Use portable sched_yield() rather than pthread_yield()

[Harry M]

The sched_yield() call is the standard and portable routine. Current calls to pthread_yield() in Virtualbox sources (host and guests) should be replaced by calls to sched_yield(). If sched_yield() is not available on a platform, then the build tools (including those for the Guest Additions) could arrange to use a shim routine that calls pthread_yield().

This would be helpful in supporting platforms that do provide support for non-portable libraries and routines.

[aeichner]

May I ask what the use case would be? Most platforms will need more changes anyway to be supported (drivers, etc.). From a quick grep the only places using pthread_yield() are:

src/VBox/Runtime/r3/posix/thread2-posix.cpp
src/VBox/Runtime/r3/posix/semevent-posix.cpp

These already contain defines to use sched_yield() on Solaris, FreeBSD, etc. so you can just add your platform when porting the runtime to it.

[Harry M]

The binary blobs included with the Guest Additions do not run on a platform that does not provide non-portable and/or non-free software. We are trying to arrange for our compatibility library to provide a shim to have pthread_yield() call to sched_yield().

In the current case, this particular instance of incompatibility will be addressed, but as a practice, it might still be a good idea to conform with standards moving forward to avoid additional, similar issues. It would probably be advantageous to your application so as to provide portability to more target platforms.