1 /*
   2  * Copyright (c) 1997, 2019, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
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  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
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  24 
  25 #ifndef SHARE_INTERPRETER_OOPMAPCACHE_HPP
  26 #define SHARE_INTERPRETER_OOPMAPCACHE_HPP
  27 
  28 #include "oops/generateOopMap.hpp"
  29 #include "runtime/mutex.hpp"
  30 
  31 // A Cache for storing (method, bci) -> oopMap.
  32 // The memory management system uses the cache when locating object
  33 // references in an interpreted frame.
  34 //
  35 // OopMapCache's are allocated lazily per InstanceKlass.
  36 
  37 // The oopMap (InterpreterOopMap) is stored as a bit mask. If the
  38 // bit_mask can fit into two words it is stored in
  39 // the _bit_mask array, otherwise it is allocated on the heap.
  40 // For OopMapCacheEntry the bit_mask is allocated in the C heap
  41 // because these entries persist between garbage collections.
  42 // For InterpreterOopMap the bit_mask is allocated in
  43 // a resource area for better performance.  InterpreterOopMap
  44 // should only be created and deleted during same garbage collection.
  45 //
  46 // If ENABBLE_ZAP_DEAD_LOCALS is defined, two bits are used
  47 // per entry instead of one. In all cases,
  48 // the first bit is set to indicate oops as opposed to other
  49 // values. If the second bit is available,
  50 // it is set for dead values. We get the following encoding:
  51 //
  52 // 00 live value
  53 // 01 live oop
  54 // 10 dead value
  55 // 11 <unused>                                   (we cannot distinguish between dead oops or values with the current oop map generator)
  56 
  57 
  58 class OffsetClosure  {
  59  public:
  60   virtual void offset_do(int offset) = 0;
  61 };
  62 
  63 class OopMapCacheEntry;
  64 
  65 class InterpreterOopMap: ResourceObj {
  66   friend class OopMapCache;
  67 
  68  public:
  69   enum {
  70     N                = 4,                // the number of words reserved
  71                                          // for inlined mask storage
  72     small_mask_limit = N * BitsPerWord,  // the maximum number of bits
  73                                          // available for small masks,
  74                                          // small_mask_limit can be set to 0
  75                                          // for testing bit_mask allocation
  76 
  77     bits_per_entry   = 2,
  78     dead_bit_number  = 1,
  79     oop_bit_number   = 0
  80   };
  81 
  82  private:
  83   Method*        _method;         // the method for which the mask is valid
  84   unsigned short _bci;            // the bci    for which the mask is valid
  85   int            _mask_size;      // the mask size in bits
  86   int            _expression_stack_size; // the size of the expression stack in slots
  87 
  88  protected:
  89   intptr_t       _bit_mask[N];    // the bit mask if
  90                                   // mask_size <= small_mask_limit,
  91                                   // ptr to bit mask otherwise
  92                                   // "protected" so that sub classes can
  93                                   // access it without using trickery in
  94                                   // methd bit_mask().
  95 #ifdef ASSERT
  96   bool _resource_allocate_bit_mask;
  97 #endif
  98 
  99   // access methods
 100   Method*        method() const                  { return _method; }
 101   void           set_method(Method* v)           { _method = v; }
 102   int            bci() const                     { return _bci; }
 103   void           set_bci(int v)                  { _bci = v; }
 104   int            mask_size() const               { return _mask_size; }
 105   void           set_mask_size(int v)            { _mask_size = v; }
 106   // Test bit mask size and return either the in-line bit mask or allocated
 107   // bit mask.
 108   uintptr_t*  bit_mask() const                   { return (uintptr_t*)(mask_size() <= small_mask_limit ? (intptr_t)_bit_mask : _bit_mask[0]); }
 109 
 110   // return the word size of_bit_mask.  mask_size() <= 4 * MAX_USHORT
 111   size_t mask_word_size() const {
 112     return (mask_size() + BitsPerWord - 1) / BitsPerWord;
 113   }
 114 
 115   uintptr_t entry_at(int offset) const           { int i = offset * bits_per_entry; return bit_mask()[i / BitsPerWord] >> (i % BitsPerWord); }
 116 
 117   void set_expression_stack_size(int sz)         { _expression_stack_size = sz; }
 118 
 119   // Lookup
 120   bool match(const methodHandle& method, int bci) const { return _method == method() && _bci == bci; }
 121   bool is_empty() const;
 122 
 123   // Initialization
 124   void initialize();
 125 
 126  public:
 127   InterpreterOopMap();
 128   ~InterpreterOopMap();
 129 
 130   // Copy the OopMapCacheEntry in parameter "from" into this
 131   // InterpreterOopMap.  If the _bit_mask[0] in "from" points to
 132   // allocated space (i.e., the bit mask was to large to hold
 133   // in-line), allocate the space from a Resource area.
 134   void resource_copy(OopMapCacheEntry* from);
 135 
 136   void iterate_oop(OffsetClosure* oop_closure) const;
 137   void print() const;
 138 
 139   int number_of_entries() const                  { return mask_size() / bits_per_entry; }
 140   bool is_dead(int offset) const                 { return (entry_at(offset) & (1 << dead_bit_number)) != 0; }
 141   bool is_oop (int offset) const                 { return (entry_at(offset) & (1 << oop_bit_number )) != 0; }
 142 
 143   int expression_stack_size() const              { return _expression_stack_size; }
 144 
 145 };
 146 
 147 class OopMapCache : public CHeapObj<mtClass> {
 148  static OopMapCacheEntry* volatile _old_entries;
 149  private:
 150   enum { _size        = 32,     // Use fixed size for now
 151          _probe_depth = 3       // probe depth in case of collisions
 152   };
 153 
 154   OopMapCacheEntry* volatile * _array;
 155 
 156   unsigned int hash_value_for(const methodHandle& method, int bci) const;
 157   OopMapCacheEntry* entry_at(int i) const;
 158   bool put_at(int i, OopMapCacheEntry* entry, OopMapCacheEntry* old);
 159 
 160   static void enqueue_for_cleanup(OopMapCacheEntry* entry);
 161 
 162   void flush();
 163 
 164  public:
 165   OopMapCache();
 166   ~OopMapCache();                                // free up memory
 167 
 168   // flush cache entry is occupied by an obsolete method
 169   void flush_obsolete_entries();
 170 
 171   // Returns the oopMap for (method, bci) in parameter "entry".
 172   // Returns false if an oop map was not found.
 173   void lookup(const methodHandle& method, int bci, InterpreterOopMap* entry);
 174 
 175   // Compute an oop map without updating the cache or grabbing any locks (for debugging)
 176   static void compute_one_oop_map(const methodHandle& method, int bci, InterpreterOopMap* entry);
 177   static void cleanup_old_entries();
 178 };
 179 
 180 #endif // SHARE_INTERPRETER_OOPMAPCACHE_HPP