Re: Draft pthread_spin_init(2) manual page

[Florian Weimer <fweimer at redhat dot com>]

On 10/18/2017 10:10 AM, Michael Kerrisk (man-pages) wrote:

> DESCRIPTION
>         The  pthread_spin_init() function allocates any resources required
>         for the use of the spin lock referred to by lock  and  initializes
>         the  lock  to be in the unlocked state.  The pshared argument must
>         have one of the following values:

I think somewhere this should say that it is not possible to change the 
address of a spinlock after initialization (you can't memcpy it 
somewhere else and expect that it will keep working).  Other pthread 
objects have the same problem, of course.

> NOTES
>         Spin locks should be employed in conjunction with real-time sched‐
>         uling policies (SCHED_FIFO, or possibly SCHED_RR).   Use  of  spin
>         locks   with   nondeterministic   scheduling   policies   such  as
>         SCHED_OTHER probably indicates a design mistake.  The  problem  is
>         that  if  a  thread operating under such a policy is scheduled off
>         the CPU while it holds a spin lock, then other threads will  waste
>         time  spinning  on  the  lock  until  the lock holder is once more
>         rescheduled and releases the lock.

Isn't the more important concern whether there are sufficient resources 
to run all the threads that block on spinlocks?

Thanks,
Florian