通过通道迭代写入时，Go文件IO失败

Question

I'm having an issue with writing lines to a csv file while iterating over a channel. I'm new to Go, but the syntax for file IO looks synchronous to me. Given that I would expect that a write operation returning successfully would indicate that the write is complete, but that's not what I'm observing. This is essentially what I have going on in my application:

package main

import (
    "encoding/csv"
    "log"
    "os"
)

func main() {
    file, err := os.Create("test.csv")
    if err != nil {
        log.Fatalf("Error opening file: %s", err.Error())
    }
    defer file.Close()

    writer := csv.NewWriter(file)
    channel := make(chan []string)
    counter := 0

    go func() {
        defer close(channel)

        for i := 0; i < 100; i++ {
            channel <- []string{"col1", "col2"}
        }
    }()

    for vals := range channel {
        if err := writer.Write(vals); err != nil {
            log.Fatalf("Error writing to csv: %s", err.Error())
        }
        counter++
    }

    log.Printf("%d lines written", counter)
}

There's a go routine passing values through a channel, and I'm iterating over those values and writing them to a CSV file. I get no errors, and at the end it logs that 100 lines have been written.

When I check the CSV file though it's empty. The behavior I'm seeing in my application is the file is written incompletely; it'll stop halfway through writing a record. I'm sure I'm missing something, but if the write returns with no errors why is there nothing in the file?

Answer 1

You are missing writer.Flush() at the end of your function.

More info here