vm/oops/symbol.hpp@fc9d8850ab8b (annotated)

src/share/vm/oops/symbol.hpp

Fri, 23 Mar 2012 11:16:05 -0400

author: coleenp
date: Fri, 23 Mar 2012 11:16:05 -0400
changeset 3682: fc9d8850ab8b
parent 2708: 1d1603768966
child 4037: da91efe96a93
permissions: -rw-r--r--

7150058: Allocate symbols from null boot loader to an arena for NMT
Summary: Move symbol allocation to an arena so NMT doesn't have to track them at startup.
Reviewed-by: never, kamg, zgu

 /*
  * Copyright (c) 1997, 2012, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
  * under the terms of the GNU General Public License version 2 only, as
  * published by the Free Software Foundation.
  *
  * This code is distributed in the hope that it will be useful, but WITHOUT
  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  * version 2 for more details (a copy is included in the LICENSE file that
  * accompanied this code).
  *
  * You should have received a copy of the GNU General Public License version
  * 2 along with this work; if not, write to the Free Software Foundation,
  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  *
  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  * or visit www.oracle.com if you need additional information or have any
  * questions.
  *
  */
 #ifndef SHARE_VM_OOPS_SYMBOL_HPP
 #define SHARE_VM_OOPS_SYMBOL_HPP
 #include "utilities/utf8.hpp"
 #include "memory/allocation.hpp"
 #include "runtime/atomic.hpp"
 // A Symbol is a canonicalized string.
 // All Symbols reside in global SymbolTable and are reference counted.
 // Reference counting
 //
 // All Symbols are allocated and added to the SymbolTable.
 // When a class is unloaded, the reference counts of the Symbol pointers in
 // the ConstantPool and in instanceKlass (see release_C_heap_structures) are
 // decremented.  When the reference count for a Symbol goes to 0, the garbage
 // collector can free the Symbol and remove it from the SymbolTable.
 //
 // 0) Symbols need to be reference counted when a pointer to the Symbol is
 // saved in persistent storage.  This does not include the pointer
 // in the SymbolTable bucket (the _literal field in HashtableEntry)
 // that points to the Symbol.  All other stores of a Symbol*
 // to a field of a persistent variable (e.g., the _name filed in
 // FieldAccessInfo or _ptr in a CPSlot) is reference counted.
 //
 // 1) The lookup of a "name" in the SymbolTable either creates a Symbol F for
 // "name" and returns a pointer to F or finds a pre-existing Symbol F for
 // "name" and returns a pointer to it. In both cases the reference count for F
 // is incremented under the assumption that a pointer to F will be created from
 // the return value. Thus the increment of the reference count is on the lookup
 // and not on the assignment to the new Symbol*.  That is
 //    Symbol* G = lookup()
 //                ^ increment on lookup()
 // and not
 //    Symbol* G = lookup()
 //              ^ increment on assignmnet
 // The reference count must be decremented manually when the copy of the
 // pointer G is destroyed.
 //
 // 2) For a local Symbol* A that is a copy of an existing Symbol* B, the
 // reference counting is elided when the scope of B is greater than the scope
 // of A.  For example, in the code fragment
 // below "klass" is passed as a parameter to the method.  Symbol* "kn"
 // is a copy of the name in "klass".
 //
 //   Symbol*  kn = klass->name();
 //   unsigned int d_hash = dictionary()->compute_hash(kn, class_loader);
 //
 // The scope of "klass" is greater than the scope of "kn" so the reference
 // counting for "kn" is elided.
 //
 // Symbol* copied from ConstantPool entries are good candidates for reference
 // counting elision.  The ConstantPool entries for a class C exist until C is
 // unloaded.  If a Symbol* is copied out of the ConstantPool into Symbol* X,
 // the Symbol* in the ConstantPool will in general out live X so the reference
 // counting on X can be elided.
 //
 // For cases where the scope of A is not greater than the scope of B,
 // the reference counting is explicitly done.  See ciSymbol,
 // ResolutionErrorEntry and ClassVerifier for examples.
 //
 // 3) When a Symbol K is created for temporary use, generally for substrings of
 // an existing symbol or to create a new symbol, assign it to a
 // TempNewSymbol. The SymbolTable methods new_symbol(), lookup()
 // and probe() all potentially return a pointer to a new Symbol.
 // The allocation (or lookup) of K increments the reference count for K
 // and the destructor decrements the reference count.
 //
 // Another example of TempNewSymbol usage is parsed_name used in
 // ClassFileParser::parseClassFile() where parsed_name is used in the cleanup
 // after a failed attempt to load a class.  Here parsed_name is a
 // TempNewSymbol (passed in as a parameter) so the reference count on its symbol
 // will be decremented when it goes out of scope.
 class Symbol : public ResourceObj {
   friend class VMStructs;
   friend class SymbolTable;
   friend class MoveSymbols;
  private:
   volatile int   _refcount;
   int            _identity_hash;
   unsigned short _length; // number of UTF8 characters in the symbol
   jbyte _body[1];
   enum {
     // max_symbol_length is constrained by type of _length
     max_symbol_length = (1 << 16) -1
   };
   static int object_size(int length) {
     size_t size = heap_word_size(sizeof(Symbol) + (length > 0 ? length - 1 : 0));
     return align_object_size(size);
   }
   void byte_at_put(int index, int value) {
     assert(index >=0 && index < _length, "symbol index overflow");
     _body[index] = value;
   }
   Symbol(const u1* name, int length, int refcount);
   void* operator new(size_t size, int len, TRAPS);
   void* operator new(size_t size, int len, Arena* arena, TRAPS);
  public:
   // Low-level access (used with care, since not GC-safe)
   const jbyte* base() const { return &_body[0]; }
   int object_size()         { return object_size(utf8_length()); }
   // Returns the largest size symbol we can safely hold.
   static int max_length()   { return max_symbol_length; }
   int identity_hash()       { return _identity_hash; }
   // Reference counting.  See comments above this class for when to use.
   int refcount() const      { return _refcount; }
   inline void increment_refcount();
   inline void decrement_refcount();
   int byte_at(int index) const {
     assert(index >=0 && index < _length, "symbol index overflow");
     return base()[index];
   }
   const jbyte* bytes() const { return base(); }
   int utf8_length() const { return _length; }
   // Compares the symbol with a string.
   bool equals(const char* str, int len) const;
   bool equals(const char* str) const { return equals(str, (int) strlen(str)); }
   // Tests if the symbol starts with the given prefix.
   bool starts_with(const char* prefix, int len) const;
   bool starts_with(const char* prefix) const {
     return starts_with(prefix, (int) strlen(prefix));
   }
   // Tests if the symbol starts with the given prefix.
   int index_of_at(int i, const char* str, int len) const;
   int index_of_at(int i, const char* str) const {
     return index_of_at(i, str, (int) strlen(str));
   }
   // Three-way compare for sorting; returns -1/0/1 if receiver is </==/> than arg
   // note that the ordering is not alfabetical
   inline int fast_compare(Symbol* other) const;
   // Returns receiver converted to null-terminated UTF-8 string; string is
   // allocated in resource area, or in the char buffer provided by caller.
   char* as_C_string() const;
   char* as_C_string(char* buf, int size) const;
   // Use buf if needed buffer length is <= size.
   char* as_C_string_flexible_buffer(Thread* t, char* buf, int size) const;
   // Returns a null terminated utf8 string in a resource array
   char* as_utf8() const { return as_C_string(); }
   char* as_utf8_flexible_buffer(Thread* t, char* buf, int size) const {
     return as_C_string_flexible_buffer(t, buf, size);
   }
   jchar* as_unicode(int& length) const;
   // Treating this symbol as a class name, returns the Java name for the class.
   // String is allocated in resource area if buffer is not provided.
   // See Klass::external_name()
   const char* as_klass_external_name() const;
   const char* as_klass_external_name(char* buf, int size) const;
   // Printing
   void print_symbol_on(outputStream* st = NULL) const;
   void print_on(outputStream* st) const;         // First level print
   void print_value_on(outputStream* st) const;   // Second level print.
   // printing on default output stream
   void print()         { print_on(tty);       }
   void print_value()   { print_value_on(tty); }
 #ifndef PRODUCT
   // Empty constructor to create a dummy symbol object on stack
   // only for getting its vtable pointer.
   Symbol() { }
   static int _total_count;
 #endif
 };
 // Note: this comparison is used for vtable sorting only; it doesn't matter
 // what order it defines, as long as it is a total, time-invariant order
 // Since Symbol*s are in C_HEAP, their relative order in memory never changes,
 // so use address comparison for speed
 int Symbol::fast_compare(Symbol* other) const {
  return (((uintptr_t)this < (uintptr_t)other) ? -1
    : ((uintptr_t)this == (uintptr_t) other) ? 0 : 1);
 }
 inline void Symbol::increment_refcount() {
   // Only increment the refcount if positive.  If negative either
   // overflow has occurred or it is a permanent symbol in a read only
   // shared archive.
   if (_refcount >= 0) {
     Atomic::inc(&_refcount);
     NOT_PRODUCT(Atomic::inc(&_total_count);)
   }
 }
 inline void Symbol::decrement_refcount() {
   if (_refcount >= 0) {
     Atomic::dec(&_refcount);
 #ifdef ASSERT
     if (_refcount < 0) {
       print();
       assert(false, "reference count underflow for symbol");
     }
 #endif
   }
 }
 #endif // SHARE_VM_OOPS_SYMBOL_HPP

Mercurial > jdk8-mips64-public > hotspot / annotate

src/share/vm/oops/symbol.hpp@fc9d8850ab8b (annotated)

src/share/vm/oops/symbol.hpp