#pragma once

// Single-instance guard, keyed by the resolved runtime directory (see rpc/runtime_dir.hpp)
// so isolated instances pointed at different runtime dirs never contend (docs/01 §2). The
// mechanism is Linux's abstract-namespace Unix socket; macOS has no abstract namespace and
// uses a real socket file plus flock() instead, which must unlink a stale socket left by a
// crashed process (docs/08-porting.md "API mapping" — the abstract version got that for
// free from the kernel).

#include <string>
#include <system_error>

namespace velox::daemon::rpc::platform {

// 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 error acquiring it.
int acquire_instance_lock(const std::string& runtime_dir);

}  // namespace velox::daemon::rpc::platform