Fix a race condition when generating async operation ids

The counter used for generating async operation ids was a plain int
shared between all ports, which was incorrect but mostly worked
fine since the ids only had to be unique on a per-port basis.
However, some compilers (notably GCC 8.1.1) generated code that
assumed that this value didn't change between reads. Using a
shortened version of enq_async_w_tmo as an example:

    int id = async_ref++;
    op->id = id; //A
    return id; //B

In GCC 7 and earlier, `async_ref` would be read once and assigned
to `id` before being incremented, which kept the values at A and B
consistent. In GCC 8, `async_ref` was read when assigned at A and
read again at B, and then incremented, which made them inconsistent
if we raced with another port.

This commit fixes the issue by removing `async_ref` altogether and
replacing it with a per-port counter which makes it impossible to
race with someone else.

0 files changed, 0 insertions, 0 deletions