Java 19 introduces a completely new concept in the field of concurrent programming—Structured concurrency(Structured Concurrency), released as a preview function. This feature is designed to simplify the management of concurrent tasks and improve the maintainability and security of multi-threaded programs. The core idea of structured concurrency is to treat concurrent tasks as part of a program, making their life cycle and control flow more orderly and clear.
1. The background of structured concurrency
In the traditional concurrent programming model, Java provides a variety of ways to handle concurrent tasks, such as using threads,ExecutorService、CompletableFuturewait. However, there are some challenges in the use of these methods, mainly manifested in:
- Complex life cycle management: Manually managing thread start, end and exception handling is prone to errors, especially when tasks depend on multiple threads, it is difficult to ensure that all tasks are properly closed or cancelled.
- Code Complexity: Multi-threaded code is usually messy, increasing maintenance difficulty. In order to handle task results between different threads, developers may need to write complex synchronization code.
- Resource leak: Improper management of threads and task life cycles may lead to resource leakage, such as the thread pool not being closed in time, or exceptions may cause threads not to be recycled correctly.
Structured concurrency makes concurrent tasks more controllable and concise by binding the life cycle of concurrent tasks to their parent scope.
2. The core concept of structured concurrency
The core goal of structured concurrency is to make concurrent tasks have a structured execution flow in a program like a function call. Specifically, it provides a mechanism to limit the execution scope of concurrent tasks within a certain code block or scope, and ensures that when the task is completed, the program can continue to execute safely.
In Java 19, structured concurrency passesStructuredTaskScopeClasses to implement. This category allows developers to start multiple concurrent tasks and process the results or perform error processing after these tasks are completed.
Key features of structured concurrency include:
- Lifecycle Management: The life cycle of concurrent tasks is synchronized with their parent scope. Once the task scope is completed, all tasks will be processed automatically (completed or cancelled).
- Exception handling: In concurrent tasks, exceptions are centrally managed to ensure that even if one task fails, the execution of the entire task group is still controllable.
- Task combination and result aggregation: Multiple concurrent tasks can be executed in combination and their results can be easily collected without complex synchronization code.
3. Examples of structured concurrency
The following is a useStructuredTaskScopeA simple example showing how to execute multiple tasks in parallel and process results:
import ;
import ;
import ;
public class StructuredConcurrencyExample {
public static void main(String[] args) {
try (var scope = new ()) {
// Start multiple concurrent tasks Callable<String> task1 = () -> {
(1000); // Simulate long-running tasks return "Task 1 Result";
};
Callable<String> task2 = () -> {
(2000); // Simulate another long-term task return "Task 2 Result";
};
// Fork concurrent tasks var future1 = (task1);
var future2 = (task2);
// Wait for all tasks to complete or a task fails (); // Wait for all tasks to complete (); // If a task fails, an exception will be thrown
// Get results ("Task 1 Result: " + ());
("Task 2 Result: " + ());
} catch (InterruptedException | ExecutionException e) {
(); // Exception handling }
}
}
Code parsing：
-
:This isStructuredTaskScopeOne implementation of , it will automatically close all other tasks when either task fails. There are other types ofStructuredTaskScope,For exampleShutdownOnSuccess, can close all other tasks after the first successful task is completed. -
(task): Start a new concurrent task. -
(): Wait for all tasks to complete, similar to()。 -
(): Check whether any task failed, if so, throw an exception.
In this example, we create two concurrent tasks running in parallel and wait for them to complete.StructuredTaskScopeSimplifies the start, wait and error handling of tasks, ensuring that the life cycle of each task is well managed.
4. Advantages of structured concurrency
Simplify concurrent code: Through structured concurrency, multiple concurrent tasks can be started and managed in a simple way without the need for explicit thread management code. This makes the code more concise and easy to understand.
Better life cycle management: The life cycle of all concurrent tasks is limited to one scope. This means we no longer need to manually manage thread pools or worry about tasks not being closed properly.
Safe exception handling: In traditional concurrent programming, handling exceptions of multiple threads is complicated, especially when one task fails, it is necessary to terminate other tasks in a timely manner. Structured concurrency provides a centralized exception handling mechanism to avoid mutual interference between tasks.
Automatic resource recycling: When the task scope ends, all relevant resources (such as threads, tasks, etc.) will be automatically recycled to avoid resource leakage.
Task results aggregation: The results of multiple concurrent tasks can be easily aggregated without writing complex synchronization logic, simplifying the processing of results of concurrent tasks.
5. Comparison between structured concurrency and traditional concurrency models
Compared with traditional concurrent programming models, structured concurrency provides a higher level of abstraction. In traditional concurrent programming, we often need to manually manage threads, task lifecycles, and resource recycling, while structured concurrency simplifies these operations.
Problems in traditional concurrency models：
- Manually managing the startup/closing of thread pools and tasks can easily lead to resource leakage.
- Exception handling is complicated, and exception management between multiple threads may require a lot of synchronization logic.
- Combination of results between multiple tasks often requires the manual management of synchronization code.
Improvements to structured concurrency：
- Automatically manage the start and shutdown of concurrent tasks without explicitly managing thread pools.
- Provides clearer task scope and lifecycle control to ensure tasks are completed or terminated as expected.
- Centralized exception handling reduces the complexity of exception propagation.
- Easily collect and process the results of multiple concurrent tasks with a concise API.
6. Structured concurrency usage scenarios
Complex concurrent task management: In complex application scenarios, multiple tasks may depend on each other, or the failure of some tasks requires cancellation of other tasks. Structured concurrency provides a natural way to manage the life cycle and dependencies of these tasks.
Multitasking result aggregation: In scenarios where multiple subtasks need to be computed in parallel and aggregated results, structured concurrency can significantly simplify the writing and maintenance of code.
Reliable error handling: For applications where all tasks must be successful or other tasks aborted in multiple tasks, structured concurrency provides a centralized error handling mechanism.
Resource-constrained applications: When strict control of resource usage (such as number of threads, memory, etc.), structured concurrency can help better manage tasks and avoid over-allocation of resources.
7. Summary
Structured concurrency introduced in Java 19 improves the security and maintainability of concurrent programming by simplifying the management of concurrent tasks. It passesStructuredTaskScopeThe abstraction makes the startup, waiting and exception handling of multi-threaded tasks clearer and controllable. Structured concurrency provides a more intuitive concurrency management method, suitable for the processing of complex concurrent tasks, aggregation of results between concurrent tasks, and reliable error management.
Although structured concurrency is currently released as a preview feature, it points out the way for future evolution of Java concurrent programming. This way, developers can write concurrent programs more concisely and efficiently, thereby reducing errors and improving program robustness.
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