lib/seqlock.h

   1 #ifndef FIO_SEQLOCK_H
   2 #define FIO_SEQLOCK_H
   3
   4 #include "types.h"
   5 #include "../arch/arch.h"
   6
   7 struct seqlock {
   8 #ifdef __cplusplus
   9         std::atomic<unsigned int> sequence;
  10 #else
  11         volatile unsigned int sequence;
  12 #endif
  13 };
  14
  15 static inline void seqlock_init(struct seqlock *s)
  16 {
  17         s->sequence = 0;
  18 }
  19
  20 static inline unsigned int read_seqlock_begin(struct seqlock *s)
  21 {
  22         unsigned int seq;
  23
  24         do {
  25                 seq = atomic_load_acquire(&s->sequence);
  26                 if (!(seq & 1))
  27                         break;
  28                 nop;
  29         } while (1);
  30
  31         return seq;
  32 }
  33
  34 static inline bool read_seqlock_retry(struct seqlock *s, unsigned int seq)
  35 {
  36         read_barrier();
  37         return s->sequence != seq;
  38 }
  39
  40 static inline void write_seqlock_begin(struct seqlock *s)
  41 {
  42         s->sequence = atomic_load_acquire(&s->sequence) + 1;
  43 }
  44
  45 static inline void write_seqlock_end(struct seqlock *s)
  46 {
  47         atomic_store_release(&s->sequence, s->sequence + 1);
  48 }
  49
  50 #endif