CUDA: How to assert in kernel code?

assertion cuda
Ashwin Nanjappa picture Ashwin Nanjappa · Feb 25, 2011 · Viewed 15.2k times · Source

What is the equivalent technique of an assertion in CUDA kernel code?

There does not seem to be an assert for CUDA kernel code. I want a way to catch programmer mistakes easily in kernel code. A mechanism where I can set conditions that need to be true and the kernel should bail out when the condition is false with an error message.

Answer

jmilloy picture jmilloy · Feb 25, 2011

For devices of cc 2.x or above, assertion , void assert(int expression), could be used within a kernel such that threads with expression == 0 send a message to stderr once a host synchronization function is called.

For other cases or when assertion cannot be used (e.g. on MacOS), you won't be able to return an error message or error code to the host from a kernel.

Instead, I would set a error state and check it from the host. Use device global memory or (better) mapped host memory for storing an error state, passed as a parameter to each kernel call. Use if statements in the kernel, and of if the statements fail, set the error code and return. You will be able to check the error code from the host after the kernel call, but keep in mind that you will have synchronize the host and device after the kernel launch before checking the error code. I guess this will work fine for development but not so much for production.

As to printing an error message straight from the device

  • In 1.x, 2.x, and 3.0 cards, you can use emulation mode to print an error message.
  • In 3.1 forward (on fermi), apparently you can use printf in kernels to print the error message. It appears that it doesn't always work right away, e.g. http://forums.nvidia.com/index.php?showtopic=182448

Related questions

Best practice for Python assert

Is there a performance or code maintenance issue with using assert as part of the standard code instead of using it just for debugging purposes? Is assert x >= 0, 'x is less than zero' better or worse than if x &…

Read More
How do I assert my exception message with JUnit Test annotation?

I have written a few JUnit tests with @Test annotation. If my test method throws a checked exception and if I want to assert the message along with the exception, is there a way to do so with JUnit @Test …

Read More
How do I use Assert.Throws to assert the type of the exception?

How do I use Assert.Throws to assert the type of the exception and the actual message wording? Something like this: Assert.Throws<Exception>( ()=>user.MakeUserActive()).WithMessage("Actual exception message") The method I am testing throws multiple …

Read More