1 /*
   2  * Copyright (c) 2001, 2014, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   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
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  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
  21  * questions.
  22  *
  23  */
  24 
  25 #include "precompiled.hpp"
  26 #include "runtime/atomic.inline.hpp"
  27 
  28 /*
  29  * This is the default implementation of byte-sized cmpxchg. It emulates jbyte-sized cmpxchg
  30  * in terms of jint-sized cmpxchg. Platforms may override this by defining their own inline definition
  31  * as well as defining VM_HAS_SPECIALIZED_CMPXCHG_BYTE. This will cause the platform specific
  32  * implementation to be used instead.
  33  */
  34 jbyte Atomic::cmpxchg_general(jbyte exchange_value, volatile jbyte* dest, jbyte compare_value) {
  35   assert(sizeof(jbyte) == 1, "assumption.");
  36   uintptr_t dest_addr = (uintptr_t)dest;
  37   uintptr_t offset = dest_addr % sizeof(jint);
  38   volatile jint* dest_int = (volatile jint*)(dest_addr - offset);
  39   jint cur = *dest_int;
  40   jbyte* cur_as_bytes = (jbyte*)(&cur);
  41   jint new_val = cur;
  42   jbyte* new_val_as_bytes = (jbyte*)(&new_val);
  43   new_val_as_bytes[offset] = exchange_value;
  44   while (cur_as_bytes[offset] == compare_value) {
  45     jint res = cmpxchg(new_val, dest_int, cur);
  46     if (res == cur) break;
  47     cur = res;
  48     new_val = cur;
  49     new_val_as_bytes[offset] = exchange_value;
  50   }
  51   return cur_as_bytes[offset];
  52 }
  53 
  54 unsigned Atomic::xchg(unsigned int exchange_value, volatile unsigned int* dest) {
  55   assert(sizeof(unsigned int) == sizeof(jint), "more work to do");
  56   return (unsigned int)Atomic::xchg((jint)exchange_value, (volatile jint*)dest);
  57 }
  58 
  59 unsigned Atomic::cmpxchg(unsigned int exchange_value,
  60                          volatile unsigned int* dest, unsigned int compare_value) {
  61   assert(sizeof(unsigned int) == sizeof(jint), "more work to do");
  62   return (unsigned int)Atomic::cmpxchg((jint)exchange_value, (volatile jint*)dest,
  63                                        (jint)compare_value);
  64 }
  65 
  66 jlong Atomic::add(jlong    add_value, volatile jlong*    dest) {
  67   jlong old = load(dest);
  68   jlong new_value = old + add_value;
  69   while (old != cmpxchg(new_value, dest, old)) {
  70     old = load(dest);
  71     new_value = old + add_value;
  72   }
  73   return old;
  74 }
  75 
  76 void Atomic::inc(volatile short* dest) {
  77   // Most platforms do not support atomic increment on a 2-byte value. However,
  78   // if the value occupies the most significant 16 bits of an aligned 32-bit
  79   // word, then we can do this with an atomic add of 0x10000 to the 32-bit word.
  80   //
  81   // The least significant parts of this 32-bit word will never be affected, even
  82   // in case of overflow/underflow.
  83   //
  84   // Use the ATOMIC_SHORT_PAIR macro to get the desired alignment.
  85 #ifdef VM_LITTLE_ENDIAN
  86   assert((intx(dest) & 0x03) == 0x02, "wrong alignment");
  87   (void)Atomic::add(0x10000, (volatile int*)(dest-1));
  88 #else
  89   assert((intx(dest) & 0x03) == 0x00, "wrong alignment");
  90   (void)Atomic::add(0x10000, (volatile int*)(dest));
  91 #endif
  92 }
  93 
  94 void Atomic::dec(volatile short* dest) {
  95 #ifdef VM_LITTLE_ENDIAN
  96   assert((intx(dest) & 0x03) == 0x02, "wrong alignment");
  97   (void)Atomic::add(-0x10000, (volatile int*)(dest-1));
  98 #else
  99   assert((intx(dest) & 0x03) == 0x00, "wrong alignment");
 100   (void)Atomic::add(-0x10000, (volatile int*)(dest));
 101 #endif
 102 }
 103