1 :mod:`select` --- Waiting for I/O completion 2 ============================================ 3 4 .. module:: select 5 :synopsis: Wait for I/O completion on multiple streams. 6 7 -------------- 8 9 This module provides access to the :c:func:`select` and :c:func:`poll` functions 10 available in most operating systems, :c:func:`devpoll` available on 11 Solaris and derivatives, :c:func:`epoll` available on Linux 2.5+ and 12 :c:func:`kqueue` available on most BSD. 13 Note that on Windows, it only works for sockets; on other operating systems, 14 it also works for other file types (in particular, on Unix, it works on pipes). 15 It cannot be used on regular files to determine whether a file has grown since 16 it was last read. 17 18 .. note:: 19 20 The :mod:`selectors` module allows high-level and efficient I/O 21 multiplexing, built upon the :mod:`select` module primitives. Users are 22 encouraged to use the :mod:`selectors` module instead, unless they want 23 precise control over the OS-level primitives used. 24 25 26 The module defines the following: 27 28 29 .. exception:: error 30 31 A deprecated alias of :exc:`OSError`. 32 33 .. versionchanged:: 3.3 34 Following :pep:`3151`, this class was made an alias of :exc:`OSError`. 35 36 37 .. function:: devpoll() 38 39 (Only supported on Solaris and derivatives.) Returns a ``/dev/poll`` 40 polling object; see section :ref:`devpoll-objects` below for the 41 methods supported by devpoll objects. 42 43 :c:func:`devpoll` objects are linked to the number of file 44 descriptors allowed at the time of instantiation. If your program 45 reduces this value, :c:func:`devpoll` will fail. If your program 46 increases this value, :c:func:`devpoll` may return an 47 incomplete list of active file descriptors. 48 49 The new file descriptor is :ref:`non-inheritable <fd_inheritance>`. 50 51 .. versionadded:: 3.3 52 53 .. versionchanged:: 3.4 54 The new file descriptor is now non-inheritable. 55 56 .. function:: epoll(sizehint=-1, flags=0) 57 58 (Only supported on Linux 2.5.44 and newer.) Return an edge polling object, 59 which can be used as Edge or Level Triggered interface for I/O 60 events. 61 62 *sizehint* informs epoll about the expected number of events to be 63 registered. It must be positive, or `-1` to use the default. It is only 64 used on older systems where :c:func:`epoll_create1` is not available; 65 otherwise it has no effect (though its value is still checked). 66 67 *flags* is deprecated and completely ignored. However, when supplied, its 68 value must be ``0`` or ``select.EPOLL_CLOEXEC``, otherwise ``OSError`` is 69 raised. 70 71 See the :ref:`epoll-objects` section below for the methods supported by 72 epolling objects. 73 74 ``epoll`` objects support the context management protocol: when used in a 75 :keyword:`with` statement, the new file descriptor is automatically closed 76 at the end of the block. 77 78 The new file descriptor is :ref:`non-inheritable <fd_inheritance>`. 79 80 .. versionchanged:: 3.3 81 Added the *flags* parameter. 82 83 .. versionchanged:: 3.4 84 Support for the :keyword:`with` statement was added. 85 The new file descriptor is now non-inheritable. 86 87 .. deprecated:: 3.4 88 The *flags* parameter. ``select.EPOLL_CLOEXEC`` is used by default now. 89 Use :func:`os.set_inheritable` to make the file descriptor inheritable. 90 91 92 .. function:: poll() 93 94 (Not supported by all operating systems.) Returns a polling object, which 95 supports registering and unregistering file descriptors, and then polling them 96 for I/O events; see section :ref:`poll-objects` below for the methods supported 97 by polling objects. 98 99 100 .. function:: kqueue() 101 102 (Only supported on BSD.) Returns a kernel queue object; see section 103 :ref:`kqueue-objects` below for the methods supported by kqueue objects. 104 105 The new file descriptor is :ref:`non-inheritable <fd_inheritance>`. 106 107 .. versionchanged:: 3.4 108 The new file descriptor is now non-inheritable. 109 110 111 .. function:: kevent(ident, filter=KQ_FILTER_READ, flags=KQ_EV_ADD, fflags=0, data=0, udata=0) 112 113 (Only supported on BSD.) Returns a kernel event object; see section 114 :ref:`kevent-objects` below for the methods supported by kevent objects. 115 116 117 .. function:: select(rlist, wlist, xlist[, timeout]) 118 119 This is a straightforward interface to the Unix :c:func:`select` system call. 120 The first three arguments are sequences of 'waitable objects': either 121 integers representing file descriptors or objects with a parameterless method 122 named :meth:`~io.IOBase.fileno` returning such an integer: 123 124 * *rlist*: wait until ready for reading 125 * *wlist*: wait until ready for writing 126 * *xlist*: wait for an "exceptional condition" (see the manual page for what 127 your system considers such a condition) 128 129 Empty sequences are allowed, but acceptance of three empty sequences is 130 platform-dependent. (It is known to work on Unix but not on Windows.) The 131 optional *timeout* argument specifies a time-out as a floating point number 132 in seconds. When the *timeout* argument is omitted the function blocks until 133 at least one file descriptor is ready. A time-out value of zero specifies a 134 poll and never blocks. 135 136 The return value is a triple of lists of objects that are ready: subsets of the 137 first three arguments. When the time-out is reached without a file descriptor 138 becoming ready, three empty lists are returned. 139 140 .. index:: 141 single: socket() (in module socket) 142 single: popen() (in module os) 143 144 Among the acceptable object types in the sequences are Python :term:`file 145 objects <file object>` (e.g. ``sys.stdin``, or objects returned by 146 :func:`open` or :func:`os.popen`), socket objects returned by 147 :func:`socket.socket`. You may also define a :dfn:`wrapper` class yourself, 148 as long as it has an appropriate :meth:`~io.IOBase.fileno` method (that 149 really returns a file descriptor, not just a random integer). 150 151 .. note:: 152 153 .. index:: single: WinSock 154 155 File objects on Windows are not acceptable, but sockets are. On Windows, 156 the underlying :c:func:`select` function is provided by the WinSock 157 library, and does not handle file descriptors that don't originate from 158 WinSock. 159 160 .. versionchanged:: 3.5 161 The function is now retried with a recomputed timeout when interrupted by 162 a signal, except if the signal handler raises an exception (see 163 :pep:`475` for the rationale), instead of raising 164 :exc:`InterruptedError`. 165 166 167 .. attribute:: PIPE_BUF 168 169 The minimum number of bytes which can be written without blocking to a pipe 170 when the pipe has been reported as ready for writing by :func:`~select.select`, 171 :func:`poll` or another interface in this module. This doesn't apply 172 to other kind of file-like objects such as sockets. 173 174 This value is guaranteed by POSIX to be at least 512. 175 176 .. availability:: Unix 177 178 .. versionadded:: 3.2 179 180 181 .. _devpoll-objects: 182 183 ``/dev/poll`` Polling Objects 184 ----------------------------- 185 186 Solaris and derivatives have ``/dev/poll``. While :c:func:`select` is 187 O(highest file descriptor) and :c:func:`poll` is O(number of file 188 descriptors), ``/dev/poll`` is O(active file descriptors). 189 190 ``/dev/poll`` behaviour is very close to the standard :c:func:`poll` 191 object. 192 193 194 .. method:: devpoll.close() 195 196 Close the file descriptor of the polling object. 197 198 .. versionadded:: 3.4 199 200 201 .. attribute:: devpoll.closed 202 203 ``True`` if the polling object is closed. 204 205 .. versionadded:: 3.4 206 207 208 .. method:: devpoll.fileno() 209 210 Return the file descriptor number of the polling object. 211 212 .. versionadded:: 3.4 213 214 215 .. method:: devpoll.register(fd[, eventmask]) 216 217 Register a file descriptor with the polling object. Future calls to the 218 :meth:`poll` method will then check whether the file descriptor has any 219 pending I/O events. *fd* can be either an integer, or an object with a 220 :meth:`~io.IOBase.fileno` method that returns an integer. File objects 221 implement :meth:`!fileno`, so they can also be used as the argument. 222 223 *eventmask* is an optional bitmask describing the type of events you want to 224 check for. The constants are the same that with :c:func:`poll` 225 object. The default value is a combination of the constants :const:`POLLIN`, 226 :const:`POLLPRI`, and :const:`POLLOUT`. 227 228 .. warning:: 229 230 Registering a file descriptor that's already registered is not an 231 error, but the result is undefined. The appropriate action is to 232 unregister or modify it first. This is an important difference 233 compared with :c:func:`poll`. 234 235 236 .. method:: devpoll.modify(fd[, eventmask]) 237 238 This method does an :meth:`unregister` followed by a 239 :meth:`register`. It is (a bit) more efficient that doing the same 240 explicitly. 241 242 243 .. method:: devpoll.unregister(fd) 244 245 Remove a file descriptor being tracked by a polling object. Just like the 246 :meth:`register` method, *fd* can be an integer or an object with a 247 :meth:`~io.IOBase.fileno` method that returns an integer. 248 249 Attempting to remove a file descriptor that was never registered is 250 safely ignored. 251 252 253 .. method:: devpoll.poll([timeout]) 254 255 Polls the set of registered file descriptors, and returns a possibly-empty list 256 containing ``(fd, event)`` 2-tuples for the descriptors that have events or 257 errors to report. *fd* is the file descriptor, and *event* is a bitmask with 258 bits set for the reported events for that descriptor --- :const:`POLLIN` for 259 waiting input, :const:`POLLOUT` to indicate that the descriptor can be written 260 to, and so forth. An empty list indicates that the call timed out and no file 261 descriptors had any events to report. If *timeout* is given, it specifies the 262 length of time in milliseconds which the system will wait for events before 263 returning. If *timeout* is omitted, -1, or :const:`None`, the call will 264 block until there is an event for this poll object. 265 266 .. versionchanged:: 3.5 267 The function is now retried with a recomputed timeout when interrupted by 268 a signal, except if the signal handler raises an exception (see 269 :pep:`475` for the rationale), instead of raising 270 :exc:`InterruptedError`. 271 272 273 .. _epoll-objects: 274 275 Edge and Level Trigger Polling (epoll) Objects 276 ---------------------------------------------- 277 278 https://linux.die.net/man/4/epoll 279 280 *eventmask* 281 282 +-------------------------+-----------------------------------------------+ 283 | Constant | Meaning | 284 +=========================+===============================================+ 285 | :const:`EPOLLIN` | Available for read | 286 +-------------------------+-----------------------------------------------+ 287 | :const:`EPOLLOUT` | Available for write | 288 +-------------------------+-----------------------------------------------+ 289 | :const:`EPOLLPRI` | Urgent data for read | 290 +-------------------------+-----------------------------------------------+ 291 | :const:`EPOLLERR` | Error condition happened on the assoc. fd | 292 +-------------------------+-----------------------------------------------+ 293 | :const:`EPOLLHUP` | Hang up happened on the assoc. fd | 294 +-------------------------+-----------------------------------------------+ 295 | :const:`EPOLLET` | Set Edge Trigger behavior, the default is | 296 | | Level Trigger behavior | 297 +-------------------------+-----------------------------------------------+ 298 | :const:`EPOLLONESHOT` | Set one-shot behavior. After one event is | 299 | | pulled out, the fd is internally disabled | 300 +-------------------------+-----------------------------------------------+ 301 | :const:`EPOLLEXCLUSIVE` | Wake only one epoll object when the | 302 | | associated fd has an event. The default (if | 303 | | this flag is not set) is to wake all epoll | 304 | | objects polling on a fd. | 305 +-------------------------+-----------------------------------------------+ 306 | :const:`EPOLLRDHUP` | Stream socket peer closed connection or shut | 307 | | down writing half of connection. | 308 +-------------------------+-----------------------------------------------+ 309 | :const:`EPOLLRDNORM` | Equivalent to :const:`EPOLLIN` | 310 +-------------------------+-----------------------------------------------+ 311 | :const:`EPOLLRDBAND` | Priority data band can be read. | 312 +-------------------------+-----------------------------------------------+ 313 | :const:`EPOLLWRNORM` | Equivalent to :const:`EPOLLOUT` | 314 +-------------------------+-----------------------------------------------+ 315 | :const:`EPOLLWRBAND` | Priority data may be written. | 316 +-------------------------+-----------------------------------------------+ 317 | :const:`EPOLLMSG` | Ignored. | 318 +-------------------------+-----------------------------------------------+ 319 320 .. versionadded:: 3.6 321 :const:`EPOLLEXCLUSIVE` was added. It's only supported by Linux Kernel 4.5 322 or later. 323 324 .. method:: epoll.close() 325 326 Close the control file descriptor of the epoll object. 327 328 329 .. attribute:: epoll.closed 330 331 ``True`` if the epoll object is closed. 332 333 334 .. method:: epoll.fileno() 335 336 Return the file descriptor number of the control fd. 337 338 339 .. method:: epoll.fromfd(fd) 340 341 Create an epoll object from a given file descriptor. 342 343 344 .. method:: epoll.register(fd[, eventmask]) 345 346 Register a fd descriptor with the epoll object. 347 348 349 .. method:: epoll.modify(fd, eventmask) 350 351 Modify a registered file descriptor. 352 353 354 .. method:: epoll.unregister(fd) 355 356 Remove a registered file descriptor from the epoll object. 357 358 359 .. method:: epoll.poll(timeout=-1, maxevents=-1) 360 361 Wait for events. timeout in seconds (float) 362 363 .. versionchanged:: 3.5 364 The function is now retried with a recomputed timeout when interrupted by 365 a signal, except if the signal handler raises an exception (see 366 :pep:`475` for the rationale), instead of raising 367 :exc:`InterruptedError`. 368 369 370 .. _poll-objects: 371 372 Polling Objects 373 --------------- 374 375 The :c:func:`poll` system call, supported on most Unix systems, provides better 376 scalability for network servers that service many, many clients at the same 377 time. :c:func:`poll` scales better because the system call only requires listing 378 the file descriptors of interest, while :c:func:`select` builds a bitmap, turns 379 on bits for the fds of interest, and then afterward the whole bitmap has to be 380 linearly scanned again. :c:func:`select` is O(highest file descriptor), while 381 :c:func:`poll` is O(number of file descriptors). 382 383 384 .. method:: poll.register(fd[, eventmask]) 385 386 Register a file descriptor with the polling object. Future calls to the 387 :meth:`poll` method will then check whether the file descriptor has any 388 pending I/O events. *fd* can be either an integer, or an object with a 389 :meth:`~io.IOBase.fileno` method that returns an integer. File objects 390 implement :meth:`!fileno`, so they can also be used as the argument. 391 392 *eventmask* is an optional bitmask describing the type of events you want to 393 check for, and can be a combination of the constants :const:`POLLIN`, 394 :const:`POLLPRI`, and :const:`POLLOUT`, described in the table below. If not 395 specified, the default value used will check for all 3 types of events. 396 397 +-------------------+------------------------------------------+ 398 | Constant | Meaning | 399 +===================+==========================================+ 400 | :const:`POLLIN` | There is data to read | 401 +-------------------+------------------------------------------+ 402 | :const:`POLLPRI` | There is urgent data to read | 403 +-------------------+------------------------------------------+ 404 | :const:`POLLOUT` | Ready for output: writing will not block | 405 +-------------------+------------------------------------------+ 406 | :const:`POLLERR` | Error condition of some sort | 407 +-------------------+------------------------------------------+ 408 | :const:`POLLHUP` | Hung up | 409 +-------------------+------------------------------------------+ 410 | :const:`POLLRDHUP`| Stream socket peer closed connection, or | 411 | | shut down writing half of connection | 412 +-------------------+------------------------------------------+ 413 | :const:`POLLNVAL` | Invalid request: descriptor not open | 414 +-------------------+------------------------------------------+ 415 416 Registering a file descriptor that's already registered is not an error, and has 417 the same effect as registering the descriptor exactly once. 418 419 420 .. method:: poll.modify(fd, eventmask) 421 422 Modifies an already registered fd. This has the same effect as 423 ``register(fd, eventmask)``. Attempting to modify a file descriptor 424 that was never registered causes an :exc:`OSError` exception with errno 425 :const:`ENOENT` to be raised. 426 427 428 .. method:: poll.unregister(fd) 429 430 Remove a file descriptor being tracked by a polling object. Just like the 431 :meth:`register` method, *fd* can be an integer or an object with a 432 :meth:`~io.IOBase.fileno` method that returns an integer. 433 434 Attempting to remove a file descriptor that was never registered causes a 435 :exc:`KeyError` exception to be raised. 436 437 438 .. method:: poll.poll([timeout]) 439 440 Polls the set of registered file descriptors, and returns a possibly-empty list 441 containing ``(fd, event)`` 2-tuples for the descriptors that have events or 442 errors to report. *fd* is the file descriptor, and *event* is a bitmask with 443 bits set for the reported events for that descriptor --- :const:`POLLIN` for 444 waiting input, :const:`POLLOUT` to indicate that the descriptor can be written 445 to, and so forth. An empty list indicates that the call timed out and no file 446 descriptors had any events to report. If *timeout* is given, it specifies the 447 length of time in milliseconds which the system will wait for events before 448 returning. If *timeout* is omitted, negative, or :const:`None`, the call will 449 block until there is an event for this poll object. 450 451 .. versionchanged:: 3.5 452 The function is now retried with a recomputed timeout when interrupted by 453 a signal, except if the signal handler raises an exception (see 454 :pep:`475` for the rationale), instead of raising 455 :exc:`InterruptedError`. 456 457 458 .. _kqueue-objects: 459 460 Kqueue Objects 461 -------------- 462 463 .. method:: kqueue.close() 464 465 Close the control file descriptor of the kqueue object. 466 467 468 .. attribute:: kqueue.closed 469 470 ``True`` if the kqueue object is closed. 471 472 473 .. method:: kqueue.fileno() 474 475 Return the file descriptor number of the control fd. 476 477 478 .. method:: kqueue.fromfd(fd) 479 480 Create a kqueue object from a given file descriptor. 481 482 483 .. method:: kqueue.control(changelist, max_events[, timeout=None]) -> eventlist 484 485 Low level interface to kevent 486 487 - changelist must be an iterable of kevent object or ``None`` 488 - max_events must be 0 or a positive integer 489 - timeout in seconds (floats possible) 490 491 .. versionchanged:: 3.5 492 The function is now retried with a recomputed timeout when interrupted by 493 a signal, except if the signal handler raises an exception (see 494 :pep:`475` for the rationale), instead of raising 495 :exc:`InterruptedError`. 496 497 498 .. _kevent-objects: 499 500 Kevent Objects 501 -------------- 502 503 https://www.freebsd.org/cgi/man.cgi?query=kqueue&sektion=2 504 505 .. attribute:: kevent.ident 506 507 Value used to identify the event. The interpretation depends on the filter 508 but it's usually the file descriptor. In the constructor ident can either 509 be an int or an object with a :meth:`~io.IOBase.fileno` method. kevent 510 stores the integer internally. 511 512 .. attribute:: kevent.filter 513 514 Name of the kernel filter. 515 516 +---------------------------+---------------------------------------------+ 517 | Constant | Meaning | 518 +===========================+=============================================+ 519 | :const:`KQ_FILTER_READ` | Takes a descriptor and returns whenever | 520 | | there is data available to read | 521 +---------------------------+---------------------------------------------+ 522 | :const:`KQ_FILTER_WRITE` | Takes a descriptor and returns whenever | 523 | | there is data available to write | 524 +---------------------------+---------------------------------------------+ 525 | :const:`KQ_FILTER_AIO` | AIO requests | 526 +---------------------------+---------------------------------------------+ 527 | :const:`KQ_FILTER_VNODE` | Returns when one or more of the requested | 528 | | events watched in *fflag* occurs | 529 +---------------------------+---------------------------------------------+ 530 | :const:`KQ_FILTER_PROC` | Watch for events on a process id | 531 +---------------------------+---------------------------------------------+ 532 | :const:`KQ_FILTER_NETDEV` | Watch for events on a network device | 533 | | [not available on Mac OS X] | 534 +---------------------------+---------------------------------------------+ 535 | :const:`KQ_FILTER_SIGNAL` | Returns whenever the watched signal is | 536 | | delivered to the process | 537 +---------------------------+---------------------------------------------+ 538 | :const:`KQ_FILTER_TIMER` | Establishes an arbitrary timer | 539 +---------------------------+---------------------------------------------+ 540 541 .. attribute:: kevent.flags 542 543 Filter action. 544 545 +---------------------------+---------------------------------------------+ 546 | Constant | Meaning | 547 +===========================+=============================================+ 548 | :const:`KQ_EV_ADD` | Adds or modifies an event | 549 +---------------------------+---------------------------------------------+ 550 | :const:`KQ_EV_DELETE` | Removes an event from the queue | 551 +---------------------------+---------------------------------------------+ 552 | :const:`KQ_EV_ENABLE` | Permitscontrol() to returns the event | 553 +---------------------------+---------------------------------------------+ 554 | :const:`KQ_EV_DISABLE` | Disablesevent | 555 +---------------------------+---------------------------------------------+ 556 | :const:`KQ_EV_ONESHOT` | Removes event after first occurrence | 557 +---------------------------+---------------------------------------------+ 558 | :const:`KQ_EV_CLEAR` | Reset the state after an event is retrieved | 559 +---------------------------+---------------------------------------------+ 560 | :const:`KQ_EV_SYSFLAGS` | internal event | 561 +---------------------------+---------------------------------------------+ 562 | :const:`KQ_EV_FLAG1` | internal event | 563 +---------------------------+---------------------------------------------+ 564 | :const:`KQ_EV_EOF` | Filter specific EOF condition | 565 +---------------------------+---------------------------------------------+ 566 | :const:`KQ_EV_ERROR` | See return values | 567 +---------------------------+---------------------------------------------+ 568 569 570 .. attribute:: kevent.fflags 571 572 Filter specific flags. 573 574 :const:`KQ_FILTER_READ` and :const:`KQ_FILTER_WRITE` filter flags: 575 576 +----------------------------+--------------------------------------------+ 577 | Constant | Meaning | 578 +============================+============================================+ 579 | :const:`KQ_NOTE_LOWAT` | low water mark of a socket buffer | 580 +----------------------------+--------------------------------------------+ 581 582 :const:`KQ_FILTER_VNODE` filter flags: 583 584 +----------------------------+--------------------------------------------+ 585 | Constant | Meaning | 586 +============================+============================================+ 587 | :const:`KQ_NOTE_DELETE` | *unlink()* was called | 588 +----------------------------+--------------------------------------------+ 589 | :const:`KQ_NOTE_WRITE` | a write occurred | 590 +----------------------------+--------------------------------------------+ 591 | :const:`KQ_NOTE_EXTEND` | the file was extended | 592 +----------------------------+--------------------------------------------+ 593 | :const:`KQ_NOTE_ATTRIB` | an attribute was changed | 594 +----------------------------+--------------------------------------------+ 595 | :const:`KQ_NOTE_LINK` | the link count has changed | 596 +----------------------------+--------------------------------------------+ 597 | :const:`KQ_NOTE_RENAME` | the file was renamed | 598 +----------------------------+--------------------------------------------+ 599 | :const:`KQ_NOTE_REVOKE` | access to the file was revoked | 600 +----------------------------+--------------------------------------------+ 601 602 :const:`KQ_FILTER_PROC` filter flags: 603 604 +----------------------------+--------------------------------------------+ 605 | Constant | Meaning | 606 +============================+============================================+ 607 | :const:`KQ_NOTE_EXIT` | the process has exited | 608 +----------------------------+--------------------------------------------+ 609 | :const:`KQ_NOTE_FORK` | the process has called *fork()* | 610 +----------------------------+--------------------------------------------+ 611 | :const:`KQ_NOTE_EXEC` | the process has executed a new process | 612 +----------------------------+--------------------------------------------+ 613 | :const:`KQ_NOTE_PCTRLMASK` | internal filter flag | 614 +----------------------------+--------------------------------------------+ 615 | :const:`KQ_NOTE_PDATAMASK` | internal filter flag | 616 +----------------------------+--------------------------------------------+ 617 | :const:`KQ_NOTE_TRACK` | follow a process across *fork()* | 618 +----------------------------+--------------------------------------------+ 619 | :const:`KQ_NOTE_CHILD` | returned on the child process for | 620 | | *NOTE_TRACK* | 621 +----------------------------+--------------------------------------------+ 622 | :const:`KQ_NOTE_TRACKERR` | unable to attach to a child | 623 +----------------------------+--------------------------------------------+ 624 625 :const:`KQ_FILTER_NETDEV` filter flags (not available on Mac OS X): 626 627 +----------------------------+--------------------------------------------+ 628 | Constant | Meaning | 629 +============================+============================================+ 630 | :const:`KQ_NOTE_LINKUP` | link is up | 631 +----------------------------+--------------------------------------------+ 632 | :const:`KQ_NOTE_LINKDOWN` | link is down | 633 +----------------------------+--------------------------------------------+ 634 | :const:`KQ_NOTE_LINKINV` | link state is invalid | 635 +----------------------------+--------------------------------------------+ 636 637 638 .. attribute:: kevent.data 639 640 Filter specific data. 641 642 643 .. attribute:: kevent.udata 644 645 User defined value. 646
