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sync: support concurrent selects on same channel(s) (#7415)

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Uwe Krüger 2020-12-20 04:52:40 +01:00 committed by GitHub
parent b29bcb3fbe
commit af9766a7d6
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2 changed files with 88 additions and 9 deletions
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75
vlib/sync/channel_select_6_test.v Normal file
View File

@ -0,0 +1,75 @@
// This test case runs concurrent 3 instances of `do_select` that
// communicate with 6 other threads doing send and receive operations.
// There are buffered and unbuffered channels - handled by one or two
// concurrend threads on the other side
fn do_select(ch1 chan int, ch2 chan int, chf1 chan f64, chf2 chan f64, sumch1 chan i64, sumch2 chan i64) {
mut sum1 := i64(0)
mut sum2 := i64(0)
f1 := 17.
f2 := 7.
for _ in 0 .. 20000 + chf1.cap / 3 {
select {
chf1 <- f1 {}
i := <-ch1 {
sum1 += i
}
j := <-ch2 {
sum2 += j
}
chf2 <- f2 {}
}
}
sumch1 <- sum1
sumch2 <- sum2
}
fn do_send_int(ch chan int, factor int) {
for i in 0 .. 10000 {
ch <- (i * factor)
}
}
fn do_rec_f64(ch chan f64, sumch chan f64) {
mut sum:= 0.
for _ in 0 .. 10000 {
sum += <-ch
}
sumch <- sum
}
fn test_select() {
ch1 := chan int{cap: 3}
ch2 := chan int{}
// buffer length of chf1 mus be mutiple of 3 (# select threads)
chf1 := chan f64{cap: 30}
chf2 := chan f64{}
chsum1 := chan i64{}
chsum2 := chan i64{}
chsumf1 := chan f64{}
chsumf2 := chan f64{}
go do_send_int(ch1, 3)
go do_select(ch1, ch2, chf1, chf2, chsum1, chsum2)
go do_rec_f64(chf1, chsumf1)
go do_rec_f64(chf2, chsumf2)
go do_rec_f64(chf2, chsumf2)
go do_select(ch1, ch2, chf1, chf2, chsum1, chsum2)
go do_send_int(ch2, 7)
go do_send_int(ch2, 17)
go do_select(ch1, ch2, chf1, chf2, chsum1, chsum2)
sum1 := <-chsum1 + <-chsum1 + <-chsum1
sum2 := <-chsum2 + <-chsum2 + <-chsum2
mut sumf1 := <-chsumf1
// empty channel buffer
for _ in 0 .. chf1.cap {
sumf1 += <-chf1
}
sumf2 := <-chsumf2 + <-chsumf2
// Use Gauß' formula
expected_sum := i64(10000) * (10000 - 1) / 2
assert sum1 == 3 * expected_sum
assert sum2 == (7 + 17) * expected_sum
assert sumf1 == 17. * f64(10000 + chf1.cap)
assert sumf2 == 7. * 20000
}

22
vlib/sync/channels.v
View File

@ -511,20 +511,18 @@ pub fn channel_select(mut channels []&Channel, dir []Direction, mut objrefs []vo
mut subscr := []Subscription{len: channels.len}
sem := new_semaphore()
for i, ch in channels {
subscr[i].sem = sem
if dir[i] == .push {
mut null16 := u16(0)
for !C.atomic_compare_exchange_weak_u16(&ch.write_sub_mtx, &null16, u16(1)) {
null16 = u16(0)
}
subscr[i].sem = sem
subscr[i].prev = &ch.write_subscriber
unsafe {
subscr[i].nxt = C.atomic_exchange_ptr(&ch.write_subscriber, &subscr[i])
}
if voidptr(subscr[i].nxt) != voidptr(0) {
unsafe {
subscr[i].nxt.prev = &subscr[i]
}
subscr[i].nxt.prev = &subscr[i].nxt
}
C.atomic_store_u16(&ch.write_sub_mtx, u16(0))
} else {
@ -532,13 +530,12 @@ pub fn channel_select(mut channels []&Channel, dir []Direction, mut objrefs []vo
for !C.atomic_compare_exchange_weak_u16(&ch.read_sub_mtx, &null16, u16(1)) {
null16 = u16(0)
}
subscr[i].sem = sem
subscr[i].prev = &ch.read_subscriber
unsafe {
subscr[i].nxt = C.atomic_exchange_ptr(&ch.read_subscriber, &subscr[i])
}
if voidptr(subscr[i].nxt) != voidptr(0) {
unsafe { subscr[i].nxt.prev = &subscr[i] }
subscr[i].nxt.prev = &subscr[i].nxt
}
C.atomic_store_u16(&ch.read_sub_mtx, u16(0))
}
@ -577,7 +574,8 @@ pub fn channel_select(mut channels []&Channel, dir []Direction, mut objrefs []vo
}
if timeout == 0 {
goto restore
} else if timeout > 0 {
}
if timeout > 0 {
remaining := timeout - stopwatch.elapsed()
if !sem.timed_wait(remaining) {
goto restore
@ -594,8 +592,11 @@ restore:
for !C.atomic_compare_exchange_weak_u16(&ch.write_sub_mtx, &null16, u16(1)) {
null16 = u16(0)
}
subscr[i].prev = subscr[i].nxt
unsafe {
*subscr[i].prev = subscr[i].nxt
}
if subscr[i].nxt != 0 {
subscr[i].nxt.prev = subscr[i].prev
// just in case we have missed a semaphore during restore
subscr[i].nxt.sem.post()
}
@ -605,8 +606,11 @@ restore:
for !C.atomic_compare_exchange_weak_u16(&ch.read_sub_mtx, &null16, u16(1)) {
null16 = u16(0)
}
subscr[i].prev = subscr[i].nxt
unsafe {
*subscr[i].prev = subscr[i].nxt
}
if subscr[i].nxt != 0 {
subscr[i].nxt.prev = subscr[i].prev
subscr[i].nxt.sem.post()
}
C.atomic_store_u16(&ch.read_sub_mtx, u16(0))