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