Is Global Variable Optimization for Infrequently Updated Slice Parameters in Go Worth the Effort?

Parameter Passing vs Global Variable Optimization

Consider the concern of optimizing function performance by making infrequently updated parameters global to avoid repetitive passing. Specifically, we examine the performance implications in the context of a checkFiles function that takes a slice of excluded patterns as an argument.

Go's Copy-on-Write Behavior

Contrarily to the belief that Go uses copy-on-write, parameters are always passed by value, resulting in a copy of the actual value being passed. For slices, this means a copy of the slice descriptor is created, while the underlying array remains shared.

Efficiency of Slice Passing

Slices in Go are compact references to their backing arrays. By design, slice passing is efficient since only the descriptor, not the entire underlying array, needs to be copied. Therefore, passing slices as parameters does not incur significant overhead, making the global variable optimization unnecessary.

Performance Benchmarking

Benchmarking the alternative approaches reveals no noticeable performance difference. A sample benchmark code demonstrates that both passing slices as parameters and accessing global slices execute with comparable efficiency.

Considerations for Efficiency

While slice passing efficiency is generally optimal, consider the following:

• If the function makes multiple accesses to the slice, passing it as an argument can allow compilers to make further optimizations.
• For exceptional cases where the slice is very large, passing a pointer to a slice may be appropriate to reduce the initial copy size.

Conclusion

In most scenarios, there is no performance benefit to making parameters global instead of passing them as parameters. Go's efficient slice handling eliminates the need for such optimizations, and parameter passing often allows for further compiler optimizations.

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