implement a maybe workable memory manager

RoaringBitmap/build.gradle.kts

@@ -12,15 +12,31 @@ dependencies {
     testImplementation("com.fasterxml.jackson.core", "jackson-databind", "2.10.3")
 }
 
+val allocationManagerTest = task<Test>("allocationManagerTest") {
+    // test needs to run in its own fork to ensure registration succeeds
+    filter {
+        //include specific method in any of the tests
+        includeTestsMatching("org.roaringbitmap.AllocationManagerTest")
+    }
+    useJUnitPlatform()
+    failFast = true
+}
+
 tasks.test {
+    dependsOn(allocationManagerTest)
     systemProperty("kryo.unsafe", "false")
     mustRunAfter(tasks.checkstyleMain)
     useJUnitPlatform()
     failFast = true
     testLogging {
         // We exclude 'passed' events
-        events( "skipped", "failed")
+        events("skipped", "failed")
         showStackTraces = true
         exceptionFormat = org.gradle.api.tasks.testing.logging.TestExceptionFormat.FULL
     }
-}
+    filter {
+        // must not run this test as registration of the allocation manager will fail,
+        // but if it succeeded it would cause other tests to fail
+        excludeTestsMatching("org.roaringbitmap.AllocationManagerTest")
+    }
+}

RoaringBitmap/src/main/java/org/roaringbitmap/AllocationManager.java

@@ -0,0 +1,181 @@
+package org.roaringbitmap;
+
+import java.lang.reflect.Array;
+import java.util.Arrays;
+import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;
+
+/**
+ * Provides A lazily initialised constant allocator. To override allocation,
+ * registration must take place before first use.
+ */
+public final class AllocationManager {
+
+  private static final AllocationManager INSTANCE = new AllocationManager();
+
+  private static final AtomicReferenceFieldUpdater<AllocationManager, Allocator> UPDATER =
+      AtomicReferenceFieldUpdater.newUpdater(AllocationManager.class, Allocator.class,
+          "providedAllocator");
+
+  private volatile Allocator providedAllocator;
+
+  private static final class RegisteredAllocator {
+    public static final Allocator ALLOCATOR;
+    static {
+      Allocator allocator = INSTANCE.providedAllocator;
+      if (allocator == null) {
+        allocator = new DefaultAllocator();
+        if (!UPDATER.compareAndSet(INSTANCE, null, allocator)) {
+          allocator = INSTANCE.providedAllocator;
+        }
+      }
+      ALLOCATOR = allocator;
+    }
+  }
+
+  /**
+   * Register an allocator. Must be registered before first use, otherwise registration will be
+   * unsuccessful
+   * @param allocator the allocator
+   * @return true if registration succeeded
+   */
+  public static boolean register(Allocator allocator) {
+    return UPDATER.compareAndSet(INSTANCE, null, allocator);
+  }
+
+  /**
+   * @see Allocator#allocateChars
+   */
+  public static char[] allocateChars(int size) {
+    return RegisteredAllocator.ALLOCATOR.allocateChars(size);
+  }
+
+  /**
+   * @see Allocator#allocateLongs
+   */
+  public static long[] allocateLongs(int size) {
+    return RegisteredAllocator.ALLOCATOR.allocateLongs(size);
+  }
+
+  /**
+   * @see Allocator#allocateObjects
+   */
+  public static Container[] allocateContainers(int size) {
+    return RegisteredAllocator.ALLOCATOR.allocateObjects(Container.class, size);
+  }
+
+  /**
+   * @see Allocator#copy
+   */
+  public static char[] copy(char[] chars) {
+    return RegisteredAllocator.ALLOCATOR.copy(chars);
+  }
+
+  /**
+   * @see Allocator#copy
+   */
+  public static char[] copy(char[] chars, int newSize) {
+    return RegisteredAllocator.ALLOCATOR.copy(chars, newSize);
+  }
+
+  /**
+   * @see Allocator#copy
+   */
+  public static long[] copy(long[] longs) {
+    return RegisteredAllocator.ALLOCATOR.copy(longs);
+  }
+
+  /**
+   * @see Allocator#copy
+   */
+  public static Container[] copy(Container[] containers) {
+    return RegisteredAllocator.ALLOCATOR.copy(containers);
+  }
+
+  /**
+   * @see Allocator#copy
+   */
+  public static Container[] copy(Container[] containers, int newSize) {
+    return RegisteredAllocator.ALLOCATOR.copy(containers, newSize);
+  }
+
+  /**
+   * @see Allocator#extend
+   */
+  public static char[] extend(char[] chars, int newSize) {
+    return RegisteredAllocator.ALLOCATOR.extend(chars, newSize);
+  }
+
+  /**
+   * @see Allocator#extend
+   */
+  public static Container[] extend(Container[] containers, int newSize) {
+    return RegisteredAllocator.ALLOCATOR.extend(containers, newSize);
+  }
+
+  /**
+   * @see Allocator#free
+   */
+  public static void free(Object object) {
+    RegisteredAllocator.ALLOCATOR.free(object);
+  }
+
+  static final class DefaultAllocator implements Allocator {
+
+    @Override
+    public char[] allocateChars(int size) {
+      return new char[size];
+    }
+
+    @Override
+    public long[] allocateLongs(int size) {
+      return new long[size];
+    }
+
+    @Override
+    @SuppressWarnings("unchecked")
+    public <T> T[] allocateObjects(Class<T> clazz, int size) {
+      return (T[]) Array.newInstance(clazz, size);
+    }
+
+    @Override
+    public long[] copy(long[] longs) {
+      return Arrays.copyOf(longs, longs.length);
+    }
+
+    @Override
+    public char[] copy(char[] chars) {
+      return Arrays.copyOf(chars, chars.length);
+    }
+
+    @Override
+    public char[] copy(char[] chars, int newSize) {
+      return Arrays.copyOf(chars, newSize);
+    }
+
+    @Override
+    public <T> T[] copy(T[] objects) {
+      return Arrays.copyOf(objects, objects.length);
+    }
+
+    @Override
+    public <T> T[] copy(T[] objects, int newSize) {
+      return Arrays.copyOf(objects, newSize);
+    }
+
+    @Override
+    public char[] extend(char[] chars, int newSize) {
+      return Arrays.copyOf(chars, newSize);
+    }
+
+    @Override
+    @SuppressWarnings("unchecked")
+    public <T> T[] extend(T[] objects, int newSize) {
+      return Arrays.copyOf(objects, newSize);
+    }
+
+    @Override
+    public void free(Object object) {
+      // do nothing
+    }
+  }
+}

RoaringBitmap/src/main/java/org/roaringbitmap/Allocator.java

@@ -0,0 +1,89 @@
+package org.roaringbitmap;
+
+public interface Allocator {
+
+  /**
+   * allocate a new array
+   * @param size the size of the array
+   * @return a newly allocated array which should be returned to the pool
+   */
+  char[] allocateChars(int size);
+
+  /**
+   * allocate a new array
+   * @param size the size of the array
+   * @return a newly allocated array which should be returned to the pool
+   */
+  long[] allocateLongs(int size);
+
+  /**
+   * Allocate a new array with the element type
+   * @param clazz the type of the elements
+   * @param size the size of the array
+   * @param <T> the type of the elements
+   * @return a newly allocated array which should be returned to the pool
+   */
+  <T> T[] allocateObjects(Class<T> clazz, int size);
+
+  /**
+   * Copies the array, does not free the input
+   * @param longs the array to be copied but not freed
+   * @return a newly allocated array which should be returned to the pool
+   */
+  long[] copy(long[] longs);
+
+  /**
+   * Copies the array, does not free the input
+   * @param chars the array to be copied but not freed
+   * @return a newly allocated array which should be returned to the pool
+   */
+  char[] copy(char[] chars);
+
+  /**
+   * Copies the array, does not free the input
+   * @param chars the array to be copied but not freed
+   * @param newSize the size of the new array
+   * @return a newly allocated array which should be returned to the pool
+   */
+  char[] copy(char[] chars, int newSize);
+
+  /**
+   * Copies the array, does not free the input
+   * @param objects to be copied but not freed
+   * @param <T> the type of the elements
+   * @return a newly allocated array which should be returned to the pool
+   */
+  <T> T[] copy(T[] objects);
+
+  /**
+   * Copies the array, does not free the input
+   * @param objects to be copied but not freed
+   * @param <T> the type of the elements
+   * @param newSize the size of the new array
+   * @return a newly allocated array which should be returned to the pool
+   */
+  <T> T[] copy(T[] objects, int newSize);
+
+  /**
+   * Copy and free the array, return a new array
+   * @param chars array which will be freed
+   * @param newSize the size of the new array
+   * @return a newly allocated array which should be returned to the pool
+   */
+  char[] extend(char[] chars, int newSize);
+
+  /**
+   * Copy and free the array, return a new array
+   * @param objects objects which will be freed
+   * @param newSize the size of the newly allocated array
+   * @param <T> the type
+   * @return a newly allocated array which should be returned to the pool
+   */
+  <T> T[] extend(T[] objects, int newSize);
+
+  /**
+   * free the object
+   * @param object the object to free, must not be used afterwards.
+   */
+  void free(Object object);
+}