Browse files

test: deflake chan/select3.go

On a slow or distracted machine, 0.1s is sometimes
not long enough for a non-blocking function call to complete.
This causes rare test flakes.
They can be easily reproduced by reducing the wait time to (say) 100ns.

For non-blocking functions, increase the window from 100ms to 10s.
Using different windows for block and non-blocking functions,
allows us to reduce the time for blocking functions.
The risk here is false negatives, but that risk is low;
this test is run repeatedly on many fast machines,
for which 10ms is ample time.
This reduces the time required to run the test by a factor of 10,
from ~1s to ~100ms.

Fixes #20299

Change-Id: Ice9a641a66c6c101d738a2ebe1bcb144ae3c9916
Run-TryBot: Josh Bleecher Snyder <>
Reviewed-by: Brad Fitzpatrick <>
TryBot-Result: Gobot Gobot <>
  • Loading branch information...
josharian committed Jul 7, 2017
1 parent 093adee commit a1e7fb4eed7fbb002d2fabbd6a809a1a49dca711
Showing with 9 additions and 2 deletions.
  1. +9 −2 test/chan/select3.go
@@ -40,8 +40,15 @@ func testBlock(signal string, f func()) {
c <- never // f didn't block
go func() {
time.Sleep(1e8) // 0.1s seems plenty long
c <- always // f blocked always
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")

0 comments on commit a1e7fb4

Please sign in to comment.