--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/hotspot/src/share/vm/oops/symbol.hpp Thu Jan 27 16:11:27 2011 -0800
@@ -0,0 +1,223 @@
+/*
+ * Copyright (c) 1997, 2009, 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"
+
+// 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 CHeapObj {
+ 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);
+ 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);
+ void* operator new(size_t size, int len);
+
+ 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; }
+ void increment_refcount();
+ 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);
+}
+#endif // SHARE_VM_OOPS_SYMBOL_HPP