The Solo Operating System: Processes, Monitors, and Classes

DATA TYPES Each program layer consists of one or more abstract data types (monitors and classes). Resource management A fifo class implements a first-in, first-out queue that is used to maintain multiprocess queues and message buffers. A resource monitor gives processes exclusive access to a computer resource. It is used to control disk access. A typewriter resource monitor gives processes exclusive access to a console and tells them whether they need to identify themselves to the operator. Console management A typewriter class transmits a single line between a process and a console (but does not give a process exclusive access to it). A terminal class gives a process the illusion that it has its own private console by giving it exclusive access to the operator for input or output of a single line. A terminal stream makes a terminal look character oriented. Disk management A disk class can access a page anywhere on disk (but does not give a process exclusive access to it). It uses a terminal to report disk failure. A disk file can access any page belonging to a particular file. The file pages, which may be scattered on disk, are addressed indirectly through a page map. The disk address of the page map identifies the file. It uses a disk to access the map and its pages. A disk table class makes a disk catalog of files look like an array of entries, some of which describe files, and some of which are empty. The entries are identified by numeric indices. It uses a disk file to access the catalog page by page. A disk catalog monitor can look up files in a disk catalog by means of their names. It uses a resource to get exclusive acess to the disk and a disk table to scan the catalog. A data file class gives a process access to a named disk file. It uses a resource, a disk catalog, and a disk file to access the disk. SOLO: PROCESSES, MONITORS AND CLASSES 5 Program management A program file class can load a named disk file into core when a process wishes to execute it. It uses a resource, a disk catalog, and a disk file to do this. A program stack monitor keeps track of nested program calls within a process. Buffer management The buffer monitors transmit various kinds of messages between processes: arguments (scalars or identifiers), lines, and pages. The following defines the purpose, specification, and implementation of each of these abstract data types.