clarify that Memoizers always take ownership of a callable #7
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Implement a LRU cache, and associated memoization factories. The simple thread-safe memoization ends up 2x to 3x slower than a thread-unsafe memoization, in part because the thread-safe memoization has to copy the return value. Therefore, it can be more desirable to use the thread-unsafe memoization with a thread_local specifier. Benchmarks (arg 1: key size, arg 2: value size): ``` LRUCacheLookup/8/16 1877 ns 1877 ns 359452 items_per_second=53.2795M/s LRUCacheLookup/8/1024 1924 ns 1924 ns 367765 items_per_second=51.9831M/s LRUCacheLookup/64/16 2629 ns 2628 ns 264012 items_per_second=38.0487M/s LRUCacheLookup/64/1024 2671 ns 2671 ns 264135 items_per_second=37.4432M/s MemoizeLRUCached/8/16 4922 ns 4921 ns 141748 items_per_second=20.3205M/s MemoizeLRUCached/8/1024 5688 ns 5687 ns 119853 items_per_second=17.5833M/s MemoizeLRUCached/64/16 5347 ns 5347 ns 129134 items_per_second=18.7031M/s MemoizeLRUCached/64/1024 6318 ns 6318 ns 110366 items_per_second=15.829M/s MemoizeLRUCachedThreadUnsafe/8/16 2156 ns 2156 ns 321327 items_per_second=46.3885M/s MemoizeLRUCachedThreadUnsafe/8/1024 2165 ns 2165 ns 322995 items_per_second=46.1982M/s MemoizeLRUCachedThreadUnsafe/64/16 3110 ns 3110 ns 225295 items_per_second=32.1552M/s MemoizeLRUCachedThreadUnsafe/64/1024 3084 ns 3084 ns 225891 items_per_second=32.4268M/s ```
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pitrou
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Feb 18, 2021
cpp/src/arrow/util/cache_internal.h
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The unique_ptr was meant to make the memoizer type movable. While moving isn't strictly required, non-movable types are generally annoying to use (especially as some compilers may not always implement return value optimization properly).
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From a deadlocked run... ``` #0 0x00007f8a5d48dccd in __lll_lock_wait () from /lib64/libpthread.so.0 #1 0x00007f8a5d486f05 in pthread_mutex_lock () from /lib64/libpthread.so.0 #2 0x00007f8a566e7e89 in arrow::internal::FnOnce<void ()>::FnImpl<arrow::Future<Aws::Utils::Outcome<Aws::S3::Model::ListObjectsV2Result, Aws::S3::S3Error> >::Callback<arrow::fs::(anonymous namespace)::TreeWalker::ListObjectsV2Handler> >::invoke() () from /arrow/r/check/arrow.Rcheck/arrow/libs/arrow.so #3 0x00007f8a5650efa0 in arrow::FutureImpl::AddCallback(arrow::internal::FnOnce<void ()>) () from /arrow/r/check/arrow.Rcheck/arrow/libs/arrow.so #4 0x00007f8a566e67a9 in arrow::fs::(anonymous namespace)::TreeWalker::ListObjectsV2Handler::SpawnListObjectsV2() () from /arrow/r/check/arrow.Rcheck/arrow/libs/arrow.so #5 0x00007f8a566e723f in arrow::fs::(anonymous namespace)::TreeWalker::WalkChild(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, int) () from /arrow/r/check/arrow.Rcheck/arrow/libs/arrow.so #6 0x00007f8a566e827d in arrow::internal::FnOnce<void ()>::FnImpl<arrow::Future<Aws::Utils::Outcome<Aws::S3::Model::ListObjectsV2Result, Aws::S3::S3Error> >::Callback<arrow::fs::(anonymous namespace)::TreeWalker::ListObjectsV2Handler> >::invoke() () from /arrow/r/check/arrow.Rcheck/arrow/libs/arrow.so #7 0x00007f8a5650efa0 in arrow::FutureImpl::AddCallback(arrow::internal::FnOnce<void ()>) () from /arrow/r/check/arrow.Rcheck/arrow/libs/arrow.so #8 0x00007f8a566e67a9 in arrow::fs::(anonymous namespace)::TreeWalker::ListObjectsV2Handler::SpawnListObjectsV2() () from /arrow/r/check/arrow.Rcheck/arrow/libs/arrow.so #9 0x00007f8a566e723f in arrow::fs::(anonymous namespace)::TreeWalker::WalkChild(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, int) () from /arrow/r/check/arrow.Rcheck/arrow/libs/arrow.so #10 0x00007f8a566e74b1 in arrow::fs::(anonymous namespace)::TreeWalker::DoWalk() () from /arrow/r/check/arrow.Rcheck/arrow/libs/arrow.so ``` The callback `ListObjectsV2Handler` is being called recursively and the mutex is non-reentrant thus deadlock. To fix it I got rid of the mutex on `TreeWalker` by using `arrow::util::internal::TaskGroup` instead of manually tracking the #/status of in-flight requests. Closes apache#9842 from westonpace/bugfix/arrow-12040 Lead-authored-by: Weston Pace <weston.pace@gmail.com> Co-authored-by: Antoine Pitrou <antoine@python.org> Signed-off-by: Antoine Pitrou <antoine@python.org>
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