Add some retry logic to ensure all parameters are fetched in the getP…

…aramList method.

Minor corrections to Linux build instructions.

.gitignore

@@ -24,6 +24,8 @@ bld/
 [Oo]bj/
 Intermediate/
 Binaries/
+llvm-build/
+llvm-source/
 
 # CMake files
 CMakeFiles/

MavLinkCom/src/impl/MavLinkNodeImpl.cpp

@@ -302,15 +302,49 @@ std::vector<MavLinkParameter> MavLinkNodeImpl::getParamList()
 
 	while (!done) {
 		waiting = true;
-		if (!paramReceived.timed_wait(5000))
+		if (!paramReceived.timed_wait(3000))
 		{
-			con->unsubscribe(subscription);
-			throw std::runtime_error(Utils::stringf("Five second timeout waiting for parameter number %d of %d", paramIndex + 1, paramCount));
+			// timeout, so we'll drop through to the code below which will try and fix this...
+			done = true;
 		}
 		waiting = false;
 	}
 	con->unsubscribe(subscription);
 
+	// note that UDP does not guarantee delivery of messages, so we have to also check if some parameters are missing and get them individually.
+	std::vector<size_t> missing;
+
+	for (size_t i = 0; i < paramCount; i++)
+	{		
+		// nested loop is inefficient, but it is needed because UDP also doesn't guarantee in-order delivery
+		bool found = false;
+		for (auto iter = result.begin(), end = result.end(); iter != end; iter++)
+		{
+			MavLinkParameter p = *iter;
+			if (p.index == i) {
+				found = true;
+				break;
+			}
+		}
+		if (!found) {
+			missing.push_back(i);
+		}
+	}
+
+	// ok, now fetch the missing parameters.
+	for (auto iter = missing.begin(), end = missing.end(); iter != end; iter++)
+	{
+		size_t index = *iter;
+		MavLinkParameter r;
+		if (getParameterByIndex(static_cast<int16_t>(*iter)).wait(2000, &r)) {
+			result.push_back(r);
+		}
+		else {
+			Utils::logMessage("Paremter %d does not seem to exist", index);
+		}
+	}
+
+
 	std::sort(result.begin(), result.end(), [&](const MavLinkParameter & p1, const MavLinkParameter & p2) {
 		return p1.name.compare(p2.name) < 0;
 	});
@@ -383,6 +417,44 @@ AsyncResult<MavLinkParameter> MavLinkNodeImpl::getParameter(const std::string& n
 	return asyncResult;
 }
 
+AsyncResult<MavLinkParameter> MavLinkNodeImpl::getParameterByIndex(int16_t index)
+{
+	auto con = ensureConnection();
+	AsyncResult<MavLinkParameter> asyncResult([=](int state) {
+		con->unsubscribe(state);
+	});
+
+	MavLinkParamRequestRead cmd;
+	cmd.param_id[0] = '\0';
+	cmd.param_index = index;
+	cmd.target_component = getTargetComponentId();
+	cmd.target_system = getTargetSystemId();
+
+	int subscription = con->subscribe([=](std::shared_ptr<MavLinkConnection> connection, const MavLinkMessage& message) {
+		if (message.msgid == MavLinkParamValue::kMessageId)
+		{
+			MavLinkParamValue param;
+			param.decode(message);
+			if (param.param_index == index)
+			{
+				MavLinkParameter  result;
+				char buf[17];
+				std::memset(buf, 0, 17);
+				std::memcpy(buf, param.param_id, 16);
+				result.name = buf;
+				result.type = param.param_type;
+				result.index = param.param_index;
+				result.value = UnpackParameter(param.param_type, param.param_value);
+				asyncResult.setResult(result);
+			}
+		}
+	});
+	asyncResult.setState(subscription);
+	sendMessage(cmd);
+
+	return asyncResult;
+}
+
 AsyncResult<bool> MavLinkNodeImpl::setParameter(MavLinkParameter  p)
 {
 	int size = static_cast<int>(p.name.size());

MavLinkCom/src/impl/MavLinkNodeImpl.hpp

@@ -86,6 +86,7 @@ namespace mavlinkcom_impl {
 		virtual void handleMessage(std::shared_ptr<MavLinkConnection> connection, const MavLinkMessage& message);
 	private:
 		void sendHeartbeat();
+		AsyncResult<MavLinkParameter> getParameterByIndex(int16_t index);
 		bool inside_handle_message_;
 		std::shared_ptr<MavLinkConnection> connection_;
 		int subscription_ = 0;

cmake/getlibcxx.sh

@@ -0,0 +1,25 @@
+#! /bin/bash
+
+SCRIPT_DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )"
+cd "$SCRIPT_DIR"
+
+# add llvm-source to root of AirSim
+cd ..
+
+# Checkout LLVM sources
+git clone --depth=1 https://github.com/llvm-mirror/llvm.git llvm-source
+git clone --depth=1 https://github.com/llvm-mirror/libcxx.git llvm-source/projects/libcxx
+git clone --depth=1 https://github.com/llvm-mirror/libcxxabi.git llvm-source/projects/libcxxabi
+
+export C_COMPILER=clang
+export COMPILER=clang++
+
+# Build and install libc++ 
+mkdir llvm-build && cd llvm-build
+cmake -DCMAKE_C_COMPILER=${C_COMPILER} -DCMAKE_CXX_COMPILER=${COMPILER} \
+      -DCMAKE_BUILD_TYPE=RelWithDebInfo -DCMAKE_INSTALL_PREFIX=/usr \
+      ../llvm-source
+make cxx
+sudo make install-cxxabi install-cxx
+
+popd

docs/linux_build.md

@@ -1,5 +1,11 @@
 # Linux Build
 
+These are the instructions to build AirSim on a Linux machine.
+Note: you can also do this from [BashOnWindows](https://msdn.microsoft.com/en-us/commandline/wsl/install_guide)
+but make sure you are `not` using a `Visual Studio Command Prompt` because we don't want cmake to accodemtally find VC++ and try and use that.
+
+We need to use `clang compiler` because Unreal engine requires that.  
+
 ## cmake
 
 First you will need at least [cmake version  3.5](https://cmake.org/install/). 
@@ -17,27 +23,23 @@ sudo apt-get update
 sudo add-apt-repository ppa:ubuntu-toolchain-r/test
 sudo apt-get update
 sudo apt-get install clang-3.9 clang++-3.9
-sudo update-alternatives --install /usr/bin/clang clang /usr/bin/clang-3.9 60 --slave /usr/bin/clang++ clang++ /usr/bin/clang++-3.9
 ````
 
-Next you will need the latest version of libc++ library, which you can build yourself by doing this:
-
+If that doesn't work then try this (for Ubuntu 16 only):
 ````
-# Checkout LLVM sources
-git clone --depth=1 https://github.com/llvm-mirror/llvm.git llvm-source
-git clone --depth=1 https://github.com/llvm-mirror/libcxx.git llvm-source/projects/libcxx
-git clone --depth=1 https://github.com/llvm-mirror/libcxxabi.git llvm-source/projects/libcxxabi
-
-export C_COMPILER=clang
-export COMPILER=clang++
+sudo apt-get update 
+wget -O - http://apt.llvm.org/llvm-snapshot.gpg.key | sudo apt-key add - 
+sudo apt-add-repository "deb http://apt.llvm.org/xenial/ llvm-toolchain-xenial-3.9 main" 
+sudo apt-get install clang-3.9 clang++-3.9
+````
+Now make clang-3.9 your default version of clang with this command:
+````
+sudo update-alternatives --install /usr/bin/clang clang /usr/bin/clang-3.9 60 --slave /usr/bin/clang++ clang++ /usr/bin/clang++-3.9
+````
+Next you will need the latest version of libc++ library, which you can get by running this:
 
-# Build and install libc++ 
-mkdir llvm-build && cd llvm-build
-cmake -DCMAKE_C_COMPILER=${C_COMPILER} -DCMAKE_CXX_COMPILER=${COMPILER} \
-      -DCMAKE_BUILD_TYPE=RelWithDebInfo -DCMAKE_INSTALL_PREFIX=/usr \
-      ../llvm-source
-make cxx -j2
-sudo make install-cxxabi install-cxx
+````
+./cmake/getlibcxx.sh
 ````
 
 Now you can run the build.sh at the root level of the AirSim repo:
@@ -50,3 +52,8 @@ This will create a `build_debug` folder containing the build output and the cmak
 ## Reset build
 
 If for any reason you need to re-run cmake to regenerate new make files just deete the `build_debug` folder.
+
+## Running Unreal on Linux
+
+Now you are ready to follow these instructions to get [Unreal working on Linux](https://wiki.unrealengine.com/Building_On_Linux#Clang) but note that everywhere
+you see Clang3.5 in the Unreal documentation replace that with clang3.9.