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Clarify that on some systems, lockf() using LOCK_EX requires that the file

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is opened for writing; this closes SF bug #485342.

Added notes that file objects are also accepted in the place of file
descriptors.
This commit is contained in:
Fred Drake 2001-11-28 07:48:32 +00:00
parent 48704ee478
commit 6a6bb1828b
1 changed files with 9 additions and 4 deletions
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13
Doc/lib/libfcntl.tex
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@ -16,13 +16,15 @@ It is an interface to the \cfunction{fcntl()} and \cfunction{ioctl()}
All functions in this module take a file descriptor \var{fd} as their
first argument. This can be an integer file descriptor, such as
returned by \code{sys.stdin.fileno()}, or a file object, such as
\code{sys.stdin} itself.
\code{sys.stdin} itself, which provides a \method{fileno()} which
returns a genuine file descriptor.
The module defines the following functions:
\begin{funcdesc}{fcntl}{fd, op\optional{, arg}}
Perform the requested operation on file descriptor \var{fd}.
Perform the requested operation on file descriptor \var{fd} (file
objects providing a \method{fileno()} method are accepted as well).
The operation is defined by \var{op} and is operating system
dependent. These codes are also found in the \module{fcntl}
module. The argument \var{arg} is optional, and defaults to the
@ -52,7 +54,8 @@ The module defines the following functions:
\end{funcdesc}
\begin{funcdesc}{flock}{fd, op}
Perform the lock operation \var{op} on file descriptor \var{fd}.
Perform the lock operation \var{op} on file descriptor \var{fd} (file
objects providing a \method{fileno()} method are accepted as well).
See the \UNIX{} manual \manpage{flock}{3} for details. (On some
systems, this function is emulated using \cfunction{fcntl()}.)
\end{funcdesc}
@ -75,7 +78,9 @@ lock acquisition. If \constant{LOCK_NB} is used and the lock cannot
be acquired, an \exception{IOError} will be raised and the exception
will have an \var{errno} attribute set to \constant{EACCES} or
\constant{EAGAIN} (depending on the operating system; for portability,
check for both values).
check for both values). On at least some systems, \constant{LOCK_EX}
can only be used if the file descriptor refers to a file opened for
writing.
\var{length} is the number of bytes to lock, \var{start} is the byte
offset at which the lock starts, relative to \var{whence}, and