thread local context (#359) causes test issue on Linux: `1: [4] fid:0 channel 2, to submit:64, submitted:Operation not permitted`

On Linux, #359 by @PhilipBAdams causes the SSDServingTest TestSearchSSDIndexFloatL2BKTDEFAULTTXT test to continously print this message over and over again:

 1: [4] fid:0 channel 2, to submit:64, submitted:Operation not permitted

This message comes from the BatchReadFileAsync function in AnnService/src/Helper/AsyncFileReader.cpp and is printed when the io_submit syscall fails:

int s = syscall(__NR_io_submit, handler->GetIOCP(channel), iocbs[i].size() - submitted[i], iocbs[i].data() + submitted[i]);
if (s > 0) {
    submitted[i] += s;
    totalSubmitted += s;
}
else {
    SPTAGLIB_LOG(Helper::LogLevel::LL_Error, "fid:%d channel %d, to submit:%d, submitted:%s\n", i, channel, iocbs[i].size() - submitted[i], strerror(-s));
}

According to the io_submit manual page, this indicates incorrectly setting the RT IO priority class:

EPERM  The aio_reqprio field is set with the class IOPRIO_CLASS_RT, but the submitting context does not have the CAP_SYS_ADMIN capability.

However, the code does not set the IO priority class anywhere.

My conclusion is that maybe the iocb structure being passed to io_submit gets corrupted somehow, but I am not sure.

Thoughts and ideas for further debugging of this are welcome.

I also tried commenting out the contents of the Helper::SetThreadAffinity function but that didn't work.

Start with SSDServingTest, specifically TestSearchSSDIndexFloatL2BKTDEFAULTTXT, and inspect BatchReadFileAsync in AnnService/src/Helper/AsyncFileReader.cpp where io_submit failures are logged. Compare the submitted iocb data and IO priority handling on Linux, including whether SetThreadAffinity is relevant. Done means the test no longer repeatedly reports Operation not permitted.