    /usr/libexec/java_home -V

lists one line per Java environment installed (and known to the `/usr/bin/java` command).  

You can still have other Java distributions which are not registered.  They are typically downloaded  as ZIP files without an installer.

We are developing a program which receives and forwards &quot;messages&quot;, while keeping a temporary history of those messages, so that it can tell you the message history if requested. Messages are identified numerically, are typically around 1 kilobyte in size, and we need to keep hundreds of thousands of these messages.

We wish to optimize this program for latency: the time between sending and receiving a message must be below 10 milliseconds.

The program is written in Haskell and compiled with GHC. However, we have found that garbage collection pauses are far too long for our latency requirements: over 100 milliseconds in our real-world program.

The following program is a simplified version of our application. It uses a `Data.Map.Strict` to store messages. Messages are `ByteString`s identified by an `Int`. 1,000,000 messages are inserted in increasing numeric order, and the oldest messages are continually removed to keep the history at a maximum of 200,000 messages.

    module Main (main) where

    import qualified Control.Exception as Exception
    import qualified Control.Monad as Monad
    import qualified Data.ByteString as ByteString
    import qualified Data.Map.Strict as Map

    data Msg = Msg !Int !ByteString.ByteString

    type Chan = Map.Map Int ByteString.ByteString

    message :: Int -&gt; Msg
    message n = Msg n (ByteString.replicate 1024 (fromIntegral n))

    pushMsg :: Chan -&gt; Msg -&gt; IO Chan
    pushMsg chan (Msg msgId msgContent) =
      Exception.evaluate $
        let
          inserted = Map.insert msgId msgContent chan
        in
          if 200000 &lt; Map.size inserted
          then Map.deleteMin inserted
          else inserted

    main :: IO ()
    main = Monad.foldM_ pushMsg Map.empty (map message [1..1000000])

We compiled and ran this program using:

    $ ghc --version
    The Glorious Glasgow Haskell Compilation System, version 7.10.3
    $ ghc -O2 -optc-O3 Main.hs
    $ ./Main +RTS -s
       3,116,460,096 bytes allocated in the heap
         385,101,600 bytes copied during GC
         235,234,800 bytes maximum residency (14 sample(s))
         124,137,808 bytes maximum slop
                 600 MB total memory in use (0 MB lost due to fragmentation)

                                         Tot time (elapsed)  Avg pause  Max pause
      Gen  0      6558 colls,     0 par    0.238s   0.280s     0.0000s    0.0012s
      Gen  1        14 colls,     0 par    0.179s   0.250s     0.0179s    0.0515s

      INIT    time    0.000s  (  0.000s elapsed)
      MUT     time    0.652s  (  0.745s elapsed)
      GC      time    0.417s  (  0.530s elapsed)
      EXIT    time    0.010s  (  0.052s elapsed)
      Total   time    1.079s  (  1.326s elapsed)

      %GC     time      38.6%  (40.0% elapsed)

      Alloc rate    4,780,213,353 bytes per MUT second

      Productivity  61.4% of total user, 49.9% of total elapsed

The important metric here is the &quot;max pause&quot; of 0.0515s, or 51 milliseconds. We wish to reduce this by at least an order of magnitude.

Experimentation shows that the length of a GC pause is determined by the number of messages in the history. The relationship is roughly linear, or perhaps super-linear. The following table shows this relationship. ([You can see our benchmarking tests here](https://github.com/jameshfisher/ghc_gc_benchmarks), and [some charts here](https://docs.google.com/spreadsheets/d/1mDXrk8bqPb_nsR__pzHtSxwO8a_6bPVL8hd3Y9lCIm0/edit?usp=sharing).)

    msgs history length  max GC pause (ms)
    ===================  =================
    12500                                3
    25000                                6
    50000                               13
    100000                              30
    200000                              56
    400000                             104
    800000                             199
    1600000                            487
    3200000                           1957
    6400000                           5378

We have experimented with several other variables to find whether they can reduce this latency, none of which make a big difference. Among these unimportant variables are: optimization (`-O`, `-O2`); RTS GC options (`-G`, `-H`, `-A`, `-c`), number of cores (`-N`), different data structures (`Data.Sequence`), the size of messages, and the amount of generated short-lived garbage. The overwhelming determining factor is the number of messages in the history.

Our working theory is that the pauses are linear in the number of messages because each GC cycle has to walk over all the working accessible memory and copy it, which are clearly linear operations.

Questions:

* Is this linear-time theory correct? Can the length of GC pauses be expressed in this simple way, or is the reality more complex?
* If GC pause is linear in the working memory, is there any way to reduce the constant factors involved?
* Are there any options for incremental GC, or anything like it? We can only see research papers. We are very willing to trade throughput for lower latency.
* Are there any ways to &quot;partition&quot; memory for smaller, GC cycles, other than splitting into multiple processes?

Reducing garbage-collection pause time in a Haskell program

I&#39;m making a homepage using, Bootstrap, JQuery and Chart.js (v2). I had my implementation working using v1, but recently just got into Bower and downloaded v2 using that.

I&#39;m making a grid of 4 columns each containing a pie chart, however the scaling in v2 is sort of confusing for me to get working. I want the charts to be responsive so they scale properly with the smaller devices such as tablets and smartphones, and one of my problems is getting rid of the legend of the charts as well as the hover information when hovering the mouse over the sections of my chart.

#index.html

    &lt;body&gt;
        &lt;div class=&quot;container&quot;&gt;
            &lt;div class=&quot;row&quot;&gt;
                &lt;div class=&quot;col-xs-3&quot;&gt;
                    &lt;canvas id=&quot;chart1&quot;&gt;&lt;/canvas&gt;
                &lt;/div&gt;
                &lt;div class=&quot;col-xs-3&quot;&gt;
                    &lt;canvas id=&quot;chart1&quot;&gt;&lt;/canvas&gt;
                &lt;/div&gt;
                &lt;div class=&quot;col-xs-3&quot;&gt;
                    &lt;canvas id=&quot;chart1&quot;&gt;&lt;/canvas&gt;
                &lt;/div&gt;
                &lt;div class=&quot;col-xs-3&quot;&gt;
                    &lt;canvas id=&quot;chart1&quot;&gt;&lt;/canvas&gt;
                &lt;/div&gt;
            &lt;/div&gt;
        &lt;/div&gt;
    &lt;/body&gt;

#functions.js

    $(document).ready(function(){
        var canvas = $(&quot;#chart1&quot;);
        var data = {
            labels: [],
            datasets: [{
                data: [10, 10],
                backgroundColor: [&quot;#F7464A&quot;, &quot;#FDB45C&quot;],
                hoverBackgroundColor: [&quot;#FF5A5E&quot;, &quot;#FFC870&quot;]
            }]
        };

        var chart1 = new Chart(canvas, {
            type: &quot;pie&quot;,
            data: data,
        });
    });

If I remove the empty &quot;labels&quot; field the chart doesn&#39;t work anymore. And by the looks of it there is a small spacing at the top of the chart which could indicate that the headers are written, but they are just empty strings.

Does anyone have an idea of how to remove the legend, and the hover description? I simply can&#39;t get my head around how this is used

I will get my hands around a jsfiddle as soon as I get time!

EDIT: Link to the docs: [https://nnnick.github.io/Chart.js/docs-v2/#getting-started][1]


  [1]: https://nnnick.github.io/Chart.js/docs-v2/#getting-started

Removing legend on charts with chart.js v2

How can I get all the Java versions installed on my Mac?

Is there a terminal command for this? 

When I run **`java -version`**, I get the current JRE version that is in use in my system, but I want to list all the JREs installed on my Mac.

See all the Java versions installed on Mac

How can I get all the Java versions installed on my Mac?
Is there a terminal command for this?
When I run <code>java -version</code>, I get the current JRE version that is in use in my system, but I want to list all the JREs installed on my Mac.

How to I print information from a map that has the object as the value?

I have created the following map:

    Map&lt;String, Object&gt; objectSet = new HashMap&lt;&gt;();

The object has its own class with its own instance variables

I have already populated the above map with data. 

I have created a `printMap` method, but I can only seem to print the Keys of the map

How to do I get the map to print the `&lt;Object&gt;` values using a for each loop?

So far, I&#39;ve got:

    for (String keys : objectSet.keySet())
    {
       System.out.println(keys);
    }


The above prints out the keys. I want to be able to print out the object variables too.

Printing a java map Map&lt;String, Object&gt; - How?

I am going through this book on restful web services with spring. I decided to move away from what they were doing and use java configuration files. For some reason, after switching over to the Java configuration, the service would run (in the console window) correctly but when I actually go to the endpoint on localhost i get this:

&gt; White label Error Page
&gt; 
&gt; This application has no explicit mapping for /error, so you are seeing
&gt; this as a fallback.
&gt; 
&gt; Sat Apr 23 20:48:25 PDT 2016 There was an unexpected error (type=Not
&gt; Found, status=404). No message available

And this is the response from the GET request:

    {
        &quot;timestamp&quot;: 1461470029110,
        &quot;status&quot;: 404,
        &quot;error&quot;: &quot;Not Found&quot;,
        &quot;message&quot;: &quot;No message available&quot;,
        &quot;path&quot;: &quot;/greeting&quot;
    }

The next chapter of this story begins with me going to the getting started page on the Spring website http://spring.io/guides/gs/rest-service/ I decided to start a small project recreating their basic tutorial. I will post the code I wrote below for you to see. The problem is, I am having the exact same issue. The service runs but I can&#39;t hit the endpoints. I am not sure what is going on and I have seen others with similar issues, but the answers have not applied/helped with mine. I am sure it is something obvious that I am doing wrong and any help would be greatly appreciated. One last piece of information, if at all relevant, I am using IntelliJ IDEA 15 CE as my IDE.  

The endpoint being hit:

http://localhost:8080/greeting 

My controller 

   

    @RestController
    public class GreetingController {
        private static final String template = &quot;Hello, %s!&quot;;
        private final AtomicLong counter = new AtomicLong();
        
        @RequestMapping(&quot;/greeting&quot;)
        public Greeting greeting(@RequestParam(value = &quot;name&quot;, defaultValue = &quot;World&quot;)String name) {
            return new Greeting(counter.incrementAndGet(), String.format(template, name));
        }
    }

My Resource Representation class

   

    public class Greeting {
        private final long id;
        private final String content;
        
        public Greeting(long id, String content) {
            this.id = id;
            this.content = content;
        }
        
        public long getId() {
            return id;
        }
        
        public String getContent() {
            return content;
        }
    }

My Main

    @SpringBootApplication
    public class Application
    {
        public static void main(String[] args)
        {
            SpringApplication.run(Application.class, args);
        }
    }

My POM file

    &lt;?xml version=&quot;1.0&quot; encoding=&quot;UTF-8&quot;?&gt;
    &lt;project xmlns=&quot;http://maven.apache.org/POM/4.0.0&quot;
         xmlns:xsi=&quot;http://www.w3.org/2001/XMLSchema-instance&quot;
         xsi:schemaLocation=&quot;http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd&quot;&gt;
    &lt;modelVersion&gt;4.0.0&lt;/modelVersion&gt;

    &lt;groupId&gt;com.organization_name.webservices&lt;/groupId&gt;
    &lt;artifactId&gt;helloworld&lt;/artifactId&gt;
    &lt;version&gt;1.0-SNAPSHOT&lt;/version&gt;

    &lt;parent&gt;
        &lt;groupId&gt;org.springframework.boot&lt;/groupId&gt;
        &lt;artifactId&gt;spring-boot-starter-parent&lt;/artifactId&gt;
        &lt;version&gt;1.3.3.RELEASE&lt;/version&gt;
    &lt;/parent&gt;
    
    &lt;dependencies&gt;
        &lt;dependency&gt;
            &lt;groupId&gt;org.springframework.boot&lt;/groupId&gt;
            &lt;artifactId&gt;spring-boot-starter-web&lt;/artifactId&gt;
        &lt;/dependency&gt;
    &lt;/dependencies&gt;

    &lt;properties&gt;
        &lt;java.version&gt;1.8&lt;/java.version&gt;
    &lt;/properties&gt;


    &lt;build&gt;
        &lt;plugins&gt;
            &lt;plugin&gt;
                &lt;groupId&gt;org.springframework.boot&lt;/groupId&gt;
                &lt;artifactId&gt;spring-boot-maven-plugin&lt;/artifactId&gt;
            &lt;/plugin&gt;
        &lt;/plugins&gt;
    &lt;/build&gt;

    &lt;repositories&gt;
        &lt;repository&gt;
            &lt;id&gt;spring-releases&lt;/id&gt;
            &lt;url&gt;https://repo.spring.io/libs-release&lt;/url&gt;
        &lt;/repository&gt;
    &lt;/repositories&gt;
    &lt;pluginRepositories&gt;
        &lt;pluginRepository&gt;
            &lt;id&gt;spring-releases&lt;/id&gt;
            &lt;url&gt;https://repo.spring.io/libs-release&lt;/url&gt;
        &lt;/pluginRepository&gt;
    &lt;/pluginRepositories&gt;
&lt;/project&gt;

Command line to run

    mvn spring-boot:run   

My complete log from the console

     .   ____          _            __ _ _
     /\\ / ___&#39;_ __ _ _(_)_ __  __ _ \ \ \ \
    ( ( )\___ | &#39;_ | &#39;_| | &#39;_ \/ _` | \ \ \ \
     \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
      &#39;  |____| .__|_| |_|_| |_\__, | / / / /
     =========|_|==============|___/=/_/_/_/
     :: Spring Boot ::        (v1.3.3.RELEASE)
    
    2016-04-23 20:47:53.153  INFO 7898 --- [           main] c.t.webservices.application.Application  : Starting Application on Macintosh.local with PID 7898 (/Users/&lt;my_user&gt;/Downloads/B04788_Code/HelloWorld/target/classes started by &lt;my_user&gt; in /Users/&lt;my_user&gt;/Downloads/B04788_Code/HelloWorld)
    2016-04-23 20:47:53.156  INFO 7898 --- [           main] c.t.webservices.application.Application  : No active profile set, falling back to default profiles: default
    2016-04-23 20:47:53.242  INFO 7898 --- [           main] ationConfigEmbeddedWebApplicationContext : Refreshing org.springframework.boot.context.embedded.AnnotationConfigEmbeddedWebApplicationContext@68ceda24: startup date [Sat Apr 23 20:47:53 PDT 2016]; root of context hierarchy
    2016-04-23 20:47:54.084  INFO 7898 --- [           main] o.s.b.f.s.DefaultListableBeanFactory     : Overriding bean definition for bean &#39;beanNameViewResolver&#39; with a different definition: replacing [Root bean: class [null]; scope=; abstract=false; lazyInit=false; autowireMode=3; dependencyCheck=0; autowireCandidate=true; primary=false; factoryBeanName=org.springframework.boot.autoconfigure.web.ErrorMvcAutoConfiguration$WhitelabelErrorViewConfiguration; factoryMethodName=beanNameViewResolver; initMethodName=null; destroyMethodName=(inferred); defined in class path resource [org/springframework/boot/autoconfigure/web/ErrorMvcAutoConfiguration$WhitelabelErrorViewConfiguration.class]] with [Root bean: class [null]; scope=; abstract=false; lazyInit=false; autowireMode=3; dependencyCheck=0; autowireCandidate=true; primary=false; factoryBeanName=org.springframework.boot.autoconfigure.web.WebMvcAutoConfiguration$WebMvcAutoConfigurationAdapter; factoryMethodName=beanNameViewResolver; initMethodName=null; destroyMethodName=(inferred); defined in class path resource [org/springframework/boot/autoconfigure/web/WebMvcAutoConfiguration$WebMvcAutoConfigurationAdapter.class]]
    2016-04-23 20:47:54.811  INFO 7898 --- [           main] s.b.c.e.t.TomcatEmbeddedServletContainer : Tomcat initialized with port(s): 8080 (http)
    2016-04-23 20:47:54.840  INFO 7898 --- [           main] o.apache.catalina.core.StandardService   : Starting service Tomcat
    2016-04-23 20:47:54.841  INFO 7898 --- [           main] org.apache.catalina.core.StandardEngine  : Starting Servlet Engine: Apache Tomcat/8.0.32
    2016-04-23 20:47:54.960  INFO 7898 --- [ost-startStop-1] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring embedded WebApplicationContext
    2016-04-23 20:47:54.960  INFO 7898 --- [ost-startStop-1] o.s.web.context.ContextLoader            : Root WebApplicationContext: initialization completed in 1736 ms
    2016-04-23 20:47:55.214  INFO 7898 --- [ost-startStop-1] o.s.b.c.e.ServletRegistrationBean        : Mapping servlet: &#39;dispatcherServlet&#39; to [/]
    2016-04-23 20:47:55.218  INFO 7898 --- [ost-startStop-1] o.s.b.c.embedded.FilterRegistrationBean  : Mapping filter: &#39;characterEncodingFilter&#39; to: [/*]
    2016-04-23 20:47:55.219  INFO 7898 --- [ost-startStop-1] o.s.b.c.embedded.FilterRegistrationBean  : Mapping filter: &#39;hiddenHttpMethodFilter&#39; to: [/*]
    2016-04-23 20:47:55.219  INFO 7898 --- [ost-startStop-1] o.s.b.c.embedded.FilterRegistrationBean  : Mapping filter: &#39;httpPutFormContentFilter&#39; to: [/*]
    2016-04-23 20:47:55.219  INFO 7898 --- [ost-startStop-1] o.s.b.c.embedded.FilterRegistrationBean  : Mapping filter: &#39;requestContextFilter&#39; to: [/*]
    2016-04-23 20:47:55.545  INFO 7898 --- [           main] s.w.s.m.m.a.RequestMappingHandlerAdapter : Looking for @ControllerAdvice: org.springframework.boot.context.embedded.AnnotationConfigEmbeddedWebApplicationContext@68ceda24: startup date [Sat Apr 23 20:47:53 PDT 2016]; root of context hierarchy
    2016-04-23 20:47:55.605  INFO 7898 --- [           main] s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped &quot;{[/error]}&quot; onto public org.springframework.http.ResponseEntity&lt;java.util.Map&lt;java.lang.String, java.lang.Object&gt;&gt; org.springframework.boot.autoconfigure.web.BasicErrorController.error(javax.servlet.http.HttpServletRequest)
    2016-04-23 20:47:55.606  INFO 7898 --- [           main] s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped &quot;{[/error],produces=[text/html]}&quot; onto public org.springframework.web.servlet.ModelAndView org.springframework.boot.autoconfigure.web.BasicErrorController.errorHtml(javax.servlet.http.HttpServletRequest,javax.servlet.http.HttpServletResponse)
    2016-04-23 20:47:55.628  INFO 7898 --- [           main] o.s.w.s.handler.SimpleUrlHandlerMapping  : Mapped URL path [/webjars/**] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler]
    2016-04-23 20:47:55.628  INFO 7898 --- [           main] o.s.w.s.handler.SimpleUrlHandlerMapping  : Mapped URL path [/**] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler]
    2016-04-23 20:47:55.657  INFO 7898 --- [           main] o.s.w.s.handler.SimpleUrlHandlerMapping  : Mapped URL path [/**/favicon.ico] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler]
    2016-04-23 20:47:55.776  INFO 7898 --- [           main] o.s.j.e.a.AnnotationMBeanExporter        : Registering beans for JMX exposure on startup
    2016-04-23 20:47:55.848  INFO 7898 --- [           main] s.b.c.e.t.TomcatEmbeddedServletContainer : Tomcat started on port(s): 8080 (http)
    2016-04-23 20:47:55.853  INFO 7898 --- [           main] c.t.webservices.application.Application  : Started Application in 3.531 seconds (JVM running for 4.702)
    2016-04-23 20:48:19.521  INFO 7898 --- [nio-8080-exec-1] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring FrameworkServlet &#39;dispatcherServlet&#39;
    2016-04-23 20:48:19.521  INFO 7898 --- [nio-8080-exec-1] o.s.web.servlet.DispatcherServlet        : FrameworkServlet &#39;dispatcherServlet&#39;: initialization started
    2016-04-23 20:48:19.533  INFO 7898 --- [nio-8080-exec-1] o.s.web.servlet.DispatcherServlet        : FrameworkServlet &#39;dispatcherServlet&#39;: initialization completed in 12 ms
    

Console update after GET request

    2016-04-23 20:48:19.521  INFO 7898 --- [nio-8080-exec-1] o.s.web.servlet.DispatcherServlet        : FrameworkServlet &#39;dispatcherServlet&#39;: initialization started
    2016-04-23 20:48:19.533  INFO 7898 --- [nio-8080-exec-1] o.s.web.servlet.DispatcherServlet        : FrameworkServlet &#39;dispatcherServlet&#39;: initialization completed in 12 ms


Console after stopping


    2016-04-23 20:53:24.494  INFO 7898 --- [       Thread-2] ationConfigEmbeddedWebApplicationContext : Closing org.springframework.boot.context.embedded.AnnotationConfigEmbeddedWebApplicationContext@68ceda24: startup date [Sat Apr 23 20:47:53 PDT 2016]; root of context hierarchy
    2016-04-23 20:53:24.495  INFO 7898 --- [       Thread-2] o.s.j.e.a.AnnotationMBeanExporter        : Unregistering JMX-exposed beans on shutdown
    
    Process finished with exit code 130



Thanks again for any help you can offer. I will keep everyone posted with updates!

Issue With Spring: There was an unexpected error (type=Not Found, status=404)

I came across a new term in Java 8: &quot;functional interface&quot;. I could only find one use of it while working with *lambda expressions*. 

Java 8 provides some built-in functional interfaces and if we want to define any functional interface then we can make use of the `@FunctionalInterface` annotation. It will allow us to declare only a single method in the interface.

For example:

    @FunctionalInterface
    interface MathOperation {
        int operation(int a, int b);
    }

How useful it is in Java 8 other than just working with *lambda expressions*? 

(The question [here][1] is different from the one I asked. It is asking why we need functional interfaces while working with lambda expressions. My question is: What are the other uses of functional interfaces besides use with lambda expressions?)


  [1]: https://stackoverflow.com/questions/33010594/why-do-i-need-a-functional-interface-to-work-with-lambdas

What are functional interfaces used for in Java 8?

A Java application starts up with one heap for all threads. Each thread has its own stack.

When a Java application is started, we use the JVM option `-Xms` and `-Xmx` to control the size of heap and `-Xss` to control the stack size.

My understanding is that the heap being created becomes a &quot;managed&quot; memory of JVM and all the object being created are placed there. 

But how does the stack creation work? Does Java create a stack for each thread when it is created? If so, where exactly the stack is on the memory? It is certainly not in the &quot;managed&quot; heap.

Does JVM create stack from native memory or does it pre-allocate a section of managed memory area for stack? If so, how does JVM know how may threads will be created?


How does Java (JVM) allocate stack for each thread

I&#39;m trying to set up gradle to launch the `bootRun` process with various spring profiles enabled.

My current `bootRun` configuration looks like: 

    bootRun {
        // pass command line options from gradle to bootRun
        // usage: gradlew bootRun &quot;-Dspring.profiles.active=local,protractor&quot;
        if (System.properties.containsKey(&#39;spring.profiles.active&#39;)) {
            systemProperty &quot;spring.profiles.active&quot;, System.properties[&#39;spring.profiles.active&#39;]
        }
    }

I&#39;d like to set system properties with a `gradle` task, and then execute `bootRun`.

My attempt looked like this:


    task bootRunDev
    
    bootRunDev  {
        System.setProperty(&quot;spring.profiles.active&quot;, &quot;Dev&quot;)
    }

A few questions:

 1. is `systemProperty` a part of the spring boot bootRun configuration?
 2. is it possible to set a system property in another task?
 3. What should my next step be? I need to get `bootRunDev` configuration to happen before `bootRun`
 4. Is there another approach I should look into



-Eric


Content Type	Original Author	Original Content on Stackoverflow
Question	eureka19	View Question on Stackoverflow
Solution 1 - Java	Thorbjørn Ravn Andersen	View Answer on Stackoverflow

See all the Java versions installed on Mac

Java Problem Overview

Java Solutions

Solution 1 - Java

Removing legend on charts with chart.js v2

Reducing garbage-collection pause time in a Haskell program

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