sync/channels: fixes for `try_push/pop()`, optimizations (#6352)

vlib/sync/bench/results.md

@@ -20,10 +20,10 @@ nobj .... number of objects to pass thru the channel
 
 | nsend | nrec | buflen | **V (gcc -O2)** | **V (clang)** | **V (tcc)** | **Go (glang)** | **Go (gccgo -O2)** |
 | :---: | :---:| :---:  |      :---:      |    :---:      |    :---:    |     :---:      |      :---:         |
-|   1   |   1  |    0   |      0.95       |    0.72       |    0.66     |      4.65      |       0.56         |
-|   1   |   1  |   100  |      3.26       |    2.51       |    2.24     |     18.90      |       6.08         |
-|   4   |   4  |    0   |      0.25       |    0.26       |    0.24     |      1.84      |       0.84         |
-|   4   |   4  |   100  |      3.11       |    2.78       |    2.63     |      7.43      |       3.71         |
+|   1   |   1  |    0   |      1.97       |    1.63       |    2.08     |      4.65      |       0.56         |
+|   1   |   1  |   100  |      3.05       |    2.29       |    1.93     |     18.90      |       6.08         |
+|   4   |   4  |    0   |      0.87       |    0.90       |    0.99     |      1.84      |       0.84         |
+|   4   |   4  |   100  |      3.35       |    3.07       |    2.92     |      7.43      |       3.71         |
 
 ## AMD Ryzen 7 3800X, Windows 10 2004 x64
 

vlib/sync/channel_try_buf_test.v

@@ -0,0 +1,17 @@
+fn test_channel_try_buffered() {
+	ch := chan int{cap: 5}
+	for z in 2..13 {
+		if ch.try_push(z) == .not_ready {
+			assert z == 7
+			break
+		}
+	}
+	mut obj := int(0)
+	for ch.try_pop(obj) == .success {
+		println(obj)
+	}
+	assert obj == 6
+	ch <- 17
+	obj = <-ch
+	assert obj == 17
+}

vlib/sync/channel_try_unbuf_test.v

@@ -0,0 +1,13 @@
+fn test_channel_try_unbuffered() {
+	ch := chan int{}
+	for z in 5..8 {
+		if ch.try_push(z) == .not_ready {
+			assert z == 5
+			break
+		}
+		panic('push on non-ready channel not detected')
+	}
+	mut obj := -17
+	for ch.try_pop(obj) == .success {}
+	assert obj == -17
+}

vlib/sync/channels.v

@@ -165,14 +165,14 @@ pub fn (mut ch Channel) push(src voidptr) {
 
 [inline]
 pub fn (mut ch Channel) try_push(src voidptr) ChanState {
-	return ch.try_push_priv(src, false)
+	return ch.try_push_priv(src, true)
 }
 
 fn (mut ch Channel) try_push_priv(src voidptr, no_block bool) ChanState {
 	if C.atomic_load_u16(&ch.closed) != 0 {
 		return .closed
 	}
-	spinloops_sem_, spinloops_ := if no_block { spinloops, spinloops_sem } else { 1, 1 }
+	spinloops_sem_, spinloops_ := if no_block { 1, 1 } else { spinloops, spinloops_sem }
 	mut have_swapped := false
 	for {
 		mut got_sem := false
@@ -200,6 +200,9 @@ fn (mut ch Channel) try_push_priv(src voidptr, no_block bool) ChanState {
 			got_sem = ch.writesem.try_wait()
 		}
 		if !got_sem {
+			if no_block {
+				return .not_ready
+			}
 			ch.writesem.wait()
 		}
 		if ch.cap == 0 {
@@ -311,6 +314,9 @@ fn (mut ch Channel) try_push_priv(src voidptr, no_block bool) ChanState {
 				}
 				return .success
 			} else {
+				if no_block {
+					return .not_ready
+				}
 				ch.writesem.post()
 			}
 		}
@@ -324,11 +330,11 @@ pub fn (mut ch Channel) pop(dest voidptr) bool {
 
 [inline]
 pub fn (mut ch Channel) try_pop(dest voidptr) ChanState {
-	return ch.try_pop_priv(dest, false)
+	return ch.try_pop_priv(dest, true)
 }
 
 fn (mut ch Channel) try_pop_priv(dest voidptr, no_block bool) ChanState {
-	spinloops_sem_, spinloops_ := if no_block { spinloops, spinloops_sem } else { 1, 1 }
+	spinloops_sem_, spinloops_ := if no_block { 1, 1 } else { spinloops, spinloops_sem } 
 	mut have_swapped := false
 	mut write_in_progress := false
 	for {