[k4st]

A nice simplification of would be to use the current CPU number as your ID. That eliminates the dependence on thread-local storage, and with high probability avoids issues where there are collisions between threads whose IDs modulo N are equivalent.

You could use an instruction like `RDTSC` to extract the CPU number. There might also be ways of getting at it efficiently with glibc/pthreads.

[haberman]

> A nice simplification of would be to use the current CPU number as your ID.

I don't think that works unfortunately. The thread could be rescheduled on a different CPU in the middle of the read-side critical section. When the critical section is exited, it will decrement a different counter. Scan() will wait until every counter is zero, but this will never happen unless another critical section is also rescheduled in the reverse order.

[k4st]

That is fine ;-) Sum up the counters.