Parallel LTL Model Checking

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Parallel LTL Model Checking

• CS 586

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The Capacity Problem
Capacity memory
statesstateSize
Increase capacity by - Increasing memory -
Decreasing states - Decreasing state size
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Double DFS in Parallel
Memory available in one machine
Memory needed to store visited states
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DDFS Search order
B
A
C
If the dfs2 from A visits C first, then the dfs2
from B will not visit C and will not detect a
cycle. Solutions?
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Solution Ideas

• Use a different algorithm.
• Schedule the dfs2 searches
• Use different bits to mark dfs2 visits
• ______ ?

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One Idea

• Forget about proving correctness.
• Each search process is random.
• Coordinate efforts to find cycles.
• Coordination scheme should be..
• Decentralized
• Fault-tolerant
• Better than no coordination at all

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Forager Allocation Problem

• Given
• several foraging sites with varying quality
• the current needs of the hive
• a pool of foragers
• Allocate the foragers to
• maximize the collection of needed resources
• Without central control.

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Scouts locate patches
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Scouts multicast their findings
Scout performs a waggle dance which is observed
by unemployed foragers. Duration and intensity of
the dance describe the quality of the patch.
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Workers visit patches.
A worker will observe a dance and leave for a
patch. Returns, unloads and dances. May visit
patch again.
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Adaptation

• Apis Mellifera
• Bee forager
• Search flight pattern
• Flower patch
• Pollen
• Waggle dance

• BEE
• (bee-based error explorer)
• Search agent
• Random walk
• Accept state
• Property Violation
• Multicast

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Decentralized Cooperative Search
B
A
C
Launch n random searches. When one finds an
accept state, advertize its location. Listen to
and possibly ignore advertizements.
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BEE Search
BEE
BEE
controller
BEE
BEE
distribute problem
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BEE Search
controller
multicast an accept state
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BEE Search
controller
more multicasts
report an error
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BEE Search
controller
search continues
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BEE Search
controller
search terminated
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Experimental Environment

• Classroom laboratory workstations
• Lowest priority level
• 8 MB of RAM per machine
• Compare with isolated parallel random walks to
  measure advantage of coordination.

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Speedup-SS7
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Speedup-11peterson
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Too Much Communication
11 Peterson
SS 7
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Negative Feedback
ACCEPT STATE FORAGING
WATER COLLECTING
water in hive
evaporative cooling
time to receive cycle advertisement
water seeking by receiver bees
recruit to cycle foraging
abandon accept state foraging
time to find an unloader
recruiting to water collecting (waggle dance)
abandoning of water collecting
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Negative Feedback