atomic.hpp revision 7432:5398ffa1a419 
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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
30class 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
140