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- fcntl(...)
- fcntl(fd, op, [arg])
Perform the operation op on file descriptor fd. The values used
for op 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 is optional, and
defaults to 0; it may be an int or a string. If arg is given as a string,
the return value of fcntl is a string of that length, containing the
resulting value put in the arg buffer by the operating system. The length
of the arg string is not allowed to exceed 1024 bytes. If the arg given
is an integer or if none is specified, the result value is an integer
corresponding to the return value of the fcntl call in the C code.
- flock(...)
- flock(fd, operation)
Perform the lock operation op on file descriptor fd. See the Unix
manual page for flock(2) for details. (On some systems, this function is
emulated using fcntl().)
- ioctl(...)
- ioctl(fd, op[, arg[, mutate_flag]])
Perform the operation op on file descriptor fd. The values used for op
are operating system dependent, and are available as constants in the
fcntl or termios library modules, using the same names as used in the
relevant C header files.
The argument arg is optional, and defaults to 0; it may be an int or a
buffer containing character data (most likely a string or an array).
If the argument is a mutable buffer (such as an array) and if the
mutate_flag argument (which is only allowed in this case) is true then the
buffer is (in effect) passed to the operating system and changes made by
the OS will be reflected in the contents of the buffer after the call has
returned. The return value is the integer returned by the ioctl system
call.
If the argument is a mutable buffer and the mutable_flag argument is not
passed or is false, the behavior is as if a string had been passed. This
behavior will change in future releases of Python.
If the argument is an immutable buffer (most likely a string) then a copy
of the buffer is passed to the operating system and the return value is a
string of the same length containing whatever the operating system put in
the buffer. The length of the arg buffer in this case is not allowed to
exceed 1024 bytes.
If the arg given is an integer or if none is specified, the result value is
an integer corresponding to the return value of the ioctl call in the C
code.
- lockf(...)
- lockf (fd, operation, length=0, start=0, whence=0)
This is essentially a wrapper around the fcntl() locking calls. fd is the
file descriptor of the file to lock or unlock, and operation is one of the
following values:
LOCK_UN - unlock
LOCK_SH - acquire a shared lock
LOCK_EX - acquire an exclusive lock
When operation is LOCK_SH or LOCK_EX, it can also be bitwise ORed with
LOCK_NB to avoid blocking on lock acquisition. If LOCK_NB is used and the
lock cannot be acquired, an IOError will be raised and the exception will
have an errno attribute set to EACCES or EAGAIN (depending on the operating
system -- for portability, check for either value).
length is the number of bytes to lock, with the default meaning to lock to
EOF. start is the byte offset, relative to whence, to that the lock
starts. whence is as with fileobj.seek(), specifically:
0 - relative to the start of the file (SEEK_SET)
1 - relative to the current buffer position (SEEK_CUR)
2 - relative to the end of the file (SEEK_END)
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