Fiber::Scheduler#unblock

VALUE
rb_fiber_scheduler_unblock(VALUE scheduler, VALUE blocker, VALUE fiber)
{
    RUBY_ASSERT(rb_obj_is_fiber(fiber));

    VALUE result;
    enum ruby_tag_type state;

    // `rb_fiber_scheduler_unblock` can be called from points where `errno` is expected to be preserved. Therefore, we should save and restore it. For example `io_binwrite` calls `rb_fiber_scheduler_unblock` and if `errno` is reset to 0 by user code, it will break the error handling in `io_write`.
    //
    // If we explicitly preserve `errno` in `io_binwrite` and other similar functions (e.g. by returning it), this code is no longer needed. I hope in the future we will be able to remove it.
    int saved_errno = errno;

    // We must prevent interrupts while invoking the unblock method, because otherwise fibers can be left permanently blocked if an interrupt occurs during the execution of user code. See also `rb_fiber_scheduler_fiber_interrupt`.
    rb_execution_context_t * volatile ec = GET_EC();
    volatile int saved_interrupt_mask = ec->interrupt_mask;
    ec->interrupt_mask |= PENDING_INTERRUPT_MASK;

    rb_control_frame_t *volatile cfp = ec->cfp;
    EC_PUSH_TAG(ec);
    if ((state = EC_EXEC_TAG()) == TAG_NONE) {
        result = rb_funcall(scheduler, id_unblock, 2, blocker, fiber);
    }
    else {
        rb_vm_rewind_cfp(ec, cfp);
    }
    EC_POP_TAG();

    ec->interrupt_mask = saved_interrupt_mask;

    if (state) {
        EC_JUMP_TAG(ec, state);
    }

    RUBY_VM_CHECK_INTS(ec);

    errno = saved_errno;

    return result;
}