C++ Agents Implementation
Chris Rouse
CSS 497
Outline
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Finish Agent Implementation
Involves changes to the following classes:
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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
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Must add methods:
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CallAll()
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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()
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Will need to update information between all agents
Manages spawning, migrating, and killing of agents
Agents_base.h/.cpp cont.
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Difficulties:
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All must pull from a single bag, causing a possibility for race
conditions
This leads to the bag of agents being a critical section
Normal
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Wiki example
Race 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
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Mutex locking will help prevent race conditions by
‘locking down’ the critical section upon use
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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
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Difficulties cont:
Waiting and Notifying
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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?
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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
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CallAll method will essentially work like so:
Step 1:
Create Bag of Agents
Step 5:
Release the Lock
Step 2:
Lock Bag Upon
First Pop Request
Step 6:
Continue Until
Out of Agents
Step 3:
Remove Last Agent
From Vector of Agents
Step 7:
Wait for Agents
to Finish Task
Step 4:
Send Copy of Command
to Popped Agent
Step 8:
Collect Finished Agents into
New Bag and Replace Old Bag
Agents.h/.cpp
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Must add methods:
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Spawn()
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Migrate()
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To move agents between Place locations
Kill()
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To create Agents in current place
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
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Messages will need to be modified:
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This will need to use the CallAll() & ManageAll() calls
mentioned earlier
Exchange_helper will need to be modified too
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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
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Still working on CallAll() method
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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
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Unfamiliar code
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No working IDE
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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
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Code is complex and often contains information that I don’t
understand
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
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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
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Some functions in the code are now deprecated and
throw errors when used
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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
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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