修复mem计算逻辑 (alibaba#12401)

* 修复mem计算逻辑

* 修复mem计算逻辑单测

* fix ci

sys/src/main/java/com/alibaba/nacos/sys/env/EnvUtil.java

@@ -328,7 +328,7 @@ public static float getCpu() {
 
     public static float getMem() {
         return (float) (1
-                - OperatingSystemBeanManager.getFreePhysicalMem() / OperatingSystemBeanManager.getTotalPhysicalMem());
+                - (double) OperatingSystemBeanManager.getFreePhysicalMem() / (double) OperatingSystemBeanManager.getTotalPhysicalMem());
     }
 
     public static String getConfPath() {

sys/src/test/java/com/alibaba/nacos/sys/env/EnvUtilTest.java

@@ -0,0 +1,53 @@
+/*
+ * Copyright 1999-2020 Alibaba Group Holding Ltd.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.alibaba.nacos.sys.env;
+
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeEach;
+
+import org.junit.jupiter.api.Test;
+import org.mockito.MockedStatic;
+import org.mockito.Mockito;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+class EnvUtilTest {
+
+    MockedStatic<OperatingSystemBeanManager> systemBeanManagerMocked;
+
+    @BeforeEach
+    void before() {
+        systemBeanManagerMocked = Mockito.mockStatic(OperatingSystemBeanManager.class);
+    }
+
+    @AfterEach
+    void after() {
+        if (!systemBeanManagerMocked.isClosed()) {
+            systemBeanManagerMocked.close();
+        }
+    }
+
+    @Test
+    public void testGetMem() {
+        systemBeanManagerMocked.when(() -> OperatingSystemBeanManager.getFreePhysicalMem()).thenReturn(123L);
+        systemBeanManagerMocked.when(() -> OperatingSystemBeanManager.getTotalPhysicalMem()).thenReturn(2048L);
+        assertEquals(EnvUtil.getMem(), 1 - ((double) 123L / (double) 2048L));
+
+        systemBeanManagerMocked.when(() -> OperatingSystemBeanManager.getFreePhysicalMem()).thenReturn(0L);
+        assertEquals(EnvUtil.getMem(), 1 - ((double) 0L / (double) 2048L));
+    }
+}