select
/dev/poll
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此模块提供访问 select() and poll() 函数可用于大多数操作系统， devpoll() 可用于 Solaris 及衍生， epoll() 可用于 Linux 2.5+ 和 kqueue() available on most BSD. Note that on Windows, it only works for sockets; on other operating systems, it also works for other file types (in particular, on Unix, it works on pipes). It cannot be used on regular files to determine whether a file has grown since it was last read.
select()
poll()
devpoll()
epoll()
kqueue()
注意
The selectors module allows high-level and efficient I/O multiplexing, built upon the select module primitives. Users are encouraged to use the selectors module instead, unless they want precise control over the OS-level primitives used.
selectors
可用性 ：非 Emscripten，非 WASI。
本模块不工作 (或不可用) 于 WebAssembly 平台 wasm32-emscripten and wasm32-wasi 。见 WebAssembly 平台 了解更多信息。
wasm32-emscripten
wasm32-wasi
模块定义如下：
被弃用别名化的 OSError .
OSError
3.3 版改变： 遵循 PEP 3151 ，此类是别名化的 OSError .
(Only supported on Solaris and derivatives.) Returns a /dev/poll polling object; see section /dev/poll Polling Objects below for the methods supported by devpoll objects.
devpoll() objects are linked to the number of file descriptors allowed at the time of instantiation. If your program reduces this value, devpoll() will fail. If your program increases this value, devpoll() may return an incomplete list of active file descriptors.
新文件描述符 不可继承 .
Added in version 3.3.
3.4 版改变： 现在，新文件描述符不可继承。
(Only supported on Linux 2.5.44 and newer.) Return an edge polling object, which can be used as Edge or Level Triggered interface for I/O events.
sizehint informs epoll about the expected number of events to be registered. It must be positive, or -1 to use the default. It is only used on older systems where epoll_create1() is not available; otherwise it has no effect (though its value is still checked).
-1
epoll_create1()
flags is deprecated and completely ignored. However, when supplied, its value must be 0 or select.EPOLL_CLOEXEC ，否则 OSError 被引发。
0
select.EPOLL_CLOEXEC
见 Edge and Level Trigger Polling (epoll) Objects section below for the methods supported by epolling objects.
epoll objects support the context management protocol: when used in a with statement, the new file descriptor is automatically closed at the end of the block.
epoll
with
3.3 版改变： 添加 flags 参数。
3.4 版改变： 支持 with statement was added. The new file descriptor is now non-inheritable.
从 3.4 版起弃用： The flags 参数。 select.EPOLL_CLOEXEC is used by default now. Use os.set_inheritable() to make the file descriptor inheritable.
os.set_inheritable()
(Not supported by all operating systems.) Returns a polling object, which supports registering and unregistering file descriptors, and then polling them for I/O events; see section 轮询对象 below for the methods supported by polling objects.
(Only supported on BSD.) Returns a kernel queue object; see section Kqueue 对象 below for the methods supported by kqueue objects.
(Only supported on BSD.) Returns a kernel event object; see section Kevent 对象 below for the methods supported by kevent objects.
This is a straightforward interface to the Unix select() system call. The first three arguments are iterables of ‘waitable objects’: either integers representing file descriptors or objects with a parameterless method named fileno() returning such an integer:
fileno()
rlist ：等待直到读取就绪
wlist ：等待直到写入就绪
xlist : wait for an “exceptional condition” (see the manual page for what your system considers such a condition)
Empty iterables are allowed, but acceptance of three empty iterables is platform-dependent. (It is known to work on Unix but not on Windows.) The optional timeout argument specifies a time-out as a floating point number in seconds. When the timeout argument is omitted the function blocks until at least one file descriptor is ready. A time-out value of zero specifies a poll and never blocks.
The return value is a triple of lists of objects that are ready: subsets of the first three arguments. When the time-out is reached without a file descriptor becoming ready, three empty lists are returned.
Among the acceptable object types in the iterables are Python 文件对象 (如 sys.stdin , or objects returned by open() or os.popen() ), socket objects returned by socket.socket() . You may also define a wrapper class yourself, as long as it has an appropriate fileno() method (that really returns a file descriptor, not just a random integer).
sys.stdin
open()
os.popen()
socket.socket()
File objects on Windows are not acceptable, but sockets are. On Windows, the underlying select() function is provided by the WinSock library, and does not handle file descriptors that don’t originate from WinSock.
3.5 版改变： The function is now retried with a recomputed timeout when interrupted by a signal, except if the signal handler raises an exception (see PEP 475 for the rationale), instead of raising InterruptedError .
InterruptedError
The minimum number of bytes which can be written without blocking to a pipe when the pipe has been reported as ready for writing by select() , poll() or another interface in this module. This doesn’t apply to other kind of file-like objects such as sockets.
This value is guaranteed by POSIX to be at least 512.
可用性 : Unix
Added in version 3.2.
Solaris 及衍生拥有 /dev/poll . While select() is O ( highest file descriptor ) 和 poll() is O ( number of file descriptors ), /dev/poll is O ( active file descriptors ).
/dev/poll behaviour is very close to the standard poll() 对象。
Close the file descriptor of the polling object.
Added in version 3.4.
True if the polling object is closed.
True
Return the file descriptor number of the polling object.
Register a file descriptor with the polling object. Future calls to the poll() method will then check whether the file descriptor has any pending I/O events. fd can be either an integer, or an object with a fileno() method that returns an integer. File objects implement fileno() , so they can also be used as the argument.
eventmask is an optional bitmask describing the type of events you want to check for. The constants are the same that with poll() object. The default value is a combination of the constants POLLIN , POLLPRI ，和 POLLOUT .
POLLIN
POLLPRI
POLLOUT
警告
Registering a file descriptor that’s already registered is not an error, but the result is undefined. The appropriate action is to unregister or modify it first. This is an important difference compared with poll() .
This method does an unregister() followed by a register() . It is (a bit) more efficient that doing the same explicitly.
unregister()
register()
Remove a file descriptor being tracked by a polling object. Just like the register() 方法， fd can be an integer or an object with a fileno() method that returns an integer.
Attempting to remove a file descriptor that was never registered is safely ignored.
Polls the set of registered file descriptors, and returns a possibly empty list containing (fd, event) 2-tuples for the descriptors that have events or errors to report. fd is the file descriptor, and event is a bitmask with bits set for the reported events for that descriptor — POLLIN for waiting input, POLLOUT to indicate that the descriptor can be written to, and so forth. An empty list indicates that the call timed out and no file descriptors had any events to report. If timeout is given, it specifies the length of time in milliseconds which the system will wait for events before returning. If timeout is omitted, -1, or None , the call will block until there is an event for this poll object.
(fd, event)
None
https://linux.die.net/man/4/epoll eventmask 常量 含义 EPOLLIN 可用于读取 EPOLLOUT 可用于写入 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 is Level Trigger behavior EPOLLONESHOT Set one-shot behavior. After one event is pulled out, the fd is internally disabled EPOLLEXCLUSIVE Wake only one epoll object when the associated fd has an event. The default (if this flag is not set) is to wake all epoll objects polling on a fd. EPOLLRDHUP Stream socket peer closed connection or shut down writing half of connection. EPOLLRDNORM 相当于 EPOLLIN EPOLLRDBAND Priority data band can be read. EPOLLWRNORM 相当于 EPOLLOUT EPOLLWRBAND Priority data may be written. EPOLLMSG Ignored. Added in version 3.6: EPOLLEXCLUSIVE was added. It’s only supported by Linux Kernel 4.5 or later.
https://linux.die.net/man/4/epoll
eventmask
常量
含义
EPOLLIN
EPOLLOUT
EPOLLPRI
EPOLLERR
EPOLLHUP
EPOLLET
Set Edge Trigger behavior, the default is Level Trigger behavior
EPOLLONESHOT
Set one-shot behavior. After one event is pulled out, the fd is internally disabled
EPOLLEXCLUSIVE
Wake only one epoll object when the associated fd has an event. The default (if this flag is not set) is to wake all epoll objects polling on a fd.
EPOLLRDHUP
Stream socket peer closed connection or shut down writing half of connection.
EPOLLRDNORM
相当于 EPOLLIN
EPOLLRDBAND
EPOLLWRNORM
相当于 EPOLLOUT
EPOLLWRBAND
EPOLLMSG
Added in version 3.6: EPOLLEXCLUSIVE was added. It’s only supported by Linux Kernel 4.5 or later.
Close the control file descriptor of the epoll object.
True if the epoll object is closed.
Return the file descriptor number of the control fd.
Create an epoll object from a given file descriptor.
Register a fd descriptor with the epoll object.
Modify a registered file descriptor.
Remove a registered file descriptor from the epoll object.
3.9 版改变： The method no longer ignores the EBADF 错误。
EBADF
Wait for events. timeout in seconds (float)
The poll() system call, supported on most Unix systems, provides better scalability for network servers that service many, many clients at the same time. poll() scales better because the system call only requires listing the file descriptors of interest, while select() builds a bitmap, turns on bits for the fds of interest, and then afterward the whole bitmap has to be linearly scanned again. select() is O ( highest file descriptor )，而 poll() is O ( number of file descriptors ).
eventmask is an optional bitmask describing the type of events you want to check for, and can be a combination of the constants POLLIN , POLLPRI ，和 POLLOUT , described in the table below. If not specified, the default value used will check for all 3 types of events.
POLLERR
POLLHUP
POLLRDHUP
Stream socket peer closed connection, or shut down writing half of connection
POLLNVAL
Registering a file descriptor that’s already registered is not an error, and has the same effect as registering the descriptor exactly once.
Modifies an already registered fd. This has the same effect as register(fd, eventmask) . Attempting to modify a file descriptor that was never registered causes an OSError exception with errno ENOENT 要被引发。
register(fd, eventmask)
ENOENT
Attempting to remove a file descriptor that was never registered causes a KeyError exception to be raised.
KeyError
Polls the set of registered file descriptors, and returns a possibly empty list containing (fd, event) 2-tuples for the descriptors that have events or errors to report. fd is the file descriptor, and event is a bitmask with bits set for the reported events for that descriptor — POLLIN for waiting input, POLLOUT to indicate that the descriptor can be written to, and so forth. An empty list indicates that the call timed out and no file descriptors had any events to report. If timeout is given, it specifies the length of time in milliseconds which the system will wait for events before returning. If timeout is omitted, negative, or None , the call will block until there is an event for this poll object.
Close the control file descriptor of the kqueue object.
True if the kqueue object is closed.
Create a kqueue object from a given file descriptor.
Low level interface to kevent
changelist must be an iterable of kevent objects or None
max_events must be 0 or a positive integer
timeout in seconds (floats possible); the default is None , to wait forever
https://man.freebsd.org/cgi/man.cgi?query=kqueue&sektion=2
Value used to identify the event. The interpretation depends on the filter but it’s usually the file descriptor. In the constructor ident can either be an int or an object with a fileno() method. kevent stores the integer internally.
Name of the kernel filter.
KQ_FILTER_READ
Takes a descriptor and returns whenever there is data available to read
KQ_FILTER_WRITE
Takes a descriptor and returns whenever there is data available to write
KQ_FILTER_AIO
KQ_FILTER_VNODE
Returns when one or more of the requested events watched in fflag occurs
KQ_FILTER_PROC
KQ_FILTER_NETDEV
Watch for events on a network device [not available on macOS]
KQ_FILTER_SIGNAL
Returns whenever the watched signal is delivered to the process
KQ_FILTER_TIMER
Filter action.
KQ_EV_ADD
KQ_EV_DELETE
KQ_EV_ENABLE
KQ_EV_DISABLE
KQ_EV_ONESHOT
KQ_EV_CLEAR
KQ_EV_SYSFLAGS
KQ_EV_FLAG1
KQ_EV_EOF
KQ_EV_ERROR
Filter specific flags.
KQ_FILTER_READ and KQ_FILTER_WRITE filter flags:
KQ_NOTE_LOWAT
KQ_FILTER_VNODE filter flags:
KQ_NOTE_DELETE
unlink() was called
KQ_NOTE_WRITE
KQ_NOTE_EXTEND
KQ_NOTE_ATTRIB
KQ_NOTE_LINK
KQ_NOTE_RENAME
KQ_NOTE_REVOKE
KQ_FILTER_PROC filter flags:
KQ_NOTE_EXIT
KQ_NOTE_FORK
the process has called fork()
KQ_NOTE_EXEC
KQ_NOTE_PCTRLMASK
KQ_NOTE_PDATAMASK
KQ_NOTE_TRACK
follow a process across fork()
KQ_NOTE_CHILD
returned on the child process for NOTE_TRACK
KQ_NOTE_TRACKERR
KQ_FILTER_NETDEV filter flags (not available on macOS):
KQ_NOTE_LINKUP
KQ_NOTE_LINKDOWN
KQ_NOTE_LINKINV
Filter specific data.
User defined value.
selectors — 高级 I/O 复用
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