Expand documentation about Singleton Containers and lambdas #6587
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Thanks for your contribution @pan-daniel! I have left some comments.
| @@ -13,7 +13,7 @@ try (GenericContainer container = new GenericContainer("imagename")) { | |||
| container.start(); | |||
| // ... use the container | |||
| // no need to call stop() afterwards | |||
| } | |||
| } | |||
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A stray format, will revert.
| Please keep in mind that putting the container in a static block will influence the configuration of the container. | ||
| You will not be able to use methods such as `forResponsePredicate` by just providing a Lambda expression, you will have to use | ||
| anonymous classes, or alternatively provide them from non-abstract class. | ||
| This is not due to the limitation of `TestContainers`, but because of how they work under the hood, namely that lambdas get compiled | ||
| to static methods on a class level. Since your container is in a static block, the container gets created | ||
| before your parent and children classes get initialized and as such you cannot pass the reference to them. | ||
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| Therefore, once again - it is advised to use anonymous classes in such case or full predicates coming in from different, non-abstract class. | ||
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| Instead of: | ||
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| ```java | ||
| abstract class AbstractContainerBaseTest { | ||
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| static final GenericContainer GENERIC_CONTAINER; | ||
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| static { | ||
| GENERIC_CONTAINER = new GENERIC_CONTAINER( | ||
| new ImageFromDockerfile().waitingFor(Wait.forHttp('/path')) | ||
| .forStatusCode(200) | ||
| .forResponsePredicate(yourLambda -> yourLambda(here)) //This is never going to get executed due to NoClassDefFoundError | ||
| ); | ||
| GENERIC_CONTAINER.start(); | ||
| } | ||
| } | ||
| ``` | ||
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| You can do an anonymous class: | ||
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| ```java | ||
| abstract class AbstractContainerBaseTest { | ||
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| static final GenericContainer GENERIC_CONTAINER; | ||
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| static { | ||
| GENERIC_CONTAINER = new GENERIC_CONTAINER( | ||
| new ImageFromDockerfile().waitingFor(Wait.forHttp('/path')) | ||
| .forStatusCode(200) | ||
| .forResponsePredicate(new Predicate<String>() { | ||
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| @Override | ||
| public boolean test(String s) { | ||
| return yourConditionHere; | ||
| } | ||
| }) | ||
| ); | ||
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| GENERIC_CONTAINER.start(); | ||
| } | ||
| } | ||
| ``` | ||
| Or full predicate coming in from different class: | ||
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| ```java | ||
| abstract class AbstractContainerBaseTest { | ||
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| static final GenericContainer GENERIC_CONTAINER; | ||
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| static { | ||
| GENERIC_CONTAINER = new GENERIC_CONTAINER( | ||
| new ImageFromDockerfile().waitingFor(Wait.forHttp('/path')) | ||
| .forStatusCode(200) | ||
| .forResponsePredicate(PredicateHolder.getPredicate()) | ||
| ); | ||
| GENERIC_CONTAINER.start(); | ||
| } | ||
| } | ||
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| public class PredicateHolder { | ||
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| public static Predicate<String> getPredicate() { | ||
| return yourLambda -> yourLambda(here); | ||
| } | ||
| } | ||
| ``` |
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There is an issue reported in JDK which describe what's happening here. So, static methods from other classes can not be called from a lambda in a static block. But, if those are used as a method reference then it will work.
Also, if a container class is created then this issue can be avoided we would encourage to do that
class HWContainer extends GenericContainer<HWContainer> {
public HWContainer() {
super("testcontainers/helloworld");
withExposedPorts(8080);
waitingFor(Wait.forHttp("/ping").forResponsePredicate(x -> Util.isContains(x)));
}
}I would like to make a note about this and give the proper context and recommendations. Also, Can you please move the inline code to actual code and use codeblock in the file to display them? I think code examples would be avoided if the note is quite clear.
Note: The project is Testcontainers not TestContainers :)
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Hey! Thanks for the response.
I do firmly believe that this is not about deadlocking per se (even though somewhat related), but rather that static block gets initialized before the initialization of a class - and since the lambda gets compiled to a static field, trying to reference something that does not exist is impossible.
The reason why I am thinking that is we will not even get to the class initialization yet, as the container is just getting started.
Could you point me in the direction why do you believe that this is the deadlock situation?
Also, when you respond I will:
- Move out the examples to examples/ module. Question here, does it need to be completely valid code with imports etc. or can I just copy this somewhat pseudocode?
- Reference the JDK bug/discussion.
- Would you rather me deleting some examples rather than including them at all? From your message I got a feeling you'd delete some of them.
Hello! : ) This is my first commit here. Hopefully I did it right!
I have stumbled upon this while using TestContainers for a slow-spinning Docker image. Naturally I wanted to use a singleton container and I tried to make it work using the
withResponsePredicate()method opposed to sleeping the health check. After some debugging I have found out that the reason it did not work, even though local uses of same predicates worked, wasNoClassDefFoundError. It will be visible inHttpWaitStrategy.java, if you put breakpoint in here:You can replicate it creating an abstract base class and trying to use any function derivative.
There are ways to work around it (at least I think so), but I have chosen instead to update documentation to save others time and to not introduce dirty hacks.