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.
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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
75 inline static jbyte load(volatile jbyte* src) { return *src; }
76 inline static jshort load(volatile jshort* src) { return *src; }
77 inline static jint load(volatile jint* src) { return *src; }
78 // See comment above about using jlong atomics on 32-bit platforms
79 inline static jlong load(volatile jlong* src);
80 inline static intptr_t load_ptr(volatile intptr_t* src) { return *src; }
81 inline static void* load_ptr(volatile void* src) { return *(void* volatile*)src; }
82
83 // Atomically add to a location. Returns updated value. add*() provide:
84 // <fence> add-value-to-dest <membar StoreLoad|StoreStore>
85 inline static jshort add (jshort add_value, volatile jshort* dest);
86 inline static jint add (jint add_value, volatile jint* dest);
87 inline static size_t add (size_t add_value, volatile size_t* dest);
88 inline static intptr_t add_ptr(intptr_t add_value, volatile intptr_t* dest);
89 inline static void* add_ptr(intptr_t add_value, volatile void* dest);
90
91 // Atomically increment location. inc*() provide:
92 // <fence> increment-dest <membar StoreLoad|StoreStore>
93 inline static void inc (volatile jint* dest);
94 inline static void inc (volatile jshort* dest);
95 inline static void inc (volatile size_t* dest);
96 inline static void inc_ptr(volatile intptr_t* dest);
97 inline static void inc_ptr(volatile void* dest);
98
99 // Atomically decrement a location. dec*() provide:
100 // <fence> decrement-dest <membar StoreLoad|StoreStore>
101 inline static void dec (volatile jint* dest);
102 inline static void dec (volatile jshort* dest);
103 inline static void dec (volatile size_t* dest);
104 inline static void dec_ptr(volatile intptr_t* dest);
105 inline static void dec_ptr(volatile void* dest);
106
107 // Performs atomic exchange of *dest with exchange_value. Returns old
108 // prior value of *dest. xchg*() provide:
109 // <fence> exchange-value-with-dest <membar StoreLoad|StoreStore>
110 inline static jint xchg (jint exchange_value, volatile jint* dest);
111 inline static unsigned int xchg (unsigned int exchange_value, volatile unsigned int* dest);
112 inline static intptr_t xchg_ptr(intptr_t exchange_value, volatile intptr_t* dest);
113 inline static void* xchg_ptr(void* exchange_value, volatile void* dest);
114
115 // Performs atomic compare of *dest and compare_value, and exchanges
116 // *dest with exchange_value if the comparison succeeded. Returns prior
117 // value of *dest. cmpxchg*() provide:
118 // <fence> compare-and-exchange <membar StoreLoad|StoreStore>
119 inline static jbyte cmpxchg (jbyte exchange_value, volatile jbyte* dest, jbyte compare_value, cmpxchg_memory_order order = memory_order_conservative);
120 inline static jint cmpxchg (jint exchange_value, volatile jint* dest, jint compare_value, cmpxchg_memory_order order = memory_order_conservative);
121 // See comment above about using jlong atomics on 32-bit platforms
122 inline static jlong cmpxchg (jlong exchange_value, volatile jlong* dest, jlong compare_value, cmpxchg_memory_order order = memory_order_conservative);
123 inline static unsigned int cmpxchg (unsigned int exchange_value, volatile unsigned int* dest, unsigned int compare_value, cmpxchg_memory_order order = memory_order_conservative);
124 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);
125 inline static void* cmpxchg_ptr(void* exchange_value, volatile void* dest, void* compare_value, cmpxchg_memory_order order = memory_order_conservative);
126 };
127
128 // platform specific in-line definitions - must come before shared definitions
129
130 #include OS_CPU_HEADER(atomic)
131
132 // shared in-line definitions
133
134 // size_t casts...
135 #if (SIZE_MAX != UINTPTR_MAX)
136 #error size_t is not WORD_SIZE, interesting platform, but missing implementation here
137 #endif
138
139 inline size_t Atomic::add(size_t add_value, volatile size_t* dest) {
140 return (size_t) add_ptr((intptr_t) add_value, (volatile intptr_t*) dest);
141 }
142
143 inline void Atomic::inc(volatile size_t* dest) {
144 inc_ptr((volatile intptr_t*) dest);
145 }
146
147 inline void Atomic::dec(volatile size_t* dest) {
148 dec_ptr((volatile intptr_t*) dest);
149 }
150
151 #ifndef VM_HAS_SPECIALIZED_CMPXCHG_BYTE
152 /*
153 * This is the default implementation of byte-sized cmpxchg. It emulates jbyte-sized cmpxchg
154 * in terms of jint-sized cmpxchg. Platforms may override this by defining their own inline definition
155 * as well as defining VM_HAS_SPECIALIZED_CMPXCHG_BYTE. This will cause the platform specific
156 * implementation to be used instead.
157 */
158 inline jbyte Atomic::cmpxchg(jbyte exchange_value, volatile jbyte* dest,
159 jbyte compare_value, cmpxchg_memory_order order) {
160 STATIC_ASSERT(sizeof(jbyte) == 1);
161 volatile jint* dest_int =
162 static_cast<volatile jint*>(align_ptr_down(dest, sizeof(jint)));
163 size_t offset = pointer_delta(dest, dest_int, 1);
164 jint cur = *dest_int;
165 jbyte* cur_as_bytes = reinterpret_cast<jbyte*>(&cur);
166
167 // current value may not be what we are looking for, so force it
168 // to that value so the initial cmpxchg will fail if it is different
169 cur_as_bytes[offset] = compare_value;
170
171 // always execute a real cmpxchg so that we get the required memory
172 // barriers even on initial failure
173 do {
174 // value to swap in matches current value ...
175 jint new_value = cur;
176 // ... except for the one jbyte we want to update
177 reinterpret_cast<jbyte*>(&new_value)[offset] = exchange_value;
178
179 jint res = cmpxchg(new_value, dest_int, cur, order);
180 if (res == cur) break; // success
181
182 // at least one jbyte in the jint changed value, so update
183 // our view of the current jint
184 cur = res;
185 // if our jbyte is still as cur we loop and try again
186 } while (cur_as_bytes[offset] == compare_value);
187
188 return cur_as_bytes[offset];
189 }
190
191 #endif // VM_HAS_SPECIALIZED_CMPXCHG_BYTE
192
193 inline unsigned Atomic::xchg(unsigned int exchange_value, volatile unsigned int* dest) {
194 assert(sizeof(unsigned int) == sizeof(jint), "more work to do");
195 return (unsigned int)Atomic::xchg((jint)exchange_value, (volatile jint*)dest);
196 }
197
198 inline unsigned Atomic::cmpxchg(unsigned int exchange_value,
199 volatile unsigned int* dest, unsigned int compare_value,
200 cmpxchg_memory_order order) {
201 assert(sizeof(unsigned int) == sizeof(jint), "more work to do");
202 return (unsigned int)Atomic::cmpxchg((jint)exchange_value, (volatile jint*)dest,
203 (jint)compare_value, order);
204 }
205
206 inline jshort Atomic::add(jshort add_value, volatile jshort* dest) {
207 // Most platforms do not support atomic add on a 2-byte value. However,
208 // if the value occupies the most significant 16 bits of an aligned 32-bit
209 // word, then we can do this with an atomic add of (add_value << 16)
210 // to the 32-bit word.
211 //
212 // The least significant parts of this 32-bit word will never be affected, even
213 // in case of overflow/underflow.
214 //
215 // Use the ATOMIC_SHORT_PAIR macro (see macros.hpp) to get the desired alignment.
216 #ifdef VM_LITTLE_ENDIAN
217 assert((intx(dest) & 0x03) == 0x02, "wrong alignment");
218 jint new_value = Atomic::add(add_value << 16, (volatile jint*)(dest-1));
219 #else
220 assert((intx(dest) & 0x03) == 0x00, "wrong alignment");
221 jint new_value = Atomic::add(add_value << 16, (volatile jint*)(dest));
222 #endif
223 return (jshort)(new_value >> 16); // preserves sign
224 }
225
226 inline void Atomic::inc(volatile jshort* dest) {
227 (void)add(1, dest);
228 }
229
230 inline void Atomic::dec(volatile jshort* dest) {
231 (void)add(-1, dest);
232 }
233
234 #endif // SHARE_VM_RUNTIME_ATOMIC_HPP