Hi,
I have a scenario which I haven't found a way to implement with the Go
channels and select statement while it's no problem to do it with the
select()/poll() functions. The scenario is as follows.
Let me use a Go-like pseudo-code to demonstrate the idea. There is a source
of a work items which are processed by several goroutines. Here is the
source procedure:
work_ch := make(chan *WorkItem)
for {
work_ch <- NewWorkItem()
}
And here is the worker thread:
for {
wi := <-work_ch
self.do_the_work(wi)
}
Now I need to suspend the work. I stop supplying the work items and want to
make sure the worker goroutines are done with the work. The source
procedure becomes something like this:
for {
if suspend_requested {
for _, worker := range workers {
worker.idle_request <- true
}
for _, worker := range workers {
<-worker.idle_response
}
report_suspend_is_success()
wait_until_unsuspended()
}
work_ch <- NewWorkItem()
}
And I want to modify the worker thread like this:
for {
select {
case wi := <- work_ch:
self.do_the_work(wi)
case <-self.idle_request:
self.idle_response <- true
}
}
However this last snippet of code does not work because the cases within
the select statement are randomly chosen when both channels are ready so I
have no guarantee that the first case is executed first.
Talking about the select() or poll() functions from the C library which
evidently were an inspiration for the Go select statement, there is no
problem with the described approach. It's because the select() function
returns a complete information about the state of all the monitored
descriptors and allows the programmer to decide what he wants to read or
write and in which order, based on readiness of every descriptor.
I think it would be a great idea to have some function similar to
select()/poll() but working with the Go channels.
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