紧急情况：运行时错误：以goroutine同时运行时，切片范围超出范围

I'm calling a function as a goroutine and using a WaitGroup to prevent closing a shared Scanner before they all finish. The myfunc() function iterates over a file. I wanted to memory-map this file and share it between all of the goroutines rather than have the I/O chokepoint of reading from disk each time. I was told that this approach would work in an answer to another question. However, while this function worked fine standalone, it's not working concurrently. I am receiving the error:

panic: runtime error: slice bounds out of range

but the error is when I call the Scan() method (not on a slice) which is confusing.

Here is a MWE:

// ... package declaration; imports; yada yada

// the actual Sizes map is much more meaningful, this is just for the MWE
var Sizes = map[int]string {
    10: "Ten",
    20: "Twenty",
    30: "Thirty",
    40: "Forty",
}

type FileScanner struct {
    io.Closer
    *bufio.Scanner
}

func main() {
    // ... validate path to file stored in filePath variable
    filePath := "/path/to/file.txt"

    // get word list scanner to be shared between goroutines
    scanner := getScannerPtr(&filePath)

    // call myfunc() for each param passed
    var wg sync.WaitGroup
    ch := make(chan string)
    for _, param := range os.Args[1:] {
        wg.Add(1)
        go myfunc(&param, scanner, ch)
        wg.Done()
    }

    // print results received from channel
    for range os.Args[1:] {
        fmt.Println(<-ch)  // print data received from channel ch
    }

    // don't close scanner until all goroutines are finished
    wg.Wait()
    defer scanner.Close()
}

func getScannerPtr(filePath *string) *FileScanner {
    f, err := os.Open(*filePath)
    if err != nil {
        fmt.Fprint(os.Stderr, "Error opening file
")
        panic(err)
    }
    scanner := bufio.NewScanner(f)
    return &FileScanner{f, scanner}
}

func myfunc(param *string, scanner *FileScanner, ch chan<-string) {
    for scanner.Scan() {
        line := strings.TrimSpace(scanner.Text())
        // ... do something with line (read only)
        // ... access shared Sizes map when doing it (read only)
        ch <- "some string result goes here"
    }
}

I originally thought the issue was concurrent access to the shared Sizes map, but moving it inside myfunc() (and inefficiently redeclaring/redefining it every time) still resulted in the same error, which has to do with calling Scan(). I'm attempting to follow the guidance I received in this answer.

Here's the full stack trace of the panic:

panic: runtime error: slice bounds out of range

goroutine 6 [running]:
bufio.(*Scanner).Scan(0xc42008a000, 0x80)
        /usr/local/go/src/bufio/scan.go:139 +0xb3e
main.crack(0xc42004c280, 0xc42000a080, 0xc42001c0c0)
        /Users/dan/go/src/crypto_ctf_challenge/main.go:113 +0x288
created by main.main
        /Users/dan/go/src/crypto_ctf_challenge/main.go:81 +0x1d8
exit status 2

Line 81 is:

go myfunc(&param, scanner, ch)

Line 113 is:

for scanner.Scan() {

Actually after review of the Scan source, it doesn't appear to be thread-safe. You can get around this by having one routine read off of the scanner, and any number of other routines consume lines and process them:

func main() {
    // ... validate path to file stored in filePath variable
    filePath := "/path/to/file.txt"

    // get word list scanner to be shared between goroutines
    scanner := getScannerPtr(&filePath)
    defer scanner.Close()

    // call myfunc() for each param passed
    var wg sync.WaitGroup
    ch := make(chan string)
    lines := make(chan string)
    go func() {
        for scanner.Scan() {
            lines <- scanner.Text()
        }
        close(lines)
    }()
    for _, param := range os.Args[1:] {
        wg.Add(1)
        go myfunc(param, lines, ch)
        wg.Done()
    }

    // print results received from channel
    for range os.Args[1:] {
        fmt.Println(<-ch)  // print data received from channel ch
    }

    // don't close scanner until all goroutines are finished
    wg.Wait()
}

func myfunc(param string, lines chan []byte, ch chan<-string) {
    for line := range lines {
        line = strings.TrimSpace(line)
        // ... do something with line (read only)
        // ... access shared Sizes map when doing it (read only)
        ch <- "some string result goes here"
    }
}

Also note that there's no point in defering the last line in a function; the whole point of defer is to call it somewhere in the body of the function and know it will be called after the function returns. Since you're using a WaitGroup to prevent the function returning until you're done with your scanner, you can safely defer the close immediately.