diff --git a/Makefile b/Makefile
index d5fd7c394..172a7607b 100644
--- a/Makefile
+++ b/Makefile
@@ -12,7 +12,7 @@ endif
 
 # specify tensor path
 BIN = xgboost
-OBJ = updater.o gbm.o io.o main.o sync_empty.o
+OBJ = updater.o gbm.o io.o main.o sync_empty.o sync_tcp.o
 MPIOBJ = sync_mpi.o
 MPIBIN = xgboost-mpi
 SLIB = wrapper/libxgboostwrapper.so 
@@ -24,11 +24,11 @@ mpi: $(MPIBIN)
 
 python: wrapper/libxgboostwrapper.so
 # now the wrapper takes in two files. io and wrapper part
-wrapper/libxgboostwrapper.so: wrapper/xgboost_wrapper.cpp $(OBJ)
 updater.o: src/tree/updater.cpp  src/tree/*.hpp src/*.h src/tree/*.h src/utils/*.h
 gbm.o: src/gbm/gbm.cpp src/gbm/*.hpp src/gbm/*.h 
 io.o: src/io/io.cpp src/io/*.hpp src/utils/*.h src/learner/dmatrix.h src/*.h
-sync_mpi.o: src/sync/sync_mpi.cpp 
+sync_mpi.o: src/sync/sync_mpi.cpp
+sync_tcp.o: src/sync/sync_tcp.cpp
 sync_empty.o: src/sync/sync_empty.cpp 
 main.o: src/xgboost_main.cpp src/utils/*.h src/*.h src/learner/*.hpp src/learner/*.h 
 xgboost-mpi:  updater.o gbm.o io.o main.o sync_mpi.o 
diff --git a/src/sync/sync_tcp.cpp b/src/sync/sync_tcp.cpp
new file mode 100644
index 000000000..2aa85ea9a
--- /dev/null
+++ b/src/sync/sync_tcp.cpp
@@ -0,0 +1,280 @@
+/*!
+ * \file sync_tcp.cpp
+ * \brief implementation of sync AllReduce using TCP sockets
+ *   with use async socket and tree-shape reduction
+ * \author Tianqi Chen
+ */
+#include "./sync.h"
+#include "../utils/socket.h"
+
+namespace MPI {
+struct Datatype {
+  size_t type_size;
+  Datatype(size_t type_size) : type_size(type_size) {}
+};
+}
+namespace xgboost {
+namespace sync {
+/*! \brief implementation of sync goes to here */
+class SyncManager {  
+ public:
+  // initialize the manager
+  inline void Init(int argc, char *argv[]) {    
+  }
+  /*!
+   * \brief perform in-place allreduce, on sendrecvbuf 
+   *        this function is not thread-safe
+   * \param sendrecvbuf buffer for both sending and recving data
+   * \param type_n4bytes the unit number of bytes the type have
+   * \param count number of elements to be reduced
+   * \param reducer reduce function
+   */
+  inline void AllReduce(void *sendrecvbuf_,
+                        size_t type_nbytes,
+                        size_t count,
+                        ReduceHandle::ReduceFunction reducer) {
+    if (parent.size() == 0 && childs.size() == 0) return;
+    char *sendrecvbuf = reinterpret_cast<char*>(sendrecvbuf_);
+    // total size of message
+    const size_t total_size = type_nbytes * count;
+    // size of space that we already performs reduce in up pass
+    size_t size_up_reduce = 0;
+    // size of space that we have already passed to parent
+    size_t size_up_out = 0;
+    // size of message we received, and send in the down pass
+    size_t size_down_in = 0;
+    // initialize the send buffer
+    for (size_t i = 0; i < childs.size(); ++i) {
+      childs[i].Init(type_nbytes, count);
+    }
+    // if no childs, no need to reduce
+    if (childs.size() == 0) size_up_reduce = total_size;    
+    // while we have not passed the messages out
+    while(true) {
+      selecter.Select();
+      // read data from childs
+      for (size_t i = 0; i < childs.size(); ++i) {
+        if (selecter.CheckRead(childs[i].sock)) {
+          childs[i].Read(size_up_out);
+        }
+      }
+      // peform reduce
+      if (childs.size() != 0) {
+        const size_t buffer_size = childs[0].buffer_size;
+        // do upstream reduce
+        size_t min_read = childs[0].size_read;
+        for (size_t i = 1; i < childs.size(); ++i) {
+          min_read = std::min(min_read, childs[i].size_read);
+        }
+        // align to type_nbytes
+        min_read = (min_read / type_nbytes * type_nbytes);
+        // start position
+        size_t start = size_up_reduce % buffer_size;
+        // peform read till end of buffer
+        if (start + min_read - size_up_reduce > buffer_size) {
+          const size_t nread = buffer_size - start;
+          utils::Assert(nread % type_nbytes == 0, "AllReduce: size check");
+          for (size_t i = 0; i < childs.size(); ++i) {
+            reducer(childs[i].buffer_head + start,
+                    sendrecvbuf + size_up_reduce,
+                    nread / type_nbytes,
+                    MPI::Datatype(type_nbytes));
+          }
+          size_up_reduce += nread;
+          start = 0;
+        }
+        // peform second phase of reduce
+        const size_t nread = min_read - size_up_reduce;
+        if (nread != 0) {
+          utils::Assert(nread % type_nbytes == 0, "AllReduce: size check");
+          for (size_t i = 0; i < childs.size(); ++i) {
+            reducer(childs[i].buffer_head + start,
+                    sendrecvbuf + size_up_reduce,
+                    nread / type_nbytes,
+                    MPI::Datatype(type_nbytes));
+          }
+        }
+        size_up_reduce += nread;
+      }
+      if (parent.size() != 0) {
+        // can pass message up to parent
+        if (selecter.CheckWrite(parent[0])) {
+          size_up_out += parent[0]
+              .Send(sendrecvbuf + size_up_out, size_up_reduce - size_up_out);
+        }
+        // read data from parent
+        if (selecter.CheckRead(parent[0])) {
+          size_down_in +=  parent[0]
+              .Recv(sendrecvbuf + size_down_in, total_size - size_down_in);
+          utils::Assert(size_down_in <= size_up_out, "AllReduce: boundary error");
+        }
+      } else {
+        // this is root, can use reduce as most recent point
+        size_down_in = size_up_out = size_up_reduce;
+      }
+      // check if we finished the job of message passing
+      size_t nfinished = size_down_in;
+      // can pass message down to childs
+      for (size_t i = 0; i < childs.size(); ++i) {
+        if (selecter.CheckWrite(childs[i].sock)) {
+          childs[i].size_write += childs[i].sock
+              .Send(sendrecvbuf + childs[i].size_write, size_down_in - childs[i].size_write);
+        }
+        nfinished = std::min(childs[i].size_write, nfinished);
+      }
+      // check boundary condition
+      if (nfinished >= total_size) {
+        utils::Assert(nfinished == total_size, "AllReduce: nfinished check");
+        break;
+      }
+    }
+  }
+  inline void Bcast(std::string *sendrecv_data, int root) {
+    if (parent.size() == 0 && childs.size() == 0) return;
+    // message send to parent
+    size_t size_up_out = 0;
+    // all messages received
+    size_t size_in = 0;
+    // all headers received so far
+    size_t header_in = 0;
+    // total size of data
+    size_t total_size;
+    // input channel, -1 means parent, -2 means unknown yet
+    // otherwise its child index
+    int in_channel = -2;
+    // root already reads all data in
+    if (root == rank) {
+      in_channel = -3;
+      total_size = size_in = sendrecv_data->length();
+      header_in = sizeof(total_size);
+    }
+    // initialize write position
+    for (size_t i = 0; i < childs.size(); ++i) {
+      childs[i].size_write = 0;
+    }
+    const int nchilds = static_cast<int>(childs.size());
+
+    while (true) {
+      selecter.Select();
+      if (selecter.CheckRead(parent[0])) {
+        utils::Assert(in_channel == -2 || in_channel == -1, "invalid in channel");
+        this->BcastRecvData(parent[0], sendrecv_data,
+                            header_in, size_in, total_size);
+        if (header_in != 0) in_channel = -1;
+      }
+      for (int i = 0; i < nchilds; ++i) {
+        if (selecter.CheckRead(childs[i].sock)) {
+          utils::Assert(in_channel == -2 || in_channel == i, "invalid in channel");
+          this->BcastRecvData(parent[0], sendrecv_data,
+                              header_in, size_in, total_size);
+          if (header_in != 0) in_channel = i;
+        }
+      }
+      if (in_channel == -2) continue;
+      if (in_channel != -1) {
+        if (selecter.CheckWrite(parent[0])) {
+          size_t nsend = size_in - size_up_out;
+          if (nsend != 0) {
+            size_up_out += parent[0].Send(&(*sendrecv_data)[0] + size_up_out, nsend);
+          }
+        }
+      } else {
+        size_up_out = size_in;
+      }
+      size_t nfinished = size_up_out;
+      for (int i = 0; i < nchilds; ++i) {
+        if (in_channel != i) {
+          if (selecter.CheckWrite(childs[i].sock)) {
+            size_t nsend = size_in - childs[i].size_write;
+            if (nsend != 0) {
+              childs[i].size_write += childs[i].sock
+                  .Send(&(*sendrecv_data)[0] + childs[i].size_write, nsend);
+            }
+          }
+          nfinished = std::min(nfinished, childs[i].size_write);
+        }
+      }
+      // check boundary condition
+      if (nfinished >= total_size) {
+        utils::Assert(nfinished == total_size, "Bcast: nfinished check");
+        break;
+      }
+    }
+  }
+
+ private:
+  inline void BcastRecvData(utils::TCPSocket &sock,
+                            std::string *sendrecv_data,   
+                            size_t &header_in,
+                            size_t &size_in,
+                            size_t &total_size) {
+    if (header_in < sizeof(total_size)) {
+      char *p = reinterpret_cast<char*>(&total_size);
+      header_in += sock.Recv(p + size_in, sizeof(total_size) - header_in);
+      if (header_in == sizeof(total_size)) {
+        sendrecv_data->resize(total_size);
+      }
+    } else {
+      size_t nread  = total_size - size_in;
+      if (nread != 0) {
+        size_in += sock
+            .Recv(&(*sendrecv_data)[0] + size_in, nread);
+      }
+    }
+  }
+  
+  // 128 MB
+  const static size_t kBufferSize = 128;
+  // an independent child record
+  struct ChildRecord {
+   public:
+    // socket to get data from child
+    utils::TCPSocket sock;
+    // size of data readed from child
+    size_t size_read;
+    // size of data write into child
+    size_t size_write;
+    // pointer to buffer head
+    char *buffer_head;
+    // buffer size, in bytes
+    size_t buffer_size;
+    // initialize buffer
+    inline void Init(size_t type_nbytes, size_t count) {
+      utils::Assert(type_nbytes < kBufferSize, "too large type_nbytes");
+      size_t n = (type_nbytes * count + 7)/ 8;
+      buffer_.resize(std::min(kBufferSize, n));
+      // make sure align to type_nbytes
+      buffer_size = buffer_.size() * sizeof(uint64_t) / type_nbytes * type_nbytes;
+      // set buffer head
+      buffer_head = reinterpret_cast<char*>(BeginPtr(buffer_));
+      // set write head
+      size_write = size_read = 0;
+    }
+    // maximum number of bytes we are able to read
+    // currently without corrupt the data
+    inline void Read(size_t size_up_out) {
+      size_t ngap = size_read - size_up_out;
+      utils::Assert(ngap <= buffer_size, "AllReduce: boundary check");
+      size_t offset = size_read % buffer_size;      
+      size_t nmax = std::min(ngap, buffer_size - offset);
+      size_t len = sock.Recv(buffer_head + offset, nmax);
+      size_read += len;
+    }
+
+   private:
+    // recv buffer to get data from child
+    // aligned with 64 bits, will be able to perform 64 bits operations freely
+    std::vector<uint64_t> buffer_;
+  };
+  // current rank
+  int rank;                  
+  // parent socket, can be of size 0 or 1
+  std::vector<utils::TCPSocket> parent;
+  // sockets of all childs, can be of size 0, 1, 2 or more
+  std::vector<ChildRecord> childs;
+  // select helper
+  utils::SelectHelper selecter;
+};
+
+}  // namespace sync
+}  // namespace xgboost
diff --git a/src/utils/socket.h b/src/utils/socket.h
index 5b216980e..5eebbd160 100644
--- a/src/utils/socket.h
+++ b/src/utils/socket.h
@@ -2,8 +2,7 @@
 #define XGBOOST_UTILS_SOCKET_H
 /*!
  * \file socket.h
- * \brief this file aims to provide a platform independent wrapper 
- *        of socket
+ * \brief this file aims to provide a wrapper of sockets
  * \author Tianqi Chen
  */
 #include <fcntl.h>
@@ -63,7 +62,7 @@ class TCPSocket {
   // constructor
   TCPSocket(void) {}
   // default conversion to int
-  inline int operator()() const {
+  inline operator int() const {
     return sockfd;
   }
   /*!
@@ -122,6 +121,7 @@ class TCPSocket {
    * \return size of data actually sent
    */
   inline size_t Send(const void *buf, size_t len, int flag = 0) {
+    if (len == 0) return 0;
     ssize_t ret = send(sockfd, buf, len, flag);
     if (ret == -1) SockError("Send", errno);
     return ret;
@@ -134,6 +134,7 @@ class TCPSocket {
    * \return size of data actually received 
    */
   inline size_t Recv(void *buf, size_t len, int flags = 0) {
+    if (len == 0) return 0;
     ssize_t ret = recv(sockfd, buf, len, flags);
     if (ret == -1) SockError("Recv", errno);
     return ret;