evConnFunc, evFileFunc, evStreamFunc, evTimerFunc, evWaitFunc, evCreate,
evDestroy, evGetNext, evDispatch, evDrop, evMainLoop, evConsTime,
evTimeSpec, evTimeVal, evAddTime, evSubTime, evCmpTime, evNowTime,
evLastEventTime, evSetTimer, evResetTimer, evClearTimer, evSetIdleTimer,
evTouchIdleTimer, evClearIdleTimer, evWaitFor, evDo, evUnwait, evDefer,
evSelectFD, evDeselectFD, evWrite, evRead, evCancelRW, evTimeRW,
evUntimeRW, evListen, evConnect, evCancelConn, evHold, evUnhold,
evTryAccept, evConsIovec, evSetDebug, evPrintf, evInitID, evTestID --
event handling library
(*evConnFunc)(evContext ctx, void *uap, int fd, const void *la,
int lalen, const void *ra, int ralen);
(*evTimerFunc)(evContext ctx, void *uap, struct timespec due,
struct timespec inter);
(*evFileFunc)(evContext ctx, void *uap, int fd, int eventmask);
(*evStreamFunc)(evContext ctx, void *uap, int fd, int bytes);
(*evWaitFunc)(evContext ctx, void *uap, const void *tag);
evGetNext(evContext ctx, evEvent *ev, int options);
evDispatch(evContext ctx, evEvent ev);
evDrop(evContext ctx, evEvent ev);
evConsTime(int sec, int usec);
evTimeSpec(struct timeval tv);
evTimeVal(struct timespec ts);
evAddTime(struct timespec addend1, struct timespec addend2);
evSubTime(struct timespec minuend, struct timespec subtrahend);
evCmpTime(struct timespec a, struct timespec b);
evSetTimer(evContext ctx, evTimerFunc func, void *uap,
struct timespec due, struct timespec inter, evTimerID *id);
evResetTimer(evContext ctx, evTimerID id, evTimerFunc func, void *uap,
struct timespec due, struct timespec inter);
evClearTimer(evContext ctx, evTimerID id);
evSetIdleTimer(evContext opaqueCtx, evTimerFunc func, void *uap,
struct timespec max_idle, evTimerID *opaqueID);
evTouchIdleTimer(evContext opaqueCtx, evTimerID id);
evResetIdleTimer(evContext opaqueCtx, evTimerID id, evTimerFunc func,
void *uap, struct timespec max_idle);
evClearIdleTimer(evContext opaqueCtx, evTimerID id);
evWaitFor(evContext opaqueCtx, const void *tag, evWaitFunc func,
void *uap, evWaitID *id);
evDo(evContext opaqueCtx, const void *tag);
evUnwait(evContext opaqueCtx, evWaitID id);
evDefer(evContext opaqueCtx, evWaitFunc func, void *uap);
evSelectFD(evContext ctx, int fd, int eventmask, evFileFunc func,
void *uap, evFileID *id);
evDeselectFD(evContext ctx, evFileID id);
evConsIovec(void *buf, size_t cnt);
evWrite(evContext ctx, int fd, const struct iovec *iov, int cnt,
evStreamFunc func, void *uap, evStreamID *id);
evRead(evContext ctx, int fd, const struct iovec *iov, int cnt,
evStreamFunc func, void *uap, evStreamID *id);
evCancelRW(evContext ctx, evStreamID id);
evTimeRW(evContext opaqueCtx, evStreamID id, evTimerID timer);
evUntimeRW(evContext opaqueCtx, evStreamID id);
evListen(evContext ctx, int fd, int maxconn, evConnFunc func, void *uap,
evConnect(evContext ctx, int fd, void *ra, int ralen, evConnFunc func,
void *uap, evConnID *id);
evCancelConn(evContext ctx, evConnID id);
evHold(evContext ctx, evConnID id);
evUnhold(evContext ctx, evConnID id);
evTryAccept(evContext ctx, evConnID id, int *sys_errno);
evSetDebug(evContext ctx, int level, FILE *output);
evPrintf(const evContext_p *ctx, int level, const char *fmt, ...);
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 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 evGetNext() and evDispatch() functions.
(Note that evGetNext() has both polling and blocking modes.)
The function 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 ``thread safe'', and permits other library functions
to use events without disrupting the application's use of events.
The function evDestroy() destroys a context that has been created by
evCreate(). All dynamic memory bound to this context will be freed. An
implicit evTimerClear() will be done on all timers set in this event context.
An implicit evDeselectFD() will be done on all file descriptors
selected in this event context.
The function evGetNext() potentially waits for and then retrieves the
next asynchronous event, placing it in the object of the ev pointer argument.
The following options are available: EV_POLL, meaning that
evGetNext() should not block, but rather return ``-1'' with errno set to
EWOULDBLOCK if no events have occurred; EV_WAIT, which tells evGetNext()
to block internally until the next event occurs; and EV_NULL, which tells
evGetNext() that it should return a special ``no-op'' event, which is
ignored by evDispatch() but handled correctly by evDrop(). EV_NULL can
be necessary to the correct functioning of a caller-written equivilent to
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 EV_POLL and EV_WAIT are mutually exclusive.
The function evDispatch() dispatches an event retrieved by evGetNext().
This usually involves calling the function that was associated with the
event when the event was registered with evSetTimer(), evResetTimer(), or
evSelectFD(). All events retrieved by evGetNext() must be given over to
evDispatch() at some point, since there is some dynamic memory associated
with each event.
The function evDrop() deallocates dynamic memory that has been allocated
by evGetNext(). Calling evDispatch() has the side effect of calling
evDrop(), but if you are going to drop the event rather than dispatch it,
you will have to call evDrop() directly.
The function evMainLoop() is just:
while ((x = evGetNext(opaqueCtx, &event, EV_WAIT)) == 0)
if ((x = evDispatch(opaqueCtx, event)) < 0)
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 evGetNext()
becomes an undefined operation.
The function evConsTime() is a constructor for ``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.)
The functions evTimeSpec() and evTimeVal() are utilities which allow the
caller to convert a ``struct timeval'' to a ``struct timespec'' (the
function of evTimeSpec()) or vice versa (the function of evTimeVal()).
Note that the name of the function indicates the type of the return
The function evAddTime() adds two ``struct timespec'' values and returns
the result as a ``struct timespec''.
The function evSubTime() subtracts its second ``struct timespec'' argument
from its first ``struct timespec'' argument and returns the result
as a ``struct timespec''.
The function evCmpTime() compares its two ``struct timespec'' arguments
and returns an ``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.
The function evNowTime() returns a ``struct timespec'' which either
describes the current time (using gettimeofday(2)), if successful, or has
its fields set to zero, if there is an error. (In the latter case, the
caller can check errno, since it will be set by gettimeofday(2).)
The function evLastEventTime() returns the ``struct timespec'' which
describes the last time that certain events happened to the event context
indicated by opaqueCtx. This value is updated by evCreate() and
evGetNext() (upon entry and after select(2) returns); it is routinely
compared with other times in the internal handling of, e.g., timers.
The function evSetTimer() registers a timer event, which will be delivered
as a function call to the function specified by the func argument.
The event will be delivered at absolute time due, and then if time inter
is not equal to ``evConsTime(0, 0)'', subsequently at intervals equal to
time inter. As a special case, specifying a due argument equal to
``evConsTime(0, 0)'' means ``due immediately''. The opaqueID argument,
if specified as a value other than NULL, will be used to store the
resulting ``timer ID'', useful as an argument to evClearTimer(). Note
that in a ``one-shot'' timer (which has an inter argument equal to
``evConsTime(0,0)'') the user function func should deallocate any dynamic
memory that is uniquely bound to the uap, since no handles to this memory
will exist within the event library after a one-shot timer has been
The function evResetTimer() resets the values of the timer specified by
id to the given arguments. The arguments are the same as in the description
of evSetTimer() above.
The function evClearTimer() will unregister the timer event specified by
id. Note that if the uap specified in the corresponding 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
evClearTimer(), no handles to this uap will exist within the event
The function evSetIdleTimer() is similar to (and built on) evSetTimer();
it registers an idle timer event which provides for the function call to
func to occur. However, for an idle timer, the call will occur after at
least ``max_idle'' time has passed since the time the idle timer was
``last touched''; originally, this is set to the time returned by
evLastEventTime() (described above) for the event context specified by
opaqueCtx. This is a ``one-shot'' timer, but the time at which the func
is actually called can be changed by recourse to evTouchIdleTimer()
(described below). The pointer to the underlying ``timer ID'' is
returned in opaqueID, if it is non-NULL.
The evTouchIdleTimer() function updates the idle timer associated with
id, setting its idea of the time it was last accessed to the value
returned by evLastEventTime() (described above) for the event context
specified by opaqueCtx. This means that the idle timer will expire after
at least max_idle time has passed since this (possibly new) time, providing
a caller mechanism for resetting the call to the func associated with
the idle timer. (See the description of evSetIdleTimer(), above, for
information about func and max_idle.)
The evResetIdleTimer() function reschedules a timer and resets the callback
function and its argument. Note that resetting a timer also
The evClearIdleTimer() function unregisters the idle timer associated
with id. See the discussion under evClearTimer(), above, for information
regarding caller handling of the uap associated with the corresponding
The function evWaitFor() places the function func on the given event context's
wait queue with the associated (possibly NULL) ``tag''; if id is
non-NULL, then it will contain the ``wait ID'' associated with the created
The function evDo() marks all of the ``waiting'' functions in the given
event context's wait queue with the associated (possibly NULL) ``tag'' as
runnable. This places these functions in a ``done'' queue which will be
read by evGetNext().
The function evUnwait() will search for the ``wait ID'' id in the wait
queue of the given event context; if an element with the given id is not
found, then the ``done'' queue of that context is searched. If found,
the queue element is removed from the appropriate list.
The function evDefer() causes a function (specified as func, with argument
uap) to be dispatched at some later time. Note that the tag argument
to func will always be NULL when dispatched.
The function evSelectFD() registers a file I/O event for the file
descriptor specified by fd. Bits in the eventmask argument are named
EV_READ, EV_WRITE, and EV_EXCEPT. At least one of these bits must be
specified. If the id argument is not equal to NULL, it will be used to
store a unique ``file event ID'' for this event, which is useful in subsequent
calls to evDeselectFD(). A file descriptor will be made nonblocking
using the O_NONBLOCK flag with fcntl(2) on its first concurrent
registration via evSelectFD(). An evSelectFD() remains in effect until
cancelled via evDeselectFD().
The function evDeselectFD() unregisters the ``file event'' specified by
the id argument. If the corresponding uap uniquely points to dynamic
memory, that memory should be freed before its handle is lost, since
after a call to evDeselectFD(), no handles to this event's uap will
remain within the event library. A file descriptor will be taken out of
nonblocking mode (see O_NONBLOCK and fcntl(2)) when its last event registration
is removed via evDeselectFD(), if it was in blocking mode before
the first registration via evSelectFD().
The function evConsIovec() is a constructor for a single struct iovec
structure, which is useful for evWrite() and evRead().
The functions evWrite() and evRead() start asynchronous stream I/O operations
on file descriptor fd. The data to be written or read is in the
scatter/gather descriptor specified by iov and cnt. The supplied function
func will be called with argument uap when the I/O operation is complete.
If id is not NULL, it will be filled a with the stream event
identifier suitable for use with evCancelRW().
The function evCancelRW() extinguishes an outstanding evWrite() or
evRead() call. System I/O calls cannot always be cancelled, but you are
guaranteed that the func function supplied to evWrite() or evRead() will
not be called after a call to evCancelRW(). Care should be taken not to
deallocate or otherwise reuse the space pointed to by the segment
descriptors in iov unless the underlying file descriptor is closed first.
The function evTimeRW() sets the stream associated with the given stream
ID ``id'' to have the idle timer associated with the timer ID ``timer''.
The function evUntimeRW() says that the stream associated with the given
stream ID ``id'' should ignore its idle timer, if present.
The functions evListen(), evConnect(), and evCancelConn() can be used to
manage asynchronous incoming and outgoing socket connections. Sockets to
be used with these functions should first be created with socket(2) and
given a local name with bind(2). It is extremely unlikely that the same
socket will ever be useful for both incoming and outgoing connections.
The id argument to evListen() and evConnect() is either NULL or the
address of a evFileID variable which can then be used in a subsequent
call to evCancelConn().
After a call to evListen(), each incoming connection arriving on fd will
cause func to be called with uap as one of its arguments. evConnect()
initiates an outgoing connection on fd to destination address ra (whose
length is ralen). When the connection is complete, func will be called
with uap as one of its arguments. The argument fd to (*func)() will be
-1 if an error occurred that prevented this connection from completing
successfully. In this case errno() will have been set and the socket
described by fd will have been closed. The evCancelConn() function will
prevent delivery of all pending and subsequent events for the outstanding
connection. The evHold() function will suspend the acceptance of new
connections on the listener specified by id. Connections will be queued
by the protocol stack up to the system's limit. The evUnhold() function
will reverse the effects of evHold(), allowing incoming connections to be
delivered for listener id. The evTryAccept() function will poll the listener
specified by id, accepting a new connection if one is available,
and queuing a connection event for later retrieval by 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 evTryAccept() will be delivered by evGetNext() before a new select is
done on the listener.
The function evSetDebug() sets the debugging level and diagnostic 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.
The function evPrintf() prints a message with the format ``fmt'' and the
following arguments (if any), on the output stream associated with the
event context pointed to by ctx. The message is output if the event context's
debug level is greater than or equal to the indicated level.
The function evInitID() will initialize an opaque ``evConn ID'', ``evFile
ID'', ``evStream ID'', ``evTimer ID'', ``evWait ID'', ``evContext'', or
``evEvent'', which is passed by reference.
The function evTestID() will examine an opaque ID and return ``TRUE''
only if it is not in its initialized state.
All the functions whose return type is ``int'' use the standard convention
of returning zero (0) to indicate success, or returning ``-1'' and
setting errno to indicate failure.
heap.h, which is in the src/lib/isc directory of the current BIND distribution.
The possible values for errno when one of the ``int'' functions in this
library returns ``-1'' include those of the Standard C Library and also:
[EINVAL] Some function argument has an unreasonable value.
[EINVAL] The specified file descriptor has an integer value greater
than the default FD_SETSIZE, meaning that the application's
limit is higher than the library's.
[ENOENT] The specified ``event ID'' does not exist.
[EWOULDBLOCK] No events have occurred and the EV_POLL option was specified.
[EBADF] The specified signal was unblocked outside the library.
gettimeofday(2), select(2), fcntl(3), malloc(3), named(8), readv(3),
This huge man page needs to be broken up into a handful of smaller ones.
The 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.
4th Berkeley Distribution March 6, 1996 4th Berkeley Distribution
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