class IO

Yields self in non-blocking mode.

When false is given as an argument, self is yielded in blocking mode. The original mode is restored after the block is executed.

static VALUE
rb_io_nonblock_block(int argc, VALUE *argv, VALUE self)
{
    int nb = 1;

    int descriptor = rb_io_descriptor(self);

    if (argc > 0) {
        VALUE v;
        rb_scan_args(argc, argv, "01", &v);
        nb = RTEST(v);
    }

    int current_flags = get_fcntl_flags(descriptor);
    int restore[2] = {descriptor, current_flags};

    if (!io_nonblock_set(descriptor, current_flags, nb))
        return rb_yield(self);

    return rb_ensure(rb_yield, self, io_nonblock_restore, (VALUE)restore);
}

Enables non-blocking mode on a stream when set to true, and blocking mode when set to false.

This method set or clear O_NONBLOCK flag for the file descriptor in ios.

The behavior of most IO methods is not affected by this flag because they retry system calls to complete their task after EAGAIN and partial read/write. (An exception is IO#syswrite which doesn’t retry.)

This method can be used to clear non-blocking mode of standard I/O. Since nonblocking methods (read_nonblock, etc.) set non-blocking mode but they doesn’t clear it, this method is usable as follows.

END { STDOUT.nonblock = false }
STDOUT.write_nonblock("foo")

Since the flag is shared across processes and many non-Ruby commands doesn’t expect standard I/O with non-blocking mode, it would be safe to clear the flag before Ruby program exits.

For example following Ruby program leaves STDIN/STDOUT/STDER non-blocking mode. (STDIN, STDOUT and STDERR are connected to a terminal. So making one of them nonblocking-mode effects other two.) Thus cat command try to read from standard input and it causes “Resource temporarily unavailable” error (EAGAIN).

% ruby -e '
STDOUT.write_nonblock("foo\n")'; cat
foo
cat: -: Resource temporarily unavailable

Clearing the flag makes the behavior of cat command normal. (cat command waits input from standard input.)

% ruby -rio/nonblock -e '
END { STDOUT.nonblock = false }
STDOUT.write_nonblock("foo")
'; cat
foo

static VALUE
rb_io_nonblock_set(VALUE self, VALUE value)
{
    if (RTEST(value)) {
        rb_io_t *fptr;
        GetOpenFile(self, fptr);
        rb_io_set_nonblock(fptr);
    }
    else {
        int descriptor = rb_io_descriptor(self);
        io_nonblock_set(descriptor, get_fcntl_flags(descriptor), RTEST(value));
    }

    return self;
}

Returns true if an IO object is in non-blocking mode.

static VALUE
rb_io_nonblock_p(VALUE io)
{
    if (get_fcntl_flags(rb_io_descriptor(io)) & O_NONBLOCK)
        return Qtrue;
    return Qfalse;
}