Mercurial > hg > truffle
view src/share/vm/oops/symbol.hpp @ 14459:194e8b7fe9ca
8033168: PPC64: gcc 4.8 warning in output_c.cpp
Summary: fix warnings
Reviewed-by: kvn
author | goetz |
---|---|
date | Thu, 30 Jan 2014 14:30:01 +0100 |
parents | b2e698d2276c |
children | cd6b3f1a94ff |
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/* * Copyright (c) 1997, 2013, 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 // fieldDescriptor 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. // This cannot be inherited from ResourceObj because it cannot have a vtable. // Since sometimes this is allocated from Metadata, pick a base allocation // type without virtual functions. class ClassLoaderData; // We separate the fields in SymbolBase from Symbol::_body so that // Symbol::size(int) can correctly calculate the space needed. class SymbolBase : public MetaspaceObj { public: ATOMIC_SHORT_PAIR( volatile short _refcount, // needs atomic operation unsigned short _length // number of UTF8 characters in the symbol (does not need atomic op) ); int _identity_hash; }; class Symbol : private SymbolBase { friend class VMStructs; friend class SymbolTable; friend class MoveSymbols; private: jbyte _body[1]; enum { // max_symbol_length is constrained by type of _length max_symbol_length = (1 << 16) -1 }; static int size(int length) { size_t sz = heap_word_size(sizeof(SymbolBase) + (length > 0 ? length : 0)); return align_object_size(sz); } 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) throw(); void* operator new(size_t size, int len, Arena* arena, TRAPS) throw(); void* operator new(size_t size, int len, ClassLoaderData* loader_data, TRAPS) throw(); void operator delete(void* p); public: // Low-level access (used with care, since not GC-safe) const jbyte* base() const { return &_body[0]; } int size() { return 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; } // For symbol table alternate hashing unsigned int new_hash(jint seed); // 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 an escaped form of a Java string. char* as_quoted_ascii() 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