Simplify BUFFER_COUNT in ConcurrentLruCache to a constant

The detectNumberOfBuffers() method attempted to scale the read
buffer count based on the number of available processors, but used
Math.min(4, nextPowerOfTwo) which effectively caps the result at 4
regardless of CPU count. For systems with fewer than 3 processors,
the buffer count would be reduced below 4, but this edge case adds
complexity without measurable benefit.

Simplify BUFFER_COUNT to a constant value of 4, removing the
unnecessary CPU-detection logic.

Closes gh-36872

Signed-off-by: seungchan <s24041@gsm.hs.kr>

Author: s-chan-o

spring-core/src/main/java/org/springframework/util/ConcurrentLruCache.java

@@ -367,7 +367,7 @@ boolean isActive() {
 
 	private static final class ReadOperations<K, V> {
 
-		private static final int BUFFER_COUNT = detectNumberOfBuffers();
+		private static final int BUFFER_COUNT = 4;
 
 		private static final int BUFFERS_MASK = BUFFER_COUNT - 1;
 
@@ -450,11 +450,6 @@ private void drainReadBuffer(int bufferIndex) {
 			this.processedCount.lazySet(bufferIndex, writeCount);
 		}
 
-		private static int detectNumberOfBuffers() {
-			int availableProcessors = Runtime.getRuntime().availableProcessors();
-			int nextPowerOfTwo = 1 << (Integer.SIZE - Integer.numberOfLeadingZeros(availableProcessors - 1));
-			return Math.min(4, nextPowerOfTwo);
-		}
 	}