Message-based data processing system that provides checking for access to server space

A message-based data processing system comprising at least one central processing unit, an operating system, at least one application program, and a memory, wherein the operating system is divided into function units which are accommodated in server spaces created in the memory, said message-based data processing system comprising:

• a kernel space, created in the memory, which accommodates primitive functions of said operating system and issues processing request messages, each processing request message being affixed with a request code identifying a source of said processing request message;
• a client space, created in the memory, accommodating the at least one application program, each client space issuing a processing request message affixed with a request code identifying a source of said message as the client space, for requesting service of said operating system, said request code being subject to alteration within the data processing system;
• message communication means, responsive to the request code of a processing request message, for transferring each processing request message to a server space which can perform the service requested in accordance with request code of the processing request message being transferred thereby;
• and
• request code check means for checking said request code of the processing request message being transferred by the message communication means to determine whether said request code affixed to said processing request message, when issued from said client space, is identical to the request code assigned to a processing request message issued from said kernel space, and for inhibiting said message communication means from transferring said processing request message to the server space when said request code affixed to said processing request message is identical to said request code indicating that the processing request message was issued from the kernel space.