No. The channel operations do not act like a fence, but like a… channel, through which happens-before relationships can be transported. The crucial point in the example you quoted is, that the channel-communication creates a happens-before relationship between the two goroutines, which then connects the happens-before relationships between channel-send/write and channel-read/print.
Let's say, hypothetically, the happens-before relationship for channel-operations was turned around: The read happens before the send. Conceptually, they happen simultaneously and just from a local perspective, both operations would still look just as much as a "fence". But suddenly, there wouldn't be a happens-before relationship between the write and the print: write ≤ channel-send ≥ channel-read ≤ print You *have* to look at relationships between goroutines. And you need (or rather it's incredibly sensible) to take the causality-lens when understanding the memory model; it was chosen for a reason. The memory model is about establishing causal relationships between events in different goroutines and about the direction of that causality. It only makes promises about what GR A observes about GR B *if* there is an edge between them and only *if* that edge is correctly oriented. On Sat, Oct 28, 2017 at 1:45 PM, T L <tapir....@gmail.com> wrote: > The first example in the "Channel communication" section, it says > > The write to a happens before the send on c, which happens before the > corresponding receive on c completes, which happens before the print. > > From the description, I feel that "the write to a happens before the send > on c" is not caused by > "the send on c happens before the corresponding receive on c completes". > And "the corresponding receive on c completes happens before the print" > is also independent to > "the send on c happens before the corresponding receive on c completes". > > So it looks channel read and write operations really act as a fance to > avoid exchanging relative orders of statements before and after the fence. > > -- > You received this message because you are subscribed to the Google Groups > "golang-nuts" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to golang-nuts+unsubscr...@googlegroups.com. > For more options, visit https://groups.google.com/d/optout. > -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
