by Mathieu Desnoyers and Paul E. McKenney
void rcu_init(void);This must be called before any of the following functions are invoked.
void rcu_read_lock(void);Begin an RCU read-side critical section. These critical sections may be nested.
void rcu_read_unlock(void);End an RCU read-side critical section.
void rcu_register_thread(void);Each thread must invoke this function before its first call to
rcu_read_lock(). Threads that never call rcu_read_lock() need
not invoke this function. In addition, rcu-bp ("bullet proof"
RCU) does not require any thread to invoke rcu_register_thread().
void rcu_unregister_thread(void);Each thread that invokes rcu_register_thread() must invoke
rcu_unregister_thread() before invoking pthread_exit()
or before returning from its top-level function.
void synchronize_rcu(void);Wait until every pre-existing RCU read-side critical section has completed. Note that this primitive will not necessarily wait for RCU read-side critical sections that have not yet started: this is not a reader-writer lock. The duration actually waited is called an RCU grace period.
void call_rcu(struct rcu_head *head,
void (*func)(struct rcu_head *head));Registers the callback indicated by "head". This means
that func will be invoked after the end of a future
RCU grace period. The rcu_head structure referenced
by head will normally be a field in a larger RCU-protected
structure. A typical implementation of func is as
follows:
void func(struct rcu_head *head)
{
struct foo *p = container_of(head, struct foo, rcu);
free(p);
}This RCU callback function can be registered as follows
given a pointer p to the enclosing structure:
call_rcu(&p->rcu, func);call_rcu should be called from registered RCU read-side threads.
For the QSBR flavor, the caller should be online.
void rcu_barrier(void);Wait for all call_rcu() work initiated prior to rcu_barrier() by
any thread on the system to have completed before rcu_barrier()
returns. rcu_barrier() should never be called from a call_rcu()
thread. This function can be used, for instance, to ensure that
all memory reclaim involving a shared object has completed
before allowing dlclose() of this shared object to complete.
struct call_rcu_data *create_call_rcu_data(unsigned long flags,
int cpu_affinity);Returns a handle that can be passed to the following
primitives. The flags argument can be zero, or can be
URCU_CALL_RCU_RT if the worker threads associated with the
new helper thread are to get real-time response. The argument
cpu_affinity specifies a CPU on which the call_rcu thread should
be affined to. It is ignored if negative.
void call_rcu_data_free(struct call_rcu_data *crdp);Terminates a call_rcu() helper thread and frees its associated
data. The caller must have ensured that this thread is no longer
in use, for example, by passing NULL to set_thread_call_rcu_data()
and set_cpu_call_rcu_data() as required.
struct call_rcu_data *get_default_call_rcu_data(void);Returns the handle for the default call_rcu() helper thread.
Creates it if necessary.
struct call_rcu_data *get_cpu_call_rcu_data(int cpu);Returns the handle for the current CPU's call_rcu() helper
thread, or NULL if the current CPU has no helper thread
currently assigned. The call to this function and use of the
returned call_rcu_data should be protected by RCU read-side
lock.
struct call_rcu_data *get_thread_call_rcu_data(void);Returns the handle for the current thread's hard-assigned
call_rcu() helper thread, or NULL if the current thread is
instead using a per-CPU or the default helper thread.
struct call_rcu_data *get_call_rcu_data(void);Returns the handle for the current thread's call_rcu() helper
thread, which is either, in increasing order of preference:
per-thread hard-assigned helper thread, per-CPU helper thread,
or default helper thread. get_call_rcu_data should be called
from registered RCU read-side threads. For the QSBR flavor, the
caller should be online.
pthread_t get_call_rcu_thread(struct call_rcu_data *crdp);Returns the helper thread's pthread identifier linked to a call rcu helper thread data.
void set_thread_call_rcu_data(struct call_rcu_data *crdp);Sets the current thread's hard-assigned call_rcu() helper to the
handle specified by crdp. Note that crdp can be NULL to
disassociate this thread from its helper. Once a thread is
disassociated from its helper, further call_rcu() invocations
use the current CPU's helper if there is one and the default
helper otherwise.
int set_cpu_call_rcu_data(int cpu, struct call_rcu_data *crdp);Sets the specified CPU's call_rcu() helper to the handle
specified by crdp. Again, crdp can be NULL to disassociate
this CPU from its helper thread. Once a CPU has been
disassociated from its helper, further call_rcu() invocations
that would otherwise have used this CPU's helper will instead
use the default helper.
The caller must wait for a grace-period to pass between return from
set_cpu_call_rcu_data() and call to call_rcu_data_free() passing the
previous call rcu data as argument.
int create_all_cpu_call_rcu_data(unsigned long flags);Creates a separate call_rcu() helper thread for each CPU.
After this primitive is invoked, the global default call_rcu()
helper thread will not be called.
The set_thread_call_rcu_data(), set_cpu_call_rcu_data(), and
create_all_cpu_call_rcu_data() functions may be combined to set up
pretty much any desired association between worker and call_rcu()
helper threads. If a given executable calls only call_rcu(),
then that executable will have only the single global default
call_rcu() helper thread. This will suffice in most cases.
void free_all_cpu_call_rcu_data(void);Clean up all the per-CPU call_rcu threads. Should be paired with
create_all_cpu_call_rcu_data() to perform teardown. Note that
this function invokes synchronize_rcu() internally, so the
caller should be careful not to hold mutexes (or mutexes within a
dependency chain) that are also taken within a RCU read-side
critical section, or in a section where QSBR threads are online.
void call_rcu_after_fork_child(void);Should be used as pthread_atfork() handler for programs using
call_rcu and performing fork() or clone() without a following
exec().