All,
While learning Go from the book "The Go Programming Language", by
Addison-Wesley I was working through an example and was taken back by how
easy it is to cause a data race. The book states that each incoming
request is run in a separate goroutine by the server so that it can handle
multiple requests simultaneously. It goes on to explain that if the
*count++* variable is accessed at the same time by different goroutines
that I could have a race and need to wrap it in mutex to lock and unlock
the variable. All of this makes sense and is pretty standard, however my
confusion/concern is that there is no apparent mechanism that tells me that
there's code that's executing multiple goroutines against my code. Yes,
you could assume that a webserver would do this, but as more and more
libraries are added how would you know without reading all the code in
every library? To see if the the race detector would find this potential
bug for me, I ran the code with the mutex(s) commented out with the -race
flag on and didn't get a warning. So how do I catch these mistakes before
there is a problem? It feels a little like walking on egg shells waiting
for you code to blow up. Every programmer I know has had a bad day, and
can easily make these types of mistakes. So how do you protect against
them in Go? Your guidance is greatly appreciated.
Thanks!
--Nick
------------------------------------------------------------------------------------------------------------------------------------
go run -race wserver2.go
------------------------------------------------------------------------------------------------------------------------------------
Web server example code:
------------------------------------------------------------------------------------------------------------------------------------
package main
import (
"fmt"
"log"
"net/http"
"sync"
)
var mu sync.Mutex
var count int
func main() {
http.HandleFunc("/", handler) // Each request calls the handler
http.HandleFunc("/count", counter)
log.Fatal(http.ListenAndServe("localhost:8000", nil))
}
// The handler echoes the Path component of the requested URL
func handler(w http.ResponseWriter, r *http.Request){
//mu.Lock()
count++
//mu.Unlock()
fmt.Fprint(w, "URL.Path = %q\n", r.URL.Path)
}
// Counter echoes the number of calls so far
func counter (w http.ResponseWriter, r *http.Request) {
//mu.Lock()
fmt.Fprint(w, "Count %d\n", count)
//mu.Unlock()
}
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