Control system, mutual exclusion method, and subject device

A mutual exclusion method implemented in a control system including a subject device to be controlled, and a plurality of control devices connected to the subject device over a network, the mutual exclusion method characterized in that:

• causing the subject device to issue a new control permission each time a control permission issuance request is received from any of the plurality of control devices and return information on the new control permission to the control device that has sent the control permission issuance request;
• causing the subject device to execute control permission management to validate only one of already-issued control permissions and invalidate a remaining control permission;
• causing the subject device to, upon receiving a control start request to which information on a control permission is attached from any of the plurality of control devices, check whether the control permission attached to the control start request is valid, permit, when the control permission is valid, exclusive control by the control device that has sent the control start request, and reject, when the control permission is invalid, control by the control device that has sent the control start request;
• and
• causing the subject device to execute the control permission management to validate only a latest control permission of the already-issued control permissions and invalidate a control permission issued before the latest control permission.

A subject device that operates in accordance with a control command from a control device and to which a plurality of the control devices are connected over a network, the subject device characterized in that:

• a control permission issuance part configured to issue a new control permission each time a control permission issuance request is received from any of the plurality of control devices and return information on the new control permission to the control device that has sent the control permission issuance request;
• a control permission management part configured to execute control permission management to validate only one of already-issued control permissions and invalidate a remaining control permission;
• a mutual exclusion part configured to, upon receiving a control start request to which information on a control permission is attached from any of the plurality of control devices, check whether the control permission attached to the control start request is valid, permit, when the control permission is valid, exclusive control by the control device that has sent the control start request, and reject, when the control permission is invalid, control by the control device that has sent the control start request;
• and
• the control permission management part executes the control permission management to validate only a latest control permission of the already-issued control permissions and invalidate a control permission issued before the latest control permission.