9 * Copyright February 2009 - Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
11 * Credits for Paul e. McKenney <paulmck@linux.vnet.ibm.com>
12 * for inspiration coming from the Linux kernel RCU and rcu-preempt.
14 * The barrier, mb, rmb, wmb, atomic_inc, smp_read_barrier_depends, ACCESS_ONCE
15 * and rcu_dereference primitives come from the Linux kernel.
17 * Distributed under GPLv2
20 /* The "volatile" is due to gcc bugs */
21 #define barrier() __asm__ __volatile__("": : :"memory")
23 /* x86 32/64 specific */
24 #define mb() asm volatile("mfence":::"memory")
25 #define rmb() asm volatile("lfence":::"memory")
26 #define wmb() asm volatile("sfence" ::: "memory")
28 static inline void atomic_inc(int *v
)
30 asm volatile("lock; incl %0"
34 /* Nop everywhere except on alpha. */
35 #define smp_read_barrier_depends()
38 * Prevent the compiler from merging or refetching accesses. The compiler
39 * is also forbidden from reordering successive instances of ACCESS_ONCE(),
40 * but only when the compiler is aware of some particular ordering. One way
41 * to make the compiler aware of ordering is to put the two invocations of
42 * ACCESS_ONCE() in different C statements.
44 * This macro does absolutely -nothing- to prevent the CPU from reordering,
45 * merging, or refetching absolutely anything at any time. Its main intended
46 * use is to mediate communication between process-level code and irq/NMI
47 * handlers, all running on the same CPU.
49 #define ACCESS_ONCE(x) (*(volatile typeof(x) *)&(x))
52 * rcu_dereference - fetch an RCU-protected pointer in an
53 * RCU read-side critical section. This pointer may later
54 * be safely dereferenced.
56 * Inserts memory barriers on architectures that require them
57 * (currently only the Alpha), and, more importantly, documents
58 * exactly which pointers are protected by RCU.
61 #define rcu_dereference(p) ({ \
62 typeof(p) _________p1 = ACCESS_ONCE(p); \
63 smp_read_barrier_depends(); \
67 #define SIGURCU SIGUSR1
72 #define YIELD_READ (1 << 0)
73 #define YIELD_WRITE (1 << 1)
75 extern int yield_active
;
77 static inline void debug_yield_read(void)
79 if (yield_active
& YIELD_READ
)
83 static inline void debug_yield_write(void)
85 if (yield_active
& YIELD_WRITE
)
89 static inline void debug_yield_read(void)
93 static inline void debug_yield_write(void)
98 /* Global quiescent period parity */
99 extern int urcu_qparity
;
101 extern int __thread urcu_active_readers
[2];
103 static inline int get_urcu_qparity(void)
109 * urcu_parity should be declared on the caller's stack.
111 static inline void rcu_read_lock(int *urcu_parity
)
114 *urcu_parity
= get_urcu_qparity();
116 urcu_active_readers
[*urcu_parity
]++;
119 * Increment active readers count before accessing the pointer.
120 * See force_mb_all_threads().
126 static inline void rcu_read_unlock(int *urcu_parity
)
132 * Finish using rcu before decrementing the pointer.
133 * See force_mb_all_threads().
135 urcu_active_readers
[*urcu_parity
]--;
139 extern void *urcu_publish_content(void **ptr
, void *new);
142 * Reader thread registration.
144 extern void urcu_register_thread(void);
145 extern void urcu_unregister_thread(void);