[Michael Lynch] encountered a strange situation. Why was compiling then running his program nearly 10x faster than just running the program by itself? [Michael] ran into this issue while benchmarking a programming project, pared it down to its essentials for repeatability and analysis, and discovered it highlighted an incorrect mental model of how bash pipelines worked.

Here’s the situation. The first thing [Michael]’s pared-down program does is start a timer. Then it simply reads and counts some bytes from stdin, then prints out how long it took for that to happen. When running the test program in the following way, it takes about 13 microseconds.

$ echo '00010203040506070809' | xxd -r -p | zig build run -Doptimize=ReleaseFast
bytes: 10
execution time: 13.549µs

When running the (already-compiled) program directly, execution time swells to 162 microseconds.

$ echo '00010203040506070809' | xxd -r -p | ./zig-out/bin/count-bytes
bytes: 10
execution time: 162.195µs

Again, the only difference between zig build run and ./zig-out/bin/count-bytes is that the first compiles the code, then immediately runs it. The second simply runs the compiled program. Continue reading “Is Your Mental Model Of Bash Pipelines Wrong?” →