This module provides base implementation of generic pipe-like message processing
daemon represented by the
It builds on top of
pyzenkit.zendaemon module and adds couple of other
Automated inclusion and bootstrapping of
Additional configurations and command line arguments related to filer protocol.
Filer daemon component¶
This module automatically takes care of inclusion and bootstrapping of
mentat.daemon.component.filer daemon component. This component implements
the filesystem message exchange queue, aka. filer protocol. This is a fairly
simple protocol inspired by Postfix MTA that uses ordinary filesystem directories
for exchanging messages between multiple modules/processess. Each process has a
directory asigned to him which represents his message queue. Passing a message for
processing means simply puting a file into this directory, or more specifically
into one of its subdirectories.
The designated filesystem message queue directory must contain and use following subdirectories:
incoming: input queue containing only complete messages
pending: daemon working directory and pending queue
tmp: work directory for other processes
errors: messages causing problems during processing
- Enqueue message
Equeuing a new message can be done by anyone including the owner of the queue and it means creating a new file in
incomingsubdirectory. However it is required that all files in this directory are complete and final, so ussually it is necessary to create the temporary file in different location (ussually
tmp) and then move it to the
Key requirement here is, that the move operation must be atomic, so that multiple instances of the same daemon may run on the same queue and thus enable cheap paralelization. The atomic move should be achived simply by keeping the whole queue directory structure on the same disk partition.
Once message is in the
incomingsubdirectory, it must be considered a property of the queue owner and no other process (except other instances of the same daemon) must not modify it in any way.
- Dequeue message
Dequeueing a message is done only by the owner of the queue and it means atomically moving the related message file into
pendingsubdirectory. In that instant process that moved the message owns it and may work with it. When the work is there are following options how to handle the message file:
Move the message file to
errorssubdirectory in case there was any error during processing.
Move the message to
incomingsubdirectory of another daemon to pass the message to next step in processing chain.
Delete the message permanently from filesystem in case it is not needed anymore.
Custom command line options¶
Name of the input queue directory.
Name of the output queue directory.
Limit on the number of the files for the output queue directory.
Waiting time when the output queue limit is reached in seconds.
Minimalistic class for demonstration purposes.
Demonstration implementation of a daemon component capable of printing the message being processed to log.
Print the message contents into the log.
Get the list of event names and their appropriate callback handlers.
This module provides base implementation of generic pipe-like message processing daemon.