🐛 Fix goroutine leaks in cache Start() methods

[dongjiang1989]

What does this PR do?

This PR fixes goroutine leaks in multiNamespaceCache.Start() and delegatingByGVKCache.Start() methods in the pkg/cache package.

Why do we need it?

Problem

Both Start() methods used unbuffered error channels (errs := make(chan error)) to collect errors from goroutines. This caused goroutine leaks in two scenarios:

1. Multiple caches return errors simultaneously: The select statement only receives the first error and returns, leaving other goroutines blocked forever on errs <- err with no receiver.

2. Context cancelled while goroutines try to send errors: When ctx.Done() triggers first, the function returns immediately. Any subsequent error sends from goroutines will block forever.

Example

// Original problematic code
errs := make(chan error)  // unbuffered
for _, cache := range caches {
    go func() {
        if err := cache.Start(ctx); err != nil {
            errs <- err  // blocks forever if no receiver!
        }
    }()
}
select {
case err := <-errs:
    return err  // only receives ONE error, others leak
case <-ctx.Done():
    return nil  // returns immediately, senders leak
}

Fix

• Use buffered channels sized to the number of caches
• Use sync.WaitGroup to track all goroutines
• Wait for all goroutines to complete before returning

// Fixed code
errs := make(chan error, len(caches))  // buffered
var wg sync.WaitGroup
for _, cache := range caches {
    wg.Go(func() {
        if err := cache.Start(ctx); err != nil {
            errs <- err  // never blocks
        }
    })
}
done := make(chan struct{})
go func() { wg.Wait(); close(done) }()
// ... wait for all goroutines to complete

[kubernetes-prow]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: dongjiang1989
Once this PR has been reviewed and has the lgtm label, please assign alvaroaleman for approval. For more information see the Code Review Process.

The full list of commands accepted by this bot can be found here.

Details

Needs approval from an approver in each of these files:

• OWNERS

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment