[compiler-rt] [llvm] [ctxprof] root autodetection mechanism (PR #133147)

[Mircea Trofin via llvm-commits]

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@@ -418,12 +436,24 @@ void __llvm_ctx_profile_start_collection() {
       resetContextNode(*Root->FirstUnhandledCalleeNode);
     __sanitizer::atomic_store_relaxed(&Root->TotalEntries, 0);
   }
+  if (AutodetectDuration) {
+    auto *RD = new (__sanitizer::InternalAlloc(sizeof(RootAutoDetector)))
+        RootAutoDetector(AllFunctionsData, RootDetector, AutodetectDuration);
+    RD->start();
+  } else {
+    __sanitizer::Printf("[ctxprof] Initial NumMemUnits: %zu \n", NumMemUnits);
+  }
   __sanitizer::atomic_store_relaxed(&ProfilingStarted, true);
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mtrofin wrote:

RD->start just sets up the waiting thread. Threads observing `ProfilingStarted` and `RootDetector` just insert sample stacks in the heap. When eventually that waiting thread started, and it finished waiting, it collects whatever threads inserted in the interim.

https://github.com/llvm/llvm-project/pull/133147