111 lines
3.5 KiB
Markdown
111 lines
3.5 KiB
Markdown
CARLA Server
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============
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Build
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-----
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Some scripts are provided for building and testing CarlaServer on Linux
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$ ./Setup.sh
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$ make
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$ make check
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The setup script downloads and compiles all the required dependencies. The
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Makefile calls CMake to build CarlaServer and installs it under "Util/Install".
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Protocol
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--------
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All the messages are prepended by a 32 bits unsigned integer (little-endian)
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indicating the size of the coming message.
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Three consecutive ports are used,
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* world-port (default 2000)
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* measurements-port = world-port + 1
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* control-port = world-port + 2
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each of these ports has an associated thread that sends/reads data
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asynchronuosly.
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###### World thread
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Server reads one, writes one. Always protobuf messages.
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[client] RequestNewEpisode
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[server] SceneDescription
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[client] EpisodeStart
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[server] EpisodeReady
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...repeat...
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###### Measurements thread
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Server only writes, first measurements message then the bulk of raw images.
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[server] Measurements
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[server] raw images
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...repeat...
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Every image is an array of uint32's
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[width, height, type, color[0], color[1],...]
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where each color is an [FColor][fcolorlink] (BGRA) as stored in Unreal Engine,
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and the possible types of images are
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type = 0 None (RGB without any post-processing)
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type = 1 SceneFinal (RGB with post-processing present at the scene)
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type = 2 Depth (Depth Map)
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type = 3 SemanticSegmentation (Semantic Segmentation)
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The measurements message is explained in detail [here](measurements.md).
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[fcolorlink]: https://docs.unrealengine.com/latest/INT/API/Runtime/Core/Math/FColor/index.html "FColor API Documentation"
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###### Control thread
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Server only reads, client sends Control message every frame.
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[client] Control
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...repeat...
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In the synchronous mode, the server halts execution each frame until the Control
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message is received.
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C API
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-----
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The library is encapsulated behind a single include file in C,
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["carla/carla_server.h"][carlaserverhlink].
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This file contains the basic interface for reading and writing messages to the
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client, hiding the networking and multi-threading part. Most of the functions
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have a time-out parameter and block until the corresponding asynchronous
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operation is completed or the time-out is met. Set a time-out of 0 to get a
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non-blocking call.
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A CarlaServer instance is created with `carla_make_server()` and should be
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destroyed after use with `carla_server_free(ptr)`.
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[carlaserverhlink]: https://github.com/carla-simulator/carla/blob/master/Util/CarlaServer/include/carla/carla_server.h
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Design
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------
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The C API takes care of dispatching the request to the corresponding server.
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There are three asynchronous servers each of them running on its own thread.
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Conceptually there are two servers, the _World Server_ and the _Agent Server_.
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The _World Server_ controls the initialization of episodes. A new episode is
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started every time it is requested to the World Server by a RequestNewEpisode
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message. Once the episode is ready, the World Server launches the Agent Server.
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The _Agent Server_ has two threads, one for sending the streaming of the
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measurements and another for receiving the control. Both agent threads
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communicate with the main thread through a lock-free double-buffer to speed up
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the streaming of messages and images.
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The encoding of the messages (protobuf) and the networking operations are
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executed asynchronously.
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