Final answer:
In non-blocking mode, slow functions return placeholders like futures, promises, or use callbacks to avoid stalling the program until the operation completes.
Step-by-step explanation:
When slow functions operate in non-blocking mode and their condition is not ready, they typically return a placeholder or indicator rather than the final expected result. This placeholder could be something like a future, promise, or a callback function. For instance, in asynchronous programming, a future or promise allows the program to continue running and does not block the execution flow. When the operation is completed, the future is 'fulfilled' with the actual result. If the function relies on callbacks, it will execute the callback function once the condition becomes ready, passing the result through the callback parameters.
Conversely, if the function cannot provide a future or call a callback immediately, it might return a special value such as null, undefined, or some kind of error condition that signals the operation is still pending. It is essential for the calling code to handle these temporary placeholders or signals appropriately to ensure smooth operation of the program.
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