Tomcat 加载包导致OOM
遇到一个问题,启动时加载facade包后,导致出现tomcat启动时出现大量OOM,创建了超过2G的UNKNOW的对象
环境介绍
当前使用的是java8+ tomcat 7.0.54
结果分析
首先获取下内存 dump,进行分析,这里我推荐使用JProfile工具可视化程度较高,方便快捷,加载完之后可以显然看到2个异常的地方
- 启动的时候创建了超过2G的Unknow对象
-
tomcat localhost-startstop线程,启动的时候出现了OOM的异常
这里的OOM堆栈的上一个行为就是创建Unknow的对象,正好印证了OOM的罪魁祸首在这个代码中
过程分析
从第二点的调用堆栈可以明显看出,在调用 org.apache.catalina.startup.ContextConfig#webConfig的时候出现的OOM,而我们提供的Facade的包的主要功能就是提供dubbo接口,而我启动的项目的dubbo加载是通过配置dubbo- reference xml进行加载,整个流程如下
- 项目为tomcat项目,需要在
web.xml写入需要加载的spring-application.xml,启动的时候才会去初始化对应的spring bean. - 我们在初始化dubbo接口的时候,dubbo的接口是写在xml中, 所以也会由上面描述的
#webConfig对我们写入的xml进行处理 - 当我们Facade的接口去初始化的时候,会通过tomcat的
classFile.parse(),这个时候解析异常,最终出现大量UNKNOW实例 (这里为啥会出现大量对象的原因没有找到,按照加载逻辑是不会同时出现图中1百万个对象)
知道了产生这个UNKNOW的过程,现在最主要的问题是什么情况下产生这个问题,实践出真知,接下来分析下产生的条件,
首先我们需要准备一个tomcat-7.0.54包
wget https://archive.apache.org/dist/tomcat/tomcat-7/v7.0.54/src/apache-tomcat-7.0.54-src.tar.gz
首先是org.apache.catalina.startup.ContextConfig#processAnnotationsStream这里就是加载jar包中的类并转成对应JavaClass
protected void processAnnotationsStream(InputStream is, WebXml fragment,
boolean handlesTypesOnly)
throws ClassFormatException, IOException {
ClassParser parser = new ClassParser(is, null);
JavaClass clazz = parser.parse();
checkHandlesTypes(clazz);
...
}
后面的主要问题在parse() 中的
public static final Attribute readAttribute(DataInputStream file,
ConstantPool constant_pool) throws IOException,
ClassFormatException
{
ConstantUtf8 c;
String name;
int name_index;
int length;
byte tag = Constants.ATTR_UNKNOWN; // Unknown attribute
// Get class name from constant pool via `name_index' indirection
// 通过“name_index”间接从常量池中获取类名
name_index = file.readUnsignedShort();
// 找到映射关系
c = (ConstantUtf8) constant_pool.getConstant(name_index,
Constants.CONSTANT_Utf8);
name = c.getBytes();
// Length of data in bytes
length = file.readInt();
// Compare strings to find known attribute
// System.out.println(name);
for (byte i = 0; i < Constants.KNOWN_ATTRIBUTES; i++)
{
if (name.equals(Constants.ATTRIBUTE_NAMES[i]))
{
tag = i; // found!
break;
}
}
// Call proper constructor, depending on `tag'
switch (tag)
{
case Constants.ATTR_UNKNOWN:
AttributeReader r = readers.get(name);
if (r != null)
{
return r.createAttribute(name_index, length, file,
constant_pool);
}
return new Unknown(name_index, length, file, constant_pool);
...
//后面忽略
}
可见其执行逻辑是:
- 读取class文件,获取当前属性
- 循环判断该属性是不是其tomcat写死的属性表中的类型
- 根据其属性创建不同的Attribute
这里涉及到属性表, 在class文件,字段表,方法表都可以携带自己的属性表集合,以描述某些场景特有信息,任何人实现的编译器都可以向属性表写入自己的属性.虚拟机在执行的时候会忽略不认识的属性.在最新的Java SE 12中,预定义属性已经增加到29项,下面是一些常用的属性
而在当前版本Tomcat中定义的属性表为:
public static final String[] ATTRIBUTE_NAMES = {
"SourceFile", "ConstantValue", "Code", "Exceptions",
"LineNumberTable", "LocalVariableTable",
"InnerClasses", "Synthetic", "Deprecated",
"PMGClass", "Signature", "StackMap",
"RuntimeVisibleAnnotations", "RuntimeInvisibleAnnotations",
"RuntimeVisibleParameterAnnotations", "RuntimeInvisibleParameterAnnotations",
"AnnotationDefault", "LocalVariableTypeTable", "EnclosingMethod", "StackMapTable",
"BootstrapMethods", "MethodParameters"
};
可见有些属性在tomcat中是没有定义到的,而当其没有找到定义的时候,就会去创建UNKNOW对象,到这里UNKNOW对象产生的流程已经出来了,不过要去验证下我们提供的jar包是否真的会产生该问题
源jar包分析
由于我们提供的jar包实体是非常的简单的,只有接口与类,pom.xml中包含的jar包如下
<dependency>
<groupId>javax.validation</groupId>
<artifactId>validation-api</artifactId>
<version>${version.validation-api}</version>
<optional>true</optional>
</dependency>
<dependency>
<groupId>com.fasterxml.jackson.core</groupId>
<artifactId>jackson-annotations</artifactId>
<version>${version.fasterxml.jackson}</version>
<optional>true</optional>
</dependency>
只有Lombok,validation,jackson的相关注解,我们在一系列排除后怀疑到了2个主要注解上
- Lombok包提供的注解
- Validation提供的注解
然后我们找了一个类,对其class进行反汇编分析
import lombok.Data;
import javax.validation.Valid;
import javax.validation.constraints.Max;
import javax.validation.constraints.NotNull;
import java.io.Serializable;
@Data
public class ReceiveLimitIdentityDTO implements Serializable {
/**
* 限制维度类型
*
*/
@NotNull(message = "限制维度类型不能为空.", groups = {ActActivityReq.GroupAdd.class, ActActivityReq.GroupModify.class})
private Integer dimensionType;
/**
* 每日统计限制
*/
@NotNull(message = "每日统计限制不能为空.", groups = {ActActivityReq.GroupAdd.class, ActActivityReq.GroupModify.class})
@Valid
private StatLimit dayStatLimit;
/**
* 累计统计限制
*/
@NotNull(message = "累计统计限制不能为空.", groups = {ActActivityReq.GroupAdd.class, ActActivityReq.GroupModify.class})
@Valid
private StatLimit totalStatLimit;
@Data
public static class StatLimit implements Serializable {
/**
* 限制类型 type 0无限次 1限次
*/
@NotNull(message = "限制类型不能为空.", groups = {ActActivityReq.GroupAdd.class, ActActivityReq.GroupModify.class})
private Integer type;
/**
* 限制次数 -1无限制
*/
@Max(value = 999, message = "限制次数不能大于999.", groups = {ActActivityReq.GroupAdd.class, ActActivityReq.GroupModify.class})
@NotNull(message = "限制次数不能为空.", groups = {ActActivityReq.GroupAdd.class, ActActivityReq.GroupModify.class})
private Integer num;
}
}
生成的反编译文件如下
Classfile /Users/fulln/IdeaProjects/demo/target/classes/com/example/demo/tomcat/ReceiveLimitIdentityDTO.class
Last modified 2021-12-13; size 3667 bytes
MD5 checksum 9c50a675fb864b5ca41a2f596ad06ebb
Compiled from "ReceiveLimitIdentityDTO.java"
public class com.example.demo.tomcat.ReceiveLimitIdentityDTO implements java.io.Serializable
minor version: 0
major version: 52
flags: ACC_PUBLIC, ACC_SUPER
Constant pool:
#1 = Methodref #21.#91 // java/lang/Object."<init>":()V
#2 = Fieldref #5.#92 // com/example/demo/tomcat/ReceiveLimitIdentityDTO.dimensionType:Ljava/lang/Integer;
#3 = Fieldref #5.#93 // com/example/demo/tomcat/ReceiveLimitIdentityDTO.dayStatLimit:Lcom/example/demo/tomcat/ReceiveLimitIdentityDTO$StatLimit;
#4 = Fieldref #5.#94 // com/example/demo/tomcat/ReceiveLimitIdentityDTO.totalStatLimit:Lcom/example/demo/tomcat/ReceiveLimitIdentityDTO$StatLimit;
#5 = Class #95 // com/example/demo/tomcat/ReceiveLimitIdentityDTO
#6 = Methodref #5.#96 // com/example/demo/tomcat/ReceiveLimitIdentityDTO.canEqual:(Ljava/lang/Object;)Z
#7 = Methodref #5.#97 // com/example/demo/tomcat/ReceiveLimitIdentityDTO.getDimensionType:()Ljava/lang/Integer;
#8 = Methodref #21.#98 // java/lang/Object.equals:(Ljava/lang/Object;)Z
#9 = Methodref #5.#99 // com/example/demo/tomcat/ReceiveLimitIdentityDTO.getDayStatLimit:()Lcom/example/demo/tomcat/ReceiveLimitIdentityDTO$StatLimit;
#10 = Methodref #5.#100 // com/example/demo/tomcat/ReceiveLimitIdentityDTO.getTotalStatLimit:()Lcom/example/demo/tomcat/ReceiveLimitIdentityDTO$StatLimit;
#11 = Methodref #21.#101 // java/lang/Object.hashCode:()I
#12 = Class #102 // java/lang/StringBuilder
#13 = Methodref #12.#91 // java/lang/StringBuilder."<init>":()V
#14 = String #103 // ReceiveLimitIdentityDTO(dimensionType=
#15 = Methodref #12.#104 // java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
#16 = Methodref #12.#105 // java/lang/StringBuilder.append:(Ljava/lang/Object;)Ljava/lang/StringBuilder;
#17 = String #106 // , dayStatLimit=
#18 = String #107 // , totalStatLimit=
#19 = String #108 // )
#20 = Methodref #12.#109 // java/lang/StringBuilder.toString:()Ljava/lang/String;
#21 = Class #110 // java/lang/Object
#22 = Class #111 // java/io/Serializable
#23 = Class #112 // com/example/demo/tomcat/ReceiveLimitIdentityDTO$StatLimit
#24 = Utf8 StatLimit
#25 = Utf8 InnerClasses
#26 = Utf8 dimensionType
#27 = Utf8 Ljava/lang/Integer;
#28 = Utf8 RuntimeVisibleAnnotations
#29 = Utf8 Ljavax/validation/constraints/NotNull;
#30 = Utf8 message
#31 = Utf8 限制维度类型不能为空.
#32 = Utf8 groups
#33 = Class #114 // com/example/demo/tomcat/ActActivityReq$GroupAdd
#34 = Utf8 GroupAdd
#35 = Utf8 Lcom/example/demo/tomcat/ActActivityReq$GroupAdd;
#36 = Class #115 // com/example/demo/tomcat/ActActivityReq$GroupModify
#37 = Utf8 GroupModify
#38 = Utf8 Lcom/example/demo/tomcat/ActActivityReq$GroupModify;
#39 = Utf8 RuntimeVisibleTypeAnnotations
...
//后面省略
发现了# 39 常量.也就是对应validate包中的 @NotNull(message = "限制维度类型不能为空.", groups = {ActActivityReq.GroupAdd.class, ActActivityReq.GroupModify.class})反汇编出来使用的属性是RuntimeVisibleTypeAnnotations,没有出现在Tomcat的属性表中,至此,产生的逻辑也出现了
待解决
现在仍然需要解决的问题是
- 即使是在字段上面,但是创建总一百万个Objects,也是不太能实现的,内存也没有出现一直增长,只是启动时的飙升
欢迎讨论指教上面疑问