path: root/contrib/bind/lib/isc/eventlib.mdoc

.\" $Id: eventlib.mdoc,v 1.22 2001/12/28 04:24:22 marka Exp $
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.Dd March 6, 1996
.Dt EVENTLIB 3
.Os BSD 4
.Sh NAME
.Nm evConnFunc ,
.Nm evFileFunc ,
.Nm evStreamFunc ,
.Nm evTimerFunc ,
.Nm evWaitFunc ,
.Nm evCreate ,
.Nm evDestroy ,
.Nm evGetNext ,
.Nm evDispatch ,
.Nm evDrop ,
.Nm evMainLoop ,
.Nm evConsTime ,
.Nm evTimeSpec ,
.Nm evTimeVal ,
.Nm evAddTime ,
.Nm evSubTime ,
.Nm evCmpTime ,
.Nm evNowTime ,
.Nm evLastEventTime ,
.Nm evSetTimer ,
.Nm evResetTimer ,
.Nm evClearTimer ,
.Nm evSetIdleTimer ,
.Nm evTouchIdleTimer ,
.Nm evClearIdleTimer ,
.Nm evWaitFor ,
.Nm evDo ,
.Nm evUnwait ,
.Nm evDefer ,
.Nm evSelectFD ,
.Nm evDeselectFD ,
.Nm evWrite ,
.Nm evRead ,
.Nm evCancelRW ,
.Nm evTimeRW ,
.Nm evUntimeRW ,
.Nm evListen ,
.Nm evConnect ,
.Nm evCancelConn ,
.Nm evHold ,
.Nm evUnhold ,
.Nm evTryAccept ,
.Nm evConsIovec ,
.Nm evSetDebug ,
.Nm evPrintf ,
.Nm evInitID ,
.Nm evTestID
.Nd event handling library
.Sh SYNOPSIS
.Fd #include <isc/eventlib.h>
.Ft typedef void
.Fn \*(lp*evConnFunc\*(rp "evContext ctx" "void *uap" "int fd" \
"const void *la" "int lalen" "const void *ra" "int ralen"
.Ft typedef void
.Fn \*(lp*evTimerFunc\*(rp "evContext ctx" "void *uap" \
"struct timespec due" "struct timespec inter"
.Ft typedef void
.Fn \*(lp*evFileFunc\*(rp "evContext ctx" "void *uap" "int fd" "int eventmask"
.Ft typedef void
.Fn \*(lp*evStreamFunc\*(rp "evContext ctx" "void *uap" "int fd" "int bytes"
.Ft typedef void
.Fn \*(lp*evWaitFunc\*(rp "evContext ctx" "void *uap" "const void *tag"
.Ft int
.Fn evCreate "evContext *ctx"
.Ft int
.Fn evDestroy "evContext ctx"
.Ft int
.Fn evGetNext "evContext ctx" "evEvent *ev" "int options"
.Ft int
.Fn evDispatch "evContext ctx" "evEvent ev"
.Ft void
.Fn evDrop "evContext ctx" "evEvent ev"
.Ft int
.Fn evMainLoop "evContext ctx"
.Ft struct timespec
.Fn evConsTime "int sec" "int usec"
.Ft struct timespec
.Fn evTimeSpec "struct timeval tv"
.Ft struct timeval
.Fn evTimeVal "struct timespec ts"
.Ft struct timespec
.Fn evAddTime "struct timespec addend1" "struct timespec addend2"
.Ft struct timespec
.Fn evSubTime "struct timespec minuend" "struct timespec subtrahend"
.Ft struct timespec
.Fn evCmpTime "struct timespec a" "struct timespec b"
.Ft struct timespec
.Fn evNowTime "void"
.Ft struct timespec
.Fn evLastEventTime "evContext opaqueCtx"
.Ft int
.Fn evSetTimer "evContext ctx" "evTimerFunc func" "void *uap" \
"struct timespec due" "struct timespec inter" "evTimerID *id"
.Ft int
.Fn evResetTimer "evContext ctx" "evTimerID id" "evTimerFunc func" \
"void *uap" "struct timespec due" "struct timespec inter"
.Ft int
.Fn evClearTimer "evContext ctx" "evTimerID id"
.Ft int
.Fn evSetIdleTimer "evContext opaqueCtx" "evTimerFunc func" "void *uap" \
"struct timespec max_idle" "evTimerID *opaqueID"
.Ft int 
.Fn evTouchIdleTimer "evContext opaqueCtx" "evTimerID id"
.Ft int 
.Fn evResetIdleTimer "evContext opaqueCtx" "evTimerID id" "evTimerFunc func" \
"void *uap" "struct timespec max_idle"
.Ft int
.Fn evClearIdleTimer "evContext opaqueCtx" "evTimerID id"
.Ft int
.Fn evWaitFor "evContext opaqueCtx" "const void *tag" \
"evWaitFunc func" "void *uap" "evWaitID *id"
.Ft int
.Fn evDo "evContext opaqueCtx" "const void *tag"
.Ft int
.Fn evUnwait "evContext opaqueCtx" "evWaitID id"
.Ft int
.Fn evDefer "evContext opaqueCtx" "evWaitFunc func" "void *uap"
.Ft int
.Fn evSelectFD "evContext ctx" "int fd" "int eventmask" \
"evFileFunc func" "void *uap" "evFileID *id"
.Ft int
.Fn evDeselectFD "evContext ctx" "evFileID id"
.Ft struct iovec
.Fn evConsIovec "void *buf" "size_t cnt"
.Ft int
.Fn evWrite "evContext ctx" "int fd" "const struct iovec *iov" "int cnt" \
"evStreamFunc func" "void *uap" "evStreamID *id"
.Ft int
.Fn evRead "evContext ctx" "int fd" "const struct iovec *iov" "int cnt" \
"evStreamFunc func" "void *uap" "evStreamID *id"
.Ft int
.Fn evCancelRW "evContext ctx" "evStreamID id"
.Ft int
.Fn evTimeRW "evContext opaqueCtx" "evStreamID id" "evTimerID timer"
.Ft int
.Fn evUntimeRW "evContext opaqueCtx" "evStreamID id"
.Ft int
.Fn evListen "evContext ctx" "int fd" "int maxconn" \
"evConnFunc func" "void *uap" "evConnID *id"
.Ft int
.Fn evConnect "evContext ctx" "int fd" "void *ra" "int ralen" \
"evConnFunc func" "void *uap" "evConnID *id"
.Ft int
.Fn evCancelConn "evContext ctx" "evConnID id"
.Ft int
.Fn evHold "evContext ctx" "evConnID id"
.Ft int
.Fn evUnhold "evContext ctx" "evConnID id"
.Ft int
.Fn evTryAccept "evContext ctx" "evConnID id" "int *sys_errno"
.Ft void
.Fn evSetDebug "evContext ctx" "int level" "FILE *output"
.Ft void
.Fn evPrintf "const evContext_p *ctx" "int level" "const char *fmt" "..."
.Ft void
.Fn evInitID "*\s-1ID\s+1"
.Ft int
.Fn evTestID "\s-1ID\s+1"
.Sh DESCRIPTION
This library provides multiple outstanding asynchronous timers and I/O
to a cooperating application.  The model is similar to that of the X
Toolkit, in that events are registered with the library and the application
spends most of its time in the
.Fn evMainLoop
function.  If an application already has a main loop, it can safely register
events with this library as long as it periodically calls the
.Fn evGetNext
and
.Fn evDispatch
functions.  (Note that
.Fn evGetNext
has both polling and blocking modes.)
.Pp
The function
.Fn evCreate
creates an event context which is needed by all the other functions in this
library.  All information used internally by this library is bound to this
context, rather than to static storage.  This makes the library 
.Dq thread safe ,
and permits other library functions to use events without
disrupting the application's use of events.
.Pp
The function
.Fn evDestroy
destroys a context that has been created by
.Fn evCreate .
All dynamic memory bound to this context will be freed.  An implicit
.Fn evTimerClear
will be done on all timers set in this event context.  An implicit
.Fn evDeselectFD
will be done on all file descriptors selected in this event context.
.Pp
The function
.Fn evGetNext
potentially waits for and then retrieves the next asynchronous event,
placing it in the object of the
.Fa ev
pointer argument.  The following
.Fa options
are available:
.Fa EV_POLL ,
meaning that
.Fn evGetNext
should not block, but rather return
.Dq Fa -1
with
.Fa errno
set to
.Fa EWOULDBLOCK
if no events have occurred;
.Fa EV_WAIT ,
which tells
.Fn evGetNext
to block internally until the next event occurs; and
.Fa EV_NULL ,
which tells
.Fn evGetNext
that it should return a special 
.Dq no-op 
event, which is ignored by
.Fn evDispatch
but handled correctly by
.Fn evDrop .
.Fa EV_NULL
can be necessary to the correct functioning of a caller\-written equivilent to
.Fn evMainLoop ,
wherein perterbations caused by external system events must be polled for, and
the default behaviour of internally ignoring such events is undesirable.
Note that
.Fa EV_POLL
and
.Fa EV_WAIT
are mutually exclusive.
.Pp
The function
.Fn evDispatch
dispatches an event retrieved by
.Fn evGetNext .
This usually involves calling the function that was associated with the event
when the event was registered with
.Fn evSetTimer ,
.Fn evResetTimer ,
or
.Fn evSelectFD .
All events retrieved by
.Fn evGetNext
must be given over to
.Fn evDispatch
at some point, since there is some dynamic memory associated with each event.
.Pp
The function
.Fn evDrop
deallocates dynamic memory that has been allocated by
.Fn evGetNext .
Calling
.Fn evDispatch
has the side effect of calling
.Fn evDrop ,
but if you are going to drop the event rather than dispatch it, you will have
to call
.Fn evDrop
directly.
.Pp
The function
.Fn evMainLoop
is just:
.Bd -literal -offset indent
while ((x = evGetNext(opaqueCtx, &event, EV_WAIT)) == 0)
	if ((x = evDispatch(opaqueCtx, event)) < 0)
		break;
return (x);
.Ed
.Pp
In other words, get events and dispatch them until an error occurs.  One such
error would be that all the events under this context become unregistered; in
that event, there will be nothing to wait for and
.Fn evGetNext
becomes an undefined operation.
.Pp
The function
.Fn evConsTime
is a constructor for
.Dq Fa struct timespec
which allows these structures to be created and then passed as arguments to
other functions without the use of temporary variables.  (If C had inline
constructors, there would be no need for this function.)
.Pp
The functions
.Fn evTimeSpec
and
.Fn evTimeVal 
are utilities which allow the caller to convert a
.Dq Fa struct timeval
to a 
.Dq Fa struct timespec
(the function of
.Fn evTimeSpec )
or vice versa (the function of
.Fn evTimeVal ) .
Note that the name of the function indicates the type of the return value.
.Pp
The function
.Fn evAddTime
adds two
.Dq Fa struct timespec
values and returns the result as a
.Dq Fa struct timespec .
.Pp
The function
.Fn evSubTime
subtracts its second
.Dq Fa struct timespec
argument from its first
.Dq Fa struct timespec
argument and returns the result as a
.Dq Fa struct timespec .
.Pp
The function
.Fn evCmpTime
compares its two
.Dq Fa struct timespec
arguments and returns an
.Dq Fa int
that is less than zero if the first argument specifies an earlier time than
the second, or more than zero if the first argument specifies a later time
than the second, or equal to zero if both arguments specify the same time.
.Pp
The function
.Fn evNowTime
returns a
.Dq Fa struct timespec
which either describes the current time (using
.Xr gettimeofday 2 ) ,
if successful, or has its fields set to zero, if there is an error.
(In the latter case, the caller can check
.Va errno ,
since it will be set by
.Xr gettimeofday 2 . )
.Pp
The function
.Fn evLastEventTime 
returns the
.Dq Fa struct timespec
which describes the last time that certain events happened to the 
event context indicated by 
.Fa opaqueCtx .
This value is updated by
.Fn evCreate 
and
.Fn evGetNext 
(upon entry and after
.Xr select 2
returns); it is routinely compared with other times in the internal handling
of, e.g., timers.
.Pp
The function
.Fn evSetTimer
registers a timer event, which will be delivered as a function call to the
function specified by the
.Fa func
argument.  The event will be delivered at absolute time
.Fa due ,
and then if time
.Fa inter
is not equal to
.Dq Fn evConsTime 0 0 ,
subsequently at intervals equal to time
.Fa inter .
As a special case, specifying a
.Fa due
argument equal to
.Dq Fn evConsTime 0 0
means 
.Dq due immediately .
The
.Fa opaqueID
argument, if specified as a value other than
.Fa NULL ,
will be used to store the resulting 
.Dq timer \s-1ID\s+1 , 
useful as an argument to
.Fn evClearTimer .
Note that in a 
.Dq one\-shot 
timer (which has an
.Fa inter
argument equal to
.Dq Fa evConsTime(0,0) )
the user function
.Fa func
should deallocate any dynamic memory that is uniquely bound to the
.Fa uap ,
since no handles to this memory will exist within the event library
after a one\-shot timer has been delivered.
.Pp
The function
.Fn evResetTimer
resets the values of the timer specified by
.Fa id
to the given arguments.  The arguments are the same as in the description of
.Fn evSetTimer
above.
.Pp
The function
.Fn evClearTimer
will unregister the timer event specified by
.Fa id .
Note that if the
.Fa uap
specified in the corresponding
.Fn evSetTimer
call is uniquely bound to any dynamic memory, then that dynamic memory should
be freed by the caller before the handle is lost.  After a call to
.Fn evClearTimer ,
no handles to this
.Fa uap
will exist within the event library.
.Pp
The function
.Fn evSetIdleTimer 
is similar to (and built on)
.Fn evSetTimer ;
it registers an idle timer event which provides for the function call to
.Fa func
to occur.  However, for an
.Em idle
timer, the call will occur after at least
.Dq Fa max_idle
time has passed since the time the idle timer was
.Dq last touched ;
originally, this is set to the time returned by
.Fn evLastEventTime 
(described above) for the event context specified by 
.Fa opaqueCtx .  
This is a 
.Dq one\-shot 
timer, but the time at which the
.Fa func
is actually called can be changed by recourse to
.Fn evTouchIdleTimer
(described below).  The pointer to the underlying 
.Dq timer \s-1ID\s+1 
is returned in
.Fa opaqueID ,
if it is
.No non- Ns Dv NULL .
.Pp
The
.Fn evTouchIdleTimer 
function updates the idle timer associated with
.Fa id ,
setting its idea of the time it was last accessed to the value returned by
.Fn evLastEventTime
(described above) for the event context specified by
.Fa opaqueCtx .
This means that the idle timer will expire after at least
.Fa max_idle
time has passed since this (possibly new) time, providing a caller mechanism
for resetting the call to the
.Fa func
associated with the idle timer.  (See the description of
.Fn evSetIdleTimer ,
above, for information about
.Fa func
and
.Fa max_idle . )
.Pp
The
.Fn evResetIdleTimer
function reschedules a timer and resets the callback function and its argument.
Note that resetting a timer also ``touches'' it.
.Pp
The
.Fn evClearIdleTimer
function unregisters the idle timer associated with
.Fa id .
See the discussion under
.Fn evClearTimer , 
above, for information regarding caller handling of the
.Fa uap
associated with the corresponding
.Fn evSetIdleTimer
call.
.Pp
The function
.Fn evWaitFor
places the function
.Fa func
on the given event context's wait queue with the associated (possibly
.Dv NULL )
.Dq Fa tag ;
if 
.Fa id
is 
.No non- Ns Dv NULL ,
then it will contain the 
.Dq wait \s-1ID\s+1 
associated with the created queue element.
.Pp
The function
.Fn evDo 
marks 
.Em all
of the 
.Dq waiting 
functions in the given event context's wait queue with the associated (possibly
.Dv NULL )
.Dq Fa tag
as runnable.  This places these functions in a
.Dq done
queue which will be read by
.Fn evGetNext .
.Pp
The function
.Fn evUnwait 
will search for the
.Dq wait \s-1ID\s+1 
.Fa id
in the wait queue of the given event context; if an element with the given
.Fa id 
is not found, then the
.Dq done
queue of that context is searched.  If found, the queue element is removed
from the appropriate list.
.Pp
The function
.Fn evDefer
causes a function (specified as
.Fa func ,
with argument
.Fa uap )
to be dispatched at some later time.  Note that the
.Fa tag
argument to
.Fa func
will always be
.Fa NULL
when dispatched.
.Pp
The function
.Fn evSelectFD
registers a file I/O event for the file descriptor specified by
.Fa fd .
Bits in the
.Fa eventmask
argument are named
.Fa EV_READ ,
.Fa EV_WRITE ,
and
.Fa EV_EXCEPT .
At least one of these bits must be specified.  If the
.Fa id
argument is not equal to
.Fa NULL ,
it will be used to store a unique ``file event \s-1ID\s+1'' for this event,
which is useful in subsequent calls to
.Fn evDeselectFD .
A file descriptor will be made nonblocking using the
.Fa O_NONBLOCK
flag with
.Xr fcntl 2
on its first concurrent registration via
.Fn evSelectFD .
An
.Fn evSelectFD
remains in effect until cancelled via
.Fn evDeselectFD .
.Pp
The function
.Fn evDeselectFD
unregisters the ``file event'' specified by the
.Fa id
argument.  If the corresponding
.Fa uap
uniquely points to dynamic memory, that memory should be freed before its
handle is lost, since after a call to
.Fn evDeselectFD ,
no handles to this event's
.Fa uap
will remain within the event library.  A file descriptor will be taken out of
nonblocking mode (see
.Fa O_NONBLOCK
and
.Xr fcntl 2 )
when its last event registration is removed via
.Fn evDeselectFD ,
if it was in blocking mode before the first registration via
.Fn evSelectFD .
.Pp
The function
.Fn evConsIovec
is a constructor for a single
.Ft struct iovec
structure, which is useful for
.Fn evWrite
and
.Fn evRead .
.Pp
The functions
.Fn evWrite
and
.Fn evRead
start asynchronous stream I/O operations on file descriptor
.Fa fd .
The data to be written or read is in the scatter/gather descriptor specified by
.Fa iov
and
.Fa cnt .
The supplied function
.Fa func
will be called with argument
.Fa uap
when the I/O operation is complete.  If
.Fa id
is not
.Fa NULL ,
it will be filled a with the stream event identifier suitable for use with
.Fn evCancelRW .
.Pp
The function
.Fn evCancelRW
extinguishes an outstanding
.Fn evWrite
or
.Fn evRead
call.  System I/O calls cannot always be cancelled, but you are guaranteed
that the
.Fa func
function supplied to
.Fn evWrite
or
.Fn evRead
will not be called after a call to
.Fn evCancelRW .
Care should be taken not to deallocate or otherwise reuse the space pointed
to by the segment descriptors in
.Fa iov
unless the underlying file descriptor is closed first.
.Pp
The function
.Fn evTimeRW
sets the stream associated with the given stream \s-1ID\s+1 
.Dq Fa id
to have the idle timer associated with the timer \s-1ID\s+1 
.Dq Fa timer .
.Pp
The function
.Fn evUntimeRW
says that the stream associated with the given stream \s-1ID\s+1
.Dq Fa id
should ignore its idle timer, if present.
.Pp
The functions
.Fn evListen ,
.Fn evConnect ,
and
.Fn evCancelConn
can be used to manage asynchronous incoming and outgoing socket connections.
Sockets to be used with these functions should first be created with
.Xr socket 2
and given a local name with
.Xr bind 2 .
It is extremely unlikely that the same socket will ever be
useful for both incoming and outgoing connections.  The
.Fa id
argument to
.Fn evListen
and
.Fn evConnect
is either
.Fa NULL
or the address of a
.Ft evFileID
variable which can then be used in a subsequent call to
.Fn evCancelConn .
.Pp
After a call to
.Fn evListen ,
each incoming connection arriving on
.Fa fd
will cause
.Fa func
to be called with
.Fa uap
as one of its arguments.
.Fn evConnect
initiates an outgoing connection on
.Fa fd
to destination address
.Fa ra
(whose length is
.Fa ralen ) .
When the connection is complete,
.Fa func
will be called with
.Fa uap
as one of its arguments.  The argument
.Fa fd
to
.Fn \*(lp*func\*(rp
will be
.Fa -1
if an error occurred that prevented this connection from completing 
successfully.  In this case
.Fn errno
will have been set and the socket described by
.Fa fd
will have been closed.  The
.Fn evCancelConn
function will prevent delivery of all pending and subsequent
events for the outstanding connection.  The
.Fn evHold
function will suspend the acceptance of new connections on the listener
specified by
.Fa id .
Connections will be queued by the protocol stack up to the system's limit.  The
.Fn evUnhold
function will reverse the effects of
.Fn evHold ,
allowing incoming connections to be delivered for listener
.Fa id .
The
.Fn evTryAccept
function will poll the listener specified by
.Fa id ,
accepting a new connection if one is available, and queuing a connection event
for later retrieval by
.Fn evGetNext .
If the connection event queued is an accept error(), sys_errno will contain
the error code; otherwise it will be zero.  All connection events queued by
.Fn evTryAccept
will be delivered by
.Fn evGetNext
before a new select is done on the listener.
.Pp
The function
.Fn evSetDebug
sets the debugging
.Fa level
and diagnostic
.Fa output
file handle for an event context.  Greater numeric levels will
result in more verbose output being sent to the output FILE during program
execution.
.Pp
The function
.Fn evPrintf
prints a message with the format
.Dq Fa fmt
and the following arguments (if any), on the output stream associated
with the event context pointed to by
.Fa ctx .
The message is output if the event context's debug level is greater than
or equal to the indicated
.Fa level .
.Pp
The function
.Fn evInitID
will initialize an opaque 
.Dq evConn \s-1ID\s+1 , 
.Dq evFile \s-1ID\s+1 , 
.Dq evStream \s-1ID\s+1 , 
.Dq evTimer \s-1ID\s+1 , 
.Dq evWait \s-1ID\s+1 , 
.Dq evContext , 
or
.Dq evEvent ,
which is passed by reference.
.Pp
The function
.Fn evTestID
will examine an opaque \s-1ID\s+1 and return
.Dq TRUE
only if it is not in its initialized state.
.Sh RETURN VALUES
All the functions whose return type is
.Dq Fa int
use the standard convention of returning zero (0) to indicate success, or
returning
.Dq Fa -1
and setting
.Fa errno
to indicate failure.
.Sh FILE
.Pa heap.h ,
which is in the 
.Pa src/lib/isc
directory of the current 
.Sy BIND
distribution.
.Sh ERRORS
The possible values for
.Fa errno
when one of the
.Dq Fa int
functions in this library returns
.Dq Fa -1
include those of the Standard C Library and also:
.Bl -tag -width EWOULDBLOCKAA
.It Bq Er EINVAL
Some function argument has an unreasonable value.
.It Bq Er EINVAL
The specified file descriptor has an integer value greater than the default
.Fa FD_SETSIZE ,
meaning that the application's limit is higher than the library's.
.It Bq Er ENOENT
The specified 
.Dq event \s-1ID\s+1 
does not exist.
.It Bq Er EWOULDBLOCK
No events have occurred and the
.Fa EV_POLL
option was specified.
.It Bq Er EBADF
The specified signal was unblocked outside the library.
.El
.Sh SEE ALSO
.Xr gettimeofday 2 ,
.Xr select 2 ,
.Xr fcntl 3 ,
.Xr malloc 3 ,
.Xr @INDOT@named @SYS_OPS_EXT@ ,
.Xr readv 3 ,
.Xr writev 3 .
.Sh BUGS
This huge man page needs to be broken up into a handful of smaller ones.
.Sh HISTORY
The
.Nm eventlib
library was designed by Paul Vixie with excellent advice from his friends
and with tips 'o the cap to the X Consortium and the implementors of DEC SRC
Modula-3.