sync/channels: provide `try_push(), try_pop() as public methods (#6101)

doc/upcoming.md

@@ -252,7 +252,7 @@ if ch.pop(&m) {
 
 The select call is somewhat tricky. The `channel_select()` function needs three arrays that
 contain the channels, the directions (pop/push) and the object references and
-a timeout of type `time.Duration` (or `0` to wait unlimited) as parameters. It returns the
+a timeout of type `time.Duration` (`time.infinite` or `-1` to wait unlimited) as parameters. It returns the
 index of the object that was pushed or popped or `-1` for timeout.
 
 ```v

vlib/sync/bench/results.md

@@ -0,0 +1,39 @@
+# Channel Benchmark Results
+
+This documents lists several benchmark results for different platforms in order to
+identify performance regressions and improvements.
+
+The are measured using the command
+
+```
+> channel_bench_* <nsend> <nrec> <buflen> <nobj>
+
+nsend ... number of threads that push objects into the channel
+nrec .... number of threads that pop objects from the channel
+buflen .. length of channel buffer queue - `0` means unbuffered channel
+nobj .... number of objects to pass thru the channel
+```
+
+## AMD Ryzen 7 3800X, Ubuntu-20.04 x86_64
+
+10000000 Objects transfered, results in Objects/µs
+
+| nsend | nrec | buflen | **V (gcc -O2)** | **V (tcc)** | **Go (glang)** | **Go (gccgo -O2)** |
+| :---: | :---:| :---:  |      :---:      |    :---:    |     :---:      |      :---:         |
+|   1   |   1  |    0   |      0.95       |    0.66     |      4.65      |       0.56         |
+|   1   |   1  |   100  |      3.26       |    2.24     |     18.90      |       6.08         |
+|   4   |   4  |    0   |      0.25       |    0.24     |      1.84      |       0.84         |
+|   4   |   4  |   100  |      2.78       |    2.63     |      7.43      |       3.71         |
+
+## Raspberry Pi 3B+, Void Linux musl 32 bit
+
+10000000 Objects transfered, results in Objects/µs
+
+| nsend | nrec | buflen | **V (gcc -O2)** | **Go (glang)** |
+| :---: | :---:| :---:  |      :---:      |     :---:      |
+|   1   |   1  |    0   |      0.37       |     0.21       |
+|   1   |   1  |   100  |      1.03       |     0.74       |
+|   4   |   4  |    0   |      0.04       |     0.38       |
+|   4   |   4  |   100  |      2.78       |     2.63       |
+|   2   |   2  |    0   |      0.05       |     0.38       |
+|   2   |   2  |   100  |      1.26       |     0.75       |

vlib/sync/channel_select_test.v

@@ -48,7 +48,7 @@ fn test_select() {
 	mut sl := i64(0)
 	mut objs := [voidptr(&ri), &sl, &rl, &rb]
 	for _ in 0 .. 1200 {
-		idx := sync.channel_select(mut channels, directions, mut objs, 0)
+		idx := sync.channel_select(mut channels, directions, mut objs, -1)
 		match idx {
 			0 {
 				sum += ri

vlib/sync/channels.v

@@ -152,17 +152,26 @@ pub fn (mut ch Channel) close() {
 	C.atomic_store_u16(&ch.write_sub_mtx, u16(0))
 }
 
+[inline]
 pub fn (mut ch Channel) push(src voidptr) {
-	if ch.try_push(src, false) == .closed {
+	if ch.try_push_priv(src, false) == .closed {
 		panic('push on closed channel')
 	}
 }
 
-fn (mut ch Channel) try_push(src voidptr, no_block bool) TransactionState {
+[inline]
+pub fn (mut ch Channel) try_push(src voidptr) TransactionState {
+	return ch.try_push_priv(src, false)
+}
+
+fn (mut ch Channel) try_push_priv(src voidptr, no_block bool) TransactionState {
 	if C.atomic_load_u16(&ch.closed) != 0 {
 		return .closed
 	}
-	spinloops_, spinloops_sem_ := if no_block { 1, 1 } else { spinloops, spinloops_sem }
+	mut spinloops_sem_, spinloops_ := if no_block { spinloops, spinloops_sem } else { 1, 1 }
+	$if macos {
+		spinloops_sem_ = 1
+	}
 	mut have_swapped := false
 	for {
 		mut got_sem := false
@@ -307,12 +316,21 @@ fn (mut ch Channel) try_push(src voidptr, no_block bool) TransactionState {
 	}
 }
 
+[inline]
 pub fn (mut ch Channel) pop(dest voidptr) bool {
-	return ch.try_pop(dest, false) == .success
+	return ch.try_pop_priv(dest, false) == .success
 }
 
-fn (mut ch Channel) try_pop(dest voidptr, no_block bool) TransactionState  {
+[inline]
-	spinloops_, spinloops_sem_ := if no_block { 1, 1 } else { spinloops, spinloops_sem }
+pub fn (mut ch Channel) try_pop(dest voidptr) TransactionState {
+	return ch.try_pop_priv(dest, false)
+}
+
+fn (mut ch Channel) try_pop_priv(dest voidptr, no_block bool) TransactionState {
+	mut spinloops_sem_, spinloops_ := if no_block { spinloops, spinloops_sem } else { 1, 1 }
+	$if macos {
+		spinloops_sem_ = 1
+	}
 	mut have_swapped := false
 	mut write_in_progress := false
 	for {
@@ -465,7 +483,11 @@ fn (mut ch Channel) try_pop(dest voidptr, no_block bool) TransactionState  {
 }
 
 // Wait `timeout` on any of `channels[i]` until one of them can push (`is_push[i] = true`) or pop (`is_push[i] = false`)
-// object referenced by `objrefs[i]`. `timeout = 0` means wait unlimited time
+// object referenced by `objrefs[i]`. `timeout < 0` means wait unlimited time. `timeout == 0` means return immediately
+// if no transaction can be performed without waiting.
+// return value: the index of the channel on which a transaction has taken place
+//               -1 if waiting for a transaction has exceeded timeout
+//               -2 if all channels are closed
 
 pub fn channel_select(mut channels []&Channel, dir []Direction, mut objrefs []voidptr, timeout time.Duration) int {
 	assert channels.len == dir.len
@@ -499,7 +521,7 @@ pub fn channel_select(mut channels []&Channel, dir []Direction, mut objrefs []vo
 			C.atomic_store_u16(&ch.read_sub_mtx, u16(0))
 		}
 	}
-	stopwatch := if timeout == 0 { time.StopWatch{} } else { time.new_stopwatch({}) }
+	stopwatch := if timeout <= 0 { time.StopWatch{} } else { time.new_stopwatch({}) }
 	mut event_idx := -1 // negative index means `timed out`
 	for {
 		rnd := rand.u32_in_range(0, u32(channels.len))
@@ -510,7 +532,7 @@ pub fn channel_select(mut channels []&Channel, dir []Direction, mut objrefs []vo
 				i -= channels.len
 			}
 			if dir[i] == .push {
-				stat := channels[i].try_push(objrefs[i], true)
+				stat := channels[i].try_push_priv(objrefs[i], true)
 				if stat == .success {
 					event_idx = i
 					goto restore
@@ -518,7 +540,7 @@ pub fn channel_select(mut channels []&Channel, dir []Direction, mut objrefs []vo
 					num_closed++
 				}
 			} else {
-				stat := channels[i].try_pop(objrefs[i], true)
+				stat := channels[i].try_pop_priv(objrefs[i], true)
 				if stat == .success {
 					event_idx = i
 					goto restore
@@ -531,7 +553,9 @@ pub fn channel_select(mut channels []&Channel, dir []Direction, mut objrefs []vo
 			event_idx = -2
 			goto restore
 		}
-		if timeout > 0 {
+		if timeout == 0 {
+			goto restore
+		} else if timeout > 0 {
 			remaining := timeout - stopwatch.elapsed()
 			if !sem.timed_wait(remaining) {
 				goto restore

vlib/sync/select_close_test.v

@@ -1,4 +1,5 @@
 import sync
+import time
 
 fn do_rec_i64(mut ch sync.Channel) {
 	mut sum := i64(0)
@@ -55,7 +56,7 @@ fn test_select() {
 	mut sl := i64(0)
 	mut objs := [voidptr(&ri), &sl, &rl, &rb]
 	for j in 0 .. 1101 {
-		idx := sync.channel_select(mut channels, directions, mut objs, 0)
+		idx := sync.channel_select(mut channels, directions, mut objs, time.infinite)
 		match idx {
 			0 {
 				sum += ri

vlib/time/time.v

@@ -366,6 +366,7 @@ pub const(
 	second      = Duration(1000) * millisecond
 	minute      = Duration(60) * second
 	hour        = Duration(60) * minute
+	infinite    = Duration(-1)
 )
 
 // nanoseconds returns the duration as an integer number of nanoseconds.