我有一个具有可扩展性问题的 32 位 Java 服务:由于用户数过多，我们会因为线程数过多而耗尽内存。从长远来看，我计划切换到 64 位并降低每用户线程的比率。在短期内，我想减少堆栈大小(-Xss，-XX:ThreadStackSize)以获得更多的空间。但这是有风险的，因为如果我把它弄得太小，我就会得到 StackOverflowErrors。

如何测量应用程序的平均和最大堆栈大小以指导我决定最佳 -Xss 值？ 我对两种可能的方法感兴趣:

最佳答案

您可以通过类似于可以编织到您的代码的方面(加载时间编织器以允许建议除系统类加载器之外的所有已加载代码)之类的东西来了解堆栈深度。该方面将处理所有已执行的代码，并且能够记录您何时调用方法以及何时返回。您可以使用它来捕获大部分堆栈使用情况(您将错过从系统类加载器加载的任何内容，例如 java.*)。虽然不完美，但它避免了必须更改代码以在样本点收集 StackTraceElement[] 并且还让您进入您可能没有编写的非 jdk 代码。

例如(aspectj):

public aspect CallStackAdvice {

   pointcut allMethods() : execution(* *(..)) && !within(CallStackLog);

   Object around(): allMethods(){
       String called = thisJoinPoint.getSignature ().toLongString ();
       CallStackLog.calling ( called );
       try {
           return proceed();
       } finally {
           CallStackLog.exiting ( called );
       }
   }

}

public class CallStackLog {

    private CallStackLog () {}

    private static ThreadLocal<ArrayDeque<String>> curStack = 
        new ThreadLocal<ArrayDeque<String>> () {
        @Override
        protected ArrayDeque<String> initialValue () {
            return new ArrayDeque<String> ();
        }
    };

    private static ThreadLocal<Boolean> ascending = 
        new ThreadLocal<Boolean> () {
        @Override
        protected Boolean initialValue () {
            return true;
        }
    };

    private static ConcurrentHashMap<Integer, ArrayDeque<String>> stacks = 
         new ConcurrentHashMap<Integer, ArrayDeque<String>> ();

    public static void calling ( String signature ) {
        ascending.set ( true );
        curStack.get ().push ( signature.intern () );
    }

    public static void exiting ( String signature ) {
        ArrayDeque<String> cur = curStack.get ();
        if ( ascending.get () ) {
            ArrayDeque<String> clon = cur.clone ();
            stacks.put ( hash ( clon ), clon );
        }
        cur.pop ();
        ascending.set ( false );
    }

    public static Integer hash ( ArrayDeque<String> a ) {
        //simplistic and wrong but ok for example
        int h = 0;
        for ( String s : a ) {
            h += ( 31 * s.hashCode () );
        }
        return h;
    }

    public static void dumpStacks(){
        //implement something to print or retrieve or use stacks
    }
}

net.sourceforge.jtds.jdbc.TdsCore net.sourceforge.jtds.jdbc.JtdsStatement.getTds()
public boolean net.sourceforge.jtds.jdbc.JtdsResultSet.next()
public void net.sourceforge.jtds.jdbc.JtdsResultSet.close()
public java.sql.Connection net.sourceforge.jtds.jdbc.Driver.connect(java.lang.String, java.util.Properties)
public void phil.RandomStackGen.MyRunnable.run()

package phil.agent;

public class MaxStackLog {

    private static ThreadLocal<Integer> curStackSize = 
        new ThreadLocal<Integer> () {
        @Override
        protected Integer initialValue () {
            return 0;
        }
    };

    private static ThreadLocal<Integer> curStackDepth = 
        new ThreadLocal<Integer> () {
        @Override
        protected Integer initialValue () {
            return 0;
        }
    };

    private static ThreadLocal<Boolean> ascending = 
        new ThreadLocal<Boolean> () {
        @Override
        protected Boolean initialValue () {
            return true;
        }
    };

    private static ConcurrentHashMap<Long, Integer> maxSizes = 
        new ConcurrentHashMap<Long, Integer> ();
    private static ConcurrentHashMap<Long, Integer> maxDepth = 
        new ConcurrentHashMap<Long, Integer> ();

    private MaxStackLog () { }

    public static void enter ( int frameSize ) {
        ascending.set ( true );
        curStackSize.set ( curStackSize.get () + frameSize );
        curStackDepth.set ( curStackDepth.get () + 1 );
    }

    public static void exit ( int frameSize ) {
        int cur = curStackSize.get ();
        int curDepth = curStackDepth.get ();
        if ( ascending.get () ) {
            long id = Thread.currentThread ().getId ();
            Integer max = maxSizes.get ( id );
            if ( max == null || cur > max ) {
                maxSizes.put ( id, cur );
            }
            max = maxDepth.get ( id );
            if ( max == null || curDepth > max ) {
                maxDepth.put ( id, curDepth );
            }
        }
        ascending.set ( false );
        curStackSize.set ( cur - frameSize );
        curStackDepth.set ( curDepth - 1 );
    }

    public static void dumpMax () {
        int max = 0;
        for ( int i : maxSizes.values () ) {
            max = Math.max ( i, max );
        }
        System.out.println ( "Max stack frame size accummulated: " + max );
        max = 0;
        for ( int i : maxDepth.values () ) {
            max = Math.max ( i, max );
        }
        System.out.println ( "Max stack depth: " + max );
    }
}

package phil.agent;

public class Agent {

    public static void premain ( String agentArguments, Instrumentation ins ) {
        try {
            ins.appendToBootstrapClassLoaderSearch ( 
                new JarFile ( 
                    new File ( "path/to/Agent.jar" ) ) );
        } catch ( IOException e ) {
            e.printStackTrace ();
        }
        ins.addTransformer ( new Transformer (), true );
        Class<?>[] classes = ins.getAllLoadedClasses ();
        int len = classes.length;
        for ( int i = 0; i < len; i++ ) {
            Class<?> clazz = classes[i];
            String name = clazz != null ? clazz.getCanonicalName () : null;
            try {
                if ( name != null && !clazz.isArray () && !clazz.isPrimitive ()
                        && !clazz.isInterface () 
                        && !name.equals ( "java.lang.Long" )
                        && !name.equals ( "java.lang.Boolean" )
                        && !name.equals ( "java.lang.Integer" )
                        && !name.equals ( "java.lang.Double" ) 
                        && !name.equals ( "java.lang.Float" )
                        && !name.equals ( "java.lang.Number" ) 
                        && !name.equals ( "java.lang.Class" )
                        && !name.equals ( "java.lang.Byte" ) 
                        && !name.equals ( "java.lang.Void" )
                        && !name.equals ( "java.lang.Short" ) 
                        && !name.equals ( "java.lang.System" )
                        && !name.equals ( "java.lang.Runtime" )
                        && !name.equals ( "java.lang.Compiler" )
                        && !name.equals ( "java.lang.StackTraceElement" )
                        && !name.startsWith ( "java.lang.ThreadLocal" )
                        && !name.startsWith ( "sun." ) 
                        && !name.startsWith ( "java.security." )
                        && !name.startsWith ( "java.lang.ref." )
                        && !name.startsWith ( "java.lang.ClassLoader" )
                        && !name.startsWith ( "java.util.concurrent.atomic" )
                        && !name.startsWith ( "java.util.concurrent.ConcurrentHashMap" )
                        && !name.startsWith ( "java.util.concurrent.locks." )
                        && !name.startsWith ( "phil.agent." ) ) {
                    ins.retransformClasses ( clazz );
                }
            } catch ( Throwable e ) {
                System.err.println ( "Cant modify: " + name );
            }
        }

        Runtime.getRuntime ().addShutdownHook ( new Thread () {
            @Override
            public void run () {
                MaxStackLog.dumpMax ();
            }
        } );
    }
}

public class Transformer implements ClassFileTransformer {

    @Override
    public byte[] transform ( ClassLoader loader, 
        String className, Class<?> classBeingRedefined,
            ProtectionDomain protectionDomain, byte[] classfileBuffer )
            throws IllegalClassFormatException {

        if ( className.startsWith ( "phil/agent" ) ) {
            return classfileBuffer;
        }

        byte[] result = classfileBuffer;
        ClassReader reader = new ClassReader ( classfileBuffer );
        MaxStackClassVisitor maxCv = new MaxStackClassVisitor ( null );
        reader.accept ( maxCv, ClassReader.SKIP_DEBUG );

        ClassWriter writer = new ClassWriter ( ClassWriter.COMPUTE_FRAMES );
        ClassVisitor visitor = 
            new CallStackClassVisitor ( writer, maxCv.frameMap, className );
        reader.accept ( visitor, ClassReader.SKIP_DEBUG );
        result = writer.toByteArray ();
        return result;
    }
}

public class MaxStackClassVisitor extends ClassVisitor {

    Map<String, Integer> frameMap = new HashMap<String, Integer> ();

    public MaxStackClassVisitor ( ClassVisitor v ) {
        super ( Opcodes.ASM4, v );
    }

    @Override
    public MethodVisitor visitMethod ( int access, String name, 
        String desc, String signature,
            String[] exceptions ) {
        return new MaxStackMethodVisitor ( 
            super.visitMethod ( access, name, desc, signature, exceptions ), 
            this, ( access + name + desc + signature ) );
    }
}

public class MaxStackMethodVisitor extends MethodVisitor {

    final MaxStackClassVisitor cv;
    final String name;

    public MaxStackMethodVisitor ( MethodVisitor mv, 
        MaxStackClassVisitor cv, String name ) {
        super ( Opcodes.ASM4, mv );
        this.cv = cv;
        this.name = name;
    }

    @Override
    public void visitMaxs ( int maxStack, int maxLocals ) {
        cv.frameMap.put ( name, ( maxStack + maxLocals ) * 4 );
        super.visitMaxs ( maxStack, maxLocals );
    }
}

public class CallStackClassVisitor extends ClassVisitor {

    final Map<String, Integer> frameSizes;
    final String className;

    public CallStackClassVisitor ( ClassVisitor v, 
        Map<String, Integer> frameSizes, String className ) {
        super ( Opcodes.ASM4, v );
        this.frameSizes = frameSizes;
        this.className = className;
    }

    @Override
    public MethodVisitor visitMethod ( int access, String name, 
        String desc, String signature, String[] exceptions ) {
        MethodVisitor m = super.visitMethod ( access, name, desc, 
                             signature, exceptions );
        return new CallStackMethodVisitor ( m, 
                 frameSizes.get ( access + name + desc + signature ) );
    }
}

public class CallStackMethodVisitor extends MethodVisitor {

    final int size;

    public CallStackMethodVisitor ( MethodVisitor mv, int size ) {
        super ( Opcodes.ASM4, mv );
        this.size = size;
    }

    @Override
    public void visitCode () {
        visitIntInsn ( Opcodes.SIPUSH, size );
        visitMethodInsn ( Opcodes.INVOKESTATIC, "phil/agent/MaxStackLog",
                "enter", "(I)V" );
        super.visitCode ();
    }

    @Override
    public void visitInsn ( int inst ) {
        switch ( inst ) {
            case Opcodes.ARETURN:
            case Opcodes.DRETURN:
            case Opcodes.FRETURN:
            case Opcodes.IRETURN:
            case Opcodes.LRETURN:
            case Opcodes.RETURN:
            case Opcodes.ATHROW:
                visitIntInsn ( Opcodes.SIPUSH, size );
                visitMethodInsn ( Opcodes.INVOKESTATIC,
                        "phil/agent/MaxStackLog", "exit", "(I)V" );
                break;
            default:
                break;
        }

        super.visitInsn ( inst );
    }
}

Manifest-Version: 1.0
Premain-Class: phil.agent.Agent
Boot-Class-Path: asm-all-4.0.jar
Can-Retransform-Classes: true

-javaagent:path/to/Agent.jar

Max stack frame size accummulated: 44140
Max stack depth: 1004

关于java - 如何测量线程堆栈深度？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/8328679/