Multi-threaded/parallel allocation

[chrisvest]

Allow the pool to populate faster by allocating multiple objects in parallel.

This adds asynchronous methods to Allocator and Reallocator for their respective operations.
The background allocation thread will use these if the pool has been configured with a PoolBuilder.setMaxConcurrentAllocations value greater than one.
Default implementations of these methods are provided, which will spawn a virtual thread for each operation.

A few fixes to leak detection have also been implemented, due to shortcomings made apparent by the asynchronous allocator operations. For instance, reallocation previously did not re-register the reallocated object. There were also a possibility of false-positives, from the references to deallocated objects being cleared before their corresponding slot had been deregistered with the leak detector. A few flaky tests in that area have also been fixed.

This fixes #216

[Copilot]

Pull request overview

Adds support for faster pool population by allowing allocations (and related allocator work) to run concurrently, addressing issue #216.

Changes:

• Introduces allocator async hooks (allocateAsync/deallocateAsync and reallocateAsync) and updates timing adaptors to record latency for async operations.
• Adds PoolBuilder#setMaxConcurrentAllocations(...) (default 1) and wires it into the threaded allocation controller to run allocator work in parallel.
• Expands/adjusts blackbox tests and testkits to exercise concurrent allocation/deallocation/reallocation and async failure propagation.

Reviewed changes

Copilot reviewed 22 out of 22 changed files in this pull request and generated 15 comments.

Show a summary per file

File	Description
src/main/java/stormpot/Allocator.java	Adds default async allocation/deallocation methods.
src/main/java/stormpot/Reallocator.java	Adds default async reallocation method.
src/main/java/stormpot/PoolBuilder.java	Adds configuration API for max concurrent allocations + docs.
src/main/java/stormpot/Pool.java	Javadoc typo fix.
src/main/java/stormpot/internal/PoolBuilderImpl.java	Stores/reads allocation concurrency setting and updates defaults/thread setup.
src/main/java/stormpot/internal/PoolBuilderDefaults.java	Adds default allocation concurrency field.
src/main/java/stormpot/internal/BAllocThread.java	Implements parallel allocator work and async completion handling.
src/main/java/stormpot/internal/Task.java	Extends task model to include async completions and switch signals.
src/main/java/stormpot/internal/AsyncAllocationCompletion.java	New task type for delivering async allocation results back to allocator thread.
src/main/java/stormpot/internal/AsyncDeallocationCompletion.java	New task type for delivering async deallocation completion back to allocator thread.
src/main/java/stormpot/internal/AllocatorSwitchRequestPending.java	New task type to wake allocator thread for allocator-switch processing.
src/main/java/stormpot/internal/ReallocatingAdaptor.java	Forwards async allocate/deallocate to underlying allocator.
src/main/java/stormpot/internal/TimingReallocatingAdaptor.java	Adds metrics recording for async allocate/deallocate.
src/main/java/stormpot/internal/TimingReallocatorAdaptor.java	Adds metrics recording for async reallocate.
src/main/java/stormpot/internal/IdentityHashSet.java	Tweaks insertion selection logic.
src/test/java/stormpot/tests/blackbox/ThreadBasedPoolTest.java	Adds concurrency/async propagation tests for threaded pools.
src/test/java/stormpot/tests/blackbox/ThreadBasedWithConcurrentAllocationPoolTest.java	New threaded-pool variant configured for concurrent allocations.
src/test/java/stormpot/tests/blackbox/AllocatorBasedPoolTest.java	Adjusts leak test mechanics and allocation-order test behavior.
src/test/java/testkits/AlloKit.java	Makes action sequencing thread-safe for concurrent test execution.
src/test/java/testkits/DelegateAllocator.java	New wrapper allocator used by async tests.
src/test/java/testkits/DelegateReallocator.java	New wrapper reallocator used by async tests.
api-changes.json	Revapi suppression entries for the new PoolBuilder interface methods.

[Copilot]

Pull request overview

Copilot reviewed 27 out of 27 changed files in this pull request and generated 9 comments.

Comments suppressed due to low confidence (1)

src/main/java/stormpot/PoolBuilder.java:176

• The Javadoc for precise leak detection says it’s enabled by default (both here and in the setter docs), but PoolBuilderTest.preciseLeakDetectionMustBeDisabledByDefault asserts the default is disabled. Please align the documentation with the actual default behavior (or update the default if the docs are correct).

  /**
   * Return whether precise object leak detection is enabled, which is
   * the case by default.
   *
   * @return {@code true} if precise object leak detection is enabled.
   * @see #setPreciseLeakDetectionEnabled(boolean)
   */
  boolean isPreciseLeakDetectionEnabled();

  /**
   * Enable or disable precise object leak detection. It is enabled by default.
   * Precise object leak detection makes the pool keep an eye on the allocated