System and method for improved efficiency and deadlock prevention in communication interfaces utilizing a first-in-first-out action queue

A data communication interface for handling communication between a data processing system and a plurality of communication channels, comprising:

• means for posting actions in response to requests from the data processing system and from the plurality of communication channels;
• means responsive to detection of posting of an action for determining if the action originated with the data processing system;
• means responsive to an affirmative determination of posting of an action originating with the data processing system for determining if the action can be executed;
• means responsive to an affirmative determination that the action can be executed for executing the action;
• means responsive to a determination that the action originated with the host data processing system but was not executable, or a determination that the action was posted in response to a request by one of said plurality of communication controllers, for adding the action to an input of a First-In-First-Out queue;
• means for examining only a first action in said First-In-First-Out queue to determine if said first action can be executed;
• means responsive to determination that the first action can be executed for executing the first action and for replacing it as first action with a next action from said First-In-First-Out queue, if any;
• and
• means responsive to determination that the first action cannot be executed for moving the first action to said input of said First-In-First-Out queue and for replacing it as first action with a next action from said First-In-First-Out queue, if any.

An automated storage library for communicating with a plurality of communication channels, the automated storage library comprising:

• a plurality of physical files;
• a plurality of magazines for holding the physical files;
• a drive unit for receiving physical files;
• means for carrying physical files between the magazines and the drive unit;
• a data processing system connected between the plurality of communication channels and the drive unit;
• means for posting actions in response to requests from the data processing system and from the plurality of communication channels;
• means responsive to detection of posting of an action for determining if the action originated with the data processing system;
• means responsive to an affirmative determination of posting of an action originating with the data processing system for determining if the action can be executed;
• means responsive to an affirmative determination that the action can be executed for executing the action;
• means responsive to a determination that the action originated with the host data processing but was not executable or a determination that the action is posted in response to a request by one of said plurality of communication channels, for adding the action to an input of a First-In-First-Out queue;
• means for examining only a first action in said First-In-First-Out queue to determine if said first action can be executed;
• means responsive to determination that the first action can be executed for executing the first action and for replacing it as first action with a next action from said First-In-First-Out queue, if any;
• and
• means responsive to determination that the first action cannot be executed for moving the first action to said input of said First-In-First-Out queue and for replacing it as first action with a next action from said First-In-First-Out queue, if any.