Package groovy.concurrent

Interface Pool

All Superinterfaces:
AutoCloseable, Executor
All Known Implementing Classes:
DefaultPool
public interface Pool extends Executor, AutoCloseable
A managed thread pool for parallel and concurrent operations.

Pool extends Executor so it can be used anywhere an executor is expected — including AsyncScope.withScope(executor, body). It also implements AutoCloseable for use in try-with-resources blocks, ensuring clean shutdown.

Factory methods provide common pool configurations:

  • virtual() — virtual-thread-per-task (JDK 21+), ideal for I/O
  • fixed(int) — fixed-size thread pool with daemon threads
  • cpu() — sized to availableProcessors(), for CPU-bound work
  • io() — larger pool for I/O-bound or blocking operations

Inspired by GPars' PGroup pool management, modernised for virtual threads. 


 try (var pool = Pool.cpu()) {
     AsyncScope.withScope(pool, scope -> {
         scope.async(() -> cpuIntensiveWork());
         scope.async(() -> moreCpuWork());
         return null;
     });
 }
Since:
6.0.0
See Also:

  • Method Summary

    Modifier and Type
    Method
    Description
    ForkJoinPool
    asForkJoinPool()
    Returns the underlying ForkJoinPool, if this pool is backed by one.
    default void
    close()
    Shuts down the pool.
    static Pool
    cpu()
    Creates a pool sized to Runtime.availableProcessors(), suitable for CPU-bound work.
    static Pool
    current()
    Returns the pool bound to the current scope, or null.
    static Pool
    fixed(int size)
    Creates a fixed-size thread pool with daemon threads.
    int
    getActiveCount()
    Returns the approximate number of threads actively executing tasks.
    int
    getPoolSize()
    Returns the configured pool size.
    static Pool
    io()
    Creates a larger pool suitable for I/O-bound or blocking operations.
    void
    shutdown()
    Initiates an orderly shutdown.
    boolean
    usesVirtualThreads()
    Returns true if this pool uses virtual threads.
    static Pool
    virtual()
    Creates a virtual-thread-per-task pool (JDK 21+).
    static <T> T
    withCurrent(Pool pool, Supplier<T> supplier)
    Executes the supplier with the given pool as current, restoring the previous binding afterwards.

    Methods inherited from interface java.util.concurrent.Executor

    execute

  • Method Details

    • virtual

      static Pool virtual()
      Creates a virtual-thread-per-task pool (JDK 21+).

      Each submitted task runs on its own virtual thread. This is ideal for I/O-bound workloads where tasks spend time waiting. On JDK versions that do not support virtual threads, falls back to a cached daemon thread pool.

      Returns:
      a new virtual thread pool

    • fixed

      static Pool fixed(int size)
      Creates a fixed-size thread pool with daemon threads.
      Parameters:
      size - the number of threads (must be > 0)
      Returns:
      a new fixed pool
      Throws:
      IllegalArgumentException - if size ≤ 0

    • cpu

      static Pool cpu()
      Creates a pool sized to Runtime.availableProcessors(), suitable for CPU-bound work.
      Returns:
      a new CPU pool

    • io

      static Pool io()
      Creates a larger pool suitable for I/O-bound or blocking operations.

      If virtual threads are available, returns a virtual thread pool (the ideal choice for I/O). Otherwise returns a fixed pool sized to ConcurrentConfig.getDefaultParallelism().

      Returns:
      a new I/O pool

    • current

      static Pool current()
      Returns the pool bound to the current scope, or null.

      Set by ParallelScope.withPool(int, java.util.function.Function<groovy.concurrent.AsyncScope, T>) using the runtime's scoped binding support.

      Returns:
      the current pool, or null if none is bound
      Since:
      6.0.0

    • withCurrent

      static <T> T withCurrent(Pool pool, Supplier<T> supplier)
      Executes the supplier with the given pool as current, restoring the previous binding afterwards.
      Type Parameters:
      T - the result type
      Parameters:
      pool - the pool to bind
      supplier - the work to execute
      Returns:
      the supplier's result
      Since:
      6.0.0

    • getPoolSize

      int getPoolSize()
      Returns the configured pool size. For virtual thread pools, returns Integer.MAX_VALUE.

    • getActiveCount

      int getActiveCount()
      Returns the approximate number of threads actively executing tasks.

    • usesVirtualThreads

      boolean usesVirtualThreads()
      Returns true if this pool uses virtual threads.

    • asForkJoinPool

      ForkJoinPool asForkJoinPool()
      Returns the underlying ForkJoinPool, if this pool is backed by one. Required for parallel stream isolation.
      Returns:
      the ForkJoinPool
      Throws:
      UnsupportedOperationException - if this pool is not ForkJoinPool-backed (e.g., virtual thread pools)
      Since:
      6.0.0

    • shutdown

      void shutdown()
      Initiates an orderly shutdown. Previously submitted tasks are executed, but no new tasks will be accepted.

    • close

      default void close()
      Shuts down the pool. Equivalent to shutdown().
      Specified by:
      close in interface AutoCloseable