Server architecture

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(jobs and their data access patterns)
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The server needs to be multithreaded to be capable of simulating catplosions and
The server needs to be multithreaded to be capable of simulating catplosions and
fluid dynamics.
fluid dynamics.
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== world simulation step ==
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* simulate world (terrain oriented jobs, ie. water, tree growth)
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** threadpool (task stealing) that handles all jobs of this simulation step
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** each job has read access to the complete world back buffer
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** each job has exclusive read/write access to one chunk'S front buffer
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** multiple jobs writing one chunk are queued in the same thread
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** after all threads are finished the front buffer gets copied onto the back buffer
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** each thread has messagebuffer, jobs the thread can write to the message buffer,
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*** after all threads are finished,
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*** the messages in the message buffer are written to the global message system
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** fluid manager : (not every frame?) fluid simulation jobs are spawned by a manager for "awake" blocks (awake can be triggered by sim-job when water reaches edge : messagebuffer)
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** light manager : not every frame, placing a torch triggers "awake"/recalc
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** simulation has a fixed frames/second speed
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*** not all jobs need to calculate themselves every frame
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* jobs writing terrain must mark (messagebuffer) the terrain as changed for network messages to be generated
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* spin lock : busy-waiting for lock to avoid sleep, if maxfps long wait needed : sleep as job.
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* to avoid ram->cpucache bottleneck, attempt to process the same chunk-coordinates in the same thread (across multiple frames?)
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** the simulation code of one chunk is implemented in lua
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== object simulation/think ==
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there are 3 types of objects : mobiles(players,enemies,animals), items(stuff to pick up), buildings (workshops, bridges, doors..)
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* every worker thread has own lua state, and global single-threaded mode also. (objects may not have local state, all must be in property name-value list)
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* access via metatable. object orientation via dummy-object setting metatable according to object type (property)
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* complex structures and can be stored in properties via serialisation (ie json)
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* objects can have tags/groups
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* objects get messages with time-of-delivery (e.g. think again in 5 seconds, get poison damage, idle wandering animals)
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* every message triggers a job (jobs are written in lua)
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* priority (starttime) queue of messages
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* key-value lists for object properties, backbuffered, objects write themselves using message-buffer (update aka value-change)
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* fight/wound etc : send message to object (allows e.g. big blob spawns small blob)
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* inter object communication via message system
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* read only access to properties of every object
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* query objects in range (by type) (optionally flag that object always wants query sightrange in think step)
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* object manager creates and destroys objects, you need to send him which one you want to kill
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* pathfinding (one path-finding request isn't calculated in a parallel way, but multiple path-finding requests can be run at the same time (no-global-data structures, fully re-entrant?))
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* ticker/timer to generate whatever timed messages (ie think message each 30 sec)
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== remaining super singlethreaded stuff ==
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* complete singlethreaded part
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* handles network (send/recv/listen/accept)
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* handle complex things like falling trees (we can move this into the multihreading section if its to expesive)
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* worldsave/load
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== usecases ==
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* drawbridge (changes terrain, managed as building)
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* fight between two mobiles
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* ai/decide-what-to-do : see and attack nearby enemy, cat-mating...
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* weather : rain produces small water ponds
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* player empties water bucket on area (awake fluid manager in this block)
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* lumberjack a tree (event based in single-threaded step)
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* cavein (check when solid tile is removed, if unconnected, apply gravity and deadly force)
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* closed-door-for-pathfinding, idea : change terrain (parameter)
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== later if neccessary, not needed for first prototype ==
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* object jobs that can run multiple frames ? (complex ai, pathfinding etc... )
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* world jobs that can access more than one chunk (treefall? area? cavein), in separate step after all the 1-chunk jobs are done
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** needs to avoid concurrent write access to overlapping area
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== glossar ==
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* world : terrain infos consisting of tiles in chunks
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== some notes ==
== some notes ==

Revision as of 20:36, 1 November 2010

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