xref: /dflybsd-src/share/man/man9/serializer.9 (revision 8351abad6f62d0aac42f868dffb3ef500f668e3e)

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.Dd January 15, 2014
.Dt SERIALIZER 9
.Os
.Sh NAME
.Nm lwkt_serialize_init ,
.Nm lwkt_serialize_enter ,
.Nm lwkt_serialize_adaptive_enter ,
.Nm lwkt_serialize_try ,
.Nm lwkt_serialize_exit ,
.Nm lwkt_serialize_handler_enable ,
.Nm lwkt_serialize_handler_disable ,
.Nm lwkt_serialize_handler_call ,
.Nm lwkt_serialize_handler_try ,
.Nm ASSERT_SERIALIZED ,
.Nm ASSERT_NOT_SERIALIZED
.Nd generic low level serializer
.Sh SYNOPSIS
.In sys/serialize.h
.Ft void
.Fn lwkt_serialize_init "lwkt_serialize_t s"
.Ft void
.Fn lwkt_serialize_enter "lwkt_serialize_t s"
.Ft void
.Fn lwkt_serialize_adaptive_enter "lwkt_serialize_t s"
.Ft int
.Fn lwkt_serialize_try "lwkt_serialize_t s"
.Ft void
.Fn lwkt_serialize_exit "lwkt_serialize_t s"
.Ft void
.Fn lwkt_serialize_handler_enable "lwkt_serialize_t s"
.Ft void
.Fn lwkt_serialize_handler_disable "lwkt_serialize_t s"
.Ft void
.Fo lwkt_serialize_handler_call
.Fa "lwkt_serialize_t s"
.Fa "void (*func)(void *, void *)"
.Fa "void *arg"
.Fa "void *frame"
.Fc
.Ft int
.Fo lwkt_serialize_handler_try
.Fa "lwkt_serialize_t s"
.Fa "void (*func)(void *, void *)"
.Fa "void *arg"
.Fa "void *frame"
.Fc
.Fn ASSERT_SERIALIZED "s"
.Fn ASSERT_NOT_SERIALIZED "s"
.Sh DESCRIPTION
The
.Nm serializer
API provides a fast locked-bus-cycle-based serialization facility
that will serialize across blocking conditions.
It is very similar to a lock but much faster for the common case.
.Pp
This API was initially designed to be a replacement for SPL calls,
but may be used whenever a low level exclusive lock (serialization)
and/or interrupt/device interaction is required.
If it is used by interrupt,
callers should enter critical section to prevent the current thread
holding the serializer being preempted by interrupt thread
which may try to hold the same serializer.
Unlike tokens this serialization is not safe from deadlocks
nor is it recursive,
and care must be taken when using it.
Note that
.Xr tsleep 9
will not release a serializer that is being held.
.Pp
There are two primary facilities \(em the serializer facility itself and
an integrated non-stackable interrupt handler disablement facility
used by drivers.
.Pp
.Fn lwkt_serialize_init ,
.Fn lwkt_serialize_enter
and
.Fn lwkt_serialize_exit
respectively initialize, hold and release the serializer
.Fa s .
.Fn lwkt_serialize_try
is a non-blocking version of
.Fn lwkt_serialize_enter .
.Pp
.Fn lwkt_serialize_adaptive_enter
is a special version of
.Fn lwkt_serialize_enter
which will try to spin a bit before the current thread is put to sleep
if the serializer
.Fa s
is contended.
By default,
.Fn lwkt_serialize_adaptive_enter
favors spinning over sleeping.
.Pp
.Fn lwkt_serialize_handler_disable ,
.Fn lwkt_serialize_handler_enable
and
.Fn lwkt_serialize_handler_call
respectively disable, enable and call an interrupt handler
.Fa func
for the serializer
.Fa s .
The arguments
.Fa arg
and
.Fa frame
will be passed to the handler.
.Fn lwkt_serialize_handler_try
is a non-blocking version of
.Fn lwkt_serialize_handler_call .
.Pp
The
.Fn ASSERT_SERIALIZED
and
.Fn ASSERT_NOT_SERIALIZED
macros assert that the serializer
.Fa s
is being held/not held.
.Sh RETURN VALUES
The
.Fn lwkt_serialize_handler_try
function return 0 on success and 1 on failure.
The
.Fn lwkt_serialize_try
function return 1 on success and 0 on failure.
.Sh FILES
The serializer itself is implemented in
.Pa /sys/kern/lwkt_serialize.c .
The header file
.Pa /sys/sys/serialize.h
describes the public interface and the structure of a serializer.
.Sh SEE ALSO
.Xr crit_enter 9 ,
.Xr spinlock 9 ,
.Xr zsleep 9
.Sh HISTORY
The
.Nm serializer
API first appeared in
.Dx 1.3 .
.Sh AUTHORS
.An -nosplit
The
.Nm serializer
API was written by
.An Matt Dillon .
This manual page was written by
.An Hasso Tepper .