1. Rajkishore Barik rajbarik@in.ibm.com
Efficient Computation of May-Happen-in-Parallel Information for Concurrent Java Programs
Rajkishore Barik
9/21/2018
LCPC'05

2. Introduction May-happen-in-parallel (MHP) analysis:
Statically determines statements that may execute in parallel in a multithreaded program
Application:
Detecting synchronization anomalies
Program optimization
Debuggers and program understanding tools
Data flow analysis
Enforce ordering among shared accesses
Complexity:
NP-complete (Taylor)
9/21/2018
LCPC'05

3. Related Work B4 analysis (Callahan and Subhlok) Ada: Java:
Interprocedural B4 analysis (Duesterwald and Soffa)
Non-concurrency analysis (Masticola and Ryder)
May-Happen-in-Parallel analysis (Naumovich and Avrunin)
Java:
Data flow analysis
Constructs: start, join, notify, wait, notifyAll, locks
Number of runtime threads need to be explicitly enumerated during static analysis
Worst-case complexity: (pN)3 where p is the number of runtime threads and N is the number of PEG nodes per thread
Happens-before, happens-after and happens-in-parallel (Sura et al.)
Constructs: start, join, locks
9/21/2018
LCPC'05

4. Example 9/21/2018 LCPC'05 1 class Shared { int field=0; }
2 class Main {
3 static Shared s;
4 public static void main(String[] args) {
5 s = new Shared();
6 s.field++;
7 Thread[] ta = new Thread[10];
8 for(int i=0;i<10;i++) {
9 ta[i] = new Task1();
ta[i].start();
11 }
12 s.field++;
13 Thread t2 = new Task1();
14 t2.start();
15 s.field++;
16 }
17 }
18 class Task1 extends Thread {
19 public void run() {
20 Main.s.field++;
21 }
22 }
9/21/2018
LCPC'05

5. Thread Model Abstract Thread (ti):
Compile-time entity that corresponds to invocation of Thread::start in a context
isUnique[ti] holds if ti has unique runtime correspondence
Intra-thread control flow graph,
ICFG(ti) = <V(ti), E(ti)>
V(ti) = USE(ti) 4 ASS(ti) 4 NEW(ti)
4 BEGIN(ti) 4 END(ti ) 4 ENTRY(ti )
4 EXIT(ti) 4 CSTART(ti) 4 CJOIN(ti)
4 CALL(ti) 4 ACQUIRE(ti) 4 RELEASE(ti)
E(ti) contains both intra and inter procedural control flow edges
locks[vi] denotes the set of objects that are locked while executing vi cV(ti)
9/21/2018
LCPC'05

6. Program Representation
Must-join abstract thread (tj):
CJOIN(ti,tj) postdom CSTART(tk,tj) and ti = tk
Thread Creation Tree (TCT)
Encodes start relationship among abstract threads
Nodes are abstract threads; Edges represent thread creation
Nodes in TCT are colored black if it is not a must-join abstract thread
yca(ti,tj) denotes the youngest common ancestor of ti and tj in TCT
canc(ti,tj) denotes the child of ti that is an ancestor of tj
9/21/2018
LCPC'05

7. MHP Computation MHP Computation: Thread-level MHP:
Thread-level MHP (Èt)
Node-level MHP (Èn)
Thread-level MHP:
ti Èt tj = true, if ti c anc(tj ) or tj c anc(ti )
9/21/2018
LCPC'05

8. MHP Computation
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LCPC'05

9. MHP Computation
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10. MHP Computation
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11. MHP Computation
Node-level MHP
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LCPC'05

12. MHP Computation
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LCPC'05

13. MHP Computation
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LCPC'05

14. MHP Computation
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LCPC'05

15. MHP Computation Algorithm
1. Identify abstract threads and their ICFGs.
2. for every abstract thread ti do
3. Compute postdom for every node in Vi.
4. Compute reachability information.
5. for every child abstract thread tj of ti do
6. Compute start-dominance information w.r.to tj.
7. end for
8. Add a node to TCT.
9. end for
10. Compute must-join chains and yca information.
11. for all abstract thread ti do
12 for all abstract thread tj do
13 for all vim cVi do
14 for all vjn cVj do
Determine vim Èvjn
16 end for
17 end for
18 end for
19 end for
9/21/2018
LCPC'05

16. Complexity Worst-case complexity is (kN)2, where
k is the number of abstract threads and
N is the number of ICFG nodes per thread
9/21/2018
LCPC'05

17. Experimental Setup Infrastructure Benchmarks Comparison
ERCO (ETH Research COmpiler at ETH, Zurich)
Pentium IV at 2.66GHz on RedHat Linux
Benchmarks
Java Grande Forum
Philo, tsp, elevator, sor and mtrt
Comparison
Naumovich et al, our approach
9/21/2018
LCPC'05

18. Experimental Results
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LCPC'05

19. Experimental Results
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LCPC'05

20. Conclusion
A new thread model based on context and flow sensitive analysis is presented.
MHP computation is split into thread-level and node-level based on TCT and is obtained efficiently.
TCT depicts interaction among threads and can perform various thread structure analysis.
Our MHP algorithm is on an average 1.77x faster than Naumovich et al.
9/21/2018
LCPC'05