cmd/anubis: Fix potential decaymap race (#683)

Fixes a potential TOCTOU issue that would cause values to be spuriously
erased.

IIUC, the following interleaving of (*DecayMap).Get() and
(*DecayMap).Set() can cause an update to be erased:

  // thread A: Get("x")
  m.lock.RLock()
  value, ok := m.data["x"]
  m.lock.RUnlock()
  ...
  if time.Now().After(value.expiry) {
      // <wait for lock!>

  // thread B: Set("x", ...)
  m.lock.Lock()
  defer m.lock.Unlock()
  m.data["x"] = DecayMapEntry{ ... }

  // thread A continues its Get("x") after acquring the lock:
  m.lock.Lock()
  delete(m.data, "x") // Oops! Newer entry is deleted!
  m.lock.Unlock()

Realistically... I think it's probably a non-issue either way, because
the worst that can happen is that a cache entry is spuriously removed,
and it'll just get re-fetched.

0 files changed, 0 insertions, 0 deletions