I/O-bound work

As explained in Rust Servers, Services, and Apps

An I/O-bound program is a program whose progress rate is primarily limited by the speed of input and output operations.

I/O-bound work is work whose progress primarily depends on the speed of an input/output subsystem rather than the CPU. File access, database access, and network TCP/HTTP requests are typical cases. section 10.1 section 10.3

While a task waits for a disk, network socket, or timer, an asynchronous runtime such as Tokio can schedule another asynchronous task. When the external operation completes, the waiting task resumes. section 10.3

Recognize I/O-bound work through its external waits:

• Reading from or writing to a file section 10.3
• Waiting for bytes on a network connection or processing HTTP requests section 10.1 section 10.3
• Accessing a database or waiting for a timer to complete section 10.1 section 10.3

Concurrent file reads with Tokio

Two file-reading futures can be spawned and joined. Each task waits independently, allowing the runtime to process the other task instead of leaving the processor idle. The sample output shows file 2 completing before file 1, despite both tasks starting together. section 10.3

Figure 10.4 Async programming in HTTP request processing

Use the HTTP request-processing diagram to compare asynchronous handling of I/O waits with thread-per-connection processing. section 10.1

I/O-bound work is a candidate for asynchronous execution, but the guideline is broad and has exceptions. CPU-bound work, such as complex number-crunching, is limited by processor speed instead. section 10.3

How Rust Servers, Services, and Apps covers it

How deep it goes

Defines the bottleneck, contrasts CPU-bound work, and demonstrates runtime scheduling without fully developing asynchronous internals.

Examples

Uses file reads, database access, TCP/HTTP requests, timers, and two Tokio-spawned file futures as examples.

What it assumes

Assumes familiarity with programs and processors while distinguishing CPU-intensive and I/O-intensive work through concrete examples.

What you can do after

Evaluate whether asynchronous task execution fits workloads whose progress depends on file, database, network, or timer operations.

How it connects

Connects I/O-bound work with asynchronous programming, concurrency, parallel processing, multithreading, CPU-bound work, and async runtimes.

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Also explained in

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  Python Concurrency with asyncioBlocking I/O work is work whose progress can wait for input or output operations that do not complete immediately.
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  Grokking ConcurrencyAn I/O-bound operation is an operation whose completion primarily depends on input/output activity or waiting for external hardware or services.
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  100 Go Mistakes and How to Avoid ThemAn I/O-bound workload is a workload whose execution time is primarily limited by input and output operations or an external system.
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  Starting Data Analytics with Generative AI and PythonAn I/O-bound task is a computation whose execution time is primarily limited by input or output operations rather than processor computation.

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Related concepts

• compute-boundcontrasts with · A computation is compute-bound when its performance is limited primarily by available processor or arithmetic capacity rather than memory transfer, input/output, or other resources.
• asyncioused by · asyncio is Python’s standard-library framework for asynchronous programming, built around coroutines, awaitable objects, and event loops.
• threading moduleused by · The threading module is Python’s standard-library interface for creating, managing, and coordinating threads and thread-synchronization primitives.
• parallelismused by · Parallelism is the concurrent execution of multiple computational operations, often across multiple processing resources.

This explainer was generated by Manning's knowledge graph from the text of Rust Servers, Services, and Apps. The section links point to the parts of the book it draws on.