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|
import time
import sync
struct St {
a int
}
fn getint() int {
return 8
}
fn f1(ch1 chan int, ch2 chan St, ch3 chan int, ch4 chan int, ch5 chan int, mut sem sync.Semaphore) {
mut a := 5
select {
a = <-ch3 {
a = 0
}
b := <-ch2 {
a = b.a
}
ch3 <- 5 {
a = 1
}
ch2 <- St{
a: 37
} {
a = 2
}
ch4 <- (6 + 7 * 9) {
a = 8
}
ch5 <- getint() {
a = 9
}
300 * time.millisecond {
a = 3
}
}
assert a == 3
sem.post()
}
fn f2(ch1 chan St, ch2 chan int, mut sem sync.Semaphore) {
mut r := 23
for i in 0 .. 2 {
select {
b := <-ch1 {
r = b.a
}
ch2 <- r {
r = 17
}
}
if i == 0 {
assert r == 17
} else {
assert r == 13
}
}
sem.post()
}
fn test_select_blocks() {
ch1 := chan int{cap: 1}
ch2 := chan St{}
ch3 := chan int{}
ch4 := chan int{}
ch5 := chan int{}
mut sem := sync.new_semaphore()
mut r := false
t := select {
b := <-ch1 {
println(b)
}
else {
// no channel ready
r = true
}
}
assert r == true
assert t == true
go f2(ch2, ch3, mut sem)
n := <-ch3
assert n == 23
ch2 <- St{
a: 13
}
sem.wait()
stopwatch := time.new_stopwatch()
go f1(ch1, ch2, ch3, ch4, ch5, mut sem)
sem.wait()
elapsed_ms := f64(stopwatch.elapsed()) / time.millisecond
// https://docs.microsoft.com/en-us/windows-hardware/drivers/kernel/high-resolution-timers
// > For example, for Windows running on an x86 processor, the default interval between
// > system clock ticks is typically about 15 milliseconds, and the minimum interval
// > between system clock ticks is about 1 millisecond.
assert elapsed_ms >= 280.0 // 300 - (15ms + 5ms just in case)
ch1.close()
ch2.close()
mut h := 7
mut is_open := true
if select {
_ := <-ch2 {
h = 0
}
ch1 <- h {
h = 1
}
else {
h = 2
}
} {
panic('channel is still open')
} else {
is_open = false
}
// no branch should have run
assert h == 7
// since all channels are closed `select` should return `false`
assert is_open == false
}
|
