setIpcFile

    pub fn setIpcFile(node: Node, expected_io_userdata: ?*anyopaque, file: Io.File) void {
        const index = node.index.unwrap() orelse return;
        const io = global_progress.io;
        assert(io.userdata == expected_io_userdata);
        for (0..ipc_storage_buffer_len) |_| {
            const slot: Ipc.Slot = @truncate(
                @atomicRmw(Ipc.SlotAtomic, &global_progress.ipc_next, .Add, 1, .monotonic),
            );
            if (slot >= ipc_storage_buffer_len) continue;
            const ipc_ptr = &global_progress.ipc[slot];
            const ipc = @atomicLoad(Ipc, ipc_ptr, .monotonic);
            if (ipc.locked or ipc.valid) continue;
            const generation = ipc.generation +% 1;
            if (@cmpxchgWeak(
                Ipc,
                ipc_ptr,
                ipc,
                .{ .locked = false, .valid = true, .generation = generation },
                .acquire,
                .monotonic,
            )) |_| continue;
            global_progress.ipc_files[slot] = file;
            storageByIndex(index).setIpcIndex(.{ .slot = slot, .generation = generation });
            break;
        } else {
            // There was no IPC slot available, so we'll drop this node's IPC info and just close
            // the fd. To avoid an old `estimated_total_items` or `completed_count` value still
            // being rendered for the node, we'll zero that field out (and the user is not allowed
            // to change it because they think we're doing IPC).
            file.close(io);
            @atomicStore(u32, &storageByIndex(index).completed_count, 0, .monotonic);
            @atomicStore(u32, &storageByIndex(index).estimated_total_count, 0, .monotonic);
        }
    }