The modified method `getMethodsByNameAndParamCount` is used (and only used) in the `FastHierarchy.getSignaturePolymorphicMethod` for resolving polymorphic methods. The for-loop will return the method list's iterator, but the list itself can be modified by another body pack transform thread, causing a `ConcurrentModificationException`. The patch fix the issue by returning a copy of this list. This patch also fixes the issue soot-oss#1811 , and a similar issue is soot-oss#1199 (fixed by soot-oss#1886 ).
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The proposed fix for the multi-threading problem doesn't resolve the root cause. The copy constructor of the lists iterates over the base collection and adds each element. Your fix reduces the time during which a concurrent modification can occur to the time of copying the list. That's for sure muchsorter than the runtime of the transformer itself, but if you're unlucky, you can still hit a I am slightly reluctant to accept an incomplete fix that - on the other hand - migth cost us some performance because the |
I see. I encountered this issue in an Android analysis project, while in the experiment, a large amount of apks fail due to CME at that site. This patch works fine for these apks. Anyway, is there any better solution? I found the list itself is a wrapped synchronized collection (https://github.com/soot-oss/soot/blob/develop/src/main/java/soot/SootClass.java#L680), while the iterator returned by this wrapper does not guarantee thread-safety. JDK officially requires synchronization on the iterating site (https://stackoverflow.com/a/1775738). Will this solution be better? If so, I will create a new PR for that. |
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We should first understand why one thread is searching for a method in a class in which another thread is still creating methods. Let's assume the thread that queries the My guess would be that we're dealing with phantom methods which are created when resolving a method reference to a callee that doesn't exist. If that is correct, the |
The modified method
getMethodsByNameAndParamCountis used (and only used) in theFastHierarchy.getSignaturePolymorphicMethodfor resolving polymorphic methods. The for-loop will return the method list's iterator, but the list itself can be modified by another body pack transform thread, causing aConcurrentModificationException 8000. The patch fix the issue by returning a copy of this list.This patch also fixes the issue #1811 , and a similar issue is #1199 (fixed by #1886 ).