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  1. Couchbase Server
  2. MB-19220

ep-engine: Ensure HashTable::size is atomic

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    • Untriaged
    • Unknown
    • KV: April 13 - April 26

    Description

      Fix data race as reported by ThreadSanitizer. I'm pretty sure this is beniegn, as size can only be modified if all HashTable mutexes are acquired (see HashTable::resize()), and all callers of getBucketForHash() either do so with at least 1 HashTable mutex acquired, or they perform double-checked locking (as per this instance).

      TSan report:

              WARNING: ThreadSanitizer: data race (pid=11329)
      		 
                Write of size 8 at 0x7ffe3a0ef1f8 by thread T9 (mutexes: write M45069, write M45070, write M45071):
      		 
                  #0 HashTable::resize(unsigned long) ep-engine/src/stored-value.cc:370 (ep-engine_hash_table_test+0x00000050173c)
      		 
                  #1 AccessGenerator::resize() ep-engine/tests/module_tests/hash_table_test.cc:314 (ep-engine_hash_table_test+0x0000004df4d9)
      		 
                  #2 AccessGenerator::operator()() ep-engine/tests/module_tests/hash_table_test.cc:304 (ep-engine_hash_table_test+0x0000004df3fd)
      		 
                  #3 SyncTestThread<bool>::run() ep-engine/tests/module_tests/threadtests.h:94 (ep-engine_hash_table_test+0x0000004e6bd8)
      		 
                  #4 _ZL23launch_sync_test_threadIbEvPv ep-engine/tests/module_tests/threadtests.h:66 (ep-engine_hash_table_test+0x0000004c9ca8)
      		 
                  #5 platform_thread_wrap platform/src/cb_pthreads.c:19 (libplatform.so.0.1.0+0x0000000035dc)
      		 
          
                Previous read of size 8 at 0x7ffe3a0ef1f8 by thread T8:
      		 
                  #0 HashTable::getBucketForHash(int) ep-engine/src/stored-value.h:1470 (ep-engine_hash_table_test+0x0000004d32b6)
      		 
                  #1 HashTable::getLockedBucket(int, int*) ep-engine/src/stored-value.h:1265 (ep-engine_hash_table_test+0x0000004d2e69)
      		 
                  #2 HashTable::getLockedBucket(std::string const&, int*) ep-engine/src/stored-value.h:1295 (ep-engine_hash_table_test+0x0000004d277b)
      		 
                  #3 HashTable::del(std::string const&) ep-engine/src/stored-value.h:1370 (ep-engine_hash_table_test+0x0000004d8f88)
      		 
                  #4 AccessGenerator::operator()() ep-engine/tests/module_tests/hash_table_test.cc:306 (ep-engine_hash_table_test+0x0000004df430)
      		 
                  #5 SyncTestThread<bool>::run() ep-engine/tests/module_tests/threadtests.h:94 (ep-engine_hash_table_test+0x0000004e6bd8)
      		 
                  #6 _ZL23launch_sync_test_threadIbEvPv ep-engine/tests/module_tests/threadtests.h:66 (ep-engine_hash_table_test+0x0000004c9ca8)
      		 
                  #7 platform_thread_wrap platform/src/cb_pthreads.c:19 (libplatform.so.0.1.0+0x0000000035dc)

      Note: this issue is not relevant to 4.0.0 and newer, as it was addressed by MB-13350 (Remove pre-C++11 atomic support).

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          Task - A task that needs to be done. MB-19323 3.1.6 release

          • Major - Major loss of function.
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              drigby Dave Rigby (Inactive)
              drigby Dave Rigby (Inactive)
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                Resolved:

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