libringbuffer/vatomic.h

   1 /*
   2  * SPDX-License-Identifier: MIT
   3  *
   4  * Copyright (C) 2010-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   5  */
   6
   7 #ifndef _LTTNG_RING_BUFFER_VATOMIC_H
   8 #define _LTTNG_RING_BUFFER_VATOMIC_H
   9
  10 #include <assert.h>
  11 #include <urcu/uatomic.h>
  12
  13 /*
  14  * Same data type (long) accessed differently depending on configuration.
  15  * v field is for non-atomic access (protected by mutual exclusion).
  16  * In the fast-path, the ring_buffer_config structure is constant, so the
  17  * compiler can statically select the appropriate branch.
  18  * local_t is used for per-cpu and per-thread buffers.
  19  * atomic_long_t is used for globally shared buffers.
  20  */
  21 union v_atomic {
  22         long a; /* accessed through uatomic */
  23         long v;
  24 };
  25
  26 static inline
  27 long v_read(const struct lttng_ust_lib_ring_buffer_config *config, union v_atomic *v_a)
  28 {
  29         assert(config->sync != RING_BUFFER_SYNC_PER_CPU);
  30         return uatomic_read(&v_a->a);
  31 }
  32
  33 static inline
  34 void v_set(const struct lttng_ust_lib_ring_buffer_config *config, union v_atomic *v_a,
  35            long v)
  36 {
  37         assert(config->sync != RING_BUFFER_SYNC_PER_CPU);
  38         uatomic_set(&v_a->a, v);
  39 }
  40
  41 static inline
  42 void v_add(const struct lttng_ust_lib_ring_buffer_config *config, long v, union v_atomic *v_a)
  43 {
  44         assert(config->sync != RING_BUFFER_SYNC_PER_CPU);
  45         uatomic_add(&v_a->a, v);
  46 }
  47
  48 static inline
  49 void v_inc(const struct lttng_ust_lib_ring_buffer_config *config, union v_atomic *v_a)
  50 {
  51         assert(config->sync != RING_BUFFER_SYNC_PER_CPU);
  52         uatomic_inc(&v_a->a);
  53 }
  54
  55 /*
  56  * Non-atomic decrement. Only used by reader, apply to reader-owned subbuffer.
  57  */
  58 static inline
  59 void _v_dec(const struct lttng_ust_lib_ring_buffer_config *config __attribute__((unused)), union v_atomic *v_a)
  60 {
  61         --v_a->v;
  62 }
  63
  64 static inline
  65 long v_cmpxchg(const struct lttng_ust_lib_ring_buffer_config *config, union v_atomic *v_a,
  66                long old, long _new)
  67 {
  68         assert(config->sync != RING_BUFFER_SYNC_PER_CPU);
  69         return uatomic_cmpxchg(&v_a->a, old, _new);
  70 }
  71
  72 #endif /* _LTTNG_RING_BUFFER_VATOMIC_H */