Скачать или смотреть Understanding the Use of disable fork Inside a Forever Loop in Fork-Join Constructs

Discover why `disable fork` can lead to undesired behavior in your System-Verilog code inside a forever loop. Learn efficient coding practices to avoid pitfalls in your verification tasks.
---
This video is based on the question https://stackoverflow.com/q/75579910/ asked by the user 'Gayathri Hariharakrishnan' ( https://stackoverflow.com/u/21016872/ ) and on the answer https://stackoverflow.com/a/75584218/ provided by the user 'dave_59' ( https://stackoverflow.com/u/2755607/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: Use of disable fork inside forever loop of fork-join

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Understanding the Use of disable fork Inside a Forever Loop in Fork-Join Constructs

In System-Verilog, concurrency is a powerful tool. However, it can sometimes lead to unexpected behavior if not used correctly. A common issue that arises is the use of disable fork within a forever loop of a fork-join block. In this post, we’ll explore a specific case and provide detailed solutions to ensure your verification tasks run smoothly.

The Problem: Execution Only Once

A user reported an issue with their System-Verilog code, which involved using disable fork inside a fork-join that was embedded within a forever loop. The expectation was that a new process would be created and subsequently killed every time one of the threads finished executing. However, it turned out that the code executed only once, leading to confusion.

Code Snippet

Here’s a brief look at the initial code that was causing the problem:

[[See Video to Reveal this Text or Code Snippet]]

The challenge with the above snippet is that once the acknowledgment receipt happens, disable fork affects the entire task rather than just the process.

The Solution: Using fork/join_any

The key misunderstanding here is how disable fork operates. When this statement is provided inside a forked process that has no children, it disables all processes associated with that fork, which includes your entire task. As a result, it prevents the task from detecting any additional changes of req after the first completed process, leading to the observed behavior.

Modified Code Structure

To fix the issue, you can adjust the structure of the code to utilize fork/join_any which allows for more flexible handling. Here's the revised code:

[[See Video to Reveal this Text or Code Snippet]]

Key Changes Made

Used fork/join_any: This allows for each of the forked processes to operate independently, and if one finishes before the other, the overall task stays active and can continue to respond to external changes.

Local Variables for References: Local variables local_req and local_ack ensure that the task maintains state across different forked executions.

Conclusion

When dealing with concurrency in System-Verilog, it is crucial to understand how constructs like fork, join, and disable fork work together. The modifications we've discussed will allow for multiple executions within a loop, providing a more robust verification task. By implementing fork/join_any and refactoring your code, you can avoid the issue of terminating tasks prematurely.

Keep experimenting with these constructs as you refine your System-Verilog skills, and always stay vigilant about the implications of concurrency in your design and verification tasks!