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  1. Cassandra
  2. CASSANDRA-4402

Atomicity violation bugs because of misusing concurrent collections


    • Type: Bug
    • Status: Resolved
    • Priority: Trivial
    • Resolution: Fixed
    • Fix Version/s: 1.2.0
    • Component/s: None
    • Labels:


      My name is Yu Lin. I'm a Ph.D. student in the CS department at
      UIUC. I'm currently doing research on mining Java concurrent library
      misusages. I found some misusages of ConcurrentHashMap in Cassandra
      1.1.1, which may result in potential atomicity violation bugs or harm
      the performance.

      The code below is a snapshot of the code in file
      src/java/org/apache/cassandra/db/Table.java from line 348 to 369

      L348 if (columnFamilyStores.containsKey(cfId))

      { L350 // this is the case when you reset local schema L351 // just reload metadata L352 ColumnFamilyStore cfs = columnFamilyStores.get(cfId); L353 assert cfs.getColumnFamilyName().equals(cfName); ... L364 }

      L365 else

      { L367 columnFamilyStores.put(cfId, ColumnFamilyStore.createColumnFamilyStore(this, cfName)); L368 }

      In the code above, an atomicity violation may occur between line 348
      and 352. Suppose thread T1 executes line 348 and finds that the
      concurrent hashmap "columnFamilyStores" contains the key
      "cfId". Before thread T1 executes line 352, another thread T2 removes
      the "cfId" key from "columnFamilyStores". Now thread T1 resumes
      execution at line 352 and will get a null value for "cfs". Then the
      next line will throw a NullPointerException when invoking the method
      on "cfs".

      Second, the snapshot above has another atomicity violation. Let's look
      at lines 348 and 367. Suppose a thread T1 executes line 348 and finds
      out the concurrent hashmap does not contain the key "cfId". Before it
      gets to execute line 367, another thread T2 puts a pair <cfid, v> in
      the concurrent hashmap "columnFamilyStores". Now thread T1 resumes
      execution and it will overwrite the value written by thread T2. Thus,
      the code no longer preserves the "put-if-absent" semantics.

      I found some similar misusages in other files:

      In src/java/org/apache/cassandra/gms/Gossiper.java, similar atomicity
      violation may occur if thread T2 puts a value to map
      "endpointStateMap" between lines <1094 and 1099>, <1173 and 1178>. Another
      atomicity violation may occur if thread T2 removes the value on key
      "endpoint" between lines <681 and 683>.


        1. 4402-v2.txt
          6 kB
          Jonathan Ellis
        2. cassandra-1.1.1-4402.txt
          4 kB
          Yu Lin



            • Assignee:
              jacklondongood Yu Lin
              jacklondongood Yu Lin
              Jonathan Ellis
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