loc's Introduction

loc

It's a fast, alloc-free and convinient version of runtime.Caller.

Performance benefits are available when using the nikandfor_loc_unsafe build tag. This relies on the internal runtime implementation, which means that older versions of the package may not compile with future versions of Go. Without the tag, it is safe to use with any version of Go.

It was born from tlog.

What is similar

Caller

pc := loc.Caller(1)
ok := pc != 0
name, file, line := pc.NameFileLine()
e := pc.FuncEntry()

// is similar to

pc, file, line, ok := runtime.Caller(1) 
f := runtime.FuncForPC(pc)
name := f.Name()
e := f.Entry()

Callers

pcs := loc.Callers(1, 3)
// or
var pcsbuf [3]loc.PC
pcs := loc.CallersFill(1, pcsbuf[:])

for _, pc := range pcs {
    name, file, file := pc.NameFileLine()
}

// is similar to
var pcbuf [3]uintptr
n := runtime.Callers(2, pcbuf[:])

frames := runtime.CallersFrames(pcbuf[:n])
for {
    frame, more := frames.Next()
    
    _, _, _ = frame.Function, frame.File, frame.Line

    if !more {
        break
    }
}

What is different

Normalized path

loc returns cropped filepath.

github.com/nikandfor/loc/func_test.go

# vs

/home/nik/nikandfor/loc/github.com/nikandfor/loc/func_test.go

Performance

In loc the full cycle (get pc than name, file and line) takes 360=200+160 (200+0 when you repeat) ns whereas runtime takes 690 (640 without func name) + 2 allocs per each frame.

It's up to 3.5x improve.

BenchmarkLocationCaller-8              	 5844801	       201.8 ns/op	       0 B/op	       0 allocs/op
BenchmarkLocationNameFileLine-8        	 7313388	       156.5 ns/op	       0 B/op	       0 allocs/op
BenchmarkRuntimeCallerNameFileLine-8   	 1709940	       689.1 ns/op	     216 B/op	       2 allocs/op
BenchmarkRuntimeCallerFileLine-8       	 1917613	       642.1 ns/op	     216 B/op	       2 allocs/op

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