protected int lowestFd() {
		Integer lowest = closedFds.pollFirst();
		if (lowest != null) {
			return lowest;
		}
		return descriptors.size();
	}
Get the first available file descriptor

@return the lowest available descriptor
Ghidra/Features/SystemEmulation/src/main/java/ghidra/pcode/emu/unix/AbstractEmuUnixSyscallUseropLibrary.java