1 /*
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   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.
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   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  *
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  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
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  20  * or visit www.oracle.com if you need additional information or have any
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  24 
  25 #ifndef SHARE_VM_RUNTIME_ATOMIC_HPP
  26 #define SHARE_VM_RUNTIME_ATOMIC_HPP
  27 
  28 #include "memory/allocation.hpp"
  29 #include "utilities/align.hpp"
  30 #include "utilities/macros.hpp"
  31 
  32 enum cmpxchg_memory_order {
  33   memory_order_relaxed,
  34   // Use value which doesn't interfere with C++2011. We need to be more conservative.
  35   memory_order_conservative = 8
  36 };
  37 
  38 class Atomic : AllStatic {
  39  public:
  40   // Atomic operations on jlong types are not available on all 32-bit
  41   // platforms. If atomic ops on jlongs are defined here they must only
  42   // be used from code that verifies they are available at runtime and
  43   // can provide an alternative action if not - see supports_cx8() for
  44   // a means to test availability.
  45 
  46   // The memory operations that are mentioned with each of the atomic
  47   // function families come from src/share/vm/runtime/orderAccess.hpp,
  48   // e.g., <fence> is described in that file and is implemented by the
  49   // OrderAccess::fence() function. See that file for the gory details
  50   // on the Memory Access Ordering Model.
  51 
  52   // All of the atomic operations that imply a read-modify-write action
  53   // guarantee a two-way memory barrier across that operation. Historically
  54   // these semantics reflect the strength of atomic operations that are
  55   // provided on SPARC/X86. We assume that strength is necessary unless
  56   // we can prove that a weaker form is sufficiently safe.
  57 
  58   // Atomically store to a location
  59   inline static void store    (jbyte    store_value, jbyte*    dest);
  60   inline static void store    (jshort   store_value, jshort*   dest);
  61   inline static void store    (jint     store_value, jint*     dest);
  62   // See comment above about using jlong atomics on 32-bit platforms
  63   inline static void store    (jlong    store_value, jlong*    dest);
  64   inline static void store_ptr(intptr_t store_value, intptr_t* dest);
  65   inline static void store_ptr(void*    store_value, void*     dest);
  66 
  67   inline static void store    (jbyte    store_value, volatile jbyte*    dest);
  68   inline static void store    (jshort   store_value, volatile jshort*   dest);
  69   inline static void store    (jint     store_value, volatile jint*     dest);
  70   // See comment above about using jlong atomics on 32-bit platforms
  71   inline static void store    (jlong    store_value, volatile jlong*    dest);
  72   inline static void store_ptr(intptr_t store_value, volatile intptr_t* dest);
  73   inline static void store_ptr(void*    store_value, volatile void*     dest);
  74 
  75   // See comment above about using jlong atomics on 32-bit platforms
  76   inline static jlong load(const volatile jlong* src);
  77 
  78   // Atomically add to a location. Returns updated value. add*() provide:
  79   // <fence> add-value-to-dest <membar StoreLoad|StoreStore>
  80   inline static jshort   add    (jshort   add_value, volatile jshort*   dest);
  81   inline static jint     add    (jint     add_value, volatile jint*     dest);
  82   inline static size_t   add    (size_t   add_value, volatile size_t*   dest);
  83   inline static intptr_t add_ptr(intptr_t add_value, volatile intptr_t* dest);
  84   inline static void*    add_ptr(intptr_t add_value, volatile void*     dest);
  85 
  86   // Atomically increment location. inc*() provide:
  87   // <fence> increment-dest <membar StoreLoad|StoreStore>
  88   inline static void inc    (volatile jint*     dest);
  89   inline static void inc    (volatile jshort*   dest);
  90   inline static void inc    (volatile size_t*   dest);
  91   inline static void inc_ptr(volatile intptr_t* dest);
  92   inline static void inc_ptr(volatile void*     dest);
  93 
  94   // Atomically decrement a location. dec*() provide:
  95   // <fence> decrement-dest <membar StoreLoad|StoreStore>
  96   inline static void dec    (volatile jint*     dest);
  97   inline static void dec    (volatile jshort*   dest);
  98   inline static void dec    (volatile size_t*   dest);
  99   inline static void dec_ptr(volatile intptr_t* dest);
 100   inline static void dec_ptr(volatile void*     dest);
 101 
 102   // Performs atomic exchange of *dest with exchange_value. Returns old
 103   // prior value of *dest. xchg*() provide:
 104   // <fence> exchange-value-with-dest <membar StoreLoad|StoreStore>
 105   inline static jint         xchg    (jint         exchange_value, volatile jint*         dest);
 106   inline static unsigned int xchg    (unsigned int exchange_value, volatile unsigned int* dest);
 107   inline static intptr_t     xchg_ptr(intptr_t     exchange_value, volatile intptr_t*     dest);
 108   inline static void*        xchg_ptr(void*        exchange_value, volatile void*         dest);
 109 
 110   // Performs atomic compare of *dest and compare_value, and exchanges
 111   // *dest with exchange_value if the comparison succeeded. Returns prior
 112   // value of *dest. cmpxchg*() provide:
 113   // <fence> compare-and-exchange <membar StoreLoad|StoreStore>
 114   inline static jbyte        cmpxchg    (jbyte        exchange_value, volatile jbyte*        dest, jbyte        compare_value, cmpxchg_memory_order order = memory_order_conservative);
 115   inline static jint         cmpxchg    (jint         exchange_value, volatile jint*         dest, jint         compare_value, cmpxchg_memory_order order = memory_order_conservative);
 116   // See comment above about using jlong atomics on 32-bit platforms
 117   inline static jlong        cmpxchg    (jlong        exchange_value, volatile jlong*        dest, jlong        compare_value, cmpxchg_memory_order order = memory_order_conservative);
 118   inline static unsigned int cmpxchg    (unsigned int exchange_value, volatile unsigned int* dest, unsigned int compare_value, cmpxchg_memory_order order = memory_order_conservative);
 119   inline static intptr_t     cmpxchg_ptr(intptr_t     exchange_value, volatile intptr_t*     dest, intptr_t     compare_value, cmpxchg_memory_order order = memory_order_conservative);
 120   inline static void*        cmpxchg_ptr(void*        exchange_value, volatile void*         dest, void*        compare_value, cmpxchg_memory_order order = memory_order_conservative);
 121 };
 122 
 123 // platform specific in-line definitions - must come before shared definitions
 124 
 125 #include OS_CPU_HEADER(atomic)
 126 
 127 // shared in-line definitions
 128 
 129 // size_t casts...
 130 #if (SIZE_MAX != UINTPTR_MAX)
 131 #error size_t is not WORD_SIZE, interesting platform, but missing implementation here
 132 #endif
 133 
 134 inline size_t Atomic::add(size_t add_value, volatile size_t* dest) {
 135   return (size_t) add_ptr((intptr_t) add_value, (volatile intptr_t*) dest);
 136 }
 137 
 138 inline void Atomic::inc(volatile size_t* dest) {
 139   inc_ptr((volatile intptr_t*) dest);
 140 }
 141 
 142 inline void Atomic::dec(volatile size_t* dest) {
 143   dec_ptr((volatile intptr_t*) dest);
 144 }
 145 
 146 #ifndef VM_HAS_SPECIALIZED_CMPXCHG_BYTE
 147 /*
 148  * This is the default implementation of byte-sized cmpxchg. It emulates jbyte-sized cmpxchg
 149  * in terms of jint-sized cmpxchg. Platforms may override this by defining their own inline definition
 150  * as well as defining VM_HAS_SPECIALIZED_CMPXCHG_BYTE. This will cause the platform specific
 151  * implementation to be used instead.
 152  */
 153 inline jbyte Atomic::cmpxchg(jbyte exchange_value, volatile jbyte* dest,
 154                              jbyte compare_value, cmpxchg_memory_order order) {
 155   STATIC_ASSERT(sizeof(jbyte) == 1);
 156   volatile jint* dest_int =
 157       reinterpret_cast<volatile jint*>(align_down(dest, sizeof(jint)));
 158   size_t offset = pointer_delta(dest, dest_int, 1);
 159   jint cur = *dest_int;
 160   jbyte* cur_as_bytes = reinterpret_cast<jbyte*>(&cur);
 161 
 162   // current value may not be what we are looking for, so force it
 163   // to that value so the initial cmpxchg will fail if it is different
 164   cur_as_bytes[offset] = compare_value;
 165 
 166   // always execute a real cmpxchg so that we get the required memory
 167   // barriers even on initial failure
 168   do {
 169     // value to swap in matches current value ...
 170     jint new_value = cur;
 171     // ... except for the one jbyte we want to update
 172     reinterpret_cast<jbyte*>(&new_value)[offset] = exchange_value;
 173 
 174     jint res = cmpxchg(new_value, dest_int, cur, order);
 175     if (res == cur) break; // success
 176 
 177     // at least one jbyte in the jint changed value, so update
 178     // our view of the current jint
 179     cur = res;
 180     // if our jbyte is still as cur we loop and try again
 181   } while (cur_as_bytes[offset] == compare_value);
 182 
 183   return cur_as_bytes[offset];
 184 }
 185 
 186 #endif // VM_HAS_SPECIALIZED_CMPXCHG_BYTE
 187 
 188 inline unsigned Atomic::xchg(unsigned int exchange_value, volatile unsigned int* dest) {
 189   assert(sizeof(unsigned int) == sizeof(jint), "more work to do");
 190   return (unsigned int)Atomic::xchg((jint)exchange_value, (volatile jint*)dest);
 191 }
 192 
 193 inline unsigned Atomic::cmpxchg(unsigned int exchange_value,
 194                          volatile unsigned int* dest, unsigned int compare_value,
 195                          cmpxchg_memory_order order) {
 196   assert(sizeof(unsigned int) == sizeof(jint), "more work to do");
 197   return (unsigned int)Atomic::cmpxchg((jint)exchange_value, (volatile jint*)dest,
 198                                        (jint)compare_value, order);
 199 }
 200 
 201 inline jshort Atomic::add(jshort add_value, volatile jshort* dest) {
 202   // Most platforms do not support atomic add on a 2-byte value. However,
 203   // if the value occupies the most significant 16 bits of an aligned 32-bit
 204   // word, then we can do this with an atomic add of (add_value << 16)
 205   // to the 32-bit word.
 206   //
 207   // The least significant parts of this 32-bit word will never be affected, even
 208   // in case of overflow/underflow.
 209   //
 210   // Use the ATOMIC_SHORT_PAIR macro (see macros.hpp) to get the desired alignment.
 211 #ifdef VM_LITTLE_ENDIAN
 212   assert((intx(dest) & 0x03) == 0x02, "wrong alignment");
 213   jint new_value = Atomic::add(add_value << 16, (volatile jint*)(dest-1));
 214 #else
 215   assert((intx(dest) & 0x03) == 0x00, "wrong alignment");
 216   jint new_value = Atomic::add(add_value << 16, (volatile jint*)(dest));
 217 #endif
 218   return (jshort)(new_value >> 16); // preserves sign
 219 }
 220 
 221 inline void Atomic::inc(volatile jshort* dest) {
 222   (void)add(1, dest);
 223 }
 224 
 225 inline void Atomic::dec(volatile jshort* dest) {
 226   (void)add(-1, dest);
 227 }
 228 
 229 #endif // SHARE_VM_RUNTIME_ATOMIC_HPP