Mach is an object-oriented operating system kernel. It defines basic abstractions like tasks, threads, ports, and memory objects. Tasks provide execution environments, threads are units of execution, ports enable communication between tasks using messages, and memory objects are sources of shared memory. Tasks communicate asynchronously through message passing to ports using the mach_msg system call.

1. Mach Kernel
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2. • Mach is object-oriented system.
• Data and the operations that manipulate that data are
encapsulated into an abstract object..
• The details of how these operations are implemented are
hidden, as are the internal data structures.
• Use of an object is done by invoking its defined
• It allows objects to reside anywhere in a network of Mach
systems, transparent to the user.
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3. Mach’s basic abstractions
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4. • Task : A task is an execution environment , a traditional
process would be implemented as a task with a single thread
of control.
– May have multiple thread.
– Resources : Address Spaces, Threads, Port rights, ports sets, local
name spaces.
– task_create(parent_task, inherit_memory, child_task)
• Thread : is the basic unit of execution and must run in the
context of a task (which provides the address space).
– All threads within a task share the tasks’ resources (ports, memory,
and so on).
– The threads belonging to a single task can execute in parallel at
different processors in a shared-memory multiprocessor.
– thread_create(parent_task, child_thread)
– thread_set_state(thread, flavour, new_state, count)
– Thread_resume(thread)
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5. • Port : is a unicast, unidirectional communication channel
with an associated message queue.
– a task must have a port right to send a message to a port.
– Communication is accomplished by sending messages to ports.
– messages are queued at the destination port if no thread is
immediately ready to receive them.
• Port Set : Set of ports treated as a single unit when
receiving a message.
– They share a common message queue.
– Each received message identifies the individual port
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6. • Messages : is the basic method of communication
between threads in Mach.
– Contain Message header.
– It is a typed collection of data objects.
– Port rights are passed in messages;
• Memory object : is a source of memory; tasks can
access it by mapping portions of an object (or the entire
object) into their address spaces.
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7. Communication Model
• Ports are the channel where communication occurs by
sending message to ports.
• Mach provides a single system call for message passing:
mach_msg
mach_msg(msg_header, option, snd_siz, rcv_siz, rcv_name,
timeout, notify)
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8. • The header is composed of:
– Port destination.
– Answer port.
– Operation identifier.
– Size of the data list.
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