[swift-corelibs-dev] libdispatch roadmap and api addition proposal

[Joakim Hassila]

Hi,

I think (and hope) that this is the proper forum for a few questions wrt to libdispatch, otherwise any pointers are appreciated.

We are currently using libdispatch extensively on Linux (and Solaris for a while longer…) based on the previous version available from Mac OS forge (with later additions merged from opensource.apple.com) over time.

I have a few questions on how (particularly Apple folks) view this going forward:

First, the previous port to Linux/Solaris of libdispatch was dependent on libkqueue and more importantly on libpthread_workqueue (to have some heuristics for managing the number of threads when lacking kernel support).

How do you view this, would you consider integrating support for libpthread_workqueue, or would you have another preference for how to manage this on other platforms (Linux for starters, but essentially any lacking the pthread_workqueue interface)?

Secondly, we have extended the public libdispatch API internally with one more flavor of dispatching, let’s call it ‘dispatch_async_inline’ - the semantics being ‘perform the processing of the work synchronously if we wouldn’t block the calling thread, if we would block, instead perform the work as a normal dispatch_async’.

Would such a change be considered to be integrated, or should we keep our internal diffs indefinitely? Just to understand if it is worth the effort with a nicely packaged pull request or not...

The rationale for the API is that we are quite latency sensitive and want to use inline processing up until the point where we can’t keep up with the available work, at which point we would switch to asynchronous processing seamlessly (we have multiple producers). This means that the thread calling this API can be stolen for a significant amount of time (emptying the queue it was assigned to), but when the system is under ‘light' load, we don’t need to incur the wakeup penalty for a completely asynchronous dispatch.

Cheers,

Joakim

PS Big kudos to whoever at Apple is responsible for driving fundamentals like this out as OSS...


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