| /* |
| * Copyright (c) 1997, 2016, 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; |
| |
| // Set _refcount to PERM_REFCOUNT to prevent the Symbol from being GC'ed. |
| #ifndef PERM_REFCOUNT |
| #define PERM_REFCOUNT -1 |
| #endif |
| |
| class Symbol : public MetaspaceObj { |
| friend class VMStructs; |
| friend class SymbolTable; |
| friend class MoveSymbols; |
| |
| private: |
| ATOMIC_SHORT_PAIR( |
| volatile short _refcount, // needs atomic operation |
| unsigned short _length // number of UTF8 characters in the symbol (does not need atomic op) |
| ); |
| short _identity_hash; |
| jbyte _body[2]; |
| |
| enum { |
| // max_symbol_length is constrained by type of _length |
| max_symbol_length = (1 << 16) -1 |
| }; |
| |
| static int size(int length) { |
| // minimum number of natural words needed to hold these bits (no non-heap version) |
| return (int)heap_word_size(sizeof(Symbol) + (length > 2 ? length - 2 : 0)); |
| } |
| |
| 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; } |
| unsigned identity_hash() const { |
| unsigned addr_bits = (unsigned)((uintptr_t)this >> (LogMinObjAlignmentInBytes + 3)); |
| return ((unsigned)_identity_hash & 0xffff) | |
| ((addr_bits ^ (_length << 8) ^ (( _body[0] << 8) | _body[1])) << 16); |
| } |
| |
| // For symbol table alternate hashing |
| unsigned int new_hash(juint seed); |
| |
| // Reference counting. See comments above this class for when to use. |
| int refcount() const { return _refcount; } |
| void increment_refcount(); |
| void decrement_refcount(); |
| // Set _refcount non zero to avoid being reclaimed by GC. |
| void set_permanent() { |
| assert(LogTouchedMethods, "Should not be called with LogTouchedMethods off"); |
| if (_refcount != PERM_REFCOUNT) { |
| _refcount = PERM_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(const 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_utf8_on(outputStream* st) 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(const 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 |