testing: add -test.timeout option.

Since Go code can deadlock, this lets a testsuite driver set a
time limit for the test to run.  This is simple but imperfect,
in that it only catches deadlocks in Go code, not in the
runtime scheduler.

R=r, rsc, iant2
CC=golang-dev
https://golang.org/cl/4326048

src/pkg/testing/testing.go

@@ -61,6 +61,7 @@ var (
 	memProfile     = flag.String("test.memprofile", "", "write a memory profile to the named file after execution")
 	memProfileRate = flag.Int("test.memprofilerate", 0, "if >=0, sets runtime.MemProfileRate")
 	cpuProfile     = flag.String("test.cpuprofile", "", "write a cpu profile to the named file during execution")
+	timeout        = flag.Int64("test.timeout", 0, "if > 0, sets time limit for tests in seconds")
 )
 
 // Short reports whether the -test.short flag is set.
@@ -158,7 +159,9 @@ func Main(matchString func(pat, str string) (bool, os.Error), tests []InternalTe
 	flag.Parse()
 
 	before()
+	startAlarm()
 	RunTests(matchString, tests)
+	stopAlarm()
 	RunBenchmarks(matchString, benchmarks)
 	after()
 }
@@ -241,3 +244,24 @@ func after() {
 		f.Close()
 	}
 }
+
+var timer *time.Timer
+
+// startAlarm starts an alarm if requested.
+func startAlarm() {
+	if *timeout > 0 {
+		timer = time.AfterFunc(*timeout*1e9, alarm)
+	}
+}
+
+// stopAlarm turns off the alarm.
+func stopAlarm() {
+	if *timeout > 0 {
+		timer.Stop()
+	}
+}
+
+// alarm is called if the timeout expires.
+func alarm() {
+	panic("test timed out")
+}