Initial commit: Go 1.23 release state

test/chan/select3.go

@@ -0,0 +1,226 @@
+// run
+
+// Copyright 2010 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Test the semantics of the select statement
+// for basic empty/non-empty cases.
+
+package main
+
+import "time"
+
+const always = "function did not"
+const never = "function did"
+
+func unreachable() {
+	panic("control flow shouldn't reach here")
+}
+
+// Calls f and verifies that f always/never panics depending on signal.
+func testPanic(signal string, f func()) {
+	defer func() {
+		s := never
+		if recover() != nil {
+			s = always // f panicked
+		}
+		if s != signal {
+			panic(signal + " panic")
+		}
+	}()
+	f()
+}
+
+// Calls f and empirically verifies that f always/never blocks depending on signal.
+func testBlock(signal string, f func()) {
+	c := make(chan string)
+	go func() {
+		f()
+		c <- never // f didn't block
+	}()
+	go func() {
+		if signal == never {
+			// Wait a long time to make sure that we don't miss our window by accident on a slow machine.
+			time.Sleep(10 * time.Second)
+		} else {
+			// Wait as short a time as we can without false negatives.
+			// 10ms should be long enough to catch most failures.
+			time.Sleep(10 * time.Millisecond)
+		}
+		c <- always // f blocked always
+	}()
+	if <-c != signal {
+		panic(signal + " block")
+	}
+}
+
+func main() {
+	const async = 1 // asynchronous channels
+	var nilch chan int
+	closedch := make(chan int)
+	close(closedch)
+
+	// sending/receiving from a nil channel blocks
+	testBlock(always, func() {
+		nilch <- 7
+	})
+	testBlock(always, func() {
+		<-nilch
+	})
+
+	// sending/receiving from a nil channel inside a select is never selected
+	testPanic(never, func() {
+		select {
+		case nilch <- 7:
+			unreachable()
+		default:
+		}
+	})
+	testPanic(never, func() {
+		select {
+		case <-nilch:
+			unreachable()
+		default:
+		}
+	})
+
+	// sending to an async channel with free buffer space never blocks
+	testBlock(never, func() {
+		ch := make(chan int, async)
+		ch <- 7
+	})
+
+	// receiving from a closed channel never blocks
+	testBlock(never, func() {
+		for i := 0; i < 10; i++ {
+			if <-closedch != 0 {
+				panic("expected zero value when reading from closed channel")
+			}
+			if x, ok := <-closedch; x != 0 || ok {
+				println("closedch:", x, ok)
+				panic("expected 0, false from closed channel")
+			}
+		}
+	})
+
+	// sending to a closed channel panics.
+	testPanic(always, func() {
+		closedch <- 7
+	})
+
+	// receiving from a non-ready channel always blocks
+	testBlock(always, func() {
+		ch := make(chan int)
+		<-ch
+	})
+
+	// empty selects always block
+	testBlock(always, func() {
+		select {}
+	})
+
+	// selects with only nil channels always block
+	testBlock(always, func() {
+		select {
+		case <-nilch:
+			unreachable()
+		}
+	})
+	testBlock(always, func() {
+		select {
+		case nilch <- 7:
+			unreachable()
+		}
+	})
+	testBlock(always, func() {
+		select {
+		case <-nilch:
+			unreachable()
+		case nilch <- 7:
+			unreachable()
+		}
+	})
+
+	// selects with non-ready non-nil channels always block
+	testBlock(always, func() {
+		ch := make(chan int)
+		select {
+		case <-ch:
+			unreachable()
+		}
+	})
+
+	// selects with default cases don't block
+	testBlock(never, func() {
+		select {
+		default:
+		}
+	})
+	testBlock(never, func() {
+		select {
+		case <-nilch:
+			unreachable()
+		default:
+		}
+	})
+	testBlock(never, func() {
+		select {
+		case nilch <- 7:
+			unreachable()
+		default:
+		}
+	})
+
+	// selects with ready channels don't block
+	testBlock(never, func() {
+		ch := make(chan int, async)
+		select {
+		case ch <- 7:
+		default:
+			unreachable()
+		}
+	})
+	testBlock(never, func() {
+		ch := make(chan int, async)
+		ch <- 7
+		select {
+		case <-ch:
+		default:
+			unreachable()
+		}
+	})
+
+	// selects with closed channels behave like ordinary operations
+	testBlock(never, func() {
+		select {
+		case <-closedch:
+		}
+	})
+	testBlock(never, func() {
+		select {
+		case x := (<-closedch):
+			_ = x
+		}
+	})
+	testBlock(never, func() {
+		select {
+		case x, ok := (<-closedch):
+			_, _ = x, ok
+		}
+	})
+	testPanic(always, func() {
+		select {
+		case closedch <- 7:
+		}
+	})
+
+	// select should not get confused if it sees itself
+	testBlock(always, func() {
+		c := make(chan int)
+		select {
+		case c <- 1:
+		case <-c:
+		}
+	})
+}