Re: advice for implementing an atomics wrapper

[Ronald Klop]

Hi,

The __APPLE__ implementation also pointed to the implementation in that file 
and I used it to come up with a patch.

#elif defined(__FreeBSD__)

void notifyOne(const void* uaddr) {
   _umtx_op(const_cast<void*>(uaddr), UMTX_OP_WAKE, 1, NULL, NULL);
}

void notifyMany(const void* uaddr, int nToWake) {
   _umtx_op(const_cast<void*>(uaddr), UMTX_OP_WAKE, nToWake, NULL, NULL);
}

void notifyAll(const void* uaddr) {
   _umtx_op(const_cast<void*>(uaddr), UMTX_OP_WAKE, INT_MAX, NULL, NULL);
}

bool waitUntil(const void* uaddr,
              uint32_t old,
              boost::optional<system_clock::time_point> deadline) {
   struct timespec timeout;
   bool timeoutOverflow = false;
   if (deadline) {
       int64_t micros = durationCount<Microseconds>(*deadline - 
system_clock::now());
       if (micros <= 0) {
           return false;  // Synthesize a timeout.
       }

       if (micros > int64_t(std::numeric_limits<uint32_t>::max())) {
           // 2**32 micros is a little over an hour. If this happens, we wait 
as long as we can,
           // then return as-if a spurious wakeup happened, rather than a 
timeout. This will cause
           // the caller to loop and we will compute a smaller time each pass, 
eventually reaching
           // a representable timeout.
           micros = std::numeric_limits<uint32_t>::max();
           timeoutOverflow = true;
       }

       timeout.tv_sec = micros / 1000;
       timeout.tv_nsec = (micros % 1000) * 1000;
   }

   if (_umtx_op(const_cast<void*>(uaddr), UMTX_OP_WAIT, old, (void*)sizeof(struct 
timespec), &timeout) != -1)
       return true;

   // There isn't a good list of possible errors, so assuming that anything 
other than a timeout
   // error is a possible spurious wakeup.
   return timeoutOverflow || errno != ETIMEDOUT;
}


It compiles and runs in my simple tests (although I don't know if my simple 
tests execute this part of mongodb code). Suggestions are of course welcome.

Regards,
Ronald.


Van: Michael Gmelin <gre...@freebsd.org>
Datum: dinsdag, 23 juli 2024 17:32
Aan: Ronald Klop <ronald-li...@klop.ws>
Onderwerp: Re: advice for implementing an atomics wrapper

Does this help? https://reviews.llvm.org/D142134

On 23. Jul 2024, at 16:17, Ronald Klop <ronald-li...@klop.ws> wrote:

>

Sorry,

Something broke the pasted URL.
https://github.com/mongodb/mongo/blob/master/src/mongo/platform/waitable_atomic.cpp

Another attempt.

Ronald.

Van: Ronald Klop <ronald-li...@klop.ws>

Datum: dinsdag, 23 juli 2024 16:14
Aan: freebsd-po...@freebsd.org
Onderwerp: advice for implementing an atomics wrapper

Hi,

For mongodb 8.0 I need to give a FreeBSD implementation of this file.

https://github.com/mongodb/mongo/blob/master/src/mongo/platform/waitable_atomic.cpp

Using the __Apple__ definition gives:
ld.lld: error: undefined symbol: __ulock_wake
ld.lld: error: undefined symbol: __ulock_wait

And the __linux__ definition uses futex which FreeBSD does not have AFAIK.

What is an easy way to port this file?

Regards,
Ronald.