Hi Fabian,
You could add a signal channel to tell your goroutine to exit. Editing your
pseudo code:
data := make(chan byte)
done := make(chan struct{})
fd := some file descriptor
go func() {
buf = make([]byte, 1)
for {
n, err = syscall.Read(fd, buf)
if err != nil {
close(data)
return
}
select {
case data <- buf[0]:
case <- done:
return
}
}
}
select {
case b := <- data:
// do something with b
case <- timeout:
close(done)
syscall.Close(fd)
}
Hope this helps.
Cheers,
Alex
On Sunday, 24 July 2016 18:50:37 UTC-4, fabian....@gmail.com wrote:
>
> Hi,
>
> I would like to call syscall.Read() with a timeout. Coming from C, my
> first idea was to use syscall.Select(), which should work fine. However, I
> came across this answer from 2014 by Ian Lance Taylor to a similar question
> (https://groups.google.com/d/msg/golang-nuts/al-6_QFgYaM/UkCqyCQVq_0J):
>
> The usual approach in Go is to use a simple goroutine that reads from the
>> file and writes to a channel. Then you can use the select statement to
>> check the channel when appropriate. It's unusual to want to use the poll
>> or select system calls since the language gives you other ways to do the
>> same thing.
>
>
> I tried it, but I find it harder than it sounds. Here's my pseudo code:
>
> data := make(chan byte)
> fd := some file descriptor
>
> go func() {
> buf = make([]byte, 1)
> for {
> n, err = syscall.Read(fd, buf)
> if err != nil {
> close(data)
> return
> }
> data <- buf[0]
> }
> }
>
> select {
> case b := <- data:
> // do something with b
> case <- timeout:
> syscall.Close(fd)
> }
>
> The idea is obvious: When the timeout is reached, fd is closed, which
> interrupts the blocking syscall.Read(), which terminates the goroutine.
>
> However, there is a race condition: If the timeout is reached immediately
> after a successful syscall.Read(), the line 'data <- buf[0]' will block
> forever, as no consumer reads data anymore. Adding capacity to the data
> channel doesn't help, because theoretically the loop might repeat multiple
> times between the timeout is received and fd is actually closed.
>
> How can I refactor this pseudo code to get rid of the race condition? How
> can I implement a syscall.Read() with timeout using a goroutine, channel,
> and golang's select statement?
>
> Thanks for your help
> Fabian
>
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