• Table of Contents

<aside> <img src="/icons/map-pin_gray.svg" alt="/icons/map-pin_gray.svg" width="40px" /> Before starting Week 4, the prof expanded on more scheduling algorithms relating to Week 2, where we previously only covered FIFO.

Scheduling Algorithms

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Multithreading

The discussion so far has presented the concept of a process as embodying two characteristics.

1. Resource ownership: A process includes a virtual address space to hold the process image.

2. Scheduling/execution: The execution of a process follows an execution path (trace) through one or more programs.

   

   Figure 4.1 Program flow of control without and with interrupts.

To distinguish the two characteristics between a process and a thread:

• The unit of dispatching is usually referred to as a thread (or lightweight process).
• The unit of resource ownership is usually referred to as a process (or task).

Multithreading refers to the ability of an OS to support multiple, concurrent paths of execution within a single process.

Figure 4.2 Processes and threads.

The two arrangements shown in the left half are single-threaded approaches, such as MS-DOS. The right half depicts multithreaded approaches, such as Java runtime environment. Each thread has the following:

• An execution state — Running, Ready, etc.
• A saved thread context when not running.
• An execution stack.
• Some per-thread static storage for local variables.
• Access to the memory and resources of its process, shared with all other threads in that process.

The key benefits of threads derive from the performance implications:

1. Less time to create a new thread or terminate a thread than a process.