In the ‘Standard Delegates’ section of the Delegation Properties page, there is one sentence says:

If you want thread safety, use blockingLazy() instead: it guarantees that the values will be computed only in one thread and that all threads will see the same value.

But I searched the kotlin standard library and can’t find the blockingLazy() method.

I was using the kotlin 1.9.10:

$ kotlin -version
Kotlin version 1.9.10-release-459 (JRE 17.0.8+9-LTS-211)

and kotlin standard library 1.9.0:

<dependency>
    <groupId>org.jetbrains.kotlin</groupId>
    <artifactId>kotlin-stdlib</artifactId>
    <version>1.9.0</version>
</dependency>

It seems that kotlin has removed the blockingLazy method.

I did find a lazy method which allow passing a lock parameter. It should be the new way to use a blocking lazy.

So I implement a thread-safe version here:

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class ThreadSafeLazyExample {
    init {
        println("Created!")
    }

    private val lazyLock: Int = 1

    // a thread safe lazy
    val lazyStr: String by lazy(lazyLock) {
        println("computed!")
        "my lazy"
    }
}

fun main() {
    val sample = ThreadSafeLazyExample()
    println("lazyStr is ${sample.lazyStr}")
    println(" =${sample.lazyStr}")
}

近期无法通过git从github克隆项目的解决办法

问题描述

前些天，同事问我：“你能从github上克隆代码吗？”我的第一感觉是他的网络有问题。但是当我在自己的电脑上测试了之后
才发现，真是这样。

直到今天，我要往github上推送我的笔记（我的笔记托管在github上），git push命令提示:

ssh: connect to host github.com port 22: Operation timed out

网上一通搜索，从一位开发者那里得知，我们伟大的GFW从1月16号开始和谐了github的默认ip地址。

解决办法

那么，该怎么办呢？

办法总是有的。原来github除了在22端口上提供ssh服务，在另外一个域名ssh.github.com的443端口也提供ssh服务。

打开~/.ssh/config文件：

Host github.com
    HostName github.com
    User git
    PreferredAuthentications publickey
    IdentitiesOnly yes
    IdentityFile ~/.ssh/id_rsa

把HostName改为ssh.github.com, 然后增加一行Port: 433，保存。修改后的文件如下：

Host github.com
    HostName ssh.github.com
    User git
    Port 443
    PreferredAuthentications publickey
    IdentitiesOnly yes
    IdentityFile ~/.ssh/id_rsa

这样，我们就又能愉快地访问github了。

行是知之始，知是行之成。 —— 王阳明