udp: comments and minor code tweaks for udp zero copy impl

1 files changed, 41 insertions, 18 deletions

diff --git a/host/lib/transport/udp_zero_copy_asio.cpp b/host/lib/transport/udp_zero_copy_asio.cpp
index 48b0941eb..87c5ec823 100644
--- a/host/lib/transport/udp_zero_copy_asio.cpp
+++ b/host/lib/transport/udp_zero_copy_asio.cpp
@@ -187,13 +187,19 @@ public:
         return get_buff_size<Opt>();
     }
 
-    UHD_INLINE void handle_recv(udp_zero_copy_asio_mrb *mrb){
-        _pending_recv_buffs.push_with_pop_on_full(mrb);
-    }
-
-    managed_recv_buffer::sptr get_recv_buff(double timeout){
-        udp_zero_copy_asio_mrb *mrb;
-
+    /*******************************************************************
+     * Receive implementation:
+     *
+     * Use select to perform a blocking receive with timeout.
+     * Return the managed receive buffer with the new length.
+     * When the caller is finished with the managed buffer,
+     * the managed receive buffer is released back into the queue.
+     *
+     * Assumptions:
+     *  - A managed buffer is always available.
+     *  - The queue can never be over-filled.
+     ******************************************************************/
+    UHD_INLINE bool is_recv_socket_ready(double timeout){
         //setup timeval for timeout
         timeval tv;
         tv.tv_sec = 0;
@@ -204,17 +210,22 @@ public:
         FD_ZERO(&rset);
         FD_SET(_sock_fd, &rset);
 
-        //call select to perform timed wait and grab an available buffer now
-        //if the condition is true, call receive and return the managed buffer
-        if (
-            ::select(_sock_fd+1, &rset, NULL, NULL, &tv) > 0
-            and _pending_recv_buffs.pop_with_haste(mrb)
-        ){
+        //call select with timeout on receive socket
+        return ::select(_sock_fd+1, &rset, NULL, NULL, &tv) > 0;
+    }
+
+    managed_recv_buffer::sptr get_recv_buff(double timeout){
+        udp_zero_copy_asio_mrb *mrb = NULL;
+        if (is_recv_socket_ready(timeout) and _pending_recv_buffs.pop_with_haste(mrb)){
             return mrb->get_new(::recv(_sock_fd, mrb->cast<char *>(), _recv_frame_size, 0));
         }
         return managed_recv_buffer::sptr();
     }
 
+    UHD_INLINE void handle_recv(udp_zero_copy_asio_mrb *mrb){
+        _pending_recv_buffs.push_with_pop_on_full(mrb);
+    }
+
     void release(udp_zero_copy_asio_mrb *mrb){
         handle_recv(mrb);
     }
@@ -222,18 +233,30 @@ public:
     size_t get_num_recv_frames(void) const {return _num_recv_frames;}
     size_t get_recv_frame_size(void) const {return _recv_frame_size;}
 
-    UHD_INLINE void handle_send(udp_zero_copy_asio_msb *msb){
-        _pending_send_buffs.push_with_pop_on_full(msb);
-    }
-
+    /*******************************************************************
+     * Send implementation:
+     *
+     * Get a managed receive buffer immediately with max length set.
+     * The caller will fill the buffer and commit it when finished.
+     * The commit routine will perform a blocking send operation,
+     * and push the managed send buffer back into the queue.
+     *
+     * Assumptions:
+     *  - A managed buffer is always available.
+     *  - The queue can never be over-filled.
+     ******************************************************************/
     managed_send_buffer::sptr get_send_buff(double){
-        udp_zero_copy_asio_msb *msb;
+        udp_zero_copy_asio_msb *msb = NULL;
         if (_pending_send_buffs.pop_with_haste(msb)){
             return msb->get_new(_send_frame_size);
         }
         return managed_send_buffer::sptr();
     }
 
+    UHD_INLINE void handle_send(udp_zero_copy_asio_msb *msb){
+        _pending_send_buffs.push_with_pop_on_full(msb);
+    }
+
     void commit(udp_zero_copy_asio_msb *msb, size_t len){
         ::send(_sock_fd, msb->cast<const char *>(), len, 0);
         handle_send(msb);