API.txt

   1 Userspace RCU API
   2 by Mathieu Desnoyers and Paul E. McKenney
   3
   4
   5 void rcu_init(void);
   6
   7         This must be called before any of the following functions
   8         are invoked.
   9
  10 void rcu_read_lock(void);
  11
  12         Begin an RCU read-side critical section.  These critical
  13         sections may be nested.
  14
  15 void rcu_read_unlock(void);
  16
  17         End an RCU read-side critical section.
  18
  19 void rcu_register_thread(void)
  20
  21         Each thread must invoke this function before its first call to
  22         rcu_read_lock().  Threads that never call rcu_read_lock() need
  23         not invoke this function.  In addition, rcu-bp ("bullet proof"
  24         RCU) does not require any thread to invoke rcu_register_thread().
  25
  26 void rcu_unregister_thread(void)
  27
  28         Each thread that invokes rcu_register_thread() must invoke
  29         rcu_unregister_thread() before invoking pthread_exit()
  30         or before returning from its top-level function.
  31
  32 void synchronize_rcu(void);
  33
  34         Wait until every pre-existing RCU read-side critical section
  35         has completed.  Note that this primitive will not necessarily
  36         wait for RCU read-side critical sections that have not yet
  37         started: this is not a reader-writer lock.  The duration
  38         actually waited is called an RCU grace period.
  39
  40 void call_rcu(struct rcu_head *head,
  41               void (*func)(struct rcu_head *head));
  42
  43         Registers the callback indicated by "head".  This means
  44         that "func" will be invoked after the end of a future
  45         RCU grace period.  The rcu_head structure referenced
  46         by "head" will normally be a field in a larger RCU-protected
  47         structure.  A typical implementation of "func" is as
  48         follows:
  49
  50                 void func(struct rcu_head *head)
  51                 {
  52                         struct foo *p = container_of(head, struct foo, rcu);
  53
  54                         free(p);
  55                 }
  56
  57         This RCU callback function can be registered as follows
  58         given a pointer "p" to the enclosing structure:
  59
  60                 call_rcu(&p->rcu, func);
  61
  62 struct call_rcu_data *create_call_rcu_data(unsigned long flags,
  63                                            int cpu_affinity);
  64
  65         Returns a handle that can be passed to the following
  66         primitives.  The "flags" argument can be zero, or can be
  67         URCU_CALL_RCU_RT if the worker threads associated with the
  68         new helper thread are to get real-time response. The argument
  69         "cpu_affinity" specifies a cpu on which the call_rcu thread should
  70         be affined to. It is ignored if negative.
  71
  72 struct call_rcu_data *get_default_call_rcu_data(void);
  73
  74         Returns the handle of the default call_rcu() helper thread.
  75
  76 struct call_rcu_data *get_call_rcu_data(void);
  77
  78         Returns the handle of the current thread's call_rcu() helper
  79         thread, which might well be the default helper thread.
  80
  81 struct call_rcu_data *get_thread_call_rcu_data(void);
  82
  83         Returns the handle for the current thread's hard-assigned
  84         call_rcu() helper thread, or NULL if the current thread is
  85         instead using a per-CPU or the default helper thread.
  86
  87 void set_thread_call_rcu_data(struct call_rcu_data *crdp);
  88
  89         Sets the current thread's hard-assigned call_rcu() helper to the
  90         handle specified by "crdp".  Note that "crdp" can be NULL to
  91         disassociate this thread from its helper.  Once a thread is
  92         disassociated from its helper, further call_rcu() invocations
  93         use the current CPU's helper if there is one and the default
  94         helper otherwise.
  95
  96 int set_cpu_call_rcu_data(int cpu, struct call_rcu_data *crdp);
  97
  98         Sets the specified CPU's call_rcu() helper to the handle
  99         specified by "crdp".  Again, "crdp" can be NULL to disassociate
 100         this CPU from its helper thread.  Once a CPU has been
 101         disassociated from its helper, further call_rcu() invocations
 102         that would otherwise have used this CPU's helper will instead
 103         use the default helper.
 104
 105 int create_all_cpu_call_rcu_data(unsigned long flags)
 106
 107         Creates a separate call_rcu() helper thread for each CPU.
 108         After this primitive is invoked, the global default call_rcu()
 109         helper thread will not be called.
 110
 111         The set_thread_call_rcu_data(), set_cpu_call_rcu_data(), and
 112         create_all_cpu_call_rcu_data() functions may be combined to set up
 113         pretty much any desired association between worker and call_rcu()
 114         helper threads.  If a given executable calls only call_rcu(),
 115         then that executable will have only the single global default
 116         call_rcu() helper thread.  This will suffice in most cases.
 117
 118 void call_rcu_data_free(struct call_rcu_data *crdp)
 119
 120         Terminates a call_rcu() helper thread and frees its associated
 121         data.  The caller must have ensured that this thread is no longer
 122         in use, for example, by passing NULL to set_thread_call_rcu_data()
 123         and set_cpu_call_rcu_data() as required.