time: add After

Permits one to easily put a timeout in a select:

select {
case <-ch:
	// foo
case <-time.After(1e6):
	// bar
}

R=r, rog, rsc, sameer1, PeterGo, iant, nigeltao_gnome
CC=golang-dev
https://golang.org/cl/2321043

diff --git a/src/pkg/time/sleep.go b/src/pkg/time/sleep.go
index 5de5374cea7f43cf29bd3eb13a4292fe0885e196..702ced1304afe66fc3eb18729f7731b09fb1f7b6 100644 (file)
--- a/src/pkg/time/sleep.go
+++ b/src/pkg/time/sleep.go
@@ -9,18 +9,38 @@ import (
        "syscall"
 )
 
-// Sleep pauses the current goroutine for at least ns nanoseconds. Higher resolution
-// sleeping may be provided by syscall.Nanosleep on some operating systems.
+// Sleep pauses the current goroutine for at least ns nanoseconds.
+// Higher resolution sleeping may be provided by syscall.Nanosleep 
+// on some operating systems.
 func Sleep(ns int64) os.Error {
-       // TODO(cw): use monotonic-time once it's available
+       _, err := sleep(Nanoseconds(), ns)
+       return err
+}
+
+// After waits at least ns nanoseconds before sending the current time
+// on the returned channel.
+func After(ns int64) <-chan int64 {
        t := Nanoseconds()
+       ch := make(chan int64, 1)
+       go func() {
+               t, _ = sleep(t, ns)
+               ch <- t
+       }()
+       return ch
+}
+
+// sleep takes the current time and a duration,
+// pauses for at least ns nanoseconds, and
+// returns the current time and an error.
+func sleep(t, ns int64) (int64, os.Error) {
+       // TODO(cw): use monotonic-time once it's available
        end := t + ns
        for t < end {
                errno := syscall.Sleep(end - t)
                if errno != 0 && errno != syscall.EINTR {
-                       return os.NewSyscallError("sleep", errno)
+                       return 0, os.NewSyscallError("sleep", errno)
                }
                t = Nanoseconds()
        }
-       return nil
+       return t, nil
 }

diff --git a/src/pkg/time/sleep_test.go b/src/pkg/time/sleep_test.go
index 7ec6c49439c2cd684ce5fdc16cf70ea5f04d80c8..4934a38691310db4502f7fe02ba4374f28b48036 100644 (file)
--- a/src/pkg/time/sleep_test.go
+++ b/src/pkg/time/sleep_test.go
@@ -24,3 +24,15 @@ func TestSleep(t *testing.T) {
                t.Fatalf("Sleep(%d) slept for only %d ns", delay, duration)
        }
 }
+
+func TestAfter(t *testing.T) {
+       const delay = int64(100e6)
+       start := Nanoseconds()
+       end := <-After(delay)
+       if duration := Nanoseconds() - start; duration < delay {
+               t.Fatalf("After(%d) slept for only %d ns", delay, duration)
+       }
+       if min := start + delay; end < min {
+               t.Fatalf("After(%d) expect >= %d, got %d", delay, min, end)
+       }
+}