Add coroutine support for sdbusplus::asio method calls

Using a coroutine to asynchronously execute method calls gives the best
of both worlds:
1) better readability because the code reads like synchronous code
2) better throughput because it is actually asynchronous

When passed in a boost::asio::yield_context, the sdbusplus::asio dbus
connection members async_send and async_method_call will execute
asynchronously using coroutines.

This also adds an example of how this works in the
example/asio-example.cpp file.

Change-Id: Ifb71b2c757ecbfd16b3be95bdefc45a701ca0d51
Signed-off-by: Vernon Mauery <vernon.mauery@linux.intel.com>

1 files changed, 74 insertions, 1 deletions

diff --git a/example/asio-example.cpp b/example/asio-example.cpp
index cced85d..9819eba 100644
--- a/example/asio-example.cpp
+++ b/example/asio-example.cpp
@@ -1,4 +1,5 @@
 #include <boost/asio.hpp>
+#include <boost/asio/spawn.hpp>
 #include <chrono>
 #include <ctime>
 #include <iostream>
@@ -9,6 +10,7 @@
 #include <sdbusplus/server.hpp>
 #include <sdbusplus/timer.hpp>
 
+using variant = sdbusplus::message::variant<int, std::string>;
 int foo(int test)
 {
     return ++test;
@@ -24,6 +26,68 @@ int voidBar(void)
     return 42;
 }
 
+void do_start_async_method_call_one(
+    std::shared_ptr<sdbusplus::asio::connection> conn,
+    boost::asio::yield_context yield)
+{
+    boost::system::error_code ec;
+    variant testValue;
+    conn->yield_method_call<>(yield[ec], "xyz.openbmc_project.asio-test",
+                              "/xyz/openbmc_project/test",
+                              "org.freedesktop.DBus.Properties", "Set",
+                              "xyz.openbmc_project.test", "int", variant(24));
+    testValue = conn->yield_method_call<variant>(
+        yield[ec], "xyz.openbmc_project.asio-test", "/xyz/openbmc_project/test",
+        "org.freedesktop.DBus.Properties", "Get", "xyz.openbmc_project.test",
+        "int");
+    if (!ec && testValue.get<int>() == 24)
+    {
+        std::cout << "async call to Properties.Get serialized via yield OK!\n";
+    }
+    else
+    {
+        std::cout << "ec = " << ec << ": " << testValue.get<int>() << "\n";
+    }
+    conn->yield_method_call<void>(
+        yield[ec], "xyz.openbmc_project.asio-test", "/xyz/openbmc_project/test",
+        "org.freedesktop.DBus.Properties", "Set", "xyz.openbmc_project.test",
+        "int", variant(42));
+    testValue = conn->yield_method_call<variant>(
+        yield[ec], "xyz.openbmc_project.asio-test", "/xyz/openbmc_project/test",
+        "org.freedesktop.DBus.Properties", "Get", "xyz.openbmc_project.test",
+        "int");
+    if (!ec && testValue.get<int>() == 42)
+    {
+        std::cout << "async call to Properties.Get serialized via yield OK!\n";
+    }
+    else
+    {
+        std::cout << "ec = " << ec << ": " << testValue.get<int>() << "\n";
+    }
+}
+
+void do_start_async_method_call_two(
+    std::shared_ptr<sdbusplus::asio::connection> conn,
+    boost::asio::yield_context yield)
+{
+    boost::system::error_code ec;
+    int32_t testCount;
+    std::string testValue;
+    std::tie(testCount, testValue) =
+        conn->yield_method_call<int32_t, std::string>(
+            yield[ec], "xyz.openbmc_project.asio-test",
+            "/xyz/openbmc_project/test", "xyz.openbmc_project.test",
+            "TestMethod", int32_t(42));
+    if (!ec && testCount == 42 && testValue == "success: 42")
+    {
+        std::cout << "async call to TestMethod serialized via yield OK!\n";
+    }
+    else
+    {
+        std::cout << "ec = " << ec << ": " << testValue << "\n";
+    }
+}
+
 int main()
 {
     using GetSubTreeType = std::vector<std::pair<
@@ -121,7 +185,8 @@ int main()
 
     // test method creation
     iface->register_method("TestMethod", [](const int32_t& callCount) {
-        return "success: " + std::to_string(callCount);
+        return std::make_tuple(callCount,
+                               "success: " + std::to_string(callCount));
     });
 
     iface->register_method("TestFunction", foo);
@@ -141,6 +206,14 @@ int main()
     // add the sd_event wrapper to the io object
     sdbusplus::asio::sd_event_wrapper sdEvents(io);
 
+    // set up a client to make an async call to the server
+    // using coroutines (userspace cooperative multitasking)
+    boost::asio::spawn(io, [conn](boost::asio::yield_context yield) {
+        do_start_async_method_call_one(conn, yield);
+    });
+    boost::asio::spawn(io, [conn](boost::asio::yield_context yield) {
+        do_start_async_method_call_two(conn, yield);
+    });
     io.run();
 
     return 0;