sd0/sd1 in Win32?

Community Support
1

As I understand, if I need call from C into q’s main loop, I’ll need to use sd0/sd1.

But may I understand what the parameter of type I mean? The sample code given are for Linux, where sys/eventfd.h is used. How about Win32? What kind of handle can I pass into sd0/sd1?

2

Hi,

The parameter of type I is just an integer. This integer is supposed to be a valid file descriptor
https://en.wikipedia.org/wiki/File_descriptor or the Windows equivalent (file handles/socket descriptors).
This abstraction can behave a bit differently on Unix and Windows systems however (Windows handles
are not usable in the all the same contexts as the unix ones).

For example on Windows, you can take a winsock socket and cast it to an int to listen for messages:

e.g
SOCKET sock = CreateSocket();
sd1((I) sock, ProcessUpdate);

and then to stop listening when you are done:

sd0((I) sock);

Note that sd0 will close the file descriptor. You may want to look at sd0x which takes a second integer
parameter that specifies whether to close the file descriptor.

Thanks

Mark Rooney
Financial Software Developer
AQUAQ Analytics

3

Thanks for the insight, Mark. Does this mean that I’ll need to reserve some ports (potentially a lot of them if I’m to make use of sd1 extensively) for my application? Since the I argument is to be sockets, I’ll need to basically run a lot of TCP sockets locally for this purpose?

The use case I have is that I’m having interfacing with an asychronous API where results for each function call are always returned via a callback function in some thread other than the main thread. Thus, in order to pass the result back to q, I cannot call k(0, …, (K)0) directly. I was trying to use sd0/sd1 in order to call k(0, …, (K)0) in the main thread, but I’m facing two problems:

  1. Managing one socket per async function call seems to be quite a daunting task.

  2. As explained in the cookbook, K objects allocated in one thread shall not be freed on another thread. Therefore, I assume that it’d be unsafe if I need to convert the result from the async API into K object before invoking the callback (since the conversion will be allocating K objects in the async thread instead of the main thread)?

How can I solve the above two problems in a manageable manner?

4

a wise man once pointed me to
  https://github.com/ncm/selectable-socketpair

which was useful for me, but might not be exactly what you want.

5

Thanks for the pointer, effbiae.

It doesn’t solve my problem exactly, but it provides a great help pointing to the right direction. I have to say that sd0/sd1 is indeed quite troublesome on Win32 in this sense. But thanks to your help, I’ve managed to woked out a solution using socket pairs.