复制代码//Class.newInstance()
//只能调用public属性的无参构造函数  
A a = (A)Class.forName(A.class.getName()).newInstance();  

//Constructor.newInstance()
Class c= Class.forName(A.class.getName());
   
/*以下调用无参的、私有构造函数*/  
//获得无参构造
Constructor c0=c.getDeclaredConstructor();  
//设置无参构造是可访问的
c0.setAccessible(true);   
A a0=(A)c0.newInstance();
    
//调用无参构造函数，生成对象实例
/*以下调用带参的、私有构造函数*/   
Constructor c1=c.getDeclaredConstructor(new Class[]{int.class,int.class});   
c1.setAccessible(true);   
//调用有参构造函数，生成对象实例 
A a1=(A)c1.newInstance(new Object[]{5,6});

复制代码//获取Class对象
Class aClass = MyObject.class
//通过Class对象获取Field对象
Field field = aClass.getDeclaredField("someField");
//设置可访问权限
field.setAccessible(true);

MyObject objectInstance = new MyObject();

//获取特定的对象的变量属性值
Object value = field.get(objectInstance);
//给特定对象的变量设置属性
field.set(objetInstance, value);

复制代码java.lang.NullPointerException
  at ......
  at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
  at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
  at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
  at java.lang.reflect.Method.invoke(Method.java:497)

复制代码//获取一个方法名为doSomesthing，参数类型为String的方法
Method method = MyObject.class.getMethod("doSomething", String.class);

//调用静态的doSomesthing方法，传递参数"parameter-value1"
Object returnValue = method.invoke(null, "parameter-value1");

复制代码    

    //add方法也就是直接调用offer方法
    public boolean offer(E e) {
        //不允许插入null
        if (e == null)
            throw new NullPointerException();
        modCount++;
        int i = size;
        //容量不够则进行扩容
        if (i >= queue.length)
            grow(i + 1);
        siftUp(i, e);//这里调用了上浮
        size = i + 1;
        return true;
    }
    
    //上浮分为两种情况，判断是否设置了comparator
    private void siftUp(int k, E x) {
        if (comparator != null)
            siftUpUsingComparator(k, x);
        else
            siftUpComparable(k, x);
    }

    //我们只分析这种没有设置comparator的方法，另一种类比
    private void siftUpComparable(int k, E x) {
        Comparable<? super E> key = (Comparable<? super E>) x;
        while (k > 0) {
            //找到父节点
            int parent = (k - 1) >>> 1;
            Object e = queue[parent];
            //如果当前节点大于父节点则上浮结束
            if (key.compareTo((E) e) >= 0)
                break;
            //否则，将父节点下沉
            queue[k] = e;
            k = parent;
        }
        //将节点赋值到正确的上浮位置
        queue[k] = key;
    }
    
    //poll方法
    public E poll() {
        //如果没有元素，则返回null
        if (size == 0)
            return null;
        int s = --size;
        modCount++;
        //返回根节点
        E result = (E) queue[0];
        E x = (E) queue[s];
        //将队尾元素移到根节点，并进行下沉
        queue[s] = null;
        //队列中不止一个元素，则进行下沉
        if (s != 0)
            siftDown(0, x);
        return result;
    }
    
    //下沉方法的实现与上浮类似，就不赘述了。

复制代码/**
     * No1.塔树选择和最大问题
     *
     * 一个高度为N的由正整数组成的三角形，从上走到下，求经过的数字和的最大值。
     * 每次只能走到下一层相邻的数上，例如从第3层的6向下走，只能走到第4层的2或9上。
     *      5
     *     8 4
     *    3 6 9
     *   7 2 9 5
     * 例子中的最优方案是：5 + 8 + 6 + 9 = 28
     *
     * 输入：符合塔树的二维数组。
     * 输出：经过的最大值。
     */

/**
     * No2.∑乘法表问题
     *
     * ∑ | a	b	c
     * ——————————————
     * a | b	b	a
     * b | c	b	a
     * c | a	c	c
     *
     * 依此乘法表,对任一定义于∑上的字符串,适当加括号表达式后得到一个表达式。
     * 例如,对于字符串x=bbbba,它的其中一个加括号表达式为i(b(bb))(ba)。
     * 依乘法表,该表达式的值为a。试设计一个动态规划算法,对任一定义于∑上的字符串x=x1x2…xn。
     * 计算有多少种不同的加括号方式,使由x导出的加括号表达式的值为a。
     *
     * 输入：输入一个以a,b,c组成的任意一个字符串。
     * 输出：计算出的加括号方式数。
     */

/**
     * No.3跳台阶
     *
     * 一只青蛙一次可以跳上1级台阶，也可以跳上2级。
     * 求该青蛙跳上一个n级的台阶总共有多少种跳法。
     *
     * 输入：台阶数n。
     * 输出：跳法总数。
     */

/**
     * No.4最长递增子序列(LIS)
     *
     * 给定一个长度为N的数组，找出一个最长的单调自增子序列（不一定连续，但是顺序不能乱）。
     * 例如：给定一个长度为6的数组A{5， 6， 7， 1， 2， 8}。
     * 则其最长的单调递增子序列为{5，6，7，8}，长度为4。
     *
     * 输入：一个数组。
     * 输出：最长递增子序列的长度。
     */

/**
     * No.5背包问题
     *
     * 有N件物品和一个容量为V的背包。
     * 第i件物品的大小是c[i]，价值是w[i]。
     * 求解将哪些物品装入背包可使价值总和最大。
     *
     * 输入：物品大小数组c,物品价值数组w,背包容量。
     * 输出：最大的价值。
     */

/**
     * No.6最长公共子序列(LCS)
     *
     * 给出两个字符串a, b，求它们的最长的公共子序列。
     *
     * 输入：字符串a和字符串b。
     * 输出：最长的公共子序列的长度。
     */

复制代码mysql> create user 用户名 identified by "密码"

复制代码mysql> show databases;

+--------------------+

| Database           |

+--------------------+

| information_schema |

+--------------------+

1 row in set (0.00 sec)

复制代码mysql> rename user 旧用户名 to 新用户名

复制代码shell> mysqladmin -u 用户名 -p password "新密码"



提示需要输入旧密码

复制代码mysql> alter user 'root'@'localhost' IDENTIFIED BY '新密码'

复制代码mysql> alter user user() IDENTIFIED BY '新密码'

复制代码mysql> SET PASSWORD FOR 'root'@'localhost' = '新密码'

复制代码mysql> SET PASSWORD = '新密码';

复制代码mysql> grant usage on *.* to "用户名"@"%" identified by "新密码"

复制代码shell> service mysqld stop

复制代码ALTER USER 'root'@'localhost' IDENTIFIED BY '新密码';

复制代码shell> mysqld --user=root --init-file=/root/mysql-init &

复制代码[ERROR] Could not open unix socket lock file /var/lib/mysql/mysql.sock.lock

复制代码chown -R mysql:mysql /var/lib/mysql/mysql.sock



chown -R mysql:mysql /var/lib/mysql/mysql.sock.lock

复制代码mysql> drop user 用户名

复制代码mysql> grant all on *.* to 用户名

复制代码mysql> revoke all on *.* from 用户名

复制代码mysql> grant all on 数据库名.* to 用户名

复制代码mysql> revoke all on 数据库名.* from 用户名

复制代码mysql> grant select,insert,update on 数据库名.表名 to 用户名

复制代码shell>mysqldump -h 主机名 -u 用户名 -p --all-databases > dump.sql



提示输入密码

复制代码shell>mysqldump -h 主机名 -u 用户名 -p --databases 库名1 [库名2 ...] > dump.sql



提示输入密码

复制代码shell>mysqldump -h 主机名 -u 用户名 -p 库名 表名1 [表名2 ...] > dump.sql



提示输入密码

复制代码shell> mysql -uroot -p < dump.sql



提示输入密码

复制代码mysql> source  dump.sql

复制代码shell> mysql -uroot -p 库名 < dump.sql



提示输入密码

复制代码The authenticity of host 'host (12.18.429.21)' can't be established.
　　RSA key fingerprint is 98:2e:d7:e0:de:9f:ac:67:28:c2:42:2d:37:16:58:4d.
　　Are you sure you want to continue connecting (yes/no)?

复制代码　　Warning: Permanently added 'host,12.18.429.21' (RSA) to the list of known hosts.

复制代码ssh-keygen -t rsa //此处一路回车,生成秘钥

scp .ssh/id_rsa.pub 192.168.32.102:~/ //把秘钥拷贝到其他远程机器

ssh 192.168.30.102 ‘cat id_rsa.pub >> .ssh/authorized_keys’ //(远程执行命令)在远程机器上生成认证文件

复制代码#!/usr/bin bash
docommand()
{
    hosts=`sed -n '/^[^#]/p' hostlist`
    for host in $hosts
        do
            echo "" # 换个行
            ssh $host "$@"
        done
    return 0
}
if [ $# -lt 1  ]
then
    echo "$0 cmd"
    exit
fi
docommand "$@"

复制代码192.168.32.102
192.168.32.105
192.168.32.109
192.168.32.110

复制代码alias devpssh='bash /home/developer/runcommand.sh'

复制代码devpssh 'cat /var/log/nginx/api_acces.log | grep curuserid=2614677 | tail -1'

复制代码pdfsigner.detach()

复制代码pdfsigner.signExternalContainer()

复制代码/**
 * Interface to sign a document. The signing is fully done externally, including the container composition.
 * 这是一个用来签署文件的接口，它让所有的签名都完全来自于外部扩展实现。
 * @author Paulo Soares
 */
public interface IExternalSignatureContainer {

    /**
     * Produces the container with the signature.
     * @param data the data to sign
     * @return a container with the signature and other objects, like CRL and OCSP. The container will generally be a PKCS7 one.
     * @throws GeneralSecurityException
     */
    byte[] sign(InputStream data) throws GeneralSecurityException;

    /**
     * Modifies the signature dictionary to suit the container. At least the keys {@link PdfName#Filter} and
     * {@link PdfName#SubFilter} will have to be set.
     * @param signDic the signature dictionary
     */
    void modifySigningDictionary(PdfDictionary signDic);
}

复制代码    /**
     * Sign the document using an external container, usually a PKCS7. The signature is fully composed
     * externally, iText will just put the container inside the document.
     * <br><br>
     * NOTE: This method closes the underlying pdf document. This means, that current instance
     * of PdfSigner cannot be used after this method call.
     *
     * @param externalSignatureContainer the interface providing the actual signing
     * @param estimatedSize              the reserved size for the signature
     * @throws GeneralSecurityException
     * @throws IOException
     */
    public void signExternalContainer(IExternalSignatureContainer externalSignatureContainer, int estimatedSize) throws GeneralSecurityException, IOException {
        //省略部分源码
        
        //关注这里，调用getRangeStream()方法获取到要签名的数据
        //传入到externalSignatureContainer.sign()方法里给我们签
        InputStream data = getRangeStream();
        byte[] encodedSig = externalSignatureContainer.sign(data);
        
        //省略部分源码


    /**
     * Gets the document bytes that are hashable when using external signatures. 在使用外部签名的时候会返回可用于哈希的文件字节。
     * The general sequence is:
     * {@link #preClose(Map)}, {@link #getRangeStream()} and {@link #close(PdfDictionary)}.
     *
     * @return The {@link InputStream} of bytes to be signed.
     * 返回用于签名的字节
     */
    protected InputStream getRangeStream() throws IOException {
        RandomAccessSourceFactory fac = new RandomAccessSourceFactory();
        return new RASInputStream(fac.createRanged(getUnderlyingSource(), range));
    }

复制代码IExternalSignatureContainer externalP7DetachSignatureContainer = new IExternalSignatureContainer() {
        @Override
        public byte[] sign(InputStream data) throws GeneralSecurityException {
        
            //将要签名的数据进行 P7不带原文 签名
            byte[] result = SignUtil.P7DetachSigned(data);
            
            return result;
        }

        //必须设置 PdfName.Filter 和 PdfName.SubFilter
        @Override
        public void modifySigningDictionary(PdfDictionary signDic) {
            signDic.put(PdfName.Filter, PdfName.Adobe_PPKLite);
            //注意这里
            signDic.put(PdfName.SubFilter, PdfName.Adbe_pkcs7_detached);
        }
    };

复制代码IExternalSignatureContainer externalP7Sha1SignatureContainer = new IExternalSignatureContainer() {
        @Override
        public byte[] sign(InputStream data) throws GeneralSecurityException {
        
            //对要签名的数据先进行哈希
            byte[]hashData = HashUtil.hash(data , "SHA-1");
            //将哈希后的数据进行 P7带原文 签名
            byte[] result = SignUtil.P7AttachSigned(hashData);
            
            return result;
        }

        //必须设置 PdfName.Filter 和 PdfName.SubFilter
        @Override
        public void modifySigningDictionary(PdfDictionary signDic) {
            signDic.put(PdfName.Filter, PdfName.Adobe_PPKLite);
            //注意这里
            signDic.put(PdfName.SubFilter, PdfName.Adbe_pkcs7_sha1);
        }
    };

复制代码PdfReader pdfReader = new PdfReader(new ByteArrayInputStream(pdfFile));
PdfSigner pdfSigner = new PdfSigner(pdfReader, new FileOutputStream(signedPath), false);

//estimatedSize可以自己设置预估大小
//但建议开启一个循环来判断，如果太小就增大值，直到签名成功
pdfSigner.signExternalContainer(externalP7DetachSignatureContainer, estimatedSize);

复制代码        //是否签名成功标志
        boolean success = false;
        //预估大小
        int estimatedSize = 3000;

        //通过调整预估大小直到签名成功
        while (!success) {
            try {
                PdfReader pdfReader = new PdfReader(new ByteArrayInputStream(pdfFile));
                PdfSigner pdfSigner = new PdfSigner(pdfReader, new FileOutputStream(signedPath), false);
                pdfSigner.signExternalContainer(externalP7DetachSignatureContainer, estimatedSize);

                success = true;

            } catch (IOException e) {
                e.printStackTrace();
                estimatedSize += 1000;
            } catch (GeneralSecurityException e) {
                e.printStackTrace();
            }
        }

复制代码    /**
     * 对pdf进行签名图片操作（添加签章）
     *
     * @param pdfSigner
     * @param imgBytes 图片文件
     * @param leftBottomX 图片的左下方x坐标
     * @param leftBottomY 图片的左下方y坐标
     * @param imgWidth 图片的宽度
     * @param imgHeight 图片的高度
     * @param pageNum 页码
     */
    private void doImageStamp(PdfSigner pdfSigner, byte[] imgBytes, int leftBottomX, int leftBottomY, int imgWidth, int imgHeight, int pageNum) {

        ImageData imageData = ImageDataFactory.create(imgBytes);

        PdfSignatureAppearance appearance = pdfSigner.getSignatureAppearance();
        Rectangle rectangle = new Rectangle(leftBottomX , leftBottomY , imgWidth , imgHeight);

        appearance.setPageRect(rectangle)
                .setPageNumber(pageNum)
                .setSignatureGraphic(imageData)
       .setRenderingMode(PdfSignatureAppearance.RenderingMode.GRAPHIC);

    }

复制代码    /**
     * 验签pdf
     *
     * @param pdf 签名好的pdf
     * @return 验签结果 true/false
     */
    public boolean verifyPdf(byte[] pdf) {

        boolean result = false;

        try {
            PdfReader pdfReader = new PdfReader(new ByteArrayInputStream(pdf));
            PdfDocument pdfDocument = new PdfDocument(pdfReader);
            SignatureUtil signatureUtil = new SignatureUtil(pdfDocument);
            List<String> signedNames = signatureUtil.getSignatureNames();

            //遍历签名的内容并做验签
            for (String signedName : signedNames) {

                //获取源数据
                byte[] originData = getOriginData(pdfReader, signatureUtil, signedName);

                //获取签名值
                byte[] signedData = getSignData(signatureUtil , signedName);

                //校验签名
                result = SignUtil.verifyP7DetachData(originData , signedData);

            }
        } catch (IOException e) {
            e.printStackTrace();
        }

        return result;
    }

复制代码    /**
     * 验签pdf
     *
     * @param pdf 签名好的pdf
     * @return 验签结果 true/false
     */
    public boolean verifyPdf(byte[] pdf) {

        boolean result = false;

        try {
            PdfReader pdfReader = new PdfReader(new ByteArrayInputStream(pdf));
            PdfDocument pdfDocument = new PdfDocument(pdfReader);
            SignatureUtil signatureUtil = new SignatureUtil(pdfDocument);
            List<String> signedNames = signatureUtil.getSignatureNames();

            //遍历签名的内容并做验签
            for (String signedName : signedNames) {

                //获取签名值
                byte[] signedData = getSignData(signatureUtil , signedName);

                //校验签名
                result = SignUtil.verifyP7AttachData(signedData);

            }
        } catch (IOException e) {
            e.printStackTrace();
        }

        return result;
    }

复制代码    /**
     * 获取签名数据
     * @param signatureUtil
     * @param signedName
     * @return
     */
    private byte[] getSignData(SignatureUtil signatureUtil, String signedName) {
        PdfDictionary pdfDictionary = signatureUtil.getSignatureDictionary(signedName);
        PdfString contents = pdfDictionary.getAsString(PdfName.Contents);
        return contents.getValueBytes();
    }

    /**
     * 获取源数据（如果subFilter使用的是Adbe.pkcs7.detached就需要在验签的时候获取 源数据 并与 签名数据 进行 p7detach 校验）
     * @param pdfReader
     * @param signatureUtil
     * @param signedName
     * @return
     */
    private byte[] getOriginData(PdfReader pdfReader, SignatureUtil signatureUtil, String signedName) {

        byte[] originData = null;

        try {
            PdfSignature pdfSignature = signatureUtil.getSignature(signedName);
            PdfArray pdfArray = pdfSignature.getByteRange();
            RandomAccessFileOrArray randomAccessFileOrArray = pdfReader.getSafeFile();
            InputStream rg = new RASInputStream(new RandomAccessSourceFactory().createRanged(randomAccessFileOrArray.createSourceView(), SignatureUtil.asLongArray(pdfArray)));
            ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
            byte[] buf = new byte[8192];
            int n = 0;
            while (-1 != (n = rg.read(buf))) {
                outputStream.write(buf, 0, n);
            }

            originData = outputStream.toByteArray();
        } catch (IOException e) {
            e.printStackTrace();
        }

        return originData;

    }

复制代码/**
 * 获取签名信息实体类
 */
public class PdfSignInfo {

    private Date signDate;
    private String digestAlgorithm;
    private String reason;
    private String location;
    private String signatureName;
    private String encryptionAlgorithm;
    private String signerName;
    private String contactInfo;
    private int revisionNumber;
    
    public int getRevisionNumber() {
        return revisionNumber;
    }

    public String getContactInfo() {
        return contactInfo;
    }

    public String getSignerName() {
        return signerName;
    }

    public void setSignerName(String signerName) {
        this.signerName = signerName;
    }

    public String getEncryptionAlgorithm() {
        return encryptionAlgorithm;
    }

    public void setEncryptionAlgorithm(String encryptionAlgorithm) {
        this.encryptionAlgorithm = encryptionAlgorithm;
    }

    public String getSignatureName() {
        return signatureName;
    }

    public void setSignatureName(String signatureName) {
        this.signatureName = signatureName;
    }

    public void setSignDate(Date signDate) {
        this.signDate = signDate;
    }

    public Date getSignDate() {
        return signDate;
    }

    public String getReason() {
        return reason;
    }

    public void setReason(String reason) {
        this.reason = reason;
    }

    public String getLocation() {
        return location;
    }

    public void setLocation(String location) {
        this.location = location;
    }

    public String getDigestAlgorithm() {
        return digestAlgorithm;
    }

    public void setDigestAlgorithm(String digestAlgorithm) {
        this.digestAlgorithm = digestAlgorithm;
    }

    public void setContactInfo(String contactInfo) {
        this.contactInfo = contactInfo;
    }

    public void setRevisionNumber(int revisionNumber) {
        this.revisionNumber = revisionNumber;
    }
}

复制代码    /**
     * 解析返回签名信息
     * @param pdf
     * @return
     */
    public List<PdfSignInfo> getPdfSignInfo(byte[] pdf){

        //添加BC库支持
        BouncyCastleProvider provider = new BouncyCastleProvider();
        Security.addProvider(provider);

        List<PdfSignInfo> signInfoList = new ArrayList<>();

        try {
            PdfReader  pdfReader = new PdfReader(new ByteArrayInputStream(pdf));
            PdfDocument pdfDocument = new PdfDocument(pdfReader);

            SignatureUtil signatureUtil = new SignatureUtil(pdfDocument);

            List<String> signedNames = signatureUtil.getSignatureNames();

            //遍历签名信息
            for (String signedName : signedNames) {

                PdfSignInfo pdfSignInfo = new PdfSignInfo();
                pdfSignInfo.setSignatureName(signedName);
                pdfSignInfo.setRevisionNumber(signatureUtil.getRevision(signedName));

                PdfPKCS7 pdfPKCS7 = signatureUtil.verifySignature(signedName , "BC");

                pdfSignInfo.setSignDate(pdfPKCS7.getSignDate().getTime());
                pdfSignInfo.setDigestAlgorithm(pdfPKCS7.getDigestAlgorithm());
                pdfSignInfo.setLocation(pdfPKCS7.getLocation());
                pdfSignInfo.setReason(pdfPKCS7.getReason());
                pdfSignInfo.setEncryptionAlgorithm(pdfPKCS7.getEncryptionAlgorithm());

                X509Certificate signCert = pdfPKCS7.getSigningCertificate();

                pdfSignInfo.setSignerName(CertificateInfo.getSubjectFields(signCert).getField("CN"));

                PdfDictionary sigDict = signatureUtil.getSignatureDictionary(signedName);
                PdfString contactInfo = sigDict.getAsString(PdfName.ContactInfo);
                if (contactInfo != null) {
                    pdfSignInfo.setContactInfo(contactInfo.toString());
                }

                signInfoList.add(pdfSignInfo);

            }
        } catch (IOException e) {
            e.printStackTrace();
        }

        return signInfoList;

    }

复制代码<transportConnector name="openwire" uri="tcp://0.0.0.0:61616?maximumConnections=1000&amp;wireFormat.maxFrameSize=104857600"/>
<transportConnector name="amqp" uri="amqp://0.0.0.0:5672?maximumConnections=1000&amp;wireFormat.maxFrameSize=104857600"/>
<transportConnector name="stomp" uri="stomp://0.0.0.0:61613?maximumConnections=1000&amp;wireFormat.maxFrameSize=104857600"/>
<transportConnector name="mqtt" uri="mqtt://0.0.0.0:1883?maximumConnections=1000&amp;wireFormat.maxFrameSize=104857600"/>
<transportConnector name="ws" uri="ws://0.0.0.0:61614?maximumConnections=1000&amp;wireFormat.maxFrameSize=104857600"/>

复制代码//根据URI创建NMS连接工厂
NMSConnectionFactory factory = new NMSConnectionFactory(brokerUri);
//根据用户名密码创建连接
IConnection connection = factory.CreateConnection(user, password);
//打开连接
connection.Start();
//创建Session
ISession session = connection.CreateSession(AcknowledgementMode.AutoAcknowledge);
//根据destination创建主题
IDestination dest = session.GetQueue(destination);
//创建生产者
IMessageProducer producer = session.CreateProducer(dest);
producer.DeliveryMode = MsgDeliveryMode.NonPersistent;
//发送消息
String body = "hello,javaJMS!!  I'm C#";
producer.Send(session.CreateTextMessage(body));
//关闭连接
connection.Close();

复制代码package main

import "time"

func main() {
    var ch = make(chan int, 100)
    go func() {
        for i := 0; i < 100; i++ {
            ch <- 1
        }
    }()

    for {
        // the wrong part
        if len(ch) == 100 {
            sum := 0
            itemNum := len(ch)
            for i := 0; i < itemNum; i++ {
                sum += <-ch
            }
            if sum == itemNum {
                return
            }
        }
    }

}

复制代码GODEBUG="schedtrace=300,scheddetail=1" ./test1

复制代码package main

import (
    "fmt"
    "io"
    "log"
    "net/http"
    "runtime"
    "time"
)

func main() {
    runtime.GOMAXPROCS(runtime.NumCPU())
    go server()
    go printNum()
    var i = 1
    for {
        // will block here, and never go out
        i++
    }
    fmt.Println("for loop end")
    time.Sleep(time.Second * 3600)
}

func printNum() {
    i := 0
    for {
        fmt.Println(i)
        i++
    }
}

func HelloServer(w http.ResponseWriter, req *http.Request) {
    io.WriteString(w, "hello, world!\n")
}

func server() {
    http.HandleFunc("/", HelloServer)
    err := http.ListenAndServe(":12345", nil)

    if err != nil {
        log.Fatal("ListenAndServe: ", err)
    }
}

复制代码curl localhost:12345

复制代码1. 卡死在 for 循环上
2. gcwaiting=1
3. 没有系统调用

复制代码perf top

复制代码  99.52%  ffff                     [.] main.main
   0.06%  [kernel]                 [k] __do_softirq
   0.05%  [kernel]                 [k] 0x00007fff81843a35
   0.03%  [kernel]                 [k] mpt_put_msg_frame
   0.03%  [kernel]                 [k] finish_task_switch
   0.03%  [kernel]                 [k] tick_nohz_idle_enter
   0.02%  perf                     [.] 0x00000000000824d7
   0.02%  [kernel]                 [k] e1000_xmit_frame
   0.02%  [kernel]                 [k] VbglGRPerform

复制代码package main
import (
    "fmt"
    "io"
    "log"
    "net/http"
    "runtime"
    "time"
)
func main() {
    runtime.GOMAXPROCS(runtime.NumCPU())
    go server()
    go printNum()
    var i = 1
    for {
        // will block here, and never go out
        i++
    }
    fmt.Println("for loop end")
    time.Sleep(time.Second * 3600)
}
func printNum() {
    i := 0
    for {
        fmt.Println(i)
        i++
    }
}
func HelloServer(w http.ResponseWriter, req *http.Request) {
    fmt.Println("hello world")
    io.WriteString(w, "hello, world!\n")
}
func server() {
    http.HandleFunc("/", HelloServer)
    err := http.ListenAndServe(":12345", nil)
    if err != nil {
        log.Fatal("ListenAndServe: ", err)
    }
}

复制代码curl localhost:12345

复制代码dlv debug hang.go

复制代码received SIGINT, stopping process (will not forward signal)> main.main() ./hang.go:17 (PC: 0x12dd7c8)
    12: func main() {
    13:         runtime.GOMAXPROCS(runtime.NumCPU())
    14:         go server()
    15:         go printNum()
    16:         var i = 1
=>  17:         for {
    18:                 // will block here, and never go out
    19:                 i++
    20:         }
    21:         fmt.Println("for loop end")
    22:         time.Sleep(time.Second * 3600)
(dlv)

复制代码package main
import (
    "fmt"
    "time"
)
func deadloop() {
    for {
    }
}
func main() {
    go deadloop()
    for {
        time.Sleep(time.Second * 1)
        fmt.Println("I got scheduled!")
    }
}

复制代码package main
import (
    "fmt"
    "log"
    "net/http"
    _ "net/http/pprof"
    // "runtime"
    "time"
)
func deadloop() {
    for {
    }
}
func main() {
    go func() {
        log.Println(http.ListenAndServe("localhost:6060", nil))
    }()
    go deadloop()
    i := 3
    for {
        time.Sleep(time.Second * 1)
        i--
        fmt.Println("I got scheduled!")
        if i == 0 {
            runtime.GC()
        }
    }
}

复制代码$ go build hang2.go
$ GODEBUG="schedtrace=300,scheddetail=1" ./hang2
SCHED 2443ms: gomaxprocs=4 idleprocs=3 threads=7 spinningthreads=0 idlethreads=2 runqueue=0 gcwaiting=0 nmidlelocked=0 stopwait=0 sysmonwait=0
  P0: status=1 schedtick=4 syscalltick=5 m=5 runqsize=0 gfreecnt=1
  P1: status=0 schedtick=14 syscalltick=0 m=-1 runqsize=0 gfreecnt=0
  P2: status=0 schedtick=3 syscalltick=4 m=-1 runqsize=0 gfreecnt=0
......  
SCHED 2751ms: gomaxprocs=4 idleprocs=0 threads=7 spinningthreads=0 idlethreads=2 runqueue=0 gcwaiting=1 nmidlelocked=0 stopwait=1 sysmonwait=0
  P0: status=1 schedtick=4 syscalltick=5 m=5 runqsize=0 gfreecnt=1
  P1: status=3 schedtick=14 syscalltick=0 m=-1 runqsize=0 gfreecnt=0
  P2: status=3 schedtick=3 syscalltick=10 m=-1 runqsize=0 gfreecnt=0
  P3: status=3 schedtick=1 syscalltick=26 m=0 runqsize=0 gfreecnt=0
  M6: p=-1 curg=-1 mallocing=0 throwing=0 preemptoff= locks=0 dying=0 helpgc=0 spinning=false blocked=false lockedg=-1
  M5: p=0 curg=19 mallocing=0 throwing=0 preemptoff= locks=0 dying=0 helpg