1 /*
2 * Copyright (c) 1999, 2014, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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5 * This code is free software; you can redistribute it and/or modify it
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13 * accompanied this code).
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24
25 #ifndef SHARE_VM_RUNTIME_ATOMIC_HPP
26 #define SHARE_VM_RUNTIME_ATOMIC_HPP
27
28 #include "memory/allocation.hpp"
29
30 class Atomic : AllStatic {
31 public:
32 // Atomic operations on jlong types are not available on all 32-bit
33 // platforms. If atomic ops on jlongs are defined here they must only
34 // be used from code that verifies they are available at runtime and
35 // can provide an alternative action if not - see supports_cx8() for
36 // a means to test availability.
37
38 // The memory operations that are mentioned with each of the atomic
39 // function families come from src/share/vm/runtime/orderAccess.hpp,
40 // e.g., <fence> is described in that file and is implemented by the
41 // OrderAccess::fence() function. See that file for the gory details
42 // on the Memory Access Ordering Model.
43
44 // All of the atomic operations that imply a read-modify-write action
45 // guarantee a two-way memory barrier across that operation. Historically
46 // these semantics reflect the strength of atomic operations that are
47 // provided on SPARC/X86. We assume that strength is necessary unless
48 // we can prove that a weaker form is sufficiently safe.
49
50 // Atomically store to a location
51 inline static void store (jbyte store_value, jbyte* dest);
52 inline static void store (jshort store_value, jshort* dest);
53 inline static void store (jint store_value, jint* dest);
54 // See comment above about using jlong atomics on 32-bit platforms
55 inline static void store (jlong store_value, jlong* dest);
56 inline static void store_ptr(intptr_t store_value, intptr_t* dest);
57 inline static void store_ptr(void* store_value, void* dest);
58
59 inline static void store (jbyte store_value, volatile jbyte* dest);
60 inline static void store (jshort store_value, volatile jshort* dest);
61 inline static void store (jint store_value, volatile jint* dest);
62 // See comment above about using jlong atomics on 32-bit platforms
63 inline static void store (jlong store_value, volatile jlong* dest);
64 inline static void store_ptr(intptr_t store_value, volatile intptr_t* dest);
65 inline static void store_ptr(void* store_value, volatile void* dest);
66
67 // See comment above about using jlong atomics on 32-bit platforms
68 inline static jlong load(volatile jlong* src);
69
70 // Atomically add to a location. Returns updated value. add*() provide:
71 // <fence> add-value-to-dest <membar StoreLoad|StoreStore>
72 inline static jint add (jint add_value, volatile jint* dest);
73 inline static size_t add (size_t add_value, volatile size_t* dest);
74 inline static intptr_t add_ptr(intptr_t add_value, volatile intptr_t* dest);
75 inline static void* add_ptr(intptr_t add_value, volatile void* dest);
76 // See comment above about using jlong atomics on 32-bit platforms
77 static jlong add (jlong add_value, volatile jlong* dest);
78
79 // Atomically increment location. inc*() provide:
80 // <fence> increment-dest <membar StoreLoad|StoreStore>
81 inline static void inc (volatile jint* dest);
82 static void inc (volatile jshort* dest);
83 inline static void inc (volatile size_t* dest);
84 inline static void inc_ptr(volatile intptr_t* dest);
85 inline static void inc_ptr(volatile void* dest);
86
87 // Atomically decrement a location. dec*() provide:
88 // <fence> decrement-dest <membar StoreLoad|StoreStore>
89 inline static void dec (volatile jint* dest);
90 static void dec (volatile jshort* dest);
91 inline static void dec (volatile size_t* dest);
92 inline static void dec_ptr(volatile intptr_t* dest);
93 inline static void dec_ptr(volatile void* dest);
94
95 // Performs atomic exchange of *dest with exchange_value. Returns old
96 // prior value of *dest. xchg*() provide:
97 // <fence> exchange-value-with-dest <membar StoreLoad|StoreStore>
98 inline static jint xchg(jint exchange_value, volatile jint* dest);
99 static unsigned int xchg(unsigned int exchange_value, volatile unsigned int* dest);
100
101 inline static intptr_t xchg_ptr(intptr_t exchange_value, volatile intptr_t* dest);
102 inline static void* xchg_ptr(void* exchange_value, volatile void* dest);
103
104 // Performs atomic compare of *dest and compare_value, and exchanges
105 // *dest with exchange_value if the comparison succeeded. Returns prior
106 // value of *dest. cmpxchg*() provide:
107 // <fence> compare-and-exchange <membar StoreLoad|StoreStore>
108 #ifdef X86
109 inline static
110 #else
111 static
112 #endif // X86
113 jbyte cmpxchg (jbyte exchange_value, volatile jbyte* dest, jbyte compare_value);
114 inline static jint cmpxchg (jint exchange_value, volatile jint* dest, jint compare_value);
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);
117
118 static unsigned int cmpxchg(unsigned int exchange_value,
119 volatile unsigned int* dest,
120 unsigned int compare_value);
121
122 inline static intptr_t cmpxchg_ptr(intptr_t exchange_value, volatile intptr_t* dest, intptr_t compare_value);
123 inline static void* cmpxchg_ptr(void* exchange_value, volatile void* dest, void* compare_value);
124 };
125
126 // To use Atomic::inc(jshort* dest) and Atomic::dec(jshort* dest), the address must be specially
127 // aligned, such that (*dest) occupies the upper 16 bits of an aligned 32-bit word. The best way to
128 // achieve is to place your short value next to another short value, which doesn't need atomic ops.
129 //
130 // Example
131 // ATOMIC_SHORT_PAIR(
132 // volatile short _refcount, // needs atomic operation
133 // unsigned short _length // number of UTF8 characters in the symbol (does not need atomic op)
134 // );
135
136 #ifdef VM_LITTLE_ENDIAN
137 #define ATOMIC_SHORT_PAIR(atomic_decl, non_atomic_decl) \
138 non_atomic_decl; \
139 atomic_decl
140 #else
141 #define ATOMIC_SHORT_PAIR(atomic_decl, non_atomic_decl) \
142 atomic_decl; \
143 non_atomic_decl
144 #endif
145
146 #endif // SHARE_VM_RUNTIME_ATOMIC_HPP