Thread

• A sequence of computational instructions run one after another

Single-threaded Programs

• Simple programs typically have only one thread
• Many programs you have written fall into this category
• They are easy to reason about and understand

Multi-threaded Programs

• Contain multiple threads of execution
• Are suitable for parallel processing tasks
• Make effective use of modern computer architectures

Programs and Threads

• Programs are a collection of instructions
• A thread is a collection of instructions being executed
• Every running program has at least one thread

Process

• Most operating systems implement a container to hold threads
• This container is called a process

Lifetime

• Threads exist from the time their first instruction begins executing until the time of last instruction execution
• Threads with overlapping lifetimes are running concurrently
• A key feature of most operating systems is allow threads to run concurrently

Why is it desirable for the computer to execute multiple threads concurrently, rather than waiting for one to finish before starting another?

Responsiveness

• Allows rapid response to input even while working on other computations
• This is demonstrated by the example as both threads can respond to a timer

Resource Utilization

• The computer has many hardware resources (CPU, memory, disks, etc)
• We want use all of these resources efficiently
• We need to be able to pause a thread waiting on I/O to allow the CPU to be used for other tasks

Modularization

• We may also like threads for creating cleaner programs
• Aspects of computation can be handled independently

Web Server Example

• What does a web server do?
• How might threads help?

Multiprocessor Example

• Nearly all systems now have multiple processors
• How are threads useful here?
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