ThenCompose Hangs/timeout Web Graphql Application

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Introduction

When building a Spring Boot GraphQL application, it's not uncommon to encounter issues with data loading and composition. One such issue is the use of thenCompose to combine multiple data loaders, which can lead to a hanging or timeout application. In this article, we'll explore the problem of thenCompose hangs/timeout in a Spring Boot GraphQL application and provide a solution to resolve it.

Understanding thenCompose

thenCompose is a method in Java's CompletableFuture class that allows us to combine multiple asynchronous operations into a single future. It's commonly used in data loading scenarios where we need to fetch data from multiple sources. However, when used incorrectly, it can lead to a hanging or timeout application.

The Problem

In a Spring Boot GraphQL application, we often have fields that depend on multiple data loaders. To resolve these fields, we use thenCompose to combine the data loaders. However, when the data loaders take a long time to complete or fail, the application can hang or timeout. This is because thenCompose waits for all the data loaders to complete before returning the result, which can lead to a deadlock situation.

Example Use Case

Let's consider an example where we have a GraphQL query that fetches a user's profile information, including their name, email, and address. The address field depends on two data loaders: one for the street and one for the city. We can use thenCompose to combine these data loaders as follows:

public CompletableFuture<UserProfile> getUserProfile() {
    return dataLoader1.loadUserStreet()
            .thenCompose(street -> dataLoader2.loadUserCity())
            .thenApply(city -> {
                UserProfile userProfile = new UserProfile();
                userProfile.setName("John Doe");
                userProfile.setEmail("john.doe@example.com");
                userProfile.setAddress(new Address(street, city));
                return userProfile;
            });
}

The Issue

In this example, if the dataLoader1.loadUserStreet() or dataLoader2.loadUserCity() operations take a long time to complete or fail, the application will hang or timeout. This is because thenCompose waits for both operations to complete before returning the result.

Solution

To resolve the issue, we can use a technique called "async/await" to handle the data loaders asynchronously. We can use the CompletableFuture.allOf() method to wait for all the data loaders to complete, but with a timeout. If any of the data loaders take longer than the timeout, we can cancel the operation and return an error.

public CompletableFuture<UserProfile> getUserProfile() {
    CompletableFuture<String> streetFuture = dataLoader1.loadUserStreet();
    CompletableFuture<String> cityFuture = dataLoader2.loadUserCity();

return CompletableFuture.allOf(streetFuture, cityFuture)
        .thenApply(v -&gt; {
            String street = streetFuture.join();
            String city = cityFuture.join();
            UserProfile userProfile = new UserProfile();
            userProfile.setName(&quot;John Doe&quot;);
            userProfile.setEmail(&quot;john.doe@example.com&quot;);
            userProfile.setAddress(new Address(street, city));
            userProfile;
        })
        .exceptionally(ex -&gt; {
            // Handle the exception
            return null;
        });



}

Benefits

By using the CompletableFuture.allOf() method with a timeout, we can avoid the deadlock situation caused by thenCompose. We can also handle any exceptions that occur during the data loading process.

Conclusion

In conclusion, the use of thenCompose can lead to a hanging or timeout application in a Spring Boot GraphQL application. By using the CompletableFuture.allOf() method with a timeout, we can resolve this issue and handle data loaders asynchronously. This technique can be applied to any data loading scenario where we need to combine multiple data loaders.

Best Practices

When using thenCompose or CompletableFuture.allOf() in a Spring Boot GraphQL application, follow these best practices:

  • Use a timeout when waiting for data loaders to complete.
  • Handle any exceptions that occur during the data loading process.
  • Use async/await to handle data loaders asynchronously.
  • Avoid using thenCompose when dealing with multiple data loaders.

Additional Resources

For more information on using CompletableFuture and thenCompose in a Spring Boot GraphQL application, refer to the following resources:

Introduction

In our previous article, we discussed the issue of thenCompose hangs/timeout in a Spring Boot GraphQL application and provided a solution using CompletableFuture.allOf() with a timeout. In this article, we'll answer some frequently asked questions (FAQs) related to this topic.

Q: What is the main cause of thenCompose hangs/timeout?

A: The main cause of thenCompose hangs/timeout is when the data loaders take a long time to complete or fail. This can lead to a deadlock situation where the application waits for all the data loaders to complete before returning the result.

Q: How can I avoid thenCompose hangs/timeout?

A: To avoid thenCompose hangs/timeout, you can use CompletableFuture.allOf() with a timeout. This method allows you to wait for all the data loaders to complete, but with a timeout. If any of the data loaders take longer than the timeout, you can cancel the operation and return an error.

Q: What is the difference between thenCompose and CompletableFuture.allOf()?

A: thenCompose is a method that combines multiple asynchronous operations into a single future. It's commonly used in data loading scenarios where we need to fetch data from multiple sources. CompletableFuture.allOf(), on the other hand, is a method that waits for all the futures to complete, but with a timeout. It's used to avoid the deadlock situation caused by thenCompose.

Q: How can I handle exceptions in thenCompose?

A: To handle exceptions in thenCompose, you can use the exceptionally() method. This method allows you to handle any exceptions that occur during the data loading process.

Q: Can I use thenCompose with multiple data loaders?

A: Yes, you can use thenCompose with multiple data loaders. However, be aware that it can lead to a deadlock situation if the data loaders take a long time to complete or fail.

Q: What are some best practices for using thenCompose in Spring Boot GraphQL application?

A: Some best practices for using thenCompose in a Spring Boot GraphQL application include:

  • Using a timeout when waiting for data loaders to complete.
  • Handling any exceptions that occur during the data loading process.
  • Using async/await to handle data loaders asynchronously.
  • Avoiding using thenCompose when dealing with multiple data loaders.

Q: Can I use CompletableFuture.allOf() with multiple data loaders?

A: Yes, you can use CompletableFuture.allOf() with multiple data loaders. This method allows you to wait for all the data loaders to complete, but with a timeout.

Q: How can I implement thenCompose with multiple data loaders?

A: To implement thenCompose with multiple data loaders, you can use the following code:

public CompletableFuture<UserProfile> getUserProfile() {
    CompletableFuture<String> streetFuture = dataLoader1.loadUserStreet();
    CompletableFuture<String> cityFuture = dataLoader2.loadUserCity();
    CompletableFuture<String> countryFuture = dataLoader3.loadUserCountry();

return CompletableFuture.allOf(streetFuture, cityFuture, countryFuture)
        .thenApply(v -&gt; {
            String street = streetFuture.join();
            String city = cityFuture.join();
            String country = countryFuture.join();
            UserProfile userProfile = new UserProfile();
            userProfile.setName(&quot;John Doe&quot;);
            userProfile.setEmail(&quot;john.doe@example.com&quot;);
            userProfile.setAddress(new Address(street, city, country));
            return userProfile;
        })
        .exceptionally(ex -&gt; {
            // Handle the exception
            return null;
        });



}

Conclusion

In conclusion, thenCompose hangs/timeout in a Spring Boot GraphQL application can be resolved by using CompletableFuture.allOf() with a timeout. By following the best practices and FAQs outlined in this article, you can avoid the deadlock situation caused by thenCompose and handle data loaders asynchronously.

Additional Resources

For more information on using CompletableFuture and thenCompose in a Spring Boot GraphQL application, refer to the following resources: