On 2/23/21 4:04 PM, Axel Wagner wrote:
Because you have a concurrent read/write to a.
Specifically, the Memory model says that "the go statement that starts a
new goroutine happens before the goroutine's execution begins"
<https://golang.org/ref/mem#tmp_5>. This means the first code is fine -
the write happens before the go statement, which happens before
execution of f begins, which happens before the `print(a)`. So the write
happens before the read and everything is fine.
If you switch the two lines, the go statement still happens before
execution of f begins and thus before `print(a)`. But now, it *also*
happens before the write
("Within a single goroutine, reads and writes
must behave as if they executed in the order specified by the program").
Thanks, dude. My main confusion is why the first code does not have DATA
RACE problem, I think I understand this sentence now.
So the read and the write are concurrent - the go statement happens
before both, but they are not ordered between them.
FTR, this should also be fairly obvious without looking at the specifics
of the memory model. If you do
go f()
a = "hello world"
You start a new goroutine reading `a`, so it should be clear, that when
the assignment happens, there is a separate goroutine running that might
read from it at the same time.
On Tue, Feb 23, 2021 at 8:51 AM sanye <xba...@gmail.com
<mailto:xba...@gmail.com>> wrote:
Hello Gophers,a question bothers me while reading the doc: The Go
Memory
Model
package main
var a string
func f() {
print(a)
}
func hello() {
a = "hello, world\n"
go f()
}
func main() {
hello()
}
This code snippet is OK
But if I exchange the 2 lines in function hello, DATA RACE happens, why?
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