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