PHP マニュアル: Read file stream asynchronously.

public static bool Swoole\Async::read(
    string $filename,
    callable $callback,
    int $chunk_size = ?,
    int $offset = ?
)

filename

The name of the file.

callback

mixed callback(string $filename, string $content)

chunk_size

The chunk length.

offset

The offset.

Whether the read is succeed.