C# Method Call Depth Performance
Compare the performance of method call depths. Reducing call depth can improve speed.
Method calls can be nested. This impacts performance. The more nesting, the more depth to the stack. A method call will require stack space unless it is inlined. By flattening the call stack, we reduce stack usage and improve performance.
And: When a method terminates, its memory is forgotten from the stack and the pointer is readjusted.
Next: This program contains eight important methods: A1 through D1, and A2 through D2.
Info: When A1 is called, it calls B1 and then B1 calls C1. On the other hand, when A2 is called, it simply calls B2, C2, and D2.
Important: The A2 method should consume less stack space. It has a shorter stack.
using System; using System.Diagnostics; class Program { const int _max = 100000000; static void Main() { A1(); A2(); var s1 = Stopwatch.StartNew(); for (int i = 0; i < _max; i++) { A1(); } s1.Stop(); var s2 = Stopwatch.StartNew(); for (int i = 0; i < _max; i++) { A2(); } s2.Stop(); Console.WriteLine(((double)(s1.Elapsed.TotalMilliseconds * 1000 * 1000) / _max).ToString("0.00 ns")); Console.WriteLine(((double)(s2.Elapsed.TotalMilliseconds * 1000 * 1000) / _max).ToString("0.00 ns")); Console.Read(); } static int _i = 1; static void A1() { B1(); } static void B1() { if (_i == 0) throw new Exception(); C1(); } static void C1() { if (_i == 0) throw new Exception(); D1(); } static void D1() { if (_i == 0) throw new Exception(); } static void A2() { B2(); C2(); D2(); } static void B2() { if (_i == 0) throw new Exception(); } static void C2() { if (_i == 0) throw new Exception(); } static void D2() { if (_i == 0) throw new Exception(); } }
Output
3.54 ns Nested calls
0.96 ns Sequential calls
Also: The Exception throws in the program are to confuse the inliner in the JIT.
However: This is likely not useful except on performance-critical parts of important programs.