Nice! I wasn't aware that the select statement is also for writing to
channels, most examples only show reading from channels. Thanks a lot!
On Monday, July 25, 2016 at 5:12:48 AM UTC+2, Alex Bucataru wrote:
>
> 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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