add padding between the write counter and array buffer

ben-manes · Oct 29, 2023 · 4e6c4a1 · 4e6c4a1
1 parent ea0b0e1
commit 4e6c4a1
Showing 1 changed file with 46 additions and 27 deletions.
diff --git a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/BoundedBuffer.java b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/BoundedBuffer.java
@@ -54,8 +54,9 @@ protected Buffer<E> create(E e) {
     return new RingBuffer<>(e);
   }
 
-  static final class RingBuffer<E> extends BBHeader.ReadAndWriteCounterRef implements Buffer<E> {
-    static final VarHandle BUFFER = MethodHandles.arrayElementVarHandle(Object[].class);
+  /** Enforces a memory layout to avoid false sharing by padding the fields. */
+  static final class RingBuffer<E> extends BBHeader.PadRingBuffer implements Buffer<E> {
+    static final VarHandle READ, WRITE, BUFFER;
 
     final Object[] buffer;
 
@@ -113,6 +114,29 @@ public long reads() {
     public long writes() {
       return writeCounter;
     }
+
+    void setReadCounterOpaque(long count) {
+      READ.setOpaque(this, count);
+    }
+
+    long writeCounterOpaque() {
+      return (long) WRITE.getOpaque(this);
+    }
+
+    boolean casWriteCounter(long expect, long update) {
+      return WRITE.weakCompareAndSet(this, expect, update);
+    }
+
+    static {
+      var lookup = MethodHandles.lookup();
+      try {
+        BUFFER = MethodHandles.arrayElementVarHandle(Object[].class);
+        READ = lookup.findVarHandle(RingBuffer.class, "readCounter", long.class);
+        WRITE = lookup.findVarHandle(RingBuffer.class, "writeCounter", long.class);
+      } catch (ReflectiveOperationException e) {
+        throw new ExceptionInInitializerError(e);
+      }
+    }
   }
 }
 
@@ -161,32 +185,27 @@ abstract static class PadWriteCounter extends ReadCounterRef {
     byte p232, p233, p234, p235, p236, p237, p238, p239;
   }
 
-  /** Enforces a memory layout to avoid false sharing by padding the write counter. */
-  abstract static class ReadAndWriteCounterRef extends PadWriteCounter {
-    static final VarHandle READ, WRITE;
-
+  /** Enforces a memory layout to avoid false sharing by padding the read count. */
+  abstract static class WriteCounterRef extends PadWriteCounter {
     volatile long writeCounter;
+  }
 
-    void setReadCounterOpaque(long count) {
-      READ.setOpaque(this, count);
-    }
-
-    long writeCounterOpaque() {
-      return (long) WRITE.getOpaque(this);
-    }
-
-    boolean casWriteCounter(long expect, long update) {
-      return WRITE.weakCompareAndSet(this, expect, update);
-    }
-
-    static {
-      var lookup = MethodHandles.lookup();
-      try {
-        READ = lookup.findVarHandle(ReadCounterRef.class, "readCounter", long.class);
-        WRITE = lookup.findVarHandle(ReadAndWriteCounterRef.class, "writeCounter", long.class);
-      } catch (ReflectiveOperationException e) {
-        throw new ExceptionInInitializerError(e);
-      }
-    }
+  @SuppressWarnings("PMD.AbstractClassWithoutAbstractMethod")
+  abstract static class PadRingBuffer extends WriteCounterRef {
+    byte p240, p241, p242, p243, p244, p245, p246, p247;
+    byte p248, p249, p250, p251, p252, p253, p254, p255;
+    byte p256, p257, p258, p259, p260, p261, p262, p263;
+    byte p264, p265, p266, p267, p268, p269, p270, p271;
+    byte p272, p273, p274, p275, p276, p277, p278, p279;
+    byte p280, p281, p282, p283, p284, p285, p286, p287;
+    byte p288, p289, p290, p291, p292, p293, p294, p295;
+    byte p296, p297, p298, p299, p300, p301, p302, p303;
+    byte p304, p305, p306, p307, p308, p309, p310, p311;
+    byte p312, p313, p314, p315, p316, p317, p318, p319;
+    byte p320, p321, p322, p323, p324, p325, p326, p327;
+    byte p328, p329, p330, p331, p332, p333, p334, p335;
+    byte p336, p337, p338, p339, p340, p341, p342, p343;
+    byte p344, p345, p346, p347, p348, p349, p350, p351;
+    byte p352, p353, p354, p355, p356, p357, p358, p359;
   }
 }