SPADES. Stefano Cacciaguerra Contents. System Structure. Creating a SPADES Simulation. Miscellaneous Features

Transcription

1 SPADES System for Parallel Descrete Event Simulation Stefano Cacciaguerra 1 Contents I II III IV V Introduction System Structure Getting Started Creating a SPADES Simulation Miscellaneous Features VI Technical Details 2

2 I. Introduction The System for Parallel Discrete Simulation (SPADES) is a middleware system for agent-based distributed sim. It is targeted at the AI community where the thinking of an agent is an amount of the computation involved in a sim. SPADES is designed to ease the creation of agent-based simulations which can be distributed across machines while still being repeatable and efficient. An agent is a computational entity that receives sensations from the simulated world, goes through some amount of computation, then returns some actions to be executed. The world model operates with a view of sim events being realized one by one, while the agents simply receive sensations and send actions. 3 I. Features of SPADES based execution includes support for modeling latencies in sensation, thinking, and acting. s can be distributed, transparently, among multiple computers. The result of the sim is unaffected by network delays or load variations among the different computers (these factors affect the speed of the sim). SPADES does not require that agents are written in a particular programming language ( i.e. the agent processes can read and write to pipes). s do not take a single joint action at a particular time, rather, their actions can take effect at varying times in the sim. 4

3 I. To Aid the Creation of Sims A simulation (sim) consists of events being realized in time order (discrete event sim). The world model creates events and do arbitrary processing as the events are realized. An abstraction of sensations and actions is provided to the agent reading data from a pipe and sending actions back on another pipe. SPADES tracks the amount of computation used by agents in responding to a sensation (i.e. agent which uses more computation will respond more slowly). All networking is managed. Neither the world model nor the agents need to create sockets, know network addresses, or do any other network management. All reasoning to manage distribution among machines is done. It distributes a sim across computers maintaining correctness (causality is not violated!) and efficiently uses the resources available. SPADES manages logging for errors, tracing of execution and recording of the 5 states of the sims. II. System Architecture CLIENT SERVER Computer 1 pipe Communication Server tcp/ip Simulation Engine World Model Computer 2 pipe Communication Server Computer A Computer N pipe Communication Server 6

4 II. Simulation Engine It is the heart of the discrete event simulatorand it coordinates all network communication. All pending events are queued here without violating the causality among them. SERVER Monitor Interface is a component of the SE that allows to extract information about the evolution of the sim Simulation Engine M.I. tcp/ip World Model 7 II. World Model The designer creates a sim model of a particular environment. The SE is a library to which the world model must link, in order to exist in the same process. The world model provides functionality as: advancing the state of the world to a particular time realizing events/actions, and generating the sensations to be sent to the agents Simulation Engine SERVER M.I. World Model tcp/ip 8

5 II. Communication Server It must be run on each machine on which agents run. It manages all communications with the agents (via pipe interface) as well as all that with the SE (via socket interface) It tracks the CPU usage of the agents to calculate the thinking latency. It is possible to run an integrated communication server which runs in the same process as the simulation engine. pipe Communication Server tcp/ip 9 II. s They are the computational entities whose interactions are being simulated. An agent receives sensation messages, does some thinking (i.e. processing), and returns some actions. They interact with the communication server via pipes. They are free to use any programming language and any architecture as long as they can read and write to pipes. pipe Communication Server tcp/ip 10

6 II. Event-Based Simulation SPADES is a hybrid of a continuous and discrete event simulator: A continuous simulation advances by processing for each time quanta in turn. The SE calls to the WM to advance some number of time quanta (for simulating physical processes). A discrete event simulation is one in which the state of the sim is changed by events occurred at a discrete time. The SE with the agents SPADES is a discrete event simulator (they receive sensations and send actions). The order of event realization will not violate causality no events which are causally related will be realized out of order. 11 II. Sense-Think-Act From agent s perspective, the interaction with the sim is: 1. Wait for a sensation to be received 2. Decide on a set of actions and send them to the communication server 3. Send a done thinking message to indicate that all actions were sent Actions are sent in response to a sensation, an agent can call a special action, request time notify, (i.e. a time notify is an empty sensation). A B C D Time Sense Think Act Sense Think Act Sense Think

7 II. Sense-Think-Act All sensations and actions might have different latency. In different agents, the sense, think, and act components can be overlapped in time. The think cycles for a single agent may never overlap. Communication Server tracks the thinking time (i.e. CPU time ) of the agent to model the thinking latency: from the sending a sensation to an agent to the reception of the done thinking. The current time slice reported by the Linux kernel is in 10 ms. 13 III. Getting Started./configure make make install SPADES attempts to auto-detect a number of features with autotools: all options that begin with enable also have a disable variant, and the with options also have a without variant. enable-debug (default is off) On action logging is enabled (useful in developing a world model). Off disabling this will slightly reduce the code size and increase execution speed. enable-sample-code (default is on) On then the sample world model and the sample agents are built. This is mostly useful to test the system. 14

8 III. Files Installed Overview of what SPADES installs, after a make install execution (all paths are relative to /usr/local by default): bin/commserver This is the communication server executable. bin/show_ttimes.pl This perl script processes a recorded agent think time file into a more human readable format. bin/run_exp.pl This perl script provides a way to run SPADES many times for testing. include/spades/ All header files needed to compile your world model or agents. lib/ The library to which the world model must link and the optional agent library. lib/spades/ Libraries which are used internally by spades are installed here. share/spades/agent.conf The configuration file of agents. share/spades/commserver.conf The configuration file of communication. share/spades/agentdb.xsdthe XML schema describes the format for the agent database. 15 III. Sample World Model and s The sample world model is a two dimensional rectangle where opposite sides are connected (i.e. wrap-around ). Each agent receives the positions of all agents (i.e. sensation) and sends a particular velocity vector (i.e. action) The world model provides the correct accelerations to achieve this velocity advancing 1 ms increments. There are two kinds of agents: The wanderer moves randomly around the world. The chaser chases one of the wanderers by setting its requested velocity directly towards the current observed location of that agent. 16

9 III. Running The sample world model is not installed, change to the sample_world_model directory:./ballworld--file ballworld.conf you should see lines like this: Engine Status: PAUSED simtime=0 events=0 mean simtime/sec=0 At this point, the WM and SE are waiting for CSs to connect. commserver --file /usr/local/share/spades/commserver.conf --agent_db_fn../sample_agent/ agentdb.xml If you want to connect several computers (i.e. CSs) to the sim../ballworld--file ballworld.conf --num_comm_servers_wanted N 17 III. Running If the computer running the SE is named HOST, then each CS is started: commserver --file /usr/local/share/spades/commserver.conf --agent_db_fn../sample_agent/agentdb.xml --engine_host HOST If you want to run the integrated CS:./ballworld--file ballworld.conf --run_integrated_commserver In order to connect a monitor to the sim to watch it run: cd sample_world_model/monitor./connect If you need to connect to a remote machine, look in the connect script works and call java appropriately. 18

10 III. Log Files By default, SPADES produces a number of log files that will appear in the Logfiles directory in the current working directory: agent*-stdout.log, agent*-stderr.log The standard out and error of the agents. agent*-ttimes.log This file is a record of the agent think times. actions.log This is the action log of the simengine. events text.log This is a human readable list of all the events. The parameter use text_event_log_controls whether this file is created and text event log_fn_controls the location and file name. For the sample WM, you can examine the contents of the log file with its monitor: monitor.log Its format is completely determined by the world model. cd sample_world_model/monitor./playlog../ Logfiles/monitor.log. 19