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 typedef enum cmpxchg_cmpxchg_memory_order {
31 memory_order_relaxed,
32 // Use value which doesn't interfere with C++2011. We need to be more conservative.
33 memory_order_conservative = 8
34 } cmpxchg_memory_order;
35
36 class Atomic : AllStatic {
37 private:
38 static jbyte cmpxchg_general(jbyte exchange_value, volatile jbyte* dest, jbyte compare_value);
39
40 public:
41 // Atomic operations on jlong types are not available on all 32-bit
42 // platforms. If atomic ops on jlongs are defined here they must only
43 // be used from code that verifies they are available at runtime and
44 // can provide an alternative action if not - see supports_cx8() for
45 // a means to test availability.
46
47 // The memory operations that are mentioned with each of the atomic
48 // function families come from src/share/vm/runtime/orderAccess.hpp,
49 // e.g., <fence> is described in that file and is implemented by the
50 // OrderAccess::fence() function. See that file for the gory details
51 // on the Memory Access Ordering Model.
52
53 // All of the atomic operations that imply a read-modify-write action
54 // guarantee a two-way memory barrier across that operation. Historically
55 // these semantics reflect the strength of atomic operations that are
56 // provided on SPARC/X86. We assume that strength is necessary unless
57 // we can prove that a weaker form is sufficiently safe.
58
59 // Atomically store to a location
60 inline static void store (jbyte store_value, jbyte* dest);
61 inline static void store (jshort store_value, jshort* dest);
62 inline static void store (jint store_value, jint* dest);
63 // See comment above about using jlong atomics on 32-bit platforms
64 inline static void store (jlong store_value, jlong* dest);
65 inline static void store_ptr(intptr_t store_value, intptr_t* dest);
66 inline static void store_ptr(void* store_value, void* dest);
67
68 inline static void store (jbyte store_value, volatile jbyte* dest);
69 inline static void store (jshort store_value, volatile jshort* dest);
70 inline static void store (jint store_value, volatile jint* dest);
71 // See comment above about using jlong atomics on 32-bit platforms
72 inline static void store (jlong store_value, volatile jlong* dest);
73 inline static void store_ptr(intptr_t store_value, volatile intptr_t* dest);
74 inline static void store_ptr(void* store_value, volatile void* dest);
75
76 // See comment above about using jlong atomics on 32-bit platforms
77 inline static jlong load(volatile jlong* src);
78
79 // Atomically add to a location. Returns updated value. add*() provide:
80 // <fence> add-value-to-dest <membar StoreLoad|StoreStore>
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 // See comment above about using jlong atomics on 32-bit platforms
86 static jlong add (jlong add_value, volatile jlong* dest);
87
88 // Atomically increment location. inc*() provide:
89 // <fence> increment-dest <membar StoreLoad|StoreStore>
90 inline static void inc (volatile jint* dest);
91 static void inc (volatile jshort* dest);
92 inline static void inc (volatile size_t* dest);
93 inline static void inc_ptr(volatile intptr_t* dest);
94 inline static void inc_ptr(volatile void* dest);
95
96 // Atomically decrement a location. dec*() provide:
97 // <fence> decrement-dest <membar StoreLoad|StoreStore>
98 inline static void dec (volatile jint* dest);
99 static void dec (volatile jshort* dest);
100 inline static void dec (volatile size_t* dest);
101 inline static void dec_ptr(volatile intptr_t* dest);
102 inline static void dec_ptr(volatile void* dest);
103
104 // Performs atomic exchange of *dest with exchange_value. Returns old
105 // prior value of *dest. xchg*() provide:
106 // <fence> exchange-value-with-dest <membar StoreLoad|StoreStore>
107 inline static jint xchg (jint exchange_value, volatile jint* dest);
108 static unsigned int xchg (unsigned int exchange_value, volatile unsigned int* dest);
109 inline static intptr_t xchg_ptr(intptr_t exchange_value, volatile intptr_t* dest);
110 inline static void* xchg_ptr(void* exchange_value, volatile void* dest);
111
112 // Performs atomic compare of *dest and compare_value, and exchanges
113 // *dest with exchange_value if the comparison succeeded. Returns prior
114 // value of *dest. cmpxchg*() provide:
115 // <fence> compare-and-exchange <membar StoreLoad|StoreStore>
116 inline static jbyte cmpxchg (jbyte exchange_value, volatile jbyte* dest, jbyte compare_value, cmpxchg_memory_order order = memory_order_conservative);
117 inline static jint cmpxchg (jint exchange_value, volatile jint* dest, jint compare_value, cmpxchg_memory_order order = memory_order_conservative);
118 // See comment above about using jlong atomics on 32-bit platforms
119 inline static jlong cmpxchg (jlong exchange_value, volatile jlong* dest, jlong compare_value, cmpxchg_memory_order order = memory_order_conservative);
120 static unsigned int cmpxchg (unsigned int exchange_value, volatile unsigned int* dest, unsigned int compare_value, cmpxchg_memory_order order = memory_order_conservative);
121 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);
122 inline static void* cmpxchg_ptr(void* exchange_value, volatile void* dest, void* compare_value, cmpxchg_memory_order order = memory_order_conservative);
123 };
124
125 // To use Atomic::inc(jshort* dest) and Atomic::dec(jshort* dest), the address must be specially
126 // aligned, such that (*dest) occupies the upper 16 bits of an aligned 32-bit word. The best way to
127 // achieve is to place your short value next to another short value, which doesn't need atomic ops.
128 //
129 // Example
130 // ATOMIC_SHORT_PAIR(
131 // volatile short _refcount, // needs atomic operation
132 // unsigned short _length // number of UTF8 characters in the symbol (does not need atomic op)
133 // );
134
135 #ifdef VM_LITTLE_ENDIAN
136 #define ATOMIC_SHORT_PAIR(atomic_decl, non_atomic_decl) \
137 non_atomic_decl; \
138 atomic_decl
139 #else
140 #define ATOMIC_SHORT_PAIR(atomic_decl, non_atomic_decl) \
141 atomic_decl; \
142 non_atomic_decl
143 #endif
144
145 #endif // SHARE_VM_RUNTIME_ATOMIC_HPP