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epoch(9): fix error in example and update API reference

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Submitted by:	hps
Approved by:	sbruno
This commit is contained in:
Matt Macy 2018-05-18 04:13:58 +00:00
parent cfa866f6a1
commit 6e36248f79
1 changed files with 26 additions and 4 deletions
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30
share/man/man9/epoch.9
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@ -45,14 +45,20 @@
.In sys/proc.h
.In sys/epoch.h
.Ft epoch_t
.Fn epoch_alloc "void"
.Fn epoch_alloc "int flags"
.Ft void
.Fn epoch_enter "epoch_t epoch"
.Ft void
.Fn epoch_enter_critical "epoch_t epoch"
.Ft void
.Fn epoch_exit "epoch_t epoch"
.Ft void
.Fn epoch_exit_critical "epoch_t epoch"
.Ft void
.Fn epoch_wait "epoch_t epoch"
.Ft void
.Fn epoch_wait_critical "epoch_t epoch"
.Ft void
.Fn epoch_call "epoch_t epoch" "epoch_context_t ctx" "void (*callback) (epoch_context_t)"
.Ft int
.Fn in_epoch "void"
@ -66,14 +72,24 @@ Epochs are allocated with
.Fn epoch_alloc
and freed with
.Fn epoch_free .
The flags passed to epoch_alloc determine whether preemption is
allowed during a section (the default) or not, as specified by
EPOCH_CRITICAL.
Threads indicate the start of an epoch critical section by calling
.Fn epoch_enter .
The end of a critical section is indicated by calling
.Fn epoch_exit .
The _critical variants can be used around code in which it is safe
to have preemption disable.
A thread can wait until a grace period has elapsed
since any threads have entered
the epoch by calling
.Fn epoch_wait .
The use of a EPOCH_CRITICAL epoch type allows one to use
.Fn epoch_wait_critical
which is guaranteed to have much shorter completion times since
we know that none of the threads in an epoch section will be preempted
before completing its section.
If the thread can't sleep or is otherwise in a performance sensitive
path it can ensure that a grace period has elapsed by calling
.Fn epoch_call
@ -106,8 +122,12 @@ Async free example:
Thread 1:
.Bd -literal
int
in_pcbladdr(struct inpcb *inp, struct in_addr *faddr, struct in_laddr *laddr,
struct ucred *cred)
{
epoch_enter(net_epoch);
/* ... */
epoch_enter(net_epoch);
CK_STAILQ_FOREACH(ifa, &ifp->if_addrhead, ifa_link) {
sa = ifa->ifa_addr;
if (sa->sa_family != AF_INET)
@ -119,6 +139,7 @@ Thread 1:
}
}
epoch_exit(net_epoch);
/* ... */
}
.Ed
Thread 2:
@ -131,12 +152,13 @@ ifa_free(struct ifaddr *ifa)
epoch_call(net_epoch, &ifa->ifa_epoch_ctx, ifa_destroy);
}
void
if_purgeaddrs(struct ifnet *ifp)
{
/* .... */
IF_ADDR_WLOCK(ifp);
CK_STAILQ_REMOVE(&ifp->if_addrhead, ifa, ifaddr, ifa_link);
/* mark as unlinked */
ifa->ifa_addr->sa_family = AF_UNSPEC;
IF_ADDR_WUNLOCK(ifp);
ifa_free(ifa);
}