1 files changed, 43 insertions, 0 deletions
diff --git a/tensorflow/core/framework/control_flow.h b/tensorflow/core/framework/control_flow.h
new file mode 100644
index 0000000000..f59e0f5310
--- /dev/null
+++ b/tensorflow/core/framework/control_flow.h
@@ -0,0 +1,43 @@
+#ifndef TENSORFLOW_FRAMEWORK_CONTROL_FLOW_H_
+#define TENSORFLOW_FRAMEWORK_CONTROL_FLOW_H_
+
+#include "tensorflow/core/platform/port.h"
+#include "tensorflow/core/platform/logging.h"
+#include "tensorflow/core/lib/hash/hash.h"
+
+namespace tensorflow {
+
+const uint64 kIllegalFrameId = ~0uLL;
+const int64 kIllegalIterId = -1;
+
+// For the purpose of control flow, every tensor produced by TensorFlow is
+// conceptually tagged by a 'FrameAndIter'. FrameAndIter consists of a
+// 'frame_id' and an 'iter_id'. The tensor value it represents is produced
+// in the frame with frame_id at the iteration of iter_id.
+struct FrameAndIter {
+  uint64 frame_id = kIllegalFrameId;
+  int64 iter_id = kIllegalIterId;
+
+  FrameAndIter() {}
+
+  FrameAndIter(uint64 frame, int64 iter) {
+    frame_id = frame;
+    iter_id = iter;
+  }
+
+  bool operator==(const FrameAndIter& other) const {
+    return (frame_id == other.frame_id && iter_id == other.iter_id);
+  }
+};
+
+struct FrameAndIterHash {
+  size_t operator()(const FrameAndIter& key) const {
+    // Make sure there are no padding bytes that we don't want
+    CHECK_EQ(sizeof(uint64) + sizeof(int64), sizeof(FrameAndIter));
+    return Hash64(reinterpret_cast<const char*>(&key), sizeof(FrameAndIter));
+  }
+};
+
+}  // namespace tensorflow
+
+#endif  // TENSORFLOW_FRAMEWORK_CONTROL_FLOW_H_