[llvm] [OFFLOAD] Add support for indexed per-thread containers (PR #164263)

[Kevin Sala Penades via llvm-commits]

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@@ -14,26 +14,106 @@
 #define OFFLOAD_PERTHREADTABLE_H
 
 #include <list>
+#include <llvm/ADT/SmallVector.h>
+#include <llvm/Support/Error.h>
 #include <memory>
 #include <mutex>
+#include <type_traits>
+
+template <typename ObjectType> struct PerThread {
+  struct PerThreadData {
+    std::unique_ptr<ObjectType> ThreadEntry;
+  };
+
+  std::mutex Mutex;
+  llvm::SmallVector<std::shared_ptr<PerThreadData>> ThreadDataList;
+
+  // define default constructors, disable copy and move constructors
+  PerThread() = default;
+  PerThread(const PerThread &) = delete;
+  PerThread(PerThread &&) = delete;
+  PerThread &operator=(const PerThread &) = delete;
+  PerThread &operator=(PerThread &&) = delete;
+  ~PerThread() {
+    assert(Mutex.try_lock() && (Mutex.unlock(), true) &&
+           "Cannot be deleted while other threads are adding entries");
+    ThreadDataList.clear();
+  }
+
+private:
+  PerThreadData &getThreadData() {
+    static thread_local std::shared_ptr<PerThreadData> ThreadData = nullptr;
+    if (!ThreadData) {
+      ThreadData = std::make_shared<PerThreadData>();
+      std::lock_guard<std::mutex> Lock(Mutex);
+      ThreadDataList.push_back(ThreadData);
+    }
+    return *ThreadData;
+  }
+
+protected:
+  ObjectType &getThreadEntry() {
+    PerThreadData &ThreadData = getThreadData();
+    if (ThreadData.ThreadEntry)
+      return *ThreadData.ThreadEntry;
+    ThreadData.ThreadEntry = std::make_unique<ObjectType>();
+    return *ThreadData.ThreadEntry;
+  }
+
+public:
+  ObjectType &get() { return getThreadEntry(); }
+
+  template <class ClearFuncTy> void clear(ClearFuncTy ClearFunc) {
+    assert(Mutex.try_lock() && (Mutex.unlock(), true) &&
+           "Clear cannot be called while other threads are adding entries");
+    for (std::shared_ptr<PerThreadData> ThreadData : ThreadDataList) {
+      if (!ThreadData->ThreadEntry)
+        continue;
+      ClearFunc(*ThreadData->ThreadEntry);
+    }
+    ThreadDataList.clear();
+  }
+};
 
 // Using an STL container (such as std::vector) indexed by thread ID has
 // too many race conditions issues so we store each thread entry into a
 // thread_local variable.
 // T is the container type used to store the objects, e.g., std::vector,
----------------
kevinsala wrote:

Not sure if it's the best place to update this, but this comment is out-of-date

https://github.com/llvm/llvm-project/pull/164263