zeroshade commented on code in PR #37040:
URL: https://github.com/apache/arrow/pull/37040#discussion_r1293864559


##########
cpp/src/arrow/device.h:
##########
@@ -98,6 +101,90 @@ class ARROW_EXPORT Device : public 
std::enable_shared_from_this<Device>,
   /// \brief Return the DeviceAllocationType of this device
   virtual DeviceAllocationType device_type() const = 0;
 
+  /// \brief EXPERIMENTAL: An object that provides event/stream sync primitives
+  ///
+  /// This class is thread-safe.
+  class ARROW_EXPORT SyncEvent {
+   public:
+    virtual ~SyncEvent() = default;
+
+    /// @brief Block until sync event is completed.
+    Status wait() {
+      const std::lock_guard<std::mutex> lock(mx_);
+      return wait_internal();
+    }
+
+    /// @brief Make the provided stream wait on the sync event.
+    ///
+    /// Tells the provided stream that it should wait until the
+    /// synchronization event is completed without blocking the CPU.
+    /// @param stream Should be appropriate for the underlying device
+    Status stream_wait(void* stream) {
+      const std::lock_guard<std::mutex> lock(mx_);
+      return stream_wait_internal(stream);
+    }
+
+    void set_stream(void* stream) {
+      const std::lock_guard<std::mutex> lock(mx_);
+      stream_ = stream;
+    }
+
+    /// @brief Returns the stored raw event or creates a new one to return.
+    ///
+    /// clear_event should always be called to cleanup afterwards. If this
+    /// creates the event, then clear_event will call release_event 
+    /// internally. If this doesn't own the event, then the lifetime should
+    /// be controlled externally to this class.
+    Result<void*> get_event() {
+      const std::lock_guard<std::mutex> lock(mx_);
+      if (!sync_event_) {
+        ARROW_ASSIGN_OR_RAISE(sync_event_, create_event());
+        owns_event_ = true;
+      }
+      return sync_event_;
+    }
+
+    void clear_event() {
+      const std::lock_guard<std::mutex> lock(mx_);
+      if (owns_event_) {
+        release_event(sync_event_);
+      }
+      sync_event_ = nullptr;
+    }

Review Comment:
   We'd need to use a null deleter to wrap the void* we get from the C 
interface then. Or maybe we should just not make any thread-safety guarantees 
and let consumers deal with that for themselves, just to be safe?



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