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Check if channel receive will succeed using len instead of a select statement. #292

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Check if channel receive will succeed using len instead of a select statement. #292

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6724ecc
I noticed that the existing code probably didn't do quite what was in…
cdillond Oct 1, 2025
3f84904
switched back to select from len
cdillond Oct 1, 2025
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10 changes: 4 additions & 6 deletions token.go
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Original file line number Diff line number Diff line change
Expand Up @@ -1192,18 +1192,16 @@ func (t *tokenProcessor) iterateResponse() error {
func (t tokenProcessor) nextToken() (tokenStruct, error) {
// we do this separate non-blocking check on token channel to
// prioritize it over cancellation channel
select {
case tok, more := <-t.tokChan:
err, more := tok.(error)
if more {
if len(t.tokChan) > 0 {
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Copilot AI Oct 1, 2025

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Using len() to check if a channel receive will succeed is not reliable in concurrent code. The channel length can change between the len() check and the subsequent receive operation if another goroutine receives from the channel. This creates a race condition that could cause the goroutine to block indefinitely. The original select statement with default case was the correct approach for non-blocking receives, though the variable naming issue should be fixed differently.

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@cdillond cdillond Oct 1, 2025

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Oops - I guess I was wrong about how default cases in select statements work. Sorry!

tok := <-t.tokChan
err, ok := tok.(error)
if ok {
t.sess.LogF(t.ctx, msdsn.LogDebug, "nextToken returned an error:"+err.Error())
// this is an error and not a token
return nil, err
} else {
return tok, nil
}
default:
// there are no tokens on the channel, will need to wait
}

select {
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