thread arena

Author: Kuangcp

class/src/main/java/jvm/oom/DirectMemoryGlibcGrow.java

@@ -1,12 +1,62 @@
 package jvm.oom;
 
+import jvm.MallocBench;
+import lombok.extern.slf4j.Slf4j;
+
+import java.nio.ByteBuffer;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.ThreadLocalRandom;
+import java.util.concurrent.TimeUnit;
+
 /**
  * https://github.com/Kuangcp/Note/blob/master/Linux/Base/LinuxBase.md#glibc-ptmalloc2
  *
  * @author Kuangcp
  * 2025-05-15 21:59
+ * @see MallocBench
  */
+@Slf4j
 public class DirectMemoryGlibcGrow {
     //TODO 模拟出Glibc thread arena 占用大的情况
     //TODO 替换 jemalloc 后查看是否有问题
+
+
+    // https://medium.com/@daniyal.hass/how-glibc-memory-handling-affects-java-applications-the-hidden-cost-of-fragmentation-8e666ee6e000
+    public static void fragment() throws InterruptedException {
+        List<ByteBuffer> buffers = new ArrayList<>();
+        // Allocate large buffers and release them to see memory impact
+        for (int i = 0; i < 50; i++) {
+            int delta = ThreadLocalRandom.current().nextInt(100) + 33;
+            System.out.print(delta + ", ");
+            buffers.add(ByteBuffer.allocateDirect(delta * 1024 * 1024)); // 100 MB each
+
+            buffers.remove(0);
+//            if (i % 2 == 0) buffers.remove(0); // Simulate variable memory usage
+        }
+
+        System.out.println("Memory allocations complete. Check OS memory usage.");
+    }
+
+    public static void loopFragment() throws InterruptedException {
+        TimeUnit.SECONDS.sleep(10);
+        ExecutorService xo = Executors.newFixedThreadPool(3);
+        Runnable run = () -> {
+            try {
+                for (int i = 0; i < 1000; i++) {
+                    TimeUnit.SECONDS.sleep(3);
+                    fragment();
+                    System.out.println("loop " + i);
+                }
+            } catch (Exception e) {
+                log.error("", e);
+            }
+        };
+        xo.submit(run);
+        xo.submit(run);
+
+    }
+
 }

class/src/main/java/jvm/oom/DirectMemoryOOM.java

@@ -27,7 +27,7 @@ public class DirectMemoryOOM {
     // 注意： -XX:MaxDirectMemorySize参数只对由DirectByteBuffer分配的内存有效限制，对Unsafe直接分配的内存无效
 
     /**
-     * C语言malloc申请的也是虚拟内存,没有设置值的话操作系统不会分配物理内存
+     * C语言malloc申请的是虚拟内存,没有设置值的话操作系统不会分配物理内存
      *
      * @see java.nio.DirectByteBuffer#DirectByteBuffer(int)
      * <p>

class/src/test/java/jvm/oom/DirectMemoryGlibcGrowTest.java

@@ -0,0 +1,25 @@
+package jvm.oom;
+
+import org.junit.Test;
+
+/**
+ * @author Kuangcp
+ * 2025-05-19 21:36
+ */
+public class DirectMemoryGlibcGrowTest {
+
+    @Test
+    public void testFragment() throws Exception {
+        DirectMemoryGlibcGrow.fragment();
+        Thread.currentThread().join();
+    }
+
+    /**
+     * pmap -x 259296 | jvm-tool -s 查看块数量
+     */
+    @Test
+    public void testLoopFragment() throws Exception {
+        DirectMemoryGlibcGrow.loopFragment();
+        Thread.currentThread().join();
+    }
+}