#pragma once

// Single-instance guard: bind an abstract-namespace Unix socket whose name is derived
// from the canonical runtime directory (resolve_runtime_dir's result — already the
// per-user default, /run/user/<uid>/velox, unless XDG_RUNTIME_DIR says otherwise). A
// second daemon pointed at the same runtime dir gets EADDRINUSE and exits; one pointed at
// a different (isolated / test) runtime dir gets its own lock and starts fine. The kernel
// reclaims an abstract-namespace address when the holding process dies, so a crash never
// wedges it (docs/01 §2).
//
// Naming this "velox-daemon-<euid>" alone (the old scheme) meant exactly one name per
// user system-wide, so XDG_RUNTIME_DIR isolation never reached it: a leaked test veloxd
// with the same euid held the lock for every isolated instance too, real or test, until
// it was killed. Hashing the resolved runtime dir path instead keeps the real per-user
// daemon unique (its runtime dir is unique to it) while letting isolated instances that
// each point at their own runtime dir coexist.

#include <string>

namespace velox::daemon::rpc {

// Returns the held fd (kept open for the process lifetime; closing it releases the lock)
// or -1 if another process already holds the lock for this exact `runtime_dir`, or on any
// other socket error.
int acquire_single_instance_lock(const std::string& runtime_dir);

}  // namespace velox::daemon::rpc