Copyright (c) 2015 David Gwynne <dlg@openbsd.org>
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.Dd $Mdocdate: November 21 2016 $ .Dt SRPL_RC_INIT 9 .Os .Sh NAME .Nm srpl_rc_init , .Nm SRPL_HEAD , .Nm SRPL_ENTRY , .Nm SRPL_INIT , .Nm SRPL_FIRST , .Nm SRPL_NEXT , .Nm SRPL_FOLLOW , .Nm SRPL_FOREACH , .Nm SRPL_LEAVE , .Nm SRPL_RC_INITIALIZER .Nd singly-linked shared reference pointer list .Sh SYNOPSIS n sys/srp.h .Vt struct srpl_rc; .Ft void .Fo "srpl_rc_init" .Fa "struct srpl_rc *rc" .Fa "void (*ref)(void *, void *)" .Fa "void (*unref)(void *, void *)" .Fa "void *ctx" .Fc .Fn SRPL_HEAD "HEADNAME" "TYPE" .Fn SRPL_ENTRY "TYPE" .Ft void .Fn "SRPL_INIT" "SRPL_HEAD *sl" .Ft void * .Fn "SRPL_FIRST" "struct srp_ref *sr" "SRPL_HEAD *sl" .Ft void * .Fn "SRPL_NEXT" "struct srp_ref *sr" "struct TYPE *listelm" "FIELDNAME" .Ft void * .Fn "SRPL_FOLLOW" "struct srp_ref *sr" "struct TYPE *listelm" "FIELDNAME" .Fo "SRPL_FOREACH" .Fa "VARNAME" .Fa "struct srp_ref *sr" .Fa "SRPL_HEAD *sl" .Fa "FIELDNAME" .Fc .Ft void .Fn "SRPL_LEAVE" "struct srp_ref *sr" .Fo "SRPL_RC_INITIALIZER" .Fa "void (*ref)(void *, void *)" .Fa "void (*unref)(void *, void *)" .Fa "void *ctx" .Fc .Sh DESCRIPTION The SRPL list macros build a linked list on top of shared reference pointers. This allows concurrent traversal of a linked list and access to the items on the list.
p SRP lists are a generic type represented by a .Vt SRPL_HEAD . The elements inserted into the list must be structures that contain a .Vt SRPL_ENTRY field. Further, the elements must also support reference counting as insertion and removal operations can cause items to be temporarily referenced by multiple SRPs within the list at the same time.
p .Fn srpl_rc_init initialises the SRP list refcounts .Fa rc structure so it can be used to manage the reference counts on elements in the list. The insertion or removal of an element in an SRP list will increment the reference counts on elements within the list via calls to .Fa ref . As these references are released by the SRP infrastructure, the reference counts will be decremented by calls to .Fa unref . .Fa unref is also responsible for freeing the element when the reference count reaches 0. Both .Fa ref and .Fa unref will be called with .Fa ctx as their first argument and a pointer to the element as their second argument.
p .Fn SRPL_INIT initialises the SRP list .Fa sl to an empty state.
p .Fn SRPL_FIRST accesses the first element in the SRP list .Fa sl and holds its reference via .Fa sr .
p
.Fn SRPL_NEXT
accesses the element in the SRP list after
.Fa listelm
and holds its reference via
.Fa sr .
.Pp
Every call to
.Fn SRPL_FIRST
must have a corresponding call to
.Fn SRPL_LEAVE
to release references to the list and its elements.
p .Fn SRPL_FOLLOW accesses the element in the SRP list after .Fa listelm and swaps the previous reference held via .Fa sr for the reference of the newly accessed item.
p .Fn SRPL_FOREACH creates a loop for traversing the list. Every call to .Fn SRPL_FOREACH must have a corresponding call to .Fn SRPL_LEAVE to release references to the list and its elements.
p .Fn SRPL_LEAVE releases references to the list and its elements held by previous calls to .Fn SRPL_FIRST , .Fn SRPL_NEXT , .Fn SRPL_FOLLOW , or .Fn SRPL_FOREACH .
p An srpl_rc declaration can be initialised with the .Fn SRPL_RC_INITIALIZER macro. .Sh CONTEXT .Fn SRPL_INIT , .Fn SRPL_FIRST , .Fn SRPL_NEXT , .Fn SRPL_FOLLOW , .Fn SRPL_FOREACH , and .Fn SRPL_LEAVE may be called during autoconf, from process context, or from interrupt context.
p .Fn srpl_rc_init , may be called during autoconf or from process context. .Sh RETURN VALUES .Fn SRPL_FIRST , .Fn SRPL_NEXT , and .Fn SRPL_FOLLOW return a pointer to elements in the SRP list, or .Dv NULL if there are no more elements. .Sh SEE ALSO .Xr SRPL_FIRST_LOCKED 9 .Sh HISTORY The srp API was originally written by .An Jonathan Matthew Aq Mt jmatthew@openbsd.org and .An David Gwynne Aq Mt dlg@openbsd.org . The SRP list API first appeared in .Ox 5.9 .