transport: Implement a single-threaded I/O service

The inline_io_service connects transports to links without any
worker threads. Send operations go directly to the link, and recv
will perform the I/O as part of the get_recv_buffer() call.

The inline_io_service also supports muxed links natively. The receive
mux is entirely inline. There is no separate thread for the
inline_io_service, and that continues here. A queue is created for
each client of the mux, and packets are processed as they come in. If
a packet is to go up to a different client, the packet is queued up
for later. When that client attempts to recv(), the queue is checked
first, and the attempts to receive from the link happen ONLY if no
packet was found.

Also add mock transport to test I/O service APIs. Tests I/O service
construction and some basic packet transmision. One case will also
uses a single link that is shared between the send and recv transports.
That link is muxed between two compatible but different transports.

1 files changed, 6 insertions, 0 deletions

diff --git a/host/tests/CMakeLists.txt b/host/tests/CMakeLists.txt
index 431c380c3..0c48ae058 100644
--- a/host/tests/CMakeLists.txt
+++ b/host/tests/CMakeLists.txt
@@ -252,6 +252,12 @@ UHD_ADD_NONAPI_TEST(
     ${CMAKE_SOURCE_DIR}/lib/usrp/cores/dsp_core_utils.cpp
 )
 
+UHD_ADD_NONAPI_TEST(
+    TARGET "transport_test.cpp"
+    EXTRA_SOURCES
+    ${CMAKE_SOURCE_DIR}/lib/transport/inline_io_service.cpp
+)
+
 ########################################################################
 # demo of a loadable module
 ########################################################################