fcntl
—
fcntl
and
ioctl
系统调用
¶
本模块对文件描述符，履行文件控制和 I/O 控制。它接口到
fcntl()
and
ioctl()
Unix 例程。这些调用的完整描述，见
fcntl(2)
and
ioctl(2)
Unix 手册页。
本模块中的所有函数接受文件描述符
fd
作为其第 1 自变量。这可以是整数文件描述符，譬如返回通过
sys.stdin.fileno()
，或
io.IOBase
对象，譬如
sys.stdin
自身，其提供
fileno()
返回真正的文件描述符。
3.3 版改变：
使用此模块中的操作引发
IOError
它们现在引发
OSError
.
模块定义了下列函数：
fcntl.
fcntl
(
fd
,
cmd
,
arg=0
)
¶
履行操作
cmd
对于文件描述符
fd
(文件对象提供
fileno()
method are accepted as well). The values used for
cmd
are operating system dependent, and are available as constants in the
fcntl
module, using the same names as used in the relevant C header files. The argument
arg
can either be an integer value, or a
bytes
object. With an integer value, the return value of this function is the integer return value of the C
fcntl()
call. When the argument is bytes it represents a binary structure, e.g. created by
struct.pack()
. The binary data is copied to a buffer whose address is passed to the C
fcntl()
call. The return value after a successful call is the contents of the buffer, converted to a
bytes
object. The length of the returned object will be the same as the length of the
arg
argument. This is limited to 1024 bytes. If the information returned in the buffer by the operating system is larger than 1024 bytes, this is most likely to result in a segmentation violation or a more subtle data corruption.
若
fcntl()
失败，
OSError
被引发。
fcntl.
ioctl
(
fd
,
request
,
arg=0
,
mutate_flag=True
)
¶
此函数等同于
fcntl()
函数，除自变量处理甚至更复杂外。
The
request
parameter is limited to values that can fit in 32-bits. Additional constants of interest for use as the
request
argument can be found in the
termios
module, under the same names as used in the relevant C header files.
参数
arg
can be one of an integer, an object supporting the read-only buffer interface (like
bytes
) or an object supporting the read-write buffer interface (like
bytearray
).
In all but the last case, behaviour is as for the
fcntl()
函数。
If a mutable buffer is passed, then the behaviour is determined by the value of the mutate_flag 参数。
If it is false, the buffer’s mutability is ignored and behaviour is as for a read-only buffer, except that the 1024 byte limit mentioned above is avoided – so long as the buffer you pass is at least as long as what the operating system wants to put there, things should work.
若
mutate_flag
为 True (默认)，那么 (实际上) 会将缓冲传递给底层
ioctl()
system call, the latter’s return code is passed back to the calling Python, and the buffer’s new contents reflect the action of the
ioctl()
. This is a slight simplification, because if the supplied buffer is less than 1024 bytes long it is first copied into a static buffer 1024 bytes long which is then passed to
ioctl()
and copied back into the supplied buffer.
若
ioctl()
失败，
OSError
异常被引发。
范例：
>>> import array, fcntl, struct, termios, os >>> os.getpgrp() 13341 >>> struct.unpack('h', fcntl.ioctl(0, termios.TIOCGPGRP, " "))[0] 13341 >>> buf = array.array('h', [0]) >>> fcntl.ioctl(0, termios.TIOCGPGRP, buf, 1) 0 >>> buf array('h', [13341])
fcntl.
flock
(
fd
,
operation
)
¶
履行锁定操作
operation
对于文件描述符
fd
(文件对象提供
fileno()
方法也是可以接受的)。见 Unix 手册
flock(2)
了解细节。(在某些系统，此函数的模拟是使用
fcntl()
)。
若
flock()
失败，
OSError
异常被引发。
fcntl.
lockf
(
fd
,
cmd
,
len=0
,
start=0
,
whence=0
)
¶
这本质上是包裹器围绕
fcntl()
锁定调用。
fd
is the file descriptor of the file to lock or unlock, and
cmd
是下列值之一：
LOCK_UN
– 解锁
LOCK_SH
– 获得共享锁
LOCK_EX
– 获得独占锁
当
cmd
is
LOCK_SH
or
LOCK_EX
，它还可以是按位 OR (或) 采用
LOCK_NB
以避免阻塞，当获得锁时。若
LOCK_NB
有使用但无法获得锁，
OSError
会被引发且异常将拥有
errno
属性设置为
EACCES
or
EAGAIN
(depending on the operating system; for portability, check for both values). On at least some systems,
LOCK_EX
can only be used if the file descriptor refers to a file opened for writing.
len
是要锁定的字节数，
start
is the byte offset at which the lock starts, relative to
whence
，和
whence
is as with
io.IOBase.seek()
, specifically:
0
– 相对于文件起始 (
os.SEEK_SET
)
1
– 相对于当前缓冲位置 (
os.SEEK_CUR
)
2
– 相对于文件末尾 (
os.SEEK_END
)
默认为 start is 0, which means to start at the beginning of the file. The default for len is 0 which means to lock to the end of the file. The default for whence is also 0.
范例 (所有在 SVR4 兼容系统)：
import struct, fcntl, os f = open(...) rv = fcntl.fcntl(f, fcntl.F_SETFL, os.O_NDELAY) lockdata = struct.pack('hhllhh', fcntl.F_WRLCK, 0, 0, 0, 0, 0) rv = fcntl.fcntl(f, fcntl.F_SETLKW, lockdata)
Note that in the first example the return value variable
rv
will hold an integer value; in the second example it will hold a
bytes
object. The structure lay-out for the
lockdata
variable is system dependent — therefore using the
flock()
调用可能更好。
另请参阅