runtime: add more chan benchmarks

Add benchmarks for:
1. non-blocking failing receive (polling of "stop" chan)
2. channel-based semaphore (gate pattern)
3. select-based producer/consumer (pass data through a channel, but also wait on "stop" and "timeout" channels)

LGTM=r
R=golang-codereviews, r
CC=bradfitz, golang-codereviews, iant, khr
https://golang.org/cl/59040043

src/pkg/runtime/chan_test.go

@@ -430,6 +430,30 @@ func TestMultiConsumer(t *testing.T) {
 	}
 }
 
+func BenchmarkChanNonblocking(b *testing.B) {
+	const CallsPerSched = 1000
+	procs := runtime.GOMAXPROCS(-1)
+	N := int32(b.N / CallsPerSched)
+	c := make(chan bool, procs)
+	myc := make(chan int)
+	for p := 0; p < procs; p++ {
+		go func() {
+			for atomic.AddInt32(&N, -1) >= 0 {
+				for g := 0; g < CallsPerSched; g++ {
+					select {
+					case <-myc:
+					default:
+					}
+				}
+			}
+			c <- true
+		}()
+	}
+	for p := 0; p < procs; p++ {
+		<-c
+	}
+}
+
 func BenchmarkSelectUncontended(b *testing.B) {
 	const CallsPerSched = 1000
 	procs := runtime.GOMAXPROCS(-1)
@@ -670,6 +694,66 @@ func BenchmarkChanProdConsWork100(b *testing.B) {
 	benchmarkChanProdCons(b, 100, 100)
 }
 
+func BenchmarkSelectProdCons(b *testing.B) {
+	const CallsPerSched = 1000
+	procs := runtime.GOMAXPROCS(-1)
+	N := int32(b.N / CallsPerSched)
+	c := make(chan bool, 2*procs)
+	myc := make(chan int, 128)
+	myclose := make(chan bool)
+	for p := 0; p < procs; p++ {
+		go func() {
+			// Producer: sends to myc.
+			foo := 0
+			// Intended to not fire during benchmarking.
+			mytimer := time.After(time.Hour)
+			for atomic.AddInt32(&N, -1) >= 0 {
+				for g := 0; g < CallsPerSched; g++ {
+					// Model some local work.
+					for i := 0; i < 100; i++ {
+						foo *= 2
+						foo /= 2
+					}
+					select {
+					case myc <- 1:
+					case <-mytimer:
+					case <-myclose:
+					}
+				}
+			}
+			myc <- 0
+			c <- foo == 42
+		}()
+		go func() {
+			// Consumer: receives from myc.
+			foo := 0
+			// Intended to not fire during benchmarking.
+			mytimer := time.After(time.Hour)
+		loop:
+			for {
+				select {
+				case v := <-myc:
+					if v == 0 {
+						break loop
+					}
+				case <-mytimer:
+				case <-myclose:
+				}
+				// Model some local work.
+				for i := 0; i < 100; i++ {
+					foo *= 2
+					foo /= 2
+				}
+			}
+			c <- foo == 42
+		}()
+	}
+	for p := 0; p < procs; p++ {
+		<-c
+		<-c
+	}
+}
+
 func BenchmarkChanCreation(b *testing.B) {
 	const CallsPerSched = 1000
 	procs := runtime.GOMAXPROCS(-1)
@@ -694,9 +778,23 @@ func BenchmarkChanCreation(b *testing.B) {
 
 func BenchmarkChanSem(b *testing.B) {
 	type Empty struct{}
-	c := make(chan Empty, 1)
+	const CallsPerSched = 1000
-	for i := 0; i < b.N; i++ {
+	procs := runtime.GOMAXPROCS(0)
-		c <- Empty{}
+	N := int32(b.N / CallsPerSched)
+	c := make(chan bool, procs)
+	myc := make(chan Empty, procs)
+	for p := 0; p < procs; p++ {
+		go func() {
+			for atomic.AddInt32(&N, -1) >= 0 {
+				for g := 0; g < CallsPerSched; g++ {
+					myc <- Empty{}
+					<-myc
+				}
+			}
+			c <- true
+		}()
+	}
+	for p := 0; p < procs; p++ {
 		<-c
 	}
 }