![]() ![]() The heap is huge, global, and managed at run-time. So the stack is a good place to store values that are small, fixed-width, and/or temporary. Stack frames are small, laid out statically at compile time, and everything in a stack frame gets destroyed at the same time when its scope ends. For example, in Rust when you have a variable of type String, some of the string's data is stored on the stack and some on the heap, working with the strengths of each. The stack is fast because of its limitations. ![]() This pointer is small, so we often put it into a variable that lives on the stack. When you allocate space on the heap, you get back a pointer. The heap and stack are made to work together. That way the buffer can be allocated where the function is called as an array or other stack-based structure. Instead of returning heap-allocated objects from a function, pass a buffer into the function for it to write to. If you know the size at compile time, use the stack. So the heap is a good place to store values that are large, dynamically-sized, and/or long-lived.Īnd you don't need to choose just one. Use the heap for only allocating space for objects at runtime. The stack is fast because of its limitations. You need to look at the strengths and weaknesses of both allocation options. When bench marking with Rust there are suggestions for dealing with some of these issues: Benchmark testsĮxpanding on this some more: “The stack is fast, so it's better than the heap” is the wrong way to look at things. A compiler could well optimize a multiply into a shift or a division into a multiplication for any particular known value. Not only that, one should benchmark over a range of inputs. Nobody cares if an empty function is removed and the program exists in a single instruction, or even none.Ī function with no input could well be optimized away and whatever output it should produce be computed at compile time and used instead. The important thing to find is the time taken to produce the output from the input. I don't mean to be rude but I think your bench marking approach is futile.Īny useful program/function has input and output. Because I'm doing stuff like calling empty functions or additions and not using the results, it's very hard to test in release mode without worrying that the compiler will figure it's useless code and tell me it took 0 seconds to complete. Will have to use something like this to force the compiler to not optimize away the very functions we are trying to use. ![]()
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