Change non_blocking_send threshold to sendBufferSize (#6073) (#6077)

(cherry picked from commit 81a5b12)

Signed-off-by: Juan Lopez Fernandez <juanlopez@eprosima.com>
Co-authored-by: juanlofer-eprosima <88179026+juanlofer-eprosima@users.noreply.github.com>

Author: mergify[bot]

src/cpp/rtps/transport/TCPChannelResource.cpp

@@ -363,9 +363,10 @@ bool TCPChannelResource::check_socket_send_buffer(
 
 
     size_t future_queue_size = size_t(bytesInSendQueue) + msg_size;
-    // TCP actually allocates twice the size of the buffer requested.
-    if (future_queue_size > size_t(2 * parent_->configuration()->sendBufferSize))
+    if (future_queue_size > size_t(parent_->configuration()->sendBufferSize))
     {
+        // NOTE: TCP actually allocates about twice the size of the buffer requested, still we use the user-provided
+        // value as threshold to avoid blocking if the actual allocated space falls below our estimation
         return false;
     }
     return true;

test/unittest/transport/TCPv4Tests.cpp

@@ -1570,15 +1570,15 @@ TEST_F(TCPv4Tests, secure_non_blocking_send)
 
     // Prepare the message
     asio::error_code ec;
-    std::vector<octet> message(msg_size * 2, 0);
+    std::vector<octet> message(msg_size, 0);
     const octet* data = message.data();
     size_t size = message.size();
     NetworkBuffer buffers(data, size);
     std::vector<NetworkBuffer> buffer_list;
     buffer_list.push_back(buffers);
 
-    // Send the message with no header. Since TCP actually allocates twice the size of the buffer requested
-    // it should be able to send a message of msg_size*2.
+    // Send the message with no header. Since TCP actually allocates about twice the size of the buffer requested, and
+    // since the threshold to discard (sendBufferSize) is set to msg_size, it should be able to send a message of msg_size.
     size_t bytes_sent = sender_channel_resource->send(nullptr, 0, buffer_list, size, ec);
     ASSERT_EQ(bytes_sent, size);
 
@@ -1589,8 +1589,9 @@ TEST_F(TCPv4Tests, secure_non_blocking_send)
     ASSERT_EQ(ec, asio::error_code());
     ASSERT_EQ(bytes_read, size);
 
-    // Now try to send a message that is bigger than the buffer size: (msg_size*2 + 1) + bytes_in_send_buffer(0) > 2*sendBufferSize
-    message.resize(msg_size * 2 + 1);
+    // Now try to send a message whose size surpasses the threshold to discard (sendBufferSize):
+    //  (msg_size + 1) + bytes_in_send_buffer(0) > sendBufferSize
+    message.resize(msg_size + 1);
     data = message.data();
     size = message.size();
     buffer_list.clear();
@@ -2108,15 +2109,15 @@ TEST_F(TCPv4Tests, non_blocking_send)
 
     // Prepare the message
     asio::error_code ec;
-    std::vector<octet> message(msg_size * 2, 0);
+    std::vector<octet> message(msg_size, 0);
     const octet* data = message.data();
     size_t size = message.size();
     NetworkBuffer buffers(data, size);
     std::vector<NetworkBuffer> buffer_list;
     buffer_list.push_back(buffers);
 
-    // Send the message with no header. Since TCP actually allocates twice the size of the buffer requested
-    // it should be able to send a message of msg_size*2.
+    // Send the message with no header. Since TCP actually allocates about twice the size of the buffer requested, and
+    // since the threshold to discard (sendBufferSize) is set to msg_size, it should be able to send a message of msg_size.
     size_t bytes_sent = sender_channel_resource->send(nullptr, 0, buffer_list, size, ec);
     ASSERT_EQ(bytes_sent, size);
 
@@ -2125,8 +2126,9 @@ TEST_F(TCPv4Tests, non_blocking_send)
     size_t bytes_read = asio::read(socket, asio::buffer(buffer, size), asio::transfer_exactly(size), ec);
     ASSERT_EQ(bytes_read, size);
 
-    // Now try to send a message that is bigger than the buffer size: (msg_size*2 + 1) + bytes_in_send_buffer(0) > 2*sendBufferSize
-    message.resize(msg_size * 2 + 1);
+    // Now try to send a message whose size surpasses the threshold to discard (sendBufferSize):
+    //  (msg_size + 1) + bytes_in_send_buffer(0) > sendBufferSize
+    message.resize(msg_size + 1);
     data = message.data();
     size = message.size();
     buffer_list.clear();

test/unittest/transport/TCPv6Tests.cpp

@@ -438,15 +438,15 @@ TEST_F(TCPv6Tests, non_blocking_send)
 
     // Prepare the message
     asio::error_code ec;
-    std::vector<octet> message(msg_size * 2, 0);
+    std::vector<octet> message(msg_size, 0);
     const octet* data = message.data();
     size_t size = message.size();
     NetworkBuffer buffers(data, size);
     std::vector<NetworkBuffer> buffer_list;
     buffer_list.push_back(buffers);
 
-    // Send the message with no header. Since TCP actually allocates twice the size of the buffer requested
-    // it should be able to send a message of msg_size*2.
+    // Send the message with no header. Since TCP actually allocates about twice the size of the buffer requested, and
+    // since the threshold to discard (sendBufferSize) is set to msg_size, it should be able to send a message of msg_size.
     size_t bytes_sent = sender_channel_resource->send(nullptr, 0, buffer_list, size, ec);
     ASSERT_EQ(bytes_sent, size);
 
@@ -455,8 +455,9 @@ TEST_F(TCPv6Tests, non_blocking_send)
     size_t bytes_read = asio::read(socket, asio::buffer(buffer, size), asio::transfer_exactly(size), ec);
     ASSERT_EQ(bytes_read, size);
 
-    // Now try to send a message that is bigger than the buffer size: (msg_size*2 + 1) + bytes_in_send_buffer(0) > 2*sendBufferSize
-    message.resize(msg_size * 2 + 1);
+    // Now try to send a message whose size surpasses the threshold to discard (sendBufferSize):
+    //  (msg_size + 1) + bytes_in_send_buffer(0) > sendBufferSize
+    message.resize(msg_size + 1);
     data = message.data();
     size = message.size();
     buffer_list.clear();