1 /* 2 * Copyright (c) 1999, 2017, 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 #ifndef SHARE_VM_RUNTIME_ATOMIC_HPP 26 #define SHARE_VM_RUNTIME_ATOMIC_HPP 27 28 #include "memory/allocation.hpp" 29 #include "utilities/macros.hpp" 30 31 enum cmpxchg_memory_order { 32 memory_order_relaxed, 33 // Use value which doesn't interfere with C++2011. We need to be more conservative. 34 memory_order_conservative = 8 35 }; 36 37 class Atomic : AllStatic { 38 public: 39 // Atomic operations on jlong types are not available on all 32-bit 40 // platforms. If atomic ops on jlongs are defined here they must only 41 // be used from code that verifies they are available at runtime and 42 // can provide an alternative action if not - see supports_cx8() for 43 // a means to test availability. 44 45 // The memory operations that are mentioned with each of the atomic 46 // function families come from src/share/vm/runtime/orderAccess.hpp, 47 // e.g., <fence> is described in that file and is implemented by the 48 // OrderAccess::fence() function. See that file for the gory details 49 // on the Memory Access Ordering Model. 50 51 // All of the atomic operations that imply a read-modify-write action 52 // guarantee a two-way memory barrier across that operation. Historically 53 // these semantics reflect the strength of atomic operations that are 54 // provided on SPARC/X86. We assume that strength is necessary unless 55 // we can prove that a weaker form is sufficiently safe. 56 57 // Atomically store to a location 58 inline static void store (jbyte store_value, jbyte* dest); 59 inline static void store (jshort store_value, jshort* dest); 60 inline static void store (jint store_value, jint* dest); 61 // See comment above about using jlong atomics on 32-bit platforms 62 inline static void store (jlong store_value, jlong* dest); 63 inline static void store_ptr(intptr_t store_value, intptr_t* dest); 64 inline static void store_ptr(void* store_value, void* dest); 65 66 inline static void store (jbyte store_value, volatile jbyte* dest); 67 inline static void store (jshort store_value, volatile jshort* dest); 68 inline static void store (jint store_value, volatile jint* dest); 69 // See comment above about using jlong atomics on 32-bit platforms 70 inline static void store (jlong store_value, volatile jlong* dest); 71 inline static void store_ptr(intptr_t store_value, volatile intptr_t* dest); 72 inline static void store_ptr(void* store_value, volatile void* dest); 73 74 // See comment above about using jlong atomics on 32-bit platforms 75 inline static jlong load(volatile jlong* src); 76 77 // Atomically add to a location. Returns updated value. add*() provide: 78 // <fence> add-value-to-dest <membar StoreLoad|StoreStore> 79 inline static jshort add (jshort add_value, volatile jshort* dest); 80 inline static jint add (jint add_value, volatile jint* dest); 81 inline static size_t add (size_t add_value, volatile size_t* dest); 82 inline static intptr_t add_ptr(intptr_t add_value, volatile intptr_t* dest); 83 inline static void* add_ptr(intptr_t add_value, volatile void* dest); 84 85 // Atomically increment location. inc*() provide: 86 // <fence> increment-dest <membar StoreLoad|StoreStore> 87 inline static void inc (volatile jint* dest); 88 inline static void inc (volatile jshort* dest); 89 inline static void inc (volatile size_t* dest); 90 inline static void inc_ptr(volatile intptr_t* dest); 91 inline static void inc_ptr(volatile void* dest); 92 93 // Atomically decrement a location. dec*() provide: 94 // <fence> decrement-dest <membar StoreLoad|StoreStore> 95 inline static void dec (volatile jint* dest); 96 inline static void dec (volatile jshort* dest); 97 inline static void dec (volatile size_t* dest); 98 inline static void dec_ptr(volatile intptr_t* dest); 99 inline static void dec_ptr(volatile void* dest); 100 101 // Performs atomic exchange of *dest with exchange_value. Returns old 102 // prior value of *dest. xchg*() provide: 103 // <fence> exchange-value-with-dest <membar StoreLoad|StoreStore> 104 inline static jint xchg (jint exchange_value, volatile jint* dest); 105 inline static unsigned int xchg (unsigned int exchange_value, volatile unsigned int* dest); 106 inline static intptr_t xchg_ptr(intptr_t exchange_value, volatile intptr_t* dest); 107 inline static void* xchg_ptr(void* exchange_value, volatile void* dest); 108 109 // Performs atomic compare of *dest and compare_value, and exchanges 110 // *dest with exchange_value if the comparison succeeded. Returns prior 111 // value of *dest. cmpxchg*() provide: 112 // <fence> compare-and-exchange <membar StoreLoad|StoreStore> 113 inline static jbyte cmpxchg (jbyte exchange_value, volatile jbyte* dest, jbyte compare_value, cmpxchg_memory_order order = memory_order_conservative); 114 inline static jint cmpxchg (jint exchange_value, volatile jint* dest, jint compare_value, cmpxchg_memory_order order = memory_order_conservative); 115 // See comment above about using jlong atomics on 32-bit platforms 116 inline static jlong cmpxchg (jlong exchange_value, volatile jlong* dest, jlong compare_value, cmpxchg_memory_order order = memory_order_conservative); 117 inline static unsigned int cmpxchg (unsigned int exchange_value, volatile unsigned int* dest, unsigned int compare_value, cmpxchg_memory_order order = memory_order_conservative); 118 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); 119 inline static void* cmpxchg_ptr(void* exchange_value, volatile void* dest, void* compare_value, cmpxchg_memory_order order = memory_order_conservative); 120 }; 121 122 // platform specific in-line definitions - must come before shared definitions 123 124 #include OS_CPU_HEADER(atomic) 125 126 // shared in-line definitions 127 128 // size_t casts... 129 #if (SIZE_MAX != UINTPTR_MAX) 130 #error size_t is not WORD_SIZE, interesting platform, but missing implementation here 131 #endif 132 133 inline size_t Atomic::add(size_t add_value, volatile size_t* dest) { 134 return (size_t) add_ptr((intptr_t) add_value, (volatile intptr_t*) dest); 135 } 136 137 inline void Atomic::inc(volatile size_t* dest) { 138 inc_ptr((volatile intptr_t*) dest); 139 } 140 141 inline void Atomic::dec(volatile size_t* dest) { 142 dec_ptr((volatile intptr_t*) dest); 143 } 144 145 #ifndef VM_HAS_SPECIALIZED_CMPXCHG_BYTE 146 /* 147 * This is the default implementation of byte-sized cmpxchg. It emulates jbyte-sized cmpxchg 148 * in terms of jint-sized cmpxchg. Platforms may override this by defining their own inline definition 149 * as well as defining VM_HAS_SPECIALIZED_CMPXCHG_BYTE. This will cause the platform specific 150 * implementation to be used instead. 151 */ 152 inline jbyte Atomic::cmpxchg(jbyte exchange_value, volatile jbyte* dest, 153 jbyte compare_value, cmpxchg_memory_order order) { 154 STATIC_ASSERT(sizeof(jbyte) == 1); 155 volatile jint* dest_int = 156 static_cast<volatile jint*>(align_ptr_down(dest, sizeof(jint))); 157 size_t offset = pointer_delta(dest, dest_int, 1); 158 jint cur = *dest_int; 159 jbyte* cur_as_bytes = reinterpret_cast<jbyte*>(&cur); 160 161 // current value may not be what we are looking for, so force it 162 // to that value so the initial cmpxchg will fail if it is different 163 cur_as_bytes[offset] = compare_value; 164 165 // always execute a real cmpxchg so that we get the required memory 166 // barriers even on initial failure 167 do { 168 // value to swap in matches current value ... 169 jint new_value = cur; 170 // ... except for the one jbyte we want to update 171 reinterpret_cast<jbyte*>(&new_value)[offset] = exchange_value; 172 173 jint res = cmpxchg(new_value, dest_int, cur, order); 174 if (res == cur) break; // success 175 176 // at least one jbyte in the jint changed value, so update 177 // our view of the current jint 178 cur = res; 179 // if our jbyte is still as cur we loop and try again 180 } while (cur_as_bytes[offset] == compare_value); 181 182 return cur_as_bytes[offset]; 183 } 184 185 #endif // VM_HAS_SPECIALIZED_CMPXCHG_BYTE 186 187 inline unsigned Atomic::xchg(unsigned int exchange_value, volatile unsigned int* dest) { 188 assert(sizeof(unsigned int) == sizeof(jint), "more work to do"); 189 return (unsigned int)Atomic::xchg((jint)exchange_value, (volatile jint*)dest); 190 } 191 192 inline unsigned Atomic::cmpxchg(unsigned int exchange_value, 193 volatile unsigned int* dest, unsigned int compare_value, 194 cmpxchg_memory_order order) { 195 assert(sizeof(unsigned int) == sizeof(jint), "more work to do"); 196 return (unsigned int)Atomic::cmpxchg((jint)exchange_value, (volatile jint*)dest, 197 (jint)compare_value, order); 198 } 199 200 inline jshort Atomic::add(jshort add_value, volatile jshort* dest) { 201 // Most platforms do not support atomic add on a 2-byte value. However, 202 // if the value occupies the most significant 16 bits of an aligned 32-bit 203 // word, then we can do this with an atomic add of (add_value << 16) 204 // to the 32-bit word. 205 // 206 // The least significant parts of this 32-bit word will never be affected, even 207 // in case of overflow/underflow. 208 // 209 // Use the ATOMIC_SHORT_PAIR macro (see macros.hpp) to get the desired alignment. 210 #ifdef VM_LITTLE_ENDIAN 211 assert((intx(dest) & 0x03) == 0x02, "wrong alignment"); 212 jint new_value = Atomic::add(add_value << 16, (volatile jint*)(dest-1)); 213 #else 214 assert((intx(dest) & 0x03) == 0x00, "wrong alignment"); 215 jint new_value = Atomic::add(add_value << 16, (volatile jint*)(dest)); 216 #endif 217 return (jshort)(new_value >> 16); // preserves sign 218 } 219 220 inline void Atomic::inc(volatile jshort* dest) { 221 (void)add(1, dest); 222 } 223 224 inline void Atomic::dec(volatile jshort* dest) { 225 (void)add(-1, dest); 226 } 227 228 #endif // SHARE_VM_RUNTIME_ATOMIC_HPP