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Mach Kernel Abstractions

Mach provides a small set of abstractions that have been designed to be both simple and powerful. These are the main kernel abstractions:

• Tasks. The units of resource ownership; each task consists of a virtual address space, a port right namespace, and one or more threads. (Similar to a process.)

• Threads. The units of CPU execution within a task.

• Address space. In conjunction with memory managers, Mach implements the notion of a sparse virtual address space and shared memory.

• Memory objects. The internal units of memory management. Memory objects include named entries and regions; they are representations of potentially persistent data that may be mapped into address spaces.

• Ports. Secure, simplex communication channels, accessible only via send and receive capabilities (known as port rights).

• IPC. Message queues, remote procedure calls, notifications, semaphores, and lock sets.

• Time. Clocks, timers, and waiting.

At the trap level, the interface to most Mach abstractions consists of messages sent to and from kernel ports representing those objects. The trap-level interfaces (such as mach_msg_overwrite_trap) and message formats are themselves abstracted in normal usage by the Mach Interface Generator (MIG). MIG is used to compile procedural interfaces to the message-based APIs, based on descriptions of those APIs.

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