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
22 /* The "volatile" is due to gcc bugs */
23 #define barrier() __asm__ __volatile__("": : :"memory")
25 /* x86 32/64 specific */
26 #define mb() asm volatile("mfence":::"memory")
27 #define rmb() asm volatile("lfence":::"memory")
28 #define wmb() asm volatile("sfence" ::: "memory")
30 static inline void atomic_inc(int *v
)
32 asm volatile("lock; incl %0"
36 #define xchg(ptr, v) \
37 ((__typeof__(*(ptr)))__xchg((unsigned long)(v), (ptr), sizeof(*(ptr))))
42 #define __xg(x) ((struct __xchg_dummy *)(x))
45 * Note: no "lock" prefix even on SMP: xchg always implies lock anyway
46 * Note 2: xchg has side effect, so that attribute volatile is necessary,
47 * but generally the primitive is invalid, *ptr is output argument. --ANK
49 static inline unsigned long __xchg(unsigned long x
, volatile void *ptr
,
54 asm volatile("xchgb %b0,%1"
56 : "m" (*__xg(ptr
)), "0" (x
)
60 asm volatile("xchgw %w0,%1"
62 : "m" (*__xg(ptr
)), "0" (x
)
66 asm volatile("xchgl %0,%1"
68 : "m" (*__xg(ptr
)), "0" (x
)
75 /* Nop everywhere except on alpha. */
76 #define smp_read_barrier_depends()
79 * Prevent the compiler from merging or refetching accesses. The compiler
80 * is also forbidden from reordering successive instances of ACCESS_ONCE(),
81 * but only when the compiler is aware of some particular ordering. One way
82 * to make the compiler aware of ordering is to put the two invocations of
83 * ACCESS_ONCE() in different C statements.
85 * This macro does absolutely -nothing- to prevent the CPU from reordering,
86 * merging, or refetching absolutely anything at any time. Its main intended
87 * use is to mediate communication between process-level code and irq/NMI
88 * handlers, all running on the same CPU.
90 #define ACCESS_ONCE(x) (*(volatile typeof(x) *)&(x))
93 * rcu_dereference - fetch an RCU-protected pointer in an
94 * RCU read-side critical section. This pointer may later
95 * be safely dereferenced.
97 * Inserts memory barriers on architectures that require them
98 * (currently only the Alpha), and, more importantly, documents
99 * exactly which pointers are protected by RCU.
102 #define rcu_dereference(p) ({ \
103 typeof(p) _________p1 = ACCESS_ONCE(p); \
104 smp_read_barrier_depends(); \
108 #define SIGURCU SIGUSR1
113 #define YIELD_READ (1 << 0)
114 #define YIELD_WRITE (1 << 1)
116 extern unsigned int yield_active
;
117 extern unsigned int __thread rand_yield
;
119 static inline void debug_yield_read(void)
121 if (yield_active
& YIELD_READ
)
122 if (rand_r(&rand_yield
) & 0x1)
126 static inline void debug_yield_write(void)
128 if (yield_active
& YIELD_WRITE
)
129 if (rand_r(&rand_yield
) & 0x1)
133 static inline void debug_yield_init(void)
135 rand_yield
= time(NULL
) ^ pthread_self();
138 static inline void debug_yield_read(void)
142 static inline void debug_yield_write(void)
146 static inline void debug_yield_init(void)
153 * Limiting the nesting level to 256 to keep instructions small in the read
156 #define RCU_GP_COUNT (1U << 0)
157 #define RCU_GP_CTR_BIT (1U << 8)
158 #define RCU_GP_CTR_NEST_MASK (RCU_GP_CTR_BIT - 1)
160 /* Global quiescent period counter with low-order bits unused. */
161 extern int urcu_gp_ctr
;
163 extern int __thread urcu_active_readers
;
165 static inline int rcu_old_gp_ongoing(int *value
)
172 v
= ACCESS_ONCE(*value
);
174 return (v
& RCU_GP_CTR_NEST_MASK
) &&
175 ((v
^ ACCESS_ONCE(urcu_gp_ctr
)) & RCU_GP_CTR_BIT
);
178 static inline void rcu_read_lock(void)
183 tmp
= urcu_active_readers
;
185 if (!(tmp
& RCU_GP_CTR_NEST_MASK
))
186 urcu_active_readers
= urcu_gp_ctr
+ RCU_GP_COUNT
;
188 urcu_active_readers
= tmp
+ RCU_GP_COUNT
;
191 * Increment active readers count before accessing the pointer.
192 * See force_mb_all_threads().
198 static inline void rcu_read_unlock(void)
204 * Finish using rcu before decrementing the pointer.
205 * See force_mb_all_threads().
207 urcu_active_readers
-= RCU_GP_COUNT
;
212 * rcu_assign_pointer - assign (publicize) a pointer to a newly
213 * initialized structure that will be dereferenced by RCU read-side
214 * critical sections. Returns the value assigned.
216 * Inserts memory barriers on architectures that require them
217 * (pretty much all of them other than x86), and also prevents
218 * the compiler from reordering the code that initializes the
219 * structure after the pointer assignment. More importantly, this
220 * call documents which pointers will be dereferenced by RCU read-side
224 #define rcu_assign_pointer(p, v) \
226 if (!__builtin_constant_p(v) || \
232 #define rcu_xchg_pointer(p, v) \
234 if (!__builtin_constant_p(v) || \
240 extern void synchronize_rcu(void);
243 * Exchanges the pointer and waits for quiescent state.
244 * The pointer returned can be freed.
246 #define urcu_publish_content(p, v) \
249 debug_yield_write(); \
250 oldptr = rcu_xchg_pointer(p, v); \
256 * Reader thread registration.
258 extern void urcu_register_thread(void);
259 extern void urcu_unregister_thread(void);