Java's Concurrency Journey Continues! Exploring Structured Concurrency and Scoped Values by Embregts

Virtual threads are lightweight threads that don’t have a 1:1 mapping with OS threads, allowing millions of concurrent threads versus thousands with platform threads

Structured concurrency introduces task hierarchies and scopes that enforce parent-child relationships between tasks, leading to more maintainable concurrent code

Scoped values provide immutable thread-local variables with strictly defined lifetimes, addressing memory intensity issues of traditional ThreadLocal variables

Key benefits of structured concurrency include:

• Clear entry/exit points for tasks
• Automatic cancellation propagation
• Proper resource cleanup
• Improved error handling

Virtual threads work best for I/O-heavy tasks rather than CPU-intensive work, as they can efficiently handle blocking operations

Thread locals should be migrated to scoped values when:

• Using virtual threads
• Dealing with one-way transmission of unchanging data
• Need for strictly defined variable lifetime

Structured concurrency offers different scope types:

• ShutdownOnFailure - stops all tasks on first failure
• ShutdownOnSuccess - stops after first success
• Custom scopes for specific behaviors

Modern frameworks like Spring and Jakarta EE are adding native support for virtual threads and structured concurrency

Completable Futures remain useful for asynchronous pipelines, but structured concurrency provides better coordination of related tasks

Migration considerations:

• Start with thread-per-request scenarios
• Test performance impact
• Consider framework support
• Evaluate thread local usage patterns