[llvm] [Offload] Implement event sync in amdgpu (PR #149300)

[Ross Brunton via llvm-commits]

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@@ -1575,6 +1592,21 @@ struct AMDGPUEventTy {
     return Stream.waitEvent(*this);
   }
 
+  Error sync() {
+    std::lock_guard<std::mutex> Lock(Mutex);
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RossBrunton wrote:

Just had a quick look. Libompt allows you to "record" events after they are constructed, which I assume can also happen while you wait/sync on them, so I think the mutex is required.

https://github.com/llvm/llvm-project/pull/149300