/dev/poll Polling Objects¶

Solaris and derivatives have/dev/poll. Whileselect() isO(highest file descriptor) andpoll() isO(number of filedescriptors),/dev/poll isO(active file descriptors).

/dev/poll behaviour is very close to the standardpoll()object.

devpoll.close()¶

Close the file descriptor of the polling object.

Added in version 3.4.

devpoll.closed¶

True if the polling object is closed.

Added in version 3.4.

devpoll.fileno()¶

Return the file descriptor number of the polling object.

Added in version 3.4.

devpoll.register(fd[,eventmask])¶

Register a file descriptor with the polling object. Future calls to thepoll() method will then check whether the file descriptor has anypending I/O events.fd can be either an integer, or an object with afileno() method that returns an integer. File objectsimplementfileno(), so they can also be used as the argument.

eventmask is an optional bitmask describing the type of events you want tocheck for. The constants are the same that withpoll()object. The default value is a combination of the constantsPOLLIN,POLLPRI, andPOLLOUT.

Warning

Registering a file descriptor that’s already registered is not anerror, but the result is undefined. The appropriate action is tounregister or modify it first. This is an important differencecompared withpoll().

devpoll.modify(fd[,eventmask])¶

This method does anunregister() followed by aregister(). It is (a bit) more efficient that doing the sameexplicitly.

devpoll.unregister(fd)¶

Remove a file descriptor being tracked by a polling object. Just like theregister() method,fd can be an integer or an object with afileno() method that returns an integer.

Attempting to remove a file descriptor that was never registered issafely ignored.

devpoll.poll([timeout])¶

Polls the set of registered file descriptors, and returns a possibly empty listcontaining(fd,event) 2-tuples for the descriptors that have events orerrors to report.fd is the file descriptor, andevent is a bitmask withbits set for the reported events for that descriptor —POLLIN forwaiting input,POLLOUT to indicate that the descriptor can be writtento, and so forth. An empty list indicates that the call timed out and no filedescriptors had any events to report. Iftimeout is given, it specifies thelength of time in milliseconds which the system will wait for events beforereturning. Iftimeout is omitted, -1, orNone, the call willblock until there is an event for this poll object.

Changed in version 3.5:The function is now retried with a recomputed timeout when interrupted bya signal, except if the signal handler raises an exception (seePEP 475 for the rationale), instead of raisingInterruptedError.

Edge and Level Trigger Polling (epoll) Objects¶

https://linux.die.net/man/4/epoll

eventmask

Constant	Meaning
EPOLLIN	Available for read
EPOLLOUT	Available for write
EPOLLPRI	Urgent data for read
EPOLLERR	Error condition happened on the assoc. fd
EPOLLHUP	Hang up happened on the assoc. fd
EPOLLET	Set Edge Trigger behavior, the default isLevel Trigger behavior
EPOLLONESHOT	Set one-shot behavior. After one event ispulled out, the fd is internally disabled
EPOLLEXCLUSIVE	Wake only one epoll object when theassociated fd has an event. The default (ifthis flag is not set) is to wake all epollobjects polling on a fd.
EPOLLRDHUP	Stream socket peer closed connection or shutdown writing half of connection.
EPOLLRDNORM	Equivalent toEPOLLIN
EPOLLRDBAND	Priority data band can be read.
EPOLLWRNORM	Equivalent toEPOLLOUT
EPOLLWRBAND	Priority data may be written.
EPOLLMSG	Ignored.
EPOLLWAKEUP	Prevents sleep during event waiting.

Added in version 3.6:EPOLLEXCLUSIVE was added. It’s only supported by Linux Kernel 4.5or later.

Added in version 3.14:EPOLLWAKEUP was added. It’s only supported by Linux Kernel 3.5or later.

epoll.close()¶

Close the control file descriptor of the epoll object.

epoll.closed¶

True if the epoll object is closed.

epoll.fileno()¶

Return the file descriptor number of the control fd.

epoll.fromfd(fd)¶

Create an epoll object from a given file descriptor.

epoll.register(fd[,eventmask])¶

Register a fd descriptor with the epoll object.

epoll.modify(fd,eventmask)¶

Modify a registered file descriptor.

epoll.unregister(fd)¶

Remove a registered file descriptor from the epoll object.

Changed in version 3.9:The method no longer ignores theEBADF error.

epoll.poll(timeout=None,maxevents=-1)¶

Wait for events. timeout in seconds (float)

Changed in version 3.5:The function is now retried with a recomputed timeout when interrupted bya signal, except if the signal handler raises an exception (seePEP 475 for the rationale), instead of raisingInterruptedError.

Polling Objects¶

Thepoll() system call, supported on most Unix systems, provides betterscalability for network servers that service many, many clients at the sametime.poll() scales better because the system call only requires listingthe file descriptors of interest, whileselect() builds a bitmap, turnson bits for the fds of interest, and then afterward the whole bitmap has to belinearly scanned again.select() isO(highest file descriptor), whilepoll() isO(number of file descriptors).

poll.register(fd[,eventmask])¶

Register a file descriptor with the polling object. Future calls to thepoll() method will then check whether the file descriptor has anypending I/O events.fd can be either an integer, or an object with afileno() method that returns an integer. File objectsimplementfileno(), so they can also be used as the argument.

eventmask is an optional bitmask describing the type of events you want tocheck for, and can be a combination of the constantsPOLLIN,POLLPRI, andPOLLOUT, described in the table below. If notspecified, the default value used will check for all 3 types of events.

Constant	Meaning
POLLIN	There is data to read
POLLPRI	There is urgent data to read
POLLOUT	Ready for output: writing will not block
POLLERR	Error condition of some sort
POLLHUP	Hung up
POLLRDHUP	Stream socket peer closed connection, orshut down writing half of connection
POLLNVAL	Invalid request: descriptor not open

Registering a file descriptor that’s already registered is not an error, and hasthe same effect as registering the descriptor exactly once.

poll.modify(fd,eventmask)¶

Modifies an already registered fd. This has the same effect asregister(fd,eventmask). Attempting to modify a file descriptorthat was never registered causes anOSError exception with errnoENOENT to be raised.

poll.unregister(fd)¶

Remove a file descriptor being tracked by a polling object. Just like theregister() method,fd can be an integer or an object with afileno() method that returns an integer.

Attempting to remove a file descriptor that was never registered causes aKeyError exception to be raised.

poll.poll([timeout])¶

Polls the set of registered file descriptors, and returns a possibly empty listcontaining(fd,event) 2-tuples for the descriptors that have events orerrors to report.fd is the file descriptor, andevent is a bitmask withbits set for the reported events for that descriptor —POLLIN forwaiting input,POLLOUT to indicate that the descriptor can be writtento, and so forth. An empty list indicates that the call timed out and no filedescriptors had any events to report. Iftimeout is given, it specifies thelength of time in milliseconds which the system will wait for events beforereturning. Iftimeout is omitted, negative, orNone, the call willblock until there is an event for this poll object.

Changed in version 3.5:The function is now retried with a recomputed timeout when interrupted bya signal, except if the signal handler raises an exception (seePEP 475 for the rationale), instead of raisingInterruptedError.

Kqueue Objects¶

kqueue.close()¶

Close the control file descriptor of the kqueue object.

kqueue.closed¶

True if the kqueue object is closed.

kqueue.fileno()¶

Return the file descriptor number of the control fd.

kqueue.fromfd(fd)¶

Create a kqueue object from a given file descriptor.

kqueue.control(changelist,max_events[,timeout])→eventlist¶

Low level interface to kevent

• changelist must be an iterable of kevent objects orNone

• max_events must be 0 or a positive integer

• timeout in seconds (floats possible); the default isNone,to wait forever

Changed in version 3.5:The function is now retried with a recomputed timeout when interrupted bya signal, except if the signal handler raises an exception (seePEP 475 for the rationale), instead of raisingInterruptedError.

Kevent Objects¶

https://man.freebsd.org/cgi/man.cgi?query=kqueue&sektion=2

kevent.ident¶

Value used to identify the event. The interpretation depends on the filterbut it’s usually the file descriptor. In the constructor ident can eitherbe an int or an object with afileno() method. keventstores the integer internally.

kevent.filter¶

Name of the kernel filter.

Constant	Meaning
KQ_FILTER_READ	Takes a descriptor and returns wheneverthere is data available to read
KQ_FILTER_WRITE	Takes a descriptor and returns wheneverthere is data available to write
KQ_FILTER_AIO	AIO requests
KQ_FILTER_VNODE	Returns when one or more of the requestedevents watched infflag occurs
KQ_FILTER_PROC	Watch for events on a process id
KQ_FILTER_NETDEV	Watch for events on a network device[not available on macOS]
KQ_FILTER_SIGNAL	Returns whenever the watched signal isdelivered to the process
KQ_FILTER_TIMER	Establishes an arbitrary timer

kevent.flags¶

Filter action.

Constant	Meaning
KQ_EV_ADD	Adds or modifies an event
KQ_EV_DELETE	Removes an event from the queue
KQ_EV_ENABLE	Permitscontrol() to returns the event
KQ_EV_DISABLE	Disablesevent
KQ_EV_ONESHOT	Removes event after first occurrence
KQ_EV_CLEAR	Reset the state after an event is retrieved
KQ_EV_SYSFLAGS	internal event
KQ_EV_FLAG1	internal event
KQ_EV_EOF	Filter specific EOF condition
KQ_EV_ERROR	See return values

kevent.fflags¶

Filter specific flags.

KQ_FILTER_READ andKQ_FILTER_WRITE filter flags:

Constant	Meaning
KQ_NOTE_LOWAT	low water mark of a socket buffer

KQ_FILTER_VNODE filter flags:

Constant	Meaning
KQ_NOTE_DELETE	unlink() was called
KQ_NOTE_WRITE	a write occurred
KQ_NOTE_EXTEND	the file was extended
KQ_NOTE_ATTRIB	an attribute was changed
KQ_NOTE_LINK	the link count has changed
KQ_NOTE_RENAME	the file was renamed
KQ_NOTE_REVOKE	access to the file was revoked

KQ_FILTER_PROC filter flags:

Constant	Meaning
KQ_NOTE_EXIT	the process has exited
KQ_NOTE_FORK	the process has calledfork()
KQ_NOTE_EXEC	the process has executed a new process
KQ_NOTE_PCTRLMASK	internal filter flag
KQ_NOTE_PDATAMASK	internal filter flag
KQ_NOTE_TRACK	follow a process acrossfork()
KQ_NOTE_CHILD	returned on the child process forNOTE_TRACK
KQ_NOTE_TRACKERR	unable to attach to a child

KQ_FILTER_NETDEV filter flags (not available on macOS):

Constant	Meaning
KQ_NOTE_LINKUP	link is up
KQ_NOTE_LINKDOWN	link is down
KQ_NOTE_LINKINV	link state is invalid

kevent.data¶

Filter specific data.

kevent.udata¶

User defined value.