`dispatch_async_and_wait()` was introduced in macOS 10.14. Let's
forward declare it to ensure we can compile the test with older SDKs and
guard execution by checking if the symbol is available. (We can't use
`__builtin_available()`, because that itself requires a higher minimum
deployment target.) We also need to specify the `-undefined
dynamic_lookup` compiler flag.
Differential Revision: https://reviews.llvm.org/D85995
The linker errors caused by this revision have been addressed.
Add interceptors for `dispatch_async_and_wait[_f]()` which was added in
macOS 10.14. This pair of functions is similar to `dispatch_sync()`,
but does not force a context switch of the queue onto the caller thread
when the queue is active (and hence is more efficient). For TSan, we
can apply the same semantics as for `dispatch_sync()`.
From the header docs:
> Differences with dispatch_sync()
>
> When the runtime has brought up a thread to invoke the asynchronous
> workitems already submitted to the specified queue, that servicing
> thread will also be used to execute synchronous work submitted to the
> queue with dispatch_async_and_wait().
>
> However, if the runtime has not brought up a thread to service the
> specified queue (because it has no workitems enqueued, or only
> synchronous workitems), then dispatch_async_and_wait() will invoke the
> workitem on the calling thread, similar to the behaviour of functions
> in the dispatch_sync family.
Additional context:
> The guidance is to use `dispatch_async_and_wait()` instead of
> `dispatch_sync()` when it is necessary to mix async and sync calls on
> the same queue. `dispatch_async_and_wait()` does not guarantee
> execution on the caller thread which allows to reduce context switches
> when the target queue is active.
> https://gist.github.com/tclementdev/6af616354912b0347cdf6db159c37057
rdar://35757961
Reviewed By: kubamracek
Differential Revision: https://reviews.llvm.org/D85854
Add interceptors for `dispatch_async_and_wait[_f]()` which was added in
macOS 10.14. This pair of functions is similar to `dispatch_sync()`,
but does not force a context switch of the queue onto the caller thread
when the queue is active (and hence is more efficient). For TSan, we
can apply the same semantics as for `dispatch_sync()`.
From the header docs:
> Differences with dispatch_sync()
>
> When the runtime has brought up a thread to invoke the asynchronous
> workitems already submitted to the specified queue, that servicing
> thread will also be used to execute synchronous work submitted to the
> queue with dispatch_async_and_wait().
>
> However, if the runtime has not brought up a thread to service the
> specified queue (because it has no workitems enqueued, or only
> synchronous workitems), then dispatch_async_and_wait() will invoke the
> workitem on the calling thread, similar to the behaviour of functions
> in the dispatch_sync family.
Additional context:
> The guidance is to use `dispatch_async_and_wait()` instead of
> `dispatch_sync()` when it is necessary to mix async and sync calls on
> the same queue. `dispatch_async_and_wait()` does not guarantee
> execution on the caller thread which allows to reduce context switches
> when the target queue is active.
> https://gist.github.com/tclementdev/6af616354912b0347cdf6db159c37057
rdar://35757961
Reviewed By: kubamracek
Differential Revision: https://reviews.llvm.org/D85854
Julian Lettner