Understanding write syscalls while writing in golang

Question

I'm trying to understand concept of syscalls in linux; i wrote a simple program which calls Write 1000 time on file:

package main

import (
    "fmt"
    "os"
    "time"
    "math/rand"
)



const letterBytes = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"

func RandStringBytes(n int) []byte {
    b := make([]byte, n)
    for i := range b {
        b[i] = letterBytes[rand.Intn(len(letterBytes))]
    }
    return b
}


func main(){
    stat, err := os.Stat(os.Args[1])
    fmt.Println(stat, err)
    time.Sleep(time.Second)
    file, _ := os.OpenFile(os.Args[1], os.O_WRONLY|os.O_APPEND|os.O_CREATE, 0666)
    for i := 0; i <= 1000; i++{
        a := RandStringBytes(1000)
        file.Write(a)
    }
    file.Close()
}

So, I expect to write syscall to be called 1000 times; But, when i count syscalls via strace strace ./main file.txt 2>&1 | grep 'write' | wc -l I always get random number of write syscalls,sometimes ~200, sometimes ~300. I doubt that randomness of written strings give this effect. But the mystery is: why there is <1000 write syscalls?

I admit that maybe I misunderstood strace utility, maybe it skips some messages.

Why there is different number of syscalls than i expect?

I tried to look carefully in the go File.Write guts, but didn't find any buffers; any related googling leads to golang bufio package — Ilya Boltnev, Aug 18 '23 at 11:37
Well if it is sometimes 200 and somestimes 200, I think that's pretty stable. ;) — Itération 122442, Aug 18 '23 at 13:53
Have you tried `strace -f`? The writes may be happening on a different thread. (I found that here: https://stackoverflow.com/questions/42126345/why-isnt-strace-logging-all-my-system-calls) — Andy Schweig, Aug 18 '23 at 15:11
@AndySchweig you are absolutely right, the missing system calls was in other trehads — Ilya Boltnev, Aug 18 '23 at 15:53

Understanding write syscalls while writing in golang

0 Answers0