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 memory_order order) { 62 assert(sizeof(unsigned int) == sizeof(jint), "more work to do"); 63 return (unsigned int)Atomic::cmpxchg((jint)exchange_value, (volatile jint*)dest, 64 (jint)compare_value, order); 65 } 66 67 jlong Atomic::add(jlong add_value, volatile jlong* dest) { 68 jlong old = load(dest); 69 jlong new_value = old + add_value; 70 while (old != cmpxchg(new_value, dest, old)) { 71 old = load(dest); 72 new_value = old + add_value; 73 } 74 return old; 75 } 76 77 void Atomic::inc(volatile short* dest) { 78 // Most platforms do not support atomic increment on a 2-byte value. However, 79 // if the value occupies the most significant 16 bits of an aligned 32-bit 80 // word, then we can do this with an atomic add of 0x10000 to the 32-bit word. 81 // 82 // The least significant parts of this 32-bit word will never be affected, even 83 // in case of overflow/underflow. 84 // 85 // Use the ATOMIC_SHORT_PAIR macro to get the desired alignment. 86 #ifdef VM_LITTLE_ENDIAN 87 assert((intx(dest) & 0x03) == 0x02, "wrong alignment"); 88 (void)Atomic::add(0x10000, (volatile int*)(dest-1)); 89 #else 90 assert((intx(dest) & 0x03) == 0x00, "wrong alignment"); 91 (void)Atomic::add(0x10000, (volatile int*)(dest)); 92 #endif 93 } 94 95 void Atomic::dec(volatile short* dest) { 96 #ifdef VM_LITTLE_ENDIAN 97 assert((intx(dest) & 0x03) == 0x02, "wrong alignment"); 98 (void)Atomic::add(-0x10000, (volatile int*)(dest-1)); 99 #else 100 assert((intx(dest) & 0x03) == 0x00, "wrong alignment"); 101 (void)Atomic::add(-0x10000, (volatile int*)(dest)); 102 #endif 103 } 104