runtime: give test child time to block

The child in TestPanicSystemstack prints "x\n" and then blocks on a
lock. Receiving those bytes only indicates that the child is _about to
block_. Since we don't have a way to know when it is fully blocked,
sleep a bit to give it time to block. This makes us less likely to lose
the race and signal before the child blocks, which will fail the test as
the stack trace cannot be read from a running G.

Fixes #33626

Change-Id: I8a27b1b114bf75e1e5bcb2a7a33aa69cdbc22f40
Reviewed-on: https://go-review.googlesource.com/c/go/+/268578
Trust: Michael Pratt <mpratt@google.com>
Run-TryBot: Michael Pratt <mpratt@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>

diff --git a/src/runtime/crash_unix_test.go b/src/runtime/crash_unix_test.go
index 6c42cb9a3dfaff3708d876f76a9da5d448d0434c..c50d62d55244b5f6b14913772635ea1edfb321e7 100644 (file)
--- a/src/runtime/crash_unix_test.go
+++ b/src/runtime/crash_unix_test.go
@@ -232,13 +232,20 @@ func TestPanicSystemstack(t *testing.T) {
        }
        defer pr.Close()
 
-       // Wait for "x\nx\n" to indicate readiness.
+       // Wait for "x\nx\n" to indicate almost-readiness.
        buf := make([]byte, 4)
        _, err = io.ReadFull(pr, buf)
        if err != nil || string(buf) != "x\nx\n" {
                t.Fatal("subprocess failed; output:\n", string(buf))
        }
 
+       // The child blockers print "x\n" and then block on a lock. Receiving
+       // those bytes only indicates that the child is _about to block_. Since
+       // we don't have a way to know when it is fully blocked, sleep a bit to
+       // make us less likely to lose the race and signal before the child
+       // blocks.
+       time.Sleep(100*time.Millisecond)
+
        // Send SIGQUIT.
        if err := cmd.Process.Signal(syscall.SIGQUIT); err != nil {
                t.Fatal("signaling subprocess: ", err)