diff --git a/csrc/aio.cpp b/csrc/aio.cpp
index 0796c34..7a1d10b 100644
--- a/csrc/aio.cpp
+++ b/csrc/aio.cpp
@@ -138,4 +138,7 @@ void AIOAsyncIO::write_tensor(int fd, torch::Tensor t, unsigned long long offset
     void *buffer = t.data_ptr();
     size_t n_bytes = t.numel() * t.element_size();
     this->write(fd, buffer, n_bytes, offset, callback);
-}
\ No newline at end of file
+}
+
+void AIOAsyncIO::register_h2d(unsigned int num_tensors) {}
+void AIOAsyncIO::sync_h2d() {}
\ No newline at end of file
diff --git a/csrc/async_file_io.cpp b/csrc/async_file_io.cpp
index 918dfc8..6676c60 100644
--- a/csrc/async_file_io.cpp
+++ b/csrc/async_file_io.cpp
@@ -12,6 +12,13 @@ void AsyncFileWriter::write_tensor(torch::Tensor tensor, unsigned long long offs
     this->aio->write_tensor(this->fd, tensor, offset, callback, pinned);
 }
 
+void AsyncFileWriter::register_h2d(unsigned int num_tensors) {
+    this->aio->register_h2d(num_tensors);
+}
+
+void AsyncFileWriter::sync_h2d() {
+    this->aio->sync_h2d();
+}
 
 void AsyncFileWriter::synchronize()
 {
diff --git a/csrc/pthread_backend.cpp b/csrc/pthread_backend.cpp
index 04f0221..ede6da5 100644
--- a/csrc/pthread_backend.cpp
+++ b/csrc/pthread_backend.cpp
@@ -78,24 +78,36 @@ void PthreadAsyncIO::synchronize() {
 
 void PthreadAsyncIO::register_file(int fd) {}
 
+void PthreadAsyncIO::register_h2d(unsigned int num_tensors) {
+    this->h2d_in_progress.store(num_tensors);  // register tensors to write for this run
+}
+
+void PthreadAsyncIO::sync_h2d() {
+    std::unique_lock<std::mutex> lock(this->mtx);
+    this->cv.wait(lock, [this] { return this->h2d_in_progress == 0; });  // block until all in-progress h2d are completed
+}
+
 void PthreadAsyncIO::write_tensor(int fd, torch::Tensor t, unsigned long long offset, callback_t callback, std::optional<torch::Tensor> pinned) {
     auto stream = c10::cuda::getCurrentCUDAStream();
-    at::cuda::CUDAStreamGuard guard(stream);  // https://pytorch.org/cppdocs/notes/tensor_cuda_stream.html
-    auto event_ptr = std::make_shared<c10::Event>(torch::kCUDA);  // make a shared ptr here since event is not copyable
-    if (t.is_cuda()) {
-        if (pinned.has_value()) {
-            pinned.value().copy_(t, /*non_blocking*/ true);
-            t = pinned.value();
-        } else {
-            t = t.to(t.options().device(c10::DeviceType::CPU), /*non_blocking*/ true, /*copy*/ false);  // modified from torch::Tensor::cpu()
-        }
-    }
-    event_ptr->record(stream);
     auto fut = this->pool.submit_task(
-        [fd, t, offset, pinned, event_ptr] {
-            event_ptr->synchronize(); // sync with comm stream
-            void *buf = t.data_ptr();
-            size_t n_bytes = t.numel() * t.element_size();
+        [this, fd, t, offset, pinned, stream] {
+            at::cuda::CUDAStreamGuard guard(stream);  // https://pytorch.org/cppdocs/notes/tensor_cuda_stream.html
+            torch::Tensor cpu_tensor;
+            if (t.is_cuda()) {
+                if (pinned.has_value()) {
+                    pinned.value().copy_(t, /*non_blocking*/ false);
+                    cpu_tensor = pinned.value();
+                } else {
+                    cpu_tensor = t.to(t.options().device(c10::DeviceType::CPU), /*non_blocking*/ false, /*copy*/ false);  // modified from torch::Tensor::cpu()
+                }
+            }
+            this->h2d_in_progress.fetch_sub(1);
+            if (this->h2d_in_progress.load() == 0) {  // notify when all h2d are completed and safe to optimizer.step()
+                std::lock_guard<std::mutex> lock(this->mtx);
+                cv.notify_one();
+            }
+            void *buf = cpu_tensor.data_ptr();
+            size_t n_bytes = cpu_tensor.numel() * cpu_tensor.element_size();
             return pwrite(fd, buf, n_bytes, offset);
         }
     );
diff --git a/csrc/py_api.cpp b/csrc/py_api.cpp
index a305ac2..085a1bb 100644
--- a/csrc/py_api.cpp
+++ b/csrc/py_api.cpp
@@ -30,5 +30,7 @@ PYBIND11_MODULE(TORCH_EXTENSION_NAME, m)
         .def(py::init<int, unsigned int, const std::string &>(), py::arg("fd"), py::arg("n_entries"), py::arg("backend") = "aio")
         .def("write", &AsyncFileWriter::write, py::arg("buffer"), py::arg("n_bytes"), py::arg("offset"), py::arg("callback") = py::none())
         .def("write_tensor", &AsyncFileWriter::write_tensor, py::arg("tensor"), py::arg("offset"), py::arg("callback") = py::none(), py::arg("pinned") = py::none())
-        .def("synchronize", &AsyncFileWriter::synchronize);
+        .def("synchronize", &AsyncFileWriter::synchronize)
+        .def("sync_h2d", &AsyncFileWriter::sync_h2d)
+        .def("register_h2d", &AsyncFileWriter::register_h2d, py::arg("num_tensors"));
 }
\ No newline at end of file
diff --git a/csrc/uring.cpp b/csrc/uring.cpp
index 8cd3dc0..255e74b 100644
--- a/csrc/uring.cpp
+++ b/csrc/uring.cpp
@@ -111,4 +111,7 @@ void UringAsyncIO::write_tensor(int fd, torch::Tensor t, unsigned long long offs
     void *buffer = t.data_ptr<float>();
     size_t n_bytes = t.numel() * t.element_size();
     this->write(fd, buffer, n_bytes, offset, callback);
-}
\ No newline at end of file
+}
+
+void UringAsyncIO::register_h2d(unsigned int num_tensors) {}
+void UringAsyncIO::sync_h2d() {}
\ No newline at end of file
diff --git a/include/aio.h b/include/aio.h
index a4aee4e..fec1d24 100644
--- a/include/aio.h
+++ b/include/aio.h
@@ -27,6 +27,8 @@ class AIOAsyncIO : public AsyncIO
     void writev(int fd, const iovec *iov, unsigned int iovcnt, unsigned long long offset, callback_t callback);
     void readv(int fd, const iovec *iov, unsigned int iovcnt, unsigned long long offset, callback_t callback);
 
+    void register_h2d(unsigned int num_tensors);
+    void sync_h2d();
     void sync_write_events();
     void sync_read_events();
     void synchronize();
diff --git a/include/async_file_io.h b/include/async_file_io.h
index d12e4fe..e9bb26b 100644
--- a/include/async_file_io.h
+++ b/include/async_file_io.h
@@ -21,6 +21,8 @@ class AsyncFileWriter
     void write(size_t buffer, size_t n_bytes, unsigned long long offset, callback_t callback);
     void write_tensor(torch::Tensor tensor, unsigned long long offset, callback_t callback, std::optional<torch::Tensor> pinned);
     void synchronize();
+    void register_h2d(unsigned int num_tensors);
+    void sync_h2d();
     ~AsyncFileWriter();
 
 private:
diff --git a/include/asyncio.h b/include/asyncio.h
index 68a501a..4981390 100644
--- a/include/asyncio.h
+++ b/include/asyncio.h
@@ -45,6 +45,8 @@ class AsyncIO
     virtual void get_event(WaitType wt) = 0;
     virtual void sync_write_events() = 0;
     virtual void sync_read_events() = 0;
+    virtual void register_h2d(unsigned int num_tensors) = 0;
+    virtual void sync_h2d() = 0;
     virtual void synchronize() = 0;
 
     virtual void register_file(int fd) = 0;
diff --git a/include/pthread_backend.h b/include/pthread_backend.h
index 75c83b9..41f95d5 100644
--- a/include/pthread_backend.h
+++ b/include/pthread_backend.h
@@ -12,6 +12,9 @@
 #include <iostream>
 #include <c10/cuda/CUDAStream.h>
 #include <c10/cuda/CUDAGuard.h>
+#include <atomic>
+#include <condition_variable>
+#include <mutex>
 
 #include "asyncio.h"
 #include "threadpool.hpp"
@@ -21,12 +24,15 @@ class PthreadAsyncIO : public AsyncIO
 {
 private:
     BS::thread_pool pool;
+    std::atomic<unsigned int> h2d_in_progress;
+    std::condition_variable cv;
+    std::mutex mtx;
     std::deque<std::tuple<std::future<ssize_t>, callback_t>> write_fut;
     std::deque<std::tuple<std::future<ssize_t>, callback_t>> read_fut;
 
 public:
     PthreadAsyncIO(unsigned int n_entries)
-        : pool(n_entries) {}
+        : pool(n_entries), h2d_in_progress(0) {}
 
     ~PthreadAsyncIO() {}
 
@@ -38,6 +44,8 @@ class PthreadAsyncIO : public AsyncIO
     void get_event(WaitType wt);
     void sync_write_events();
     void sync_read_events();
+    void register_h2d(unsigned int num_tensors);
+    void sync_h2d();
     void synchronize();
 
     void register_file(int fd);
diff --git a/include/uring.h b/include/uring.h
index 6f95215..24ce52c 100644
--- a/include/uring.h
+++ b/include/uring.h
@@ -21,6 +21,8 @@ class UringAsyncIO : public AsyncIO
     void writev(int fd, const iovec *iov, unsigned int iovcnt, unsigned long long offset, callback_t callback);
     void readv(int fd, const iovec *iov, unsigned int iovcnt, unsigned long long offset, callback_t callback);
 
+    void register_h2d(unsigned int num_tensors);
+    void sync_h2d();
     void sync_write_events();
     void sync_read_events();
     void synchronize();
diff --git a/tensornvme/async_file_io.py b/tensornvme/async_file_io.py
index b223a01..45f3489 100644
--- a/tensornvme/async_file_io.py
+++ b/tensornvme/async_file_io.py
@@ -38,12 +38,19 @@ def write_tensor(self, tensor: Tensor, pinned: Optional[Tensor] = None) -> None:
         self.io.write_tensor(tensor, self.offset, partial(AsyncFileWriter.gc_callback, self.buffers, len(self.buffers) - 1), pinned)
         self.offset += tensor.numel() * tensor.element_size()
 
+    def sync_h2d(self) -> None:
+        self.io.sync_h2d()
+
+    def register_h2d(self, num_tensors: int) -> None:
+        self.io.register_h2d(num_tensors)
+
     def write_gpu_tensor(self, tensor: Tensor, pinned: Optional[Tensor] = None) -> None:
         assert tensor.device.type == 'cuda', f"tensor must be on cuda device, got {tensor.device}"
         with torch.cuda.stream(self.comm_stream):
             self.write_tensor(tensor, pinned)
 
     def sync_before_step(self):
+        self.sync_h2d()
         self.comm_stream.synchronize()
 
     @staticmethod