C++ Agents Implementation Chris Rouse CSS 497

Outline  Finish Agent Implementation  Involves changes to the following classes:  Agents_base.h/.cpp  Agent.h/.cpp  Mprocess.h/.cpp  Messages.h/.cpp  Exchange_helper.h/.cpp  Attempt to fix Eclipse IDE development problems for C++ version

Agents_base.h/.cpp  Must add methods:  CallAll()  Instantiate bag of Agents to use  Must allocate Agents for each thread  Will send a command to all agents to execute  Wait for response back  ManageAll()  Will need to update information between all agents  Manages spawning, migrating, and killing of agents

Agents_base.h/.cpp cont.  Difficulties:  All must pull from a single bag, causing a possibility for race conditions  This leads to the bag of agents being a critical section NormalWiki exampleRace Condition  To remedy the problem, we need to make use of pthread_mutex_lock() to control when a thread can access this bag

Agents_base.h/.cpp  Mutex locking will help prevent race conditions by ‘locking down’ the critical section upon use  Any requests must first acquire the lock rights before they can access the agents  If bag is already locked, other requests must wait until the lock releases and notifyAll is called before attempting to gain the lock again

Agents_base.h/.cpp  Difficulties cont:  Waiting and Notifying  Should wait to hear back about status of agent  Typically we make use of Notify and Wait  Can use provided methods barrierThreads and resumeThreads to wait and notify  What to do when an Agent doesn’t send notifications back?  At this time, we will assume that all Agents will respond and not take precautions in the event they do not  As currently planned, if an Agent doesn’t respond, the program will simply crash

Agents_base.h/.cpp  CallAll method will essentially work like so: Step 1: Create Bag of Agents Step 2: Lock Bag Upon First Pop Request Step 3: Remove Last Agent From Vector of Agents Step 4: Send Copy of Command to Popped Agent Step 5: Release the Lock Step 6: Continue Until Out of Agents Step 7: Wait for Agents to Finish Task Step 8: Collect Finished Agents into New Bag and Replace Old Bag

Agents.h/.cpp  Must add methods:  Spawn()  To create Agents in current place  Migrate()  To move agents between Place locations  Kill()  To remove an Agent when it is finished with execution  This must also handle sending the commands to the slave agents

Messages.h/.cpp & Exchange_helper.h/.cpp  Messages will need to be modified:  This will need to use the CallAll() & ManageAll() calls mentioned earlier  Exchange_helper will need to be modified too  Will need to be able to exchange agents between slaves  This will happen either locally in the same place or through a set of slave locations

Current Status  Still working on CallAll() method  Reading and understanding existing code has been time consuming and confusing  Working on recompilation of existing code using Makefile while on campus  Decided to use a single bag of Agents to more efficiently handle race condition vs. Multiple bags of Agents  Working on implementing tests to make sure Agents are being taken correctly and passed correct instructions  Wait and Notify have not been used and tested yet

Current Difficulties  Unfamiliar code  Code is complex and often contains information that I don’t understand  No working IDE  Eclipse has issues with some of the function calls and classes  Currently working on fixing problems that would prevent IDE development of the C++ version  Unknown behavior  Haven’t worked with the code’s output much yet, so any output I read needs to be checked for correct behavior, then rechecked with new changes  Code must be recompiled on campus  Code uses libraries stored in Professor Fukuda’s campus drive, so to recompile easily, needs to happen via SSH or on campus computers

Deprecation Fixes  Some functions in the code are now deprecated and throw errors when used  Most recent example is bcopy(), which is now deprecated in newer Linux systems  My original fix was to include the String.h class, which had many of the deprecated values still included in it  This call can now be made using the memcpy() call, which takes the same parameters as bcopy, and functions the same  My current copy of the code contains all changes made for bcopy using a quick Linux ‘find | xargs | sed’ command to make all the necessary replacements, though no testing as of yet

Future Plans  Finish wait/notify in Agents_base and check for errors  Test the memcpy command to make sure it works as intended  Fully test CallAll implementation  Move onto Spawn and Kill methods of Agents when complete with all the above  Continue to work on Eclipse IDE problems to enable further development easier for new research students