cs.sharedfile 20190102

Facilities for shared access to files.

Function lockfile(path, ext=None, poll_interval=None, timeout=None)

A context manager which takes and holds a lock file.

Parameters:

• path: the base associated with the lock file.
• ext: the extension to the base used to construct the lock file name. Default: ".lock"
• timeout: maximum time to wait before failing, default None (wait forever).
• poll_interval: polling frequency when timeout is not 0.

Class SharedAppendFile

A base class to share a modifiable file between multiple users.

The use case was driven from the shared CSV files used by cs.nodedb.csvdb.Backend_CSVFile, where multiple users can read from a common CSV file, and coordinate updates with a lock file.

This presents the following interfaces:

• __iter__: yields data chunks from the underlying file up to EOF; it blocks no more than reading from the file does. Note that multiple iterators share the same read pointer.

• open: a context manager returning a writable file for writing updates to the file; it blocks reads from this instance (though not, of course, by other users of the file) and arranges that users of __iter__ do not receive their own written data, thus arranging that __iter__ returns only foreign file updates.

Subclasses would normally override __iter__ to parse the received data into their natural records.

Class SharedAppendLines

MRO: SharedAppendFile
A line oriented subclass of SharedAppendFile.

Class SharedCSVFile

MRO: SharedAppendLines, SharedAppendFile
Shared access to a CSV file in UTF-8 encoding.