A Concurrent Affair » Set Constants, Options for Delay and YieldA Concurrent Affair

This morning — silently typing in bed ;) — I wrapped up some work on the SetConstantsStrategy ^[1]. There are still a few limitations, but for what I’m using it, I think it’s reasonable: It only works on static fields, so I only have to deal with the one <clinit> method, not with a varying number of constructors. It works both for final and non-final fields, but they have to be initialized with a simple value. It cannot be a method call, and it shouldn’t be in a static initializer block with some complicated if-then-else stuff. I only scan through the <clinit> code for the first putstatic referring to the field. Then I check that the preceeding instruction is one that simply loads a value, not one that makes a method call or performs arithmetic. Then I remove that instruction and replace it with one that loads the new data. For setting the probability of a yield to different values from 0.0 to 1.0 or enabling and disabling things by changing a boolean, this is good enough.

I also added boolean flags to control if the yields and delays at different places are actually enabled: Now I can independently control them at

before a Thread.start
before a Thread.exit
before a Thread.run
before a Thread.join
before an Object.notify
after an Object.notify
before an Object.wait
after an Object.wait
before a monitorenter
after a monitorenter or monitorexit

I did this because Corky and I agreed that I was placing random delays in too many places, and at least I believe there is some kind of balance between delays ^[2] at different synchronization points. Switching these on and off could give me a chance of exploring the interactions and finding that balance.

When I finished adding the flags, it occurred to me that maybe I shouldn’t have used one probability for all of the yields and then boolean flags for kind of insertion point; maybe I should have used probabilities for each of them. But for now, I’ll go with this implementation. Just to show some useless detail again, here are the command line arguments that I currently have in the instr.setconstants.xml file:

<args line="-force -nobackup
-X set-const=edu.rice.cs.cunit.SyncPointBuffer::RANDOM_YIELD_PROB:=1
-X set-const=edu.rice.cs.cunit.SyncPointBuffer::RANDOM_YIELD_THREAD_START:=false
-X set-const=edu.rice.cs.cunit.SyncPointBuffer::RANDOM_YIELD_THREAD_EXIT:=false
-X set-const=edu.rice.cs.cunit.SyncPointBuffer::RANDOM_YIELD_THREAD_RUN:=false
-X set-const=edu.rice.cs.cunit.SyncPointBuffer::RANDOM_YIELD_THREAD_JOIN:=false
-X set-const=edu.rice.cs.cunit.SyncPointBuffer::RANDOM_YIELD_PRE_NOTIFY:=false
-X set-const=edu.rice.cs.cunit.SyncPointBuffer::RANDOM_YIELD_POST_NOTIFY:=false
-X set-const=edu.rice.cs.cunit.SyncPointBuffer::RANDOM_YIELD_PRE_WAIT:=false
-X set-const=edu.rice.cs.cunit.SyncPointBuffer::RANDOM_YIELD_POST_WAIT:=false
-X set-const=edu.rice.cs.cunit.SyncPointBuffer::RANDOM_YIELD_PRE_MONITOR:=false
-X set-const=edu.rice.cs.cunit.SyncPointBuffer::RANDOM_YIELD_POST_MONITOR:=false"/>

It overrides all the yield flags and the probability. The -force flag is there to allow instrumentation of already instrumented files.

Now we’re off to a Christmas party at Dr. Nguyen’s house. Thanks for the invitation!

^[3] ^[4]

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