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/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